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1
Shih, Yu-Ting, Pei-Hao Chen, Li-Chin Lee, Chien-Sen Liao, Shih-Hao Jien, Fuh-Kwo Shiah, Tsung-Yu Lee, et al. "Dynamic responses of DOC and DIC transport to different flow regimes in a subtropical small mountainous river." Hydrology and Earth System Sciences 22, no. 12 (December 21, 2018): 6579–90. http://dx.doi.org/10.5194/hess-22-6579-2018.
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Abstract. Transport of riverine dissolved carbon (including DOC and DIC) is a crucial process linking terrestrial and aquatic C reservoirs, but has rarely been examined in subtropical small mountainous rivers (SMRs). This study monitored DOC and DIC concentrations on a biweekly basis during non-event flow periods and at 3 h intervals during two typhoon events in three SMRs in southwestern Taiwan between January 2014 and August 2016. Two models, HBV (the Hydrologiska Byråns Vattenbalansavdelning model) and a three-endmember mixing model, were applied to determine the quantities of DOC and DIC transport from different flow paths. The results show that the annual DOC and DIC fluxes were 2.7–4.8 and 48.4–54.3 t C km−2 yr−1, respectively, which were approx. 2 and 20 times higher than the global mean of 1.4 and 2.6 t C km−2 yr−1, respectively. The DIC ∕ DOC ratio was 14.08, which is much higher than the mean of large rivers worldwide (1.86), and indicates the high rates of chemical weathering in this region. The two typhoons contributed 12 %–14 % of the annual streamflow in only 3 days (about 1.0 % of the annual time), whereas 15.0 %–23.5 % and 9.2 %–12.6 % of the annual DOC and DIC flux, respectively, suggested that typhoons play a more important role in DOC transport than DIC transport. The endmember mixing model suggested that DOC and DIC export was mainly from surface runoff and deep groundwater, respectively. The unique patterns seen in Taiwan SMRs characterized by high dissolved carbon flux, high DIC ∕ DOC ratio, and large transport by intense storms should be taken into consideration when estimating global carbon budgets.
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Cui, Ji-Fa, Shi-Jie Han, Xi-Mei Zhang, Xing-Guo Han, and Zhi-Ping Wang. "Temporal–Spatial Variability of Dissolved Carbon in the Tributary Streams of the Lower Yangtze River Basin." Water 14, no. 24 (December 12, 2022): 4057. http://dx.doi.org/10.3390/w14244057.
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Dissolved carbon has been widely investigated in natural rivers worldwide. However, it has been rarely studied in riverine system of farming regions, where small streams have been usually modified by a water gate and flood levee. This study was conducted to investigate dissolved organic and inorganic carbon (DOC, DIC) in artificially modified tributary streams, namely the Desheng and Shuangqiao-Shiba streams, in a farming region of the lower Yangtze River basin. The results showed that the DOC and DIC concentrations had remarkable temporal–spatial variability in the Desheng and Shuangqiao-Shiba streams. The mean DOC concentrations were 5.4 and 6.7 mg L−1 in the Desheng and Shuangqiao-Shiba streams during the period of about 1 year, while the DIC concentrations were 14.0 and 9.6 mg L−1 in both streams, respectively. The DOC and DIC concentrations mainly showed the linear decreasing trends from source through to export in the spring, summer, autumn, and winter. The DOC concentration was almost always lower than the DIC concentration. The DOC concentration was positively correlated with the DIC concentration in the Desheng stream over the four seasons, indicating that the DOC and DIC potentially had similar sources. The DOC and DIC concentrations increased with sewage discharge, which introduced a potential hazard to human health. The water gate and flood levee in the Desheng and Shuangqiao-Shiba streams were constructed for discharging floods and recharging irrigation in the farming region, and their effects on dissolved carbon require further research.
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Song, K. S., S. Y. Zang, Y. Zhao, J. Du, L. Li, N. N. Zhang, X. D. Wang, T. T. Shao, Y. Guan, and L. Liu. "Spatiotemporal characterization of dissolved carbon for inland waters in semi-humid/semiarid region, China." Hydrology and Earth System Sciences Discussions 10, no. 5 (May 27, 2013): 6559–97. http://dx.doi.org/10.5194/hessd-10-6559-2013.
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Abstract. Spatiotemporal variations of dissolved organic carbon (DOC), inorganic carbon (DIC) in 26 waters across the semi-humid/semi-arid Songnen Plain, China were examined with data collected during 2008–2011. Fresh (n = 14) and brackish (n = 12) waters were grouped according to electrical conductivity (threshold = 1000 μS cm−1). Significant differences in the mean DOC/DIC concentrations were observed between fresh (5.63 mg L−1, 37.39 mg L−1) and brackish waters (15.33 mg L−1, 142.93 mg L−1). Colored dissolved organic matter (CDOM) and DOC concentrations were mainly controlled by climatic-hydrologic conditions. The observation indicated that the outflow conditions in the semi-endorheic region had condensed effects on the dissolved carbon, resulting in close relationships between salinity vs. DOC (R2 = 0.66), and vs. DIC (R2 = 0.94). Independent data set collected in May 2012 also confirmed this finding (DOC: R2 = 0.79), (DIC: R2 = 0.91), highlighting the potential of quantifying DOC/DIC via salinity measurements for waters dispersed in the plain. Indices based on CDOM absorption spectra, e.g. DOC specific CDOM absorption (SUVA254), absorption ratio a250 : a365 (E250:365) and spectral slope ratio (Sr, S275−295/S350−400), were applied to characterize DOM composition and quality. Our results indicate high molecular weight CDOM fractions are more abundant in fresh waters than brackish waters.
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Wang, Linhua, Haw Yen, Liding Chen, Xinhui E, and Yafeng Wang. "Characteristics of wet dissolved carbon deposition in a semi-arid catchment at the Loess Plateau, China." Biogeosciences 15, no. 11 (June 6, 2018): 3345–56. http://dx.doi.org/10.5194/bg-15-3345-2018.
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Abstract. Wet dissolved carbon deposition is a critical node of the global carbon cycle, but little is known about dissolved organic and inorganic carbon (DOC and DIC) concentrations and fluxes in the semi-arid areas of the Loess Plateau Region (LPR). In this study, we measured variations in DOC and DIC concentrations in rainfalls at Yangjuangou Ecological Restoration and Soil and Water Observatory. Rainwater samples were collected in 16 rainfall events from July to September and the event-based, monthly concentrations and fluxes of DOC and DIC were quantified. The results showed that the event-based concentrations and fluxes of DOC and DIC were highly variable, ranging from 0.56 to 28.71 mg C L−1 and from 3.47 to 17.49 mg C L−1, respectively. The corresponding event-based fluxes ranged from 0.21–258.36 mg C m−2 and from 4.12 to 42.32 mg C m−2. The monthly concentrations of DOC and DIC were 24.62 and 4.30 (July), 3.58 and 10.52 (August), and 1.01 and 5.89 (September) mg C L−1, respectively. Thus, the monthly deposition fluxes of DOC and DIC were 541.64/94.60, 131.03/385.03, and 44.44/259.16 mg C m−2 for July, August, and September, respectively. In addition, the concentrations of DOC and DIC for the concentrated rainfall season (July–September) in the studied catchment were 7.06 and 7.00 mg C L−1, respectively. The estimated annual wet dissolved carbon depositions were 1.91 and 1.89 g C m−2 yr−1 for DOC and DIC, respectively. The results of this study suggest the variation in concentrations and fluxes of DOC and DIC and explore that these variation may be related to the dissolved carbon source and the rainfall characteristics during the concentrated rainfall season in the semi-arid catchment of the LPR. Furthermore, these results also suggest that dissolved carbon may be an important external input of carbon into terrestrial ecosystems.
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Ding, Ling, Tiantian Ge, and Xuchen Wang. "Dissolved organic carbon dynamics in the East China Sea and the northwest Pacific Ocean." Ocean Science 15, no. 5 (September 6, 2019): 1177–90. http://dx.doi.org/10.5194/os-15-1177-2019.
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Abstract. Oceanic dissolved organic carbon (DOC) represents one of the largest carbon reservoirs on Earth, and its distribution and biogeochemical cycles play important roles in carbon cycling and other biogeochemical processes in the ocean. We report the distribution and concentrations of DOC for water samples collected from the shelf-edge and slope regions in the East China Sea (ECS) and the Kuroshio Extension (KE) in the northwestern North Pacific during two cruises in 2014–2015. The DOC concentrations were 45–88 µM in the ECS and 35–65 µM in the KE. In addition to biological processes that are estimated to account for 7 % and 8 %–20 % in shaping the DOC distribution in the ECS and KE regions, respectively, the DOC distribution is largely controlled by hydrodynamic mixing of different water masses. By comparing the DOC results with dissolved inorganic carbon (DIC) and dissolved inorganic radiocarbon (Δ14C-DIC) measured from the same water samples, we further demonstrate that the intrusion of the Kuroshio Current could dilute the DOC concentrations at stations in the outer shelf and slope regions of the ECS. The concentrations of DOC in the KE were significantly lower in surface waters than in the ECS, and a relatively low and stable DOC level (∼40 µM) was found in deep water (below 1500 m) at all stations. Based on the previously reported DIC and Δ14C-DIC values for the stations, the observed spatial variations of DOC in the upper 700 m among the stations in the KE were mainly influenced by mixing of the two water masses carried by the Kuroshio and Oyashio, the two dominant western boundary currents in the region. The hydrodynamic processes are thus important factors in the distribution and dynamics of DOC in the KE region.
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Song, K. S., S. Y. Zang, Y. Zhao, L. Li, J. Du, N. N. Zhang, X. D. Wang, T. T. Shao, Y. Guan, and L. Liu. "Spatiotemporal characterization of dissolved carbon for inland waters in semi-humid/semi-arid region, China." Hydrology and Earth System Sciences 17, no. 10 (October 30, 2013): 4269–81. http://dx.doi.org/10.5194/hess-17-4269-2013.
