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1
Li, Yunliang, Jing Yao e Li Zhang. "Investigation into mixing in the shallow floodplain Poyang Lake (China) using hydrological, thermal and isotopic evidence". Water Science and Technology 74, n. 11 (17 settembre 2016): 2582–98. http://dx.doi.org/10.2166/wst.2016.444.
Testo completoAbstract (sommario):
Although mixing in lakes has significant environmental and ecological implications, knowledge of mixing dynamics for shallow floodplain lakes has received little attention. In this study, hydrological, thermal and isotopic investigations were undertaken to provide evidence for the mixing in the large, shallow floodplain Poyang Lake (China). Depth profiles of water velocity, water temperature and stable hydrogen and oxygen isotope compositions were measured throughout the lake, with results showing that the water velocity differences in depth profiles are generally less than ∼0.2 m/s, indicating weak stratification. Although water temperature differences of up to ∼2 °C are observed occasionally, Poyang Lake appears to have isothermal mixed layers from the epilimnion to the hypolimnion, attributed to the presence of mostly small temperature differences (<1 °C). Additionally, isotope compositions reveal that the lake's water columns are almost homogeneous during various water-level periods. Relative to many lakes exhibiting either no mixing or partial mixing, Poyang Lake appears to be fully mixing on a seasonal basis, depending on hydrological forcings within the lake rather than meteorological conditions. The current study will help to improve our knowledge of water flow patterns and pollutant transport in Poyang Lake and other similar floodplain lakes.
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Peeters, F., A. Wüest, G. Piepke e D. M. Imboden. "Horizontal mixing in lakes". Journal of Geophysical Research: Oceans 101, n. C8 (15 agosto 1996): 18361–75. http://dx.doi.org/10.1029/96jc01145.
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Bengtsson, Lars. "Mixing in ice-covered lakes". Hydrobiologia 322, n. 1-3 (aprile 1996): 91–97. http://dx.doi.org/10.1007/bf00031811.
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Dembowska, Ewa. "Cyanobacterial blooms in shallow lakes of the Iławskie Lake District". Limnological Review 11, n. 2 (1 gennaio 2011): 69–79. http://dx.doi.org/10.2478/v10194-011-0028-y.
Testo completoAbstract (sommario):
Cyanobacterial blooms in shallow lakes of the Iławskie Lake DistrictThe dominance of blue-green algae observed in many lakes is related to a high trophic level. Shallow eutrophic lakes are particularly often abundant in blue-green algae. The research on phytoplankton, the results of which are presented in this paper, was carried out between 2002 and 2005 in six lakes. These lakes differed considerably in their size and management methods applied in the catchment (drainage) area. A few types of water blooms were distinguished, which is related to the catchment area management, the intensity of mixing and the trophic level. Algal blooms of the Planktothrix type appeared in lakes situated in an open area of agricultural catchment basins. Algal blooms of the Limnothrix type were characteristic of lakes with a forest-agricultural catchment area but surrounded by high shores, which reduced the wind influence on the mixing. Sporadic mixed algal blooms were typical of lakes situated in forest catchment areas.
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Davies‐Colley, Robert J. "Mixing depths in New Zealand lakes". New Zealand Journal of Marine and Freshwater Research 22, n. 4 (dicembre 1988): 517–28. http://dx.doi.org/10.1080/00288330.1988.9516322.
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Bergmann, Martin A., e Harold E. Welch. "Spring Meltwater Mixing in Small Arctic Lakes". Canadian Journal of Fisheries and Aquatic Sciences 42, n. 11 (1 novembre 1985): 1789–98. http://dx.doi.org/10.1139/f85-224.
Testo completoAbstract (sommario):
Meltwater mixing in small arctic lakes at Saqvaqjuac (63°68′N, 90°40′W) was studied in 1980 and 1981 to evaluate the applicability of theoretical lake water renewal times to the modeling of ice-covered lakes. Two 370-GBq tritium additions were made to 7.09-ha P&N Lake. One was mixed with the unfrozen water at the time of maximum lake-ice thickness (May 1980) and the other was mixed with the lake immediately after freezing (October 1980). Dye experiments were also performed at four lakes to define the spatial and temporal distribution of the inflow and icemelt layers. Results from the tritiated water and dye addition experiments, as well as conductance and temperature profiles, showed that during ice-on, the cold low-density meltwater floated in a thin layer 0–100 cm beneath the ice, extended over the entire subice-surface area, and left the lake without mixing with the heavier subice water. These results imply that (1) lake models incorporating a lake flushing rate term need to be reevaluated to accommodate the lack of meltwater mixing beneath spring ice and (2) more attention should be given to the early spring meltwater chemistry and its distribution within the upper lake strata.