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Abstract. Spatiotemporal variations of dissolved organic carbon (DOC) and inorganic carbon (DIC) in 26 waters across the semi-humid/semi-arid Songnen Plain, China, were examined with data collected during 2008–2011. Fresh (n = 14) and brackish (n = 12) waters were grouped according to electrical conductivity (threshold = 1000 μS cm−1) Significant differences in the average DOC and DIC concentrations were observed between the fresh (5.63 mg L−1, 37.39 mg L−1) and the brackish waters (15.33 mg L−1, 142.93 mg L−1). Colored dissolved organic matter (CDOM) and DOC concentrations were mainly controlled by climatic–hydrologic conditions. The investigation indicated that the outflow conditions in the semi-arid region had condensed effects on the dissolved carbon, resulting in close relationships between salinity vs. DOC (R2 = 0.66), and salinity vs. DIC (R2 = 0.94). An independent data set collected in May 2012 also confirmed this finding (DOC: R2 = 0.79, DIC: R2 = 0.91), highlighting the potential of quantifying DOC and DIC via salinity measurements for waters dispersed in the plain. Indices based on the CDOM absorption spectra (e.g., the DOC-specific CDOM absorption (SUVA254), absorption ratio a250 : a365 (E250 : E365) and the spectral slope ratio (Sr, S275−295/S350−400) were applied to characterize CDOM composition and quality. Our results indicate that high molecular weight CDOM fractions are more abundant in the fresh waters than the brackish waters.
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Havas, Robin, Christophe Thomazo, Miguel Iniesto, Didier Jézéquel, David Moreira, Rosaluz Tavera, Jeanne Caumartin, Elodie Muller, Purificación López-García, and Karim Benzerara. "The hidden role of dissolved organic carbon in the biogeochemical cycle of carbon in modern redox-stratified lakes." Biogeosciences 20, no. 12 (June 23, 2023): 2405–24. http://dx.doi.org/10.5194/bg-20-2405-2023.
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Abstract. The dissolved organic carbon (DOC) reservoir plays a critical role in the C cycle of marine and freshwater environments because of its size and implication in many biogeochemical reactions. Although it is poorly constrained, its importance in ancient Earth's C cycles is also commonly invoked. Yet DOC is rarely quantified and characterized in modern stratified analogues. In this study, we investigated the DOC reservoirs of four redox-stratified alkaline crater lakes in Mexico. We analyzed the concentrations and isotopic compositions of DOC throughout the four water columns and compared them with existing data on dissolved inorganic and particulate organic C reservoirs (DIC and POC). The four lakes have high DOC concentrations with great variability between and within the lakes (averaging 2 ± 4 mM; 1 SD, n=28; i.e., from ∼ 15 to 160 times the amount of POC). The δ13CDOC signatures also span a broad range of values from −29.3 ‰ to −8.7 ‰ (with as much as 12.5 ‰ variation within a single lake). The prominent DOC peaks (up to 21 mM), together with their associated isotopic variability, are interpreted as reflecting oxygenic and/or anoxygenic primary productivity through the release of excess fixed carbon in three of the lakes (Alberca de los Espinos, La Preciosa, and Atexcac). By contrast, the variability of [DOC] and δ13CDOC in the case of Lake Alchichica is mainly explained by the partial degradation of organic matter and the accumulation of DOC in anoxic waters. The DOC records detailed metabolic functions such as active DIC-uptake and DIC-concentrating mechanisms, which cannot be inferred from DIC and POC analyses alone but which are critical to the understanding of carbon fluxes from the environment to the biomass. Extrapolating our results to the geological record, we suggest that anaerobic oxidation of DOC may have caused the very negative C isotope excursions in the Neoproterozoic. It is, however, unlikely that a large oceanic DOC reservoir could overweigh the entire oceanic DIC reservoir. This study demonstrates how the analysis of DOC in modern systems deepens our understanding of the C cycle in stratified environments and helps to set boundary conditions for the Earth's past oceans.
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Lindell, Måns J., H. Wilhelm Granéli, and Stefan Bertilsson. "Seasonal photoreactivity of dissolved organic matter from lakes with contrasting humic content." Canadian Journal of Fisheries and Aquatic Sciences 57, no. 5 (May 1, 2000): 875–85. http://dx.doi.org/10.1139/f00-016.
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We studied seasonal variability in photodegradation of dissolved organic carbon (DOC) resulting from artificial ultraviolet-A (UV-A) and UV-B irradiation. Water samples were taken approximately monthly from the surface layers of two oligotrophic lakes with contrasting humic content, situated in southern Sweden. Lake water was filter-sterilized (0.2 μm) and exposed to artificial UV radiation in quartz tubes. Potential DOC photodegradation, measured as a photoproduction of dissolved inorganic carbon (DIC) and oxalic, malonic, formic, and acetic acid in irradiated samples, was observed throughout the sampling period. In addition, exposure to UV radiation resulted in a decrease in DOC, absorbance, and humic substance fluorescence. The photoproduction of DIC and the low molecular weight (LMW) organic acids varied seasonally, being generally higher in winter and spring (December-May), while DOC appeared to become less photoreactive after the extensive exposure to solar radiation during summer. Production rates of both DIC and LMW organic acids were approximately eight times higher in the humic lake despite that the DOC concentration was only two times higher than in the clearwater lake. This is most probably due to the high input of allochthonous DOC and the resulting higher absorbance to DOC ratio in the humic system. Furthermore, the longer hydraulic residence time in the clearwater system could have resulted in an accumulation of residual DOC, recalcitrant to further photodegradation.
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Song, Chunlin, Genxu Wang, Tianxu Mao, Xiaopeng Chen, Kewei Huang, Xiangyang Sun, and Zhaoyong Hu. "Importance of active layer freeze-thaw cycles on the riverine dissolved carbon export on the Qinghai-Tibet Plateau permafrost region." PeerJ 7 (June 17, 2019): e7146. http://dx.doi.org/10.7717/peerj.7146.
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The Qinghai-Tibet Plateau (QTP) is experiencing severe permafrost degradation, which can affect the hydrological and biogeochemical processes. Yet how the permafrost change affects riverine carbon export remains uncertain. Here, we investigated the seasonal variations of dissolved inorganic and organic carbon (DIC and DOC) during flow seasons in a watershed located in the central QTP permafrost region. The results showed that riverine DIC concentrations (27.81 ± 9.75 mg L−1) were much higher than DOC concentrations (6.57 ± 2.24 mg L−1). DIC and DOC fluxes were 3.95 and 0.94 g C m−2 year−1, respectively. DIC concentrations increased from initial thaw (May) to freeze period (October), while DOC concentrations remained relatively steady. Daily dissolved carbon concentrations were more closely correlated with baseflow than that with total runoff. Spatially, average DIC and DOC concentrations were positively correlated with vegetation coverage but negatively correlated with bare land coverage. DIC concentrations increased with the thawed and frozen depths due to increased soil interflow, more thaw-released carbon, more groundwater contribution, and possibly more carbonate weathering by soil CO2 formed carbonic acid. The DIC and DOC fluxes increased with thawed depth and decreased with frozen layer thickness. The seasonality of riverine dissolved carbon export was highly dependent on active layer thawing and freezing processes, which highlights the importance of changing permafrost for riverine carbon export. Future warming in the QTP permafrost region may alter the quantity and mechanisms of riverine carbon export.
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Shah, S. R., S. B. Joye, J. A. Brandes, and A. P. McNichol. "Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the seawater–brine interface." Biogeosciences 10, no. 5 (May 13, 2013): 3175–83. http://dx.doi.org/10.5194/bg-10-3175-2013.
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Abstract. Orca Basin, an intraslope basin on the Texas-Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200 m in which limited microbial activity has been reported. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to measurements made in the 1970s. Both DIC and DOC are more "aged" within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon remineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC, allowing for only limited oxidation of methane diffusing upwards from sediments. This conclusion is consistent with previous studies that identify the seawater–brine interface as the focus of microbial activity associated with Orca Basin brine. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawater–brine interface region as the likely source region for DOC to the brine as well as DIC.
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Giesler, R., S. W. Lyon, C. M. Mörth, J. Karlsson, E. M. Karlsson, E. J. Jantze, G. Destouni, and C. Humborg. "Catchment-scale dissolved carbon concentrations and export estimates across six subarctic streams in northern Sweden." Biogeosciences 11, no. 2 (January 31, 2014): 525–37. http://dx.doi.org/10.5194/bg-11-525-2014.
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Abstract. Climatic change is currently enhancing permafrost thawing and the flow of water through the landscape in subarctic and arctic catchments, with major consequences for the carbon export to aquatic ecosystems. We studied stream water carbon export in several tundra-dominated catchments in northern Sweden. There were clear seasonal differences in both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations. The highest DOC concentrations occurred during the spring freshet while the highest DIC concentrations were always observed during winter baseflow conditions for the six catchments considered in this study. Long-term trends for the period 1982 to 2010 for one of the streams showed that DIC concentrations has increased by 9% during the 28 yr of measurement while no clear trend was found for DOC. Similar increasing trends were also found for conductivity, Ca and Mg. When trends were discretized into individual months, we found a significant linear increase in DIC concentrations with time for September, November and December. In these subarctic catchments, the annual mass of C exported as DIC was in the same order of magnitude as DOC; the average proportion of DIC to the total dissolved C exported was 61% for the six streams. Furthermore, there was a direct relationship between total runoff and annual dissolved carbon fluxes for these six catchments. These relationships were more prevalent for annual DIC exports than annual DOC exports in this region. Our results also highlight that both DOC and DIC can be important in high-latitude ecosystems. This is particularly relevant in environments where thawing permafrost and changes to subsurface ice due to global warming can influence stream water fluxes of C. The large proportion of stream water DIC flux also has implications on regional C budgets and needs to be considered in order to understand climate-induced feedback mechanisms across the landscape.
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Li, Zhichun, Yanping Zhao, Xiaoguang Xu, Ruiming Han, Mingyue Wang, and Guoxiang Wang. "Migration and transformation of dissolved carbon during accumulated cyanobacteria decomposition in shallow eutrophic lakes: a simulated microcosm study." PeerJ 6 (November 7, 2018): e5922. http://dx.doi.org/10.7717/peerj.5922.
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The decomposition processes of accumulated cyanobacteria can release large amounts of organic carbon and affect the carbon cycling in shallow eutrophic lakes. However, the migration and transformation mechanisms of dissolved carbon (DC) require further study and discussion. In this study, a 73-day laboratory microcosm experiment using suction samplers (Rhizon and syringe) was conducted to understand the migration and transformation of DC during the cyanobacteria decomposition. The decomposition of cyanobacteria biomass caused anoxic and reduction conditions, and changed the acid-base environment in the water column. During the early incubation (days 0–18), a large amount of cyanobacteria-derived particulate organic matter (POM) was decomposed into dissolved organic carbon (DOC) in the overlying water, reaching the highest peak value of 1.82 g L−1 in the treatment added the high cyanobacteria biomass (470 g). After 18 days of incubation, the mineralization of increased DOC to dissolved inorganic carbon (DIC) maintained a high DIC level of overlying water in treatments added cyanobacteria biomass. The treatment added the medium cyanobacteria biomass (235 g) presented the lower DOC/total dissolved carbon ratio than the high cyanobacteria biomass associated with the lower mineralization from DOC to DIC. Due to the concentration differences of DIC at water-sediment interface, the main migration of DIC from pore water to overlying water occurred in the treatment without added cyanobacteria biomass. However, the treatments added the cyanobacteria biomass presented the obvious diffusion of DOC and the low migration of DIC at the water-sediment interface. The diffusive fluxes of DOC at the water-sediment interface increased with the cyanobacteria biomass added, reaching the maximum value of 411.01 mg/(m2·d) in the treatment added the high cyanobacteria biomass. In the overlying water, the group added the sediment and medium cyanobacteria biomass presented a faster degradation of cyanobacteria-derived POM to DOC and a higher mineralization level of DOC to DIC than added the medium cyanobacteria biomass without sediment. Therefore, during accumulated cyanobacteria decomposition, the biomass of accumulated cyanobacteria and sediment property can influence the migration and transformation of DC, playing an important role in carbon cycling in shallow eutrophic lakes.
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Shah, S. R., S. B. Joye, J. A. Brandes, and A. P. McNichol. "Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the brine-seawater interface." Biogeosciences Discussions 9, no. 12 (December 13, 2012): 17913–37. http://dx.doi.org/10.5194/bgd-9-17913-2012.
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Abstract. Orca Basin, an intraslope basin on the Texas–Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200 m. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and the isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to previous reports. Both DIC and DOC are more "aged" within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon re-mineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC with oxidation of methane diffusing upwards from sediments supplying only limited DIC to the brine. This conclusion is consistent with previous studies reporting microbial activity focused at the seawater-brine interface. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawater-brine interface region as the likely source region for DOC as well as DIC. Further investigations of the seawater-brine interface are needed to advance our understanding of the specific microbial processes contributing to dissolved carbon storage in the Orca Basin brine.
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Lloret, E., C. Dessert, E. Lajeunesse, O. Crispi, L. Pastor, J. Gaillardet, and M. F. Benedetti. "Are small mountainous tropical watersheds of oceanic islands important for carbon export?" Biogeosciences Discussions 9, no. 6 (June 18, 2012): 7117–63. http://dx.doi.org/10.5194/bgd-9-7117-2012.
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Abstract. In the tropic, the small watersheds are affected by intense meteorological events playing an important role on the erosion of soils and therefore on the associated organic carbon fluxes. We studied the geochemistry of three small watersheds around the Basse-Terre volcanic Island (FWI) during a four years period, by measuring DOC, POC and DIC concentrations. The mean annual yields ranged 8.1–15.8 t C km−2 yr−1, 1.9–8.6 t C km−2 yr−1 and 8.1–25.5 t C km−2 yr−1 for DIC, DOC and POC, respectively. Floods and extreme floods represent 45 to 70 % of the annual DOC flux, and more than 80 % of the annual POC flux. The DIC flux occurs essentially during the low water level, only 43 % of the annual DIC flux is exported during floods. The distribution of the dissolved carbon between the inorganic and the organic fraction is correlated to the hydrodynamic of rivers. During low water level and floods, the dissolved carbon is exported under the inorganic form (DIC/DOC = 2.6 ± 2.1), while during extreme floods, the dissolved carbon transported is mostly organic (DIC/DOC = 0.7 ± 0.2). The residence time of the organic carbon in Guadeloupean soils may vary from 381 to 1000 yr, and is linked to the intensity of meteorological events than the frequency of meteorological events. Looking at the global carbon mass balance, the total export of organic carbon coming from small tropical and volcanic mountainous rivers is estimated about 2.0–8.9 Tg C yr−1 for DOC and about 8.4–26.5 Tg C yr−1 for POC, emphasizing that these carbon fluxes are significant and should be included in global carbon budgets.
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Pogodaeva, Tatyana, and Tamara Khodzher. "Organic Carbon in the Bottom Sediments of Lake Baikal: Geochemical Processes of Burial and Balance Values." Water 15, no. 16 (August 15, 2023): 2941. http://dx.doi.org/10.3390/w15162941.
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This is the first study of dissolved organic matter (DOM) at the Lake Baikal water-bottom interface. High-resolution profiles of dissolved organic carbon (DOC) were obtained simultaneously with dissolved inorganic carbon (DIC), total dissolved carbon, cations (Na+, K+, Ca2+, Mg2+, Fe2+, and Mn2+), and anions (HCO3−, Cl−, NO3−, and SO42−) in the pore water of Lake Baikal deepwater oxidized sediments. We evaluated the DOC fluxes quantitatively and qualitatively. They changed their direction twice under different redox conditions in the sediments (at the redox interfaces). The study revealed that the mobilization of DOC in anoxic sediments was closely related to the reductive dissolution of Fe(III) minerals, and the oxidized surface lake sediments represented an effective DOC trap binding DOC to ferric minerals. Redox conditions appeared to be the main regulator of the DOC exchange. Oxygen conditions led to the uptake of DOC by sediments (31–78 mmol C m−2 yr−1), i.e., the Lake Baikal sediments are a sink of DOC. The DOC flux was approximately 25–35% of the carbon flux at the sediment–water interface. The results of this study allow for a better understanding of the nature and properties of DOC in freshwater ecosystems and compensate for the underestimation of DOC in the internal carbon cycle of the lake.
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Deirmendjian, Loris, Denis Loustau, Laurent Augusto, Sébastien Lafont, Christophe Chipeaux, Dominique Poirier, and Gwenaël Abril. "Hydro-ecological controls on dissolved carbon dynamics in groundwater and export to streams in a temperate pine forest." Biogeosciences 15, no. 2 (February 1, 2018): 669–91. http://dx.doi.org/10.5194/bg-15-669-2018.
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Abstract. We studied the export of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from forested shallow groundwater to first-order streams, based on groundwater and surface water sampling and hydrological data. The selected watershed was particularly convenient for such study, with a very low slope, with pine forest growing on sandy permeable podzol and with hydrology occurring exclusively through drainage of shallow groundwater (no surface runoff). A forest plot was instrumented for continuous eddy covariance measurements of precipitation, evapotranspiration, and net ecosystem exchanges of sensible and latent heat fluxes as well as CO2 fluxes. Shallow groundwater was sampled with three piezometers located in different plots, and surface waters were sampled in six first-order streams; river discharge and drainage were modeled based on four gauging stations. On a monthly basis and on the plot scale, we found a good consistency between precipitation on the one hand and the sum of evapotranspiration, shallow groundwater storage and drainage on the other hand. DOC and DIC stocks in groundwater and exports to first-order streams varied drastically during the hydrological cycle, in relation with water table depth and amplitude. In the groundwater, DOC concentrations were maximal in winter when the water table reached the superficial organic-rich layer of the soil. In contrast, DIC (in majority excess CO2) in groundwater showed maximum concentrations at low water table during late summer, concomitant with heterotrophic conditions of the forest plot. Our data also suggest that a large part of the DOC mobilized at high water table was mineralized to DIC during the following months within the groundwater itself. In first-order streams, DOC and DIC followed an opposed seasonal trend similar to groundwater but with lower concentrations. On an annual basis, leaching of carbon to streams occurred as DIC and DOC in similar proportion, but DOC export occurred in majority during short periods of the highest water table, whereas DIC export was more constant throughout the year. Leaching of forest carbon to first-order streams represented a small portion (approximately 2 %) of the net land CO2 sink at the plot. In addition, approximately 75 % of the DIC exported from groundwater was not found in streams, as it returned very fast to the atmosphere through CO2 degassing.
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Dempsey, Christopher M., Jennifer A. Brentrup, Sarah Magyan, Lesley B. Knoll, Hilary M. Swain, Evelyn E. Gaiser, Donald P. Morris, Michael T. Ganger, and Craig E. Williamson. "The relative importance of photodegradation and biodegradation of terrestrially derived dissolved organic carbon across four lakes of differing trophic status." Biogeosciences 17, no. 24 (December 15, 2020): 6327–40. http://dx.doi.org/10.5194/bg-17-6327-2020.