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Helbling, E. W., P. Carrillo, J. M. Medina-Sanchez, C. Durán, G. Herrera, M. Villar-Argaiz e V. E. Villafañe. "Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes of Southern Europe". Biogeosciences Discussions 9, n. 7 (31 luglio 2012): 9791–827. http://dx.doi.org/10.5194/bgd-9-9791-2012.
Testo completoAbstract (sommario):
Abstract. Global change, together with human activities had resulted in increasing amounts of organic material (including nutrients) received by water bodies. This input further attenuates the penetration of solar radiation leading to the view that opaque lakes are more "protected" from solar ultraviolet radiation (UVR) than clear ones. Vertical mixing, however, complicates this view as cells are exposed to fluctuating radiation regimes, which effects have in general been neglected. Even more, the combined impacts of mixing, together with those of UVR and nutrients input are virtually unknown. In this study, we carried out in situ experiments in three high mountain lakes of Spain (Lake Enol in Asturias, and lakes Las Yeguas and La Caldera in Granada) to determine the combined effects of these three variables associated to global change on photosynthetic responses of natural phytoplankton communities. The experimentation consisted in all possible combinations of the following treatments: (a) solar radiation: UVR + PAR (280–700 nm) versus PAR alone (400–700 nm); (b) nutrient addition (phosphorus (P) and nitrogen (N)): ambient versus addition (P to reach to a final concentration of 30 μg P l−1, and N to reach a N : P molar ratio of 31) and, (c) mixing: mixed (one rotation from surface to 3 m depth (speed of 1 m every 4 min, total of 10 cycles) versus static. Our findings suggest that under in situ nutrient conditions there is a synergistic effect between vertical mixing and UVR, increasing phytoplankton photosynthetic inhibition and EOC from opaque lakes as compared to algae that received constant mean irradiance within the epilimnion. The opposite occurs in clear lakes where antagonistic effects were determined, with mixing partially counteracting the negative effects of UVR. Nutrients input mimicking atmospheric pulses from Saharan dust, reversed this effect and clear lakes became more inhibited during mixing, while opaque lakes benefited from the fluctuating irradiance regime. These climate change-related nutrients input and increased mixing would not only affect photosynthesis and production of lakes, but might also further influence the microbial loop and trophic interactions via enhanced EOC under fluctuating UVR exposure.
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Helbling, E. W., P. Carrillo, J. M. Medina-Sánchez, C. Durán, G. Herrera, M. Villar-Argaiz e V. E. Villafañe. "Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes in Southern Europe". Biogeosciences 10, n. 2 (14 febbraio 2013): 1037–50. http://dx.doi.org/10.5194/bg-10-1037-2013.
Testo completoAbstract (sommario):
Abstract. Global change, together with human activities, has resulted in increasing amounts of organic material (including nutrients) that water bodies receive. This input further attenuates the penetration of solar radiation, leading to the view that opaque lakes are more "protected" from solar ultraviolet radiation (UVR) than clear ones. Vertical mixing, however, complicates this view as cells are exposed to fluctuating radiation regimes, for which the effects have, in general, been neglected. Furthermore, the combined impacts of mixing, together with those of UVR and nutrient inputs are virtually unknown. In this study, we carried out complex in situ experiments in three high mountain lakes of Spain (Lake Enol in the National Park Picos de Europa, Asturias, and lakes Las Yeguas and La Caldera in the National Park Sierra Nevada, Granada), used as model ecosystems to evaluate the joint impact of these climate change variables. The main goal of this study was to address the question of how short-term pulses of nutrient inputs, together with vertical mixing and increased UVR fluxes modify the photosynthetic responses of phytoplankton. The experimentation consisted in all possible combinations of the following treatments: (a) solar radiation: UVR &plus; PAR (280–700 nm) versus PAR (photosynthetically active radiation) alone (400–700 nm); (b) nutrient addition (phosphorus (P) and nitrogen (N)): ambient versus