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Abstract. Outgassing of carbon dioxide (CO2) from freshwater ecosystems comprises 12 %–25 % of the total carbon flux from soils and bedrock. This CO2 is largely derived from both biodegradation and photodegradation of terrestrial dissolved organic carbon (DOC) entering lakes from wetlands and soils in the watersheds of lakes. In spite of the significance of these two processes in regulating rates of CO2 outgassing, their relative importance remains poorly understood in lake ecosystems. In this study, we used groundwater from the watersheds of one subtropical and three temperate lakes of differing trophic status to simulate the effects of increases in terrestrial DOC from storm events. We assessed the relative importance of biodegradation and photodegradation in oxidizing DOC to CO2. We measured changes in DOC concentration, colored dissolved organic carbon (specific ultraviolet absorbance – SUVA320; spectral slope ratio – Sr), dissolved oxygen, and dissolved inorganic carbon (DIC) in short-term experiments from May–August 2016. In all lakes, photodegradation led to larger changes in DOC and DIC concentrations and optical characteristics than biodegradation. A descriptive discriminant analysis showed that, in brown-water lakes, photodegradation led to the largest declines in DOC concentration. In these brown-water systems, ∼ 30 % of the DOC was processed by sunlight, and a minimum of 1 % was photomineralized. In addition to documenting the importance of photodegradation in lakes, these results also highlight how lakes in the future may respond to changes in DOC inputs.
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DelDuco, Emily M., and Y. Jun Xu. "Dissolved Carbon Transport and Processing in North America’s Largest Swamp River Entering the Northern Gulf of Mexico." Water 11, no. 7 (July 7, 2019): 1395. http://dx.doi.org/10.3390/w11071395.
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Transport and transformation of riverine dissolved carbon is an important component of global carbon cycling. The Atchafalaya River (AR) flows 189 kilometers through the largest bottomland swamp in North America and discharges ~25% of the flow of the Mississippi River into the Gulf of Mexico annually, providing a unique opportunity to study the floodplain/wetland impacts on dissolved carbon. The aim of this study is to determine how dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in the AR change spatially and seasonally, and to elucidate which processes control the carbon cycling in this intricate swamp-river system. From May 2015 to May 2016, we conducted monthly river sampling from the river’s inflow to its outflow, analyzing samples for concentrations and δ13C stable isotope composition of DOC and DIC. We found that DIC concentrations in the AR were three times higher than the DOC concentrations on average, and showed more pronounced downstream changes than the DOC. During the study period, the river discharged a total of 5.35 Tg DIC and a total of 2.34 Tg DOC into the Gulf of Mexico. Based on the mass inflow–outflow balance, approximately 0.53 Tg (~10%) of the total DIC exported was produced within the floodplain/wetland system, while 0.24 Tg (~10%) of the DOC entering the basin was removed. The AR’s water was consistently oversaturated with CO2 partial pressure (pCO2) above the atmospheric pCO2 (with pCO2 varying from 551 µatm to 6922 µatm), indicating a large source of DIC from river waters to the atmosphere as well as to the coastal margins. Largest changes in carbon constituents occurred during periods of greatest inundation of the swamp-river basin and corresponded with shifts in isotopic composition. This effect was particularly pronounced during the initial flood stages, supporting the hypothesis that subtropical floodplains can act as effective enhancers of the biogeochemical cycling of dissolved carbon.
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Murseli, Sarah, Paul Middlestead, Gilles St-Jean, Xiaolei Zhao, Christabel Jean, Carley A. Crann, William E. Kieser, and Ian D. Clark. "The Preparation of Water (DIC, DOC) and Gas (CO2, CH4) Samples for Radiocarbon Analysis at AEL-AMS, Ottawa, Canada." Radiocarbon 61, no. 5 (April 22, 2019): 1563–71. http://dx.doi.org/10.1017/rdc.2019.14.
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ABSTRACTSample preparation techniques for radiocarbon analysis of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in freshwater, as well as CO2 and CH4 in gas mixtures are presented. Focused efforts have been on developing a robust and low-background wet oxidation extraction method for DOC in freshwater, following routine methods developed for stable carbon isotope analysis and adapted for radiocarbon (14C) analysis. DIC (by acidification) and DOC (by wet oxidation) are converted to CO2 in pre-baked septum-fitted borosilicate bottles, where the resulting CO2 is extracted from the dissolved and headspace portions on a low-flow He-carrier flow-through system interfaced to a vacuum extraction line. A peripheral CH4 extraction line interfaces to the flow line to separate CH4 from environmental samples following the methods of Pack et al. 2015. High sample throughput and low blanks are achievable with this method. DIC and DOC blanks are consistently <0.7 pMC, while CO2 and CH4 blanks are typically <0.1 pMC.
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Druffel, Ellen R. M., Peter M. Williams, Ken Robertson, Sheila Griffin, A. J. T. Jull, Douglas Donahue, Lawrence Toolin, and T. W. Linick. "Radiocarbon in Dissolved Organic and Inorganic Carbon From the Central North Pacific." Radiocarbon 31, no. 03 (1989): 523–32. http://dx.doi.org/10.1017/s003382220001211x.
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Radiocarbon measurements are reported for dissolved organic carbon (DOC) and inorganic carbon (DIC) from seawater samples collected from the Alcyone-5 cruise in the central North Pacific Ocean in 1985. Differences between the UV-radiation techniques used here and those reported by Williams, Oeschger and Kinney (1969) to oxidize and recover the DOC from sea water are presented. UV unoxidizable DOC in these samples is discussed in a separate publication (Druffel, Williams & Suzuki, 1989). We briefly discuss the penetration of the bomb 14C signal into the DOC and DIC pools. The temporal variability of Δ 14C in DIC in surface samples taken every 2–3 days is presented. Concentrations of total dissolved free (FAA) plus combined (hydrolyzable) amino acids (THAA) and total dissolved carbohydrates (TCHO) measured in the same water samples are also reported. Our main aim is to present the chemical and isotopic data from samples collected during the Alcyone-5 cruise. Detailed interpretation is published elsewhere.
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Soria-Reinoso, Ismael, Javier Alcocer, Salvador Sánchez-Carrillo, Felipe García-Oliva, Daniel Cuevas-Lara, Daniela Cortés-Guzmán, and Luis A. Oseguera. "The Seasonal Dynamics of Organic and Inorganic Carbon along the Tropical Usumacinta River Basin (Mexico)." Water 14, no. 17 (August 30, 2022): 2703. http://dx.doi.org/10.3390/w14172703.
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Rivers are important sites for carbon (C) transport and critical components of the global C cycle that is currently not well constrained. However, little is known about C species’ longitudinal and temporal changes in large tropical rivers. The Usumacinta River is Mexico’s main lotic system and the tenth largest in North America. Being a tropical river, it has a strong climatic seasonality. This study aims to evaluate how organic (DOC and POC) and inorganic (DIC and PIC) carbon change spatially and seasonally along the Usumacinta River (medium and lower basin) in rainy (RS-2017) and dry (DS-2018) seasons and to estimate C fluxes into the southern Gulf of Mexico. Concentrations of DOC, POC, DIC, and PIC ranged from 0.88 to 7.11 mg L−1, 0.21 to 3.78 mg L−1, 15.59 to 48.27 mg L−1, and 0.05 to 1.51 mg L−1, respectively. DOC was the dominant organic species (DOC/POC > 1). It was ~doubled in RS and showed a longitudinal increase, probably through exchange with wetlands and floodplains. Particulate carbon showed a positive relationship with the total suspended solids, suggesting that in RS, it derived from surface erosion and runoff in the watershed. DIC is reported for the first time as the highest concentration measured in tropical rivers in America. It was higher in the dry season without a longitudinal trend. The C mass inflow–outflow balance in the RS suggested net retention (DOC and POC sink) in floodplains. In contrast, in the DS, the balance suggested that floodplains supply (C source) autochthonous DOC and POC. The lower Usumacinta River basin is a sink for DIC in both seasons. Finally, the estimated annual C export for the Usumacinta-Grijalva River was 2.88 (2.65 to 3.14) Tg yr−1, of which DIC was the largest transported fraction (85%), followed by DOC (10%), POC (4%), and PIC (<1%). This investigation is the first to present the C loads in a Mexican river.
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Ohtsuka, Toshiyuki, Takeo Onishi, Shinpei Yoshitake, Mitsutoshi Tomotsune, Morimaru Kida, Yasuo Iimura, Miyuki Kondo, et al. "Lateral Export of Dissolved Inorganic and Organic Carbon from a Small Mangrove Estuary with Tidal Fluctuation." Forests 11, no. 10 (September 25, 2020): 1041. http://dx.doi.org/10.3390/f11101041.
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The significance of aquatic lateral carbon (C) export in mangrove ecosystems highlights the extensive contribution of aquatic pathways to the net ecosystem carbon budget. However, few studies have investigated lateral fluxes of dissolved organic carbon (DOC) and inorganic carbon (DIC), partly due to methodological difficulty. Therefore, we evaluated area-based lateral C fluxes in a small mangrove estuary that only had one exit for water exchange to the coast. We sampled water from the mouth of the creek and integrated discharge and consecutive concentration of mangrove-derived C (ΔC). Then, we estimated the area-normalized C fluxes based on the inundated mangrove area. DIC and DOC concentrations at the river mouth increased during ebb tide during both summer and winter. We quantified the ΔC in the estuary using a two-component conservative mixing model of freshwater and seawater. DIC and DOC proportions of ΔC concentrations at the river mouth during ebb tide was between 34% and 56% in the winter and 26% and 42% in the summer, respectively. DIC and DOC fluxes from the estuary were estimated to be 1.36 g C m−2 d−1 and 0.20 g C m−2 d−1 in the winter and 3.35 g C m−2 d−1 and 0.86 g C m−2 d−1 in the summer, respectively. Based on our method, daily fluxes are mangrove area-based DIC and DOC lateral exports that can be directly incorporated into the mangrove carbon budget.
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Wassenaar, Leonard, Ramon Aravena, and Peter Fritz. "The Geochemistry and Evolution of Natural Organic Solutes in Groundwater." Radiocarbon 31, no. 03 (1989): 865–76. http://dx.doi.org/10.1017/s0033822200012480.
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This paper describes the organic carbon cycle of the recharge environment of a shallow, sandy aquifer, with an emphasis on the origin, flux and geochemical evolution of dissolved organic carbon using liquid chromatography, carbon isotopes and GC-MS techniques. The two components of DOC investigated are hydrophobic acids and C1-C10 hydrophilic compounds. The 14C activity of these components of the DOC was measured using TAMS. 14C analyses of DOC components may provide an additional tool for groundwater dating. The initial 14C activity of DOC in a recharge zone, however, depends mainly on the residence times and cycling of DOC sources in the recharge environment. Using 14C DOC to estimate groundwater residence times between sampling points along a flow path compares well with residence times estimated on the basis of hydraulic parameters and 14C DIC under closed system conditions.
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Stubbins, A., J. Niggemann, and T. Dittmar. "Photo-lability of deep ocean dissolved black carbon." Biogeosciences Discussions 9, no. 1 (January 16, 2012): 485–505. http://dx.doi.org/10.5194/bgd-9-485-2012.
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Abstract. Dissolved black carbon (DBC), defined here as condensed aromatics isolated from seawater via PPL solid phase extraction and quantified as benzene polycarboxylic acid oxidation products, is a significant component of the oceanic dissolved organic carbon (DOC) pool. These condensed aromatics are widely distributed in the open ocean and appear to be tens of thousands of years old. As such DBC is regarded as highly refractory. In the current study, the photo-lability of DBC, DOC and coloured dissolved organic matter (CDOM; ultraviolet-visible absorbance) were determined over the course of a 28 d irradiation of North Atlantic Deep Water under a solar simulator. During the irradiation DBC fell from 1044 &pm; 164 nM C to 55 &pm; 15 nM C, a 20-fold decrease in concentration. Dissolved black carbon photo-degradation was more rapid and more extensive than for bulk CDOM and DOC. Further, the photo-lability of components of the DBC pool increased with their degree of aromatic condensation. These trends indicate that a continuum of compounds of varying photo-lability exists within the marine DOC pool. In this continuum, photo-lability scales with aromatic character, specifically the degree of condensation. Scaling the rapid photo-degradation of DBC to rates of DOC photo-mineralisation for the global ocean leads to an estimated photo-chemical half-life for oceanic DBC of less than 800 yr. This is more than an order of magnitude shorter than the apparent age of DBC in the ocean. Photo-degradation is therefore posited as the primary sink for oceanic DBC and the survival of DBC molecules in the oceans for millennia appears to be facilitated not by their inherent inertness but by the rate at which they are cycled through the surface ocean's photic zone.
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Perol, Maurice, Tudor-Eliade Ciuleanu, Oscar Arrieta, Kumar Prabhash, Konstantinos N. Syrigos, Tuncay Göksel, Keunchil Park, et al. "REVEL: A randomized, double-blind, phase III study of docetaxel (DOC) and ramucirumab (RAM; IMC-1121B) versus DOC and placebo (PL) in the second-line treatment of stage IV non-small cell lung cancer (NSCLC) following disease progression after one prior platinum-based therapy." Journal of Clinical Oncology 32, no. 18_suppl (June 20, 2014): LBA8006. http://dx.doi.org/10.1200/jco.2014.32.18_suppl.lba8006.
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LBA8006^ Background: RAM is a human IgG1 monoclonal antibody that targets the extracellular domain of VEGFR-2. The REVEL study evaluated the efficacy and safety of RAM+DOC vs. PL+DOC (DOC) in patients (pts) with stage IV nonsquamous (NSQ) and squamous (SQ) NSCLC after platinum-based therapy. Methods: Pts with NSQ and SQ stage IV NSCLC were randomized 1:1 (stratified by sex, region, ECOG PS, and prior maintenance therapy) to receive DOC 75 mg/m2 in combination with either RAM 10 mg/kg or PL on day 1 of a 21-day cycle until disease progression, unacceptable toxicity, or death. The primary endpoint was overall survival (OS). Secondary efficacy endpoints included progression-free survival (PFS), and objective response rate (ORR). Results: Between Dec 2010 and Feb 2013, 1,253 pts (26.2% SQ) were randomized (RAM+DOC: 628; DOC: 625). Pt characteristics were balanced between arms. ORR was 22.9% for RAM+DOC and 13.6% for DOC (P<0.001). The hazard ratio (HR) for PFS was 0.762 (P<0.0001); median PFS was 4.5 months (m) for RAM+DOC vs. 3.0m for DOC. REVEL met its primary endpoint; the OS HR was 0.857 (95% CI 0.751, 0.98; P=0.0235); median OS was 10.5m for RAM+DOC vs. 9.1m for DOC. OS was longer for RAM+DOC in most pt subgroups, including SQ and NSQ histology. Grade ≥3 adverse events (AEs) occurring in >5% of pts on RAM+DOC were neutropenia (34.9% vs. 28.0%), febrile neutropenia (15.9% vs. 10.0%), fatigue (11.3% vs. 8.1%), leukopenia (8.5% vs. 7.6%), hypertension (5.4% vs. 1.9%), and pneumonia (5.1% vs. 5.8%). Grade 5 AEs were comparable between arms (5.4% vs. 5.8%), as was pulmonary hemorrhage (any grade; all pts: 2.1% vs. 1.6%; SQ pts: 3.8% vs. 2.4%). Conclusions: REVEL demonstrated a statistically significant improvement in ORR, PFS, and OS for RAM+DOC vs DOC in NSCLC pts with stage IV NSCLC as second-line treatment after platinum-based therapy. Benefits were similar in NSQ and SQ pts, and no unexpected AEs were identified. Clinical trial information: NCT01168973.
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Swander, Mary. "Doc." Iowa Review 16, no. 1 (January 1986): 39–47. http://dx.doi.org/10.17077/0021-065x.3296.
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Shallenberger, Dorothy. "Doc." International Jazz Archive Journal 03, no. 2 (October 1, 2007): 139. http://dx.doi.org/10.2307/44758121.
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Hou, Jianfeng, Fei Li, Zhihui Wang, Xuqing Li, Rui Cao, and Wanqin Yang. "Dynamics of Dissolved Carbon in Subalpine Forest Streams." Forests 13, no. 5 (May 19, 2022): 795. http://dx.doi.org/10.3390/f13050795.
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Dissolved carbon (DC) in forest streams plays a crucial role in maintaining the structure and productivity of adjoining aquatic ecosystems as well as informing biogeochemical links between mountain forests and adjoining rivers. Nevertheless, the functions of forest stream DC dynamics are rarely incorporated into river management. To better understand the biogeochemical links between subalpine forests and adjoining streams, the seasonal dynamics of DC in 15 representative forest streams were investigated in a geographically fragile subalpine-gorge catchment in the upper reaches of the Yangtze River. Depending on stream characteristics and critical periods, the DC stocks in the streams ranged from 0.22 to 2.35 mg m−2 for total DC, from 0.10 to 1.66 mg m−2 for dissolved inorganic carbon (DIC), and from 0.12 to 1.27 mg m−2 for dissolved organic carbon (DOC). Moreover, the annual stocks of DC, DIC, and DOC were 1.01, 0.56, and 0.45 mg m−2, respectively. Correspondingly, the averaged export rates for DC, DIC, and DOC from the forest streams ranged from 0.27 to 1.98 mg s−1, from 0.24 to 1.48 mg s−1, and from 0.18 to 0.90 mg s−1, respectively, in the subalpine forest catchment. The annual export rates of total DC, DIC, and DOC were 1.06, 0.75, and 0.31 mg C s−1, respectively. In particular, the highest rates of export were 4.67, 3.53, and 1.34 mg s−1 for DC, DIC, and DOC, respectively, in the snowmelt period. The average ratios of DOC to DIC stock in the export water ranged from 0.23–2.41 for the 15 streams, and the average value was 0.85 during this one-year investigation. In addition, the maximum and minimum values of the DC stocks, their exports, and the DIC:DOC ratio were consistently observed during the snowmelt season and the late growing period. In summary, precipitation, temperature, water discharge rate, and sediment depth regulated the stocks and export rates of DC and its components. In general, forest streams are important links between the carbon biogeochemical cycle of subalpine forests and adjoining streams.
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Stubbins, A., J. Niggemann, and T. Dittmar. "Photo-lability of deep ocean dissolved black carbon." Biogeosciences 9, no. 5 (May 9, 2012): 1661–70. http://dx.doi.org/10.5194/bg-9-1661-2012.
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Abstract. Dissolved black carbon (DBC), defined here as condensed aromatics isolated from seawater via PPL solid phase extraction and quantified as benzenepolycarboxylic acid (BPCA) oxidation products, is a significant component of the oceanic dissolved organic carbon (DOC) pool. These condensed aromatics are widely distributed in the open ocean and appear to be tens of thousands of years old. As such DBC is regarded as highly refractory. In the current study, the photo-lability of DBC, DOC and coloured dissolved organic matter (CDOM; ultraviolet-visible absorbance) were determined over the course of a 28 day irradiation of North Atlantic Deep Water under a solar simulator. During the irradiation DBC fell from 1044 ± 164 nM-C to 55 ± 15 nM-C, a 20-fold decrease in concentration. Dissolved black carbon photo-degradation was more rapid and more extensive than for bulk CDOM and DOC. The concentration of DBC correlated with CDOM absorbance and the quality of DBC indicated by the ratios of different BPCAs correlated with CDOM absorbance spectral slope, suggesting the optical properties of CDOM may provide a proxy for both DBC concentrations and quality in natural waters. Further, the photo-lability of components of the DBC pool increased with their degree of aromatic condensation. These trends indicate that a continuum of compounds of varying photo-lability exists within the marine DOC pool. In this continuum, photo-lability scales with aromatic character, specifically the degree of condensation. Scaling the rapid photo-degradation of DBC to rates of DOC photo-mineralisation for the global ocean leads to an estimated photo-chemical half-life for oceanic DBC of less than 800 years. This is more than an order of magnitude shorter than the apparent age of DBC in the ocean. Consequently, photo-degradation is posited as the primary sink for oceanic DBC and the apparent survival of DBC molecules in the oceans for millennia appears to be facilitated not by their inherent inertness but by the rate at which they are cycled through the surface ocean's photic zone.
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Costello, Nicole. "When doc becomes doc and mom." American Association of Bovine Practitioners Conference Proceedings, no. 57 (May 14, 2024): 100–101. http://dx.doi.org/10.21423/aabppro20248997.
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As the proportion of women entering the veterinary workforce continues to grow, young veterinarians are demonstrating an increasing need for guidance in navigating pregnancy and motherhood while maintaining their role as a veterinarian. As a relatively new issue for many rural practices, the profession lacks a consistent and distinct precedent for maternity leave and what can be expected during pregnancy. One veterinarian’s experience cannot begin to cover what can be expected for everyone, but can provide tips and insight onto navigating these concerns for other new graduates and practice owners. Following the obvious challenges of pregnancy and then maternity leave comes the more difficult task of juggling on-call, daycare schedules and sick kids with a busy and unpredictable veterinary schedule. Finding a balance is not always easy but can be incredibly rewarding with the right mindset.
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Lyon, S. W., M. Mörth, C. Humborg, R. Giesler, and G. Destouni. "Investigating the relationship between subsurface hydrology and dissolved carbon fluxes for a sub-arctic catchment." Hydrology and Earth System Sciences Discussions 7, no. 2 (March 3, 2010): 1677–703. http://dx.doi.org/10.5194/hessd-7-1677-2010.
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Abstract. In recent years, there has been increased interest in carbon cycling in natural systems due to its role in a changing climate. Northern latitude systems are especially important as they may serve as a potentially large source or sink of terrestrial carbon. There are, however, a limited number of investigations reporting on actual flux rates of carbon moving from the subsurface landscape to surface water systems in northern latitudes. This study estimates dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) fluxes from the subsurface landscape for a sub-arctic catchment located in northern Sweden. Estimates are based on observed annual in-stream flux-averaged concentrations of DOC and DIC at the outlet of the 566 km2 Abiskojokken catchment and from catchment-scale transport modeling based on advective solute travel times and their spatial distributions. We also demonstrate the importance of correctly representing the spatial distribution of the advective solute travel times along the various flow and transport pathways. For the sub-arctic catchment considered in this study, there is a relative balance between the flux of DOC and DIC from the subsurface landscape to the surface water system. This balance between DOC and DIC fluxes could shift under future climatic changes that influence the hydrological and biogeochemical system.
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Szymczycha, B., A. Maciejewska, A. Szczepanska, and J. Pempkowiak. "The submarine groundwater discharge as a carbon source to the Baltic Sea." Biogeosciences Discussions 10, no. 2 (February 5, 2013): 2069–91. http://dx.doi.org/10.5194/bgd-10-2069-2013.
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Abstract. Submarine Groundwater Discharge (SGD) is an important, yet poorly recognized pathway of material transport to the marine environment. This work reports on the results of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations in the groundwater seeping to the Bay of Puck. The loads of carbon via SGD were quantified for the Baltic Sea sub-basins and the entire Baltic Sea. The annual averages of DIC and DOC concentrations in the groundwater were equal to 64.5 ± 10.0 mg C L−1 and 5.8 ± 0.9 mg C L−1. The DIC and DOC fluxes via SGD to the Baltic Sea were estimated at 283.6 ± 66.7 kt yr−1 and 25.5 ± 4.2 kt yr−1. The SGD derived carbon load to the Baltic Sea is an important component of carbon budget, which turns the status of the sea into firmly heterotrophic. The carbon load to the World Ocean, which was calculated basing on few reports on groundwater discharges and the measured carbon concentrations, amounts to- (142–155) × 103 kt yr−1 (DIC), and (13–14) × 103 kt yr−1 (DOC). The carbon flux via SGD amounts to some 25% of the riverine carbon load, and should be included into the World Ocean carbon budget.
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Lakshmi, R., and S. Baskar. "DIC-DOC-K-means: Dissimilarity-based Initial Centroid selection for DOCument clustering using K-means for improving the effectiveness of text document clustering." Journal of Information Science 45, no. 6 (December 19, 2018): 818–32. http://dx.doi.org/10.1177/0165551518816302.
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In this article, a new initial centroid selection for a K-means document clustering algorithm, namely, Dissimilarity-based Initial Centroid selection for DOCument clustering using K-means (DIC-DOC- K-means), to improve the performance of text document clustering is proposed. The first centroid is the document having the minimum standard deviation of its term frequency. Each of the other subsequent centroids is selected based on the dissimilarities of the previously selected centroids. For comparing the performance of the proposed DIC-DOC- K-means algorithm, the results of the K-means, K-means++ and weighted average of terms-based initial centroid selection + K-means (Weight_Avg_Initials + K-means) clustering algorithms are considered. The results show that the proposed DIC-DOC- K-means algorithm performs significantly better than the K-means, K-means++ and Weight_Avg_Initials+ K-means clustering algorithms for Reuters-21578 and WebKB with respect to purity, entropy and F-measure for most of the cluster sizes. The cluster sizes used for Reuters-8 are 8, 16, 24 and 32 and those for WebKB are 4, 8, 12 and 16. The results of the proposed DIC-DOC- K-means give a better performance for the number of clusters that are equal to the number of classes in the data set.
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Fiedler, S., B. S. Höll, A. Freibauer, K. Stahr, M. Drösler, M. Schloter, and H. F. Jungkunst. "The relevance of particulate organic carbon (POC) for carbon composition in the pore water of drained and rewetted fens of the "Donauried" (South-Germany)." Biogeosciences Discussions 5, no. 3 (May 15, 2008): 2049–73. http://dx.doi.org/10.5194/bgd-5-2049-2008.
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Abstract. Numerous studies have dealt with carbon (C) concentrations in Histosols, but there are no studies quantifying the relative importance of all individual C components in pore waters. For this study, measurements were made of all the carbon components (i.e., particulate organic carbon, POC; dissolved organic carbon, DOC; dissolved inorganic carbon, DIC; dissolved methane, CH4) in the soil pore water of a calcareous fen under three different water management regimes (re-wetted, deeply and moderately drained). Pore water was collected weekly or biweekly (April 2004 to April 2006) at depths between 10 and 150 cm. The main results obtained were: (1) DIC (94–280 mg C l−1) was the main C-component. (2) POC and DOC concentrations in the pore water (14–125 mg C l−1 vs. 41–95 mg C l−1) were pari passu. (3) Dissolved CH4 was the smallest C component (0.005–0.9 mg C l−1). Interestingly, about 30% of the POM particles were colonized by microbes indicating that they are active in the internal C transfer in the soil profile ("C-Shuttles"). Consequently, it was concluded that POC is at least as important as DOC for internal soil C turnover. There is no reason to assume significant biochemical differences between POC and DOC as they only differ in size. Therefore, both POC and DOC fractions are essential components of C budgets of peatlands. Furthermore dissolved CO2 in all forms of DIC apparently is an important part of peatland C-balances.
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Potter, Lee, and Y. Jun Xu. "Variability of Carbon Export in the Lower Mississippi River during an Extreme Cold and Warm Year." Water 14, no. 19 (September 27, 2022): 3044. http://dx.doi.org/10.3390/w14193044.
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The Mississippi River (MR) discharges on average 474 km3 of water annually into the Northern Gulf of Mexico (NGOM) with a large quantity of carbon, playing a vital role in the ecosystem’s food chain and water quality. In this study, we analyzed exports of dissolved inorganic (DIC) and organic carbon (DOC) from January 2021 to December 2021, during which the contiguous United States experienced one of the coldest winters as well as the hottest summer on record. Bi-weekly in situ river measurements and water sampling were conducted in the lower MR at Baton Rouge in Louisiana, USA, approximately 368 km from the river’s mouth. We found that the MR transported 12.61 Tg C of DIC and 4.54 Tg C of DOC into the NGOM during the study period. Much of the DOC mass export occurred during the winter (~38%), while much of the DIC mass export took place in the spring months (~35%). The seasonality of DOC and DIC exports was affected by their concentrations, water temperature, and discharge. DIC concentrations were significantly higher in the fall (32.0 mg L−1) than those during the winter (20.4 mg L−1), while DOC concentrations were highest during the winter months (11.3 mg L−1) and varied seasonally, however, not significantly. Partial pressure of dissolved carbon dioxide (pCO2) in the MR averaged 1703 ± 646 µatm peaking in the summer at 2594 µatm and reaching a low in the winter at 836 µatm. Outgassing of CO2 (FCO2) peaked in the spring averaging 3.43 g C m2 d−1 and was lowest in the winter at 1.62 g C m2 y−1. Our findings validate our initial hypotheses that seasonal variability and weather extremes strongly affect terrestrial-aquatic carbon transfer, and that climate change will likely intensify carbon export from the Mississippi River Basin.
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Attermeyer, K., T. Hornick, Z. E. Kayler, A. Bahr, E. Zwirnmann, H. P. Grossart, and K. Premke. "Increasing addition of autochthonous to allochthonous carbon in nutrient-rich aquatic systems stimulates carbon consumption but does not alter bacterial community composition." Biogeosciences Discussions 10, no. 8 (August 27, 2013): 14261–300. http://dx.doi.org/10.5194/bgd-10-14261-2013.
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Abstract. Dissolved organic carbon (DOC) concentrations – mainly of terrestrial origin – are increasing worldwide in inland waters. The biodegradability of the DOC varies depending on quantity and chemical quality. Heterotrophic bacteria are the main consumers of DOC and thus determine DOC temporal dynamics and availability for higher trophic levels. It is therefore crucial to understand the processes controlling the bacterial turnover of additional allochthonous and autochthonous DOC in aquatic systems. Our aim was to study bacterial carbon (C) turnover with respect to DOC quantity and chemical quality using both allochthonous and autochthonous DOC sources. We incubated a natural bacterial community with allochthonous C (13C-labeled beech leachate) and increased concentrations and pulses (intermittent occurrence of organic matter input) of autochthonous C (algae lysate). We then determined bacterial carbon consumption, activities, and community composition together with the carbon flow through bacteria using stable C isotopes. The chemical analysis of single sources revealed differences in aromaticity and fractions of low and high molecular weight substances (LMWS and HMWS, respectively) between allochthonous and autochthonous C sources. In parallel to these differences in chemical composition, we observed a higher availability of allochthonous C as evidenced by increased DOC consumption and bacterial growth efficiencies (BGE) when solely allochthonous C was provided. In treatments with mixed sources, rising concentrations of added autochthonous DOC resulted in a further, significant increase in bacterial DOC consumption from 52 to 68% when nutrients were not limiting. This rise was accompanied by a decrease in the humic substances (HS) fraction and an increase in bacterial biomass. Stable C isotope analyses of phospholipid fatty acids (PLFA) and respired dissolved inorganic carbon (DIC) supported a preferential assimilation of autochthonous C and respiration of the allochthonous C. Changes in DOC concentration and consumption in mixed treatments did not affect bacterial community composition (BCC), but BCC differed in single vs. mixed incubations. Our study highlights that DOC quantity affects bacterial C consumption but not BCC in nutrient-rich aquatic systems. BCC shifted when a mixture of allochthonous and autochthonous C was provided simultaneously to the bacterial community. Our results indicate that chemical quality rather than source of DOC per se (allochthonous vs. autochthonous) determines bacterial DOC turnover.
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Morley, Catherine. "Why A Doc With a Dip Doc?" Critical Dietetics 1, no. 1 (April 24, 2011): 30–34. http://dx.doi.org/10.32920/cd.v1i1.837.
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In 2007, when I began studies toward two diplomas, one in textile arts, and one in documentary film this seeming ‘change of focus’ prompted questions from dietetics and research colleagues: Was I changing careers? What did visual arts and film have to do with dietetics and research? In addition to personal reasons for these studies, I wanted ‘time out’ from consulting and research to develop my knowledge and skills in these artforms, and to explore them as means to broaden the reach of research findings. In this article, I discuss the potential for film and visual arts in dietetics practice and education. Arts-based inquiry and practice offer ways to disrupt power differentials, to question what counts as knowledge and whose/what voices ought to count, to invite reflections on and conversations about meanings imbedded in food and in eating behaviour, and to integrate this knowledge into collaborative, client-centred approaches to nutrition education.
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Fritz, M., T. Opel, G. Tanski, U. Herzschuh, H. Meyer, A. Eulenburg, and H. Lantuit. "Dissolved organic carbon (DOC) in Arctic ground ice." Cryosphere 9, no. 2 (April 20, 2015): 737–52. http://dx.doi.org/10.5194/tc-9-737-2015.
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Abstract. Thermal permafrost degradation and coastal erosion in the Arctic remobilize substantial amounts of organic carbon (OC) and nutrients which have accumulated in late Pleistocene and Holocene unconsolidated deposits. Permafrost vulnerability to thaw subsidence, collapsing coastlines and irreversible landscape change are largely due to the presence of large amounts of massive ground ice such as ice wedges. However, ground ice has not, until now, been considered to be a source of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and other elements which are important for ecosystems and carbon cycling. Here we show, using biogeochemical data from a large number of different ice bodies throughout the Arctic, that ice wedges have the greatest potential for DOC storage, with a maximum of 28.6 mg L−1 (mean: 9.6 mg L−1). Variation in DOC concentration is positively correlated with and explained by the concentrations and relative amounts of typically terrestrial cations such as Mg2+ and K+. DOC sequestration into ground ice was more effective during the late Pleistocene than during the Holocene, which can be explained by rapid sediment and OC accumulation, the prevalence of more easily degradable vegetation and immediate incorporation into permafrost. We assume that pristine snowmelt is able to leach considerable amounts of well-preserved and highly bioavailable DOC as well as other elements from surface sediments, which are rapidly frozen and stored in ground ice, especially in ice wedges, even before further degradation. We found that ice wedges in the Yedoma region represent a significant DOC (45.2 Tg) and DIC (33.6 Tg) pool in permafrost areas and a freshwater reservoir of 4200 km2. This study underlines the need to discriminate between particulate OC and DOC to assess the availability and vulnerability of the permafrost carbon pool for ecosystems and climate feedback upon mobilization.
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Fritz, M., T. Opel, G. Tanski, U. Herzschuh, H. Meyer, A. Eulenburg, and H. Lantuit. "Dissolved organic carbon (DOC) in Arctic ground ice." Cryosphere Discussions 9, no. 1 (January 7, 2015): 77–114. http://dx.doi.org/10.5194/tcd-9-77-2015.
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Abstract. Thermal permafrost degradation and coastal erosion in the Arctic remobilize substantial amounts of organic carbon (OC) and nutrients which have been accumulated in late Pleistocene and Holocene unconsolidated deposits. Their vulnerability to thaw subsidence, collapsing coastlines and irreversible landscape change is largely due to the presence of large amounts of massive ground ice such as ice wedges. However, ground ice has not, until now, been considered to be a source of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and other elements, which are important for ecosystems and carbon cycling. Here we show, using geochemical data from a large number of different ice bodies throughout the Arctic, that ice wedges have the greatest potential for DOC storage with a maximum of 28.6 mg L−1 (mean: 9.6 mg L−1). Variation in DOC concentration is positively correlated with and explained by the concentrations and relative amounts of typically terrestrial cations such as Mg2+ and K+. DOC sequestration into ground ice was more effective during the late Pleistocene than during the Holocene, which can be explained by rapid sediment and OC accumulation, the prevalence of more easily degradable vegetation and immediate incorporation into permafrost. We assume that pristine snowmelt is able to leach considerable amounts of well-preserved and highly bioavailable DOC as well as other elements from surface sediments, which are rapidly stored in ground ice, especially in ice wedges, even before further degradation. In the Yedoma region ice wedges represent a significant DOC (45.2 Tg) and DIC (33.6 Tg) pool in permafrost areas and a fresh-water reservoir of 4172 km3. This study underlines the need to discriminate between particulate OC and DOC to assess the availability and vulnerability of the permafrost carbon pool for ecosystems and climate feedback upon mobilization.
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Vinebrooke, R. D., and M. D. Graham. "Periphyton assemblages as indicators of recovery in acidified Canadian Shield lakes." Canadian Journal of Fisheries and Aquatic Sciences 54, no. 7 (July 1, 1997): 1557–68. http://dx.doi.org/10.1139/f97-063.
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Periphyton is very responsive to abiotic changes within recovering acidified shield lakes. We conducted a survey of acidified shield lakes to assess epilithic periphyton assemblages as indicators of natural recovery. Canonical correspondence and regression analyses both showed that dissolved inorganic carbon (DIC) was the best predictor of taxonomic composition, biomass accrual, and species richness in lakes of low alkalinity. Dissolved organic carbon (DOC) was also a significant predictor of taxonomic composition, and biomass accrual (desmids, filamentous green algae, and total). Constrained indicator species analysis identified Actinotaenium cucurbita, Cylindrocystis brebissonii, Eunotia bactriana, Fragilaria acidobiontica, Homoeothrix juliana, Tetmemorus laevis, and Zygogonium ericetorum as indicators of high-acidity (pH <5.0), clearwater lakes with low (<0.3 mg/L) DIC concentrations. Achnanthes minutissima, Cymbella microcephala, and Gomphonema acuminatum were indicative of low-acidity (pH >5.6) lakes with higher DIC concentrations (>0.6 mg/L) and positive buffering capacities. Our findings suggest that periphyton in recovering acidified shield lakes are stimulated by increasing DIC and DOC concentrations. Increases in DIC availability might enhance recolonization by diatoms in clearwater lakes, while increases in DOC concentrations may favour desmids and filamentous zygnematacean taxa, especially in naturally acidic brown-water lakes.
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Jeanneau, Laurent, Pauline Buysse, Marie Denis, Gérard Gruau, Patrice Petitjean, Anne Jaffrézic, Chris Flechard, and Valérie Viaud. "Water Table Dynamics Control Carbon Losses from the Destabilization of Soil Organic Matter in a Small, Lowland Agricultural Catchment." Soil Systems 4, no. 1 (December 20, 2019): 2. http://dx.doi.org/10.3390/soilsystems4010002.
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The biogeochemistry of soil organic matter (SOM) is driven by a combination of stabilization and destabilization mechanisms. Among the various ways in which SOM is lost, soil moisture controls the leaching of dissolved organic and inorganic carbon (DOC and DIC) and CO2 fluxes (FCO2). The aim of this study was to investigate the impact of naturally occurring water table dynamics on the couplings between these three types of C losses. The DIC and DOC concentrations in the soil solutions and the FCO2 values at the soil surface were collected fortnightly over a nine-month period at four sampling points located along two topographic transects characterized by different water table dynamics. The water table depth, soil temperature and water-filled pore space (WFPS) were monitored at each site. Linear and nonlinear regressions were used to explore the couplings between C losses, WFPS and soil temperature. The dynamics of the water table seem to drive DOC solubilization, diffusion, and export mechanisms in addition to microbial processes and the equilibrium between DIC and CO2. The main descriptors of this water table dynamic were the residence time, return time and number of oscillations of the water table. Considering both transects, FCO2 was positively correlated with DOC, which highlights the importance of substrate accessibility for SOM mineralization. This paper emphasizes the importance of the water table dynamic for the coupling between SOM carbon losses.
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Drake, Travis W., Kimberly P. Wickland, Robert G. M. Spencer, Diane M. McKnight, and Robert G. Striegl. "Ancient low–molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw." Proceedings of the National Academy of Sciences 112, no. 45 (October 26, 2015): 13946–51. http://dx.doi.org/10.1073/pnas.1511705112.
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Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high–temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low–molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2to the atmosphere by soils and nearby inland waters.
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Pokrovsky, O. S., R. M. Manasypov, S. Loiko, L. S. Shirokova, I. A. Krickov, B. G. Pokrovsky, L. G. Kolesnichenko, et al. "Permafrost coverage, watershed area and season control of dissolved carbon and major elements in western Siberian rivers." Biogeosciences 12, no. 21 (November 5, 2015): 6301–20. http://dx.doi.org/10.5194/bg-12-6301-2015.
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Abstract. Analysis of organic and inorganic carbon (DOC and DIC, respectively), pH, Na, K, Ca, Mg, Cl, SO4 and Si in ~ 100 large and small rivers (< 10 to ≤ 150 000 km2) of western Siberia sampled in winter, spring, and summer over a more than 1500 km latitudinal gradient allowed establishing main environmental factors controlling the transport of river dissolved components in this environmentally important region, comprising continuous, discontinuous, sporadic and permafrost-free zones. There was a significant latitudinal trend consisting in a general decrease in DOC, DIC, SO4, and major cation (Ca, Mg, Na, K) concentration northward, reflecting the interplay between groundwater feeding (detectable mostly in the permafrost-free zone, south of 60° N) and surface flux (in the permafrost-bearing zone). The northward decrease in concentration of inorganic components was strongly pronounced both in winter and spring, whereas for DOC, the trend of concentration decrease with latitude was absent in winter, and less pronounced in spring flood than in summer baseflow. The most significant decrease in K concentration from the southern (< 59° N) to the northern (61–67° N) watersheds occurs in spring, during intense plant litter leaching. The latitudinal trends persisted for all river watershed size, from < 100 to > 10 000 km2. Environmental factors are ranked by their increasing effect on DOC, DIC, δ13CDIC, and major elements in western Siberian rivers as follows: watershed area < season < latitude. Because the degree of the groundwater feeding is different between large and small rivers, we hypothesize that, in addition to groundwater feeding of the river, there was a significant role of surface and shallow subsurface flow linked to plant litter degradation and peat leaching. We suggest that plant-litter- and topsoil-derived DOC adsorbs on clay mineral horizons in the southern, permafrost-free and discontinuous/sporadic permafrost zone but lacks the interaction with minerals in the continuous permafrost zone. It can be anticipated that, under climate warming in western Siberia, the maximal change will occur in small (< 1000 km2 watershed) rivers DOC, DIC and ionic composition and this change will be mostly pronounced in summer.
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Nakhavali, Mahdi, Pierre Friedlingstein, Ronny Lauerwald, Jing Tang, Sarah Chadburn, Marta Camino-Serrano, Bertrand Guenet, et al. "Representation of dissolved organic carbon in the JULES land surface model (vn4.4_JULES-DOCM)." Geoscientific Model Development 11, no. 2 (February 12, 2018): 593–609. http://dx.doi.org/10.5194/gmd-11-593-2018.
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Abstract. Current global models of the carbon (C) cycle consider only vertical gas exchanges between terrestrial or oceanic reservoirs and the atmosphere, thus not considering the lateral transport of carbon from the continents to the oceans. Therefore, those models implicitly consider all of the C which is not respired to the atmosphere to be stored on land and hence overestimate the land C sink capability. A model that represents the whole continuum from atmosphere to land and into the ocean would provide a better understanding of the Earth's C cycle and hence more reliable historical or future projections. A first and critical step in that direction is to include processes representing the production and export of dissolved organic carbon in soils. Here we present an original representation of dissolved organic C (DOC) processes in the Joint UK Land Environment Simulator (JULES-DOCM) that integrates a representation of DOC production in terrestrial ecosystems based on the incomplete decomposition of organic matter, DOC decomposition within the soil column, and DOC export to the river network via leaching. The model performance is evaluated in five specific sites for which observations of soil DOC concentration are available. Results show that the model is able to reproduce the DOC concentration and controlling processes, including leaching to the riverine system, which is fundamental for integrating terrestrial and aquatic ecosystems. Future work should include the fate of exported DOC in the river system as well as DIC and POC export from soil.
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Spilling, Kristian, Kai G. Schulz, Allanah J. Paul, Tim Boxhammer, Eric P. Achterberg, Thomas Hornick, Silke Lischka, et al. "Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment." Biogeosciences 13, no. 21 (November 4, 2016): 6081–93. http://dx.doi.org/10.5194/bg-13-6081-2016.
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Abstract. About a quarter of anthropogenic CO2 emissions are currently taken up by the oceans, decreasing seawater pH. We performed a mesocosm experiment in the Baltic Sea in order to investigate the consequences of increasing CO2 levels on pelagic carbon fluxes. A gradient of different CO2 scenarios, ranging from ambient ( ∼ 370 µatm) to high ( ∼ 1200 µatm), were set up in mesocosm bags ( ∼ 55 m3). We determined standing stocks and temporal changes of total particulate carbon (TPC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC) of specific plankton groups. We also measured carbon flux via CO2 exchange with the atmosphere and sedimentation (export), and biological rate measurements of primary production, bacterial production, and total respiration. The experiment lasted for 44 days and was divided into three different phases (I: t0–t16; II: t17–t30; III: t31–t43). Pools of TPC, DOC, and DIC were approximately 420, 7200, and 25 200 mmol C m−2 at the start of the experiment, and the initial CO2 additions increased the DIC pool by ∼ 7 % in the highest CO2 treatment. Overall, there was a decrease in TPC and increase of DOC over the course of the experiment. The decrease in TPC was lower, and increase in DOC higher, in treatments with added CO2. During phase I the estimated gross primary production (GPP) was ∼ 100 mmol C m−2 day−1, from which 75–95 % was respired, ∼ 1 % ended up in the TPC (including export), and 5–25 % was added to the DOC pool. During phase II, the respiration loss increased to ∼ 100 % of GPP at the ambient CO2 concentration, whereas respiration was lower (85–95 % of GPP) in the highest CO2 treatment. Bacterial production was ∼ 30 % lower, on average, at the highest CO2 concentration than in the controls during phases II and III. This resulted in a higher accumulation of DOC and lower reduction in the TPC pool in the elevated CO2 treatments at the end of phase II extending throughout phase III. The “extra” organic carbon at high CO2 remained fixed in an increasing biomass of small-sized plankton and in the DOC pool, and did not transfer into large, sinking aggregates. Our results revealed a clear effect of increasing CO2 on the carbon budget and mineralization, in particular under nutrient limited conditions. Lower carbon loss processes (respiration and bacterial remineralization) at elevated CO2 levels resulted in higher TPC and DOC pools than ambient CO2 concentration. These results highlight the importance of addressing not only net changes in carbon standing stocks but also carbon fluxes and budgets to better disentangle the effects of ocean acidification.
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Lyon, S. W., M. Mörth, C. Humborg, R. Giesler, and G. Destouni. "The relationship between subsurface hydrology and dissolved carbon fluxes for a sub-arctic catchment." Hydrology and Earth System Sciences 14, no. 6 (June 15, 2010): 941–50. http://dx.doi.org/10.5194/hess-14-941-2010.
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Abstract. In recent years, there has been increased interest in carbon cycling in natural systems due to its role in a changing climate. Northern latitude systems are especially important as they may serve as a potentially large source or sink of terrestrial carbon. There are, however, a limited number of investigations reporting on actual flux rates of carbon moving from the subsurface landscape to surface water systems in northern latitudes. In this study, we determined dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) fluxes from the subsurface landscape for a sub-arctic catchment located in northern Sweden. These are based on observed annual flux-averaged concentrations of DOC and DIC for the 566 km2 Abiskojokken catchment. We demonstrate the importance to correctly represent the spatial distribution of the advective solute travel times along the various flow and transport pathways. The fluxes of DOC and DIC from the subsurface landscape to the surface water system were comparable in magnitude. This balance could shift under future climatic changes that influence the hydrological and biogeochemical system.
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Hartstein, Morris E. "Terrorist Doc." Missouri Review 44, no. 3 (2021): 126–40. http://dx.doi.org/10.1353/mis.2021.0043.
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Douglas, Kimberly, and Dana L. Roth. "TOC/DOC." Science & Technology Libraries 16, no. 3-4 (January 15, 1998): 131–45. http://dx.doi.org/10.1300/j122v16n03_09.
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Hebert, K. "Top doc." BMJ 326, no. 7386 (February 22, 2003): 62S—62. http://dx.doi.org/10.1136/bmj.326.7386.s62.
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Golden, Larry, Jennifer Alamía, Ria Baker, Sally Chilson, Pierre Choucroun, Katrina Cook, Sabina de Vries-Kell, Christina Marbach, and Scott Peters. "Doc Tales." Family Journal 13, no. 4 (October 2005): 487–90. http://dx.doi.org/10.1177/1066480705278727.
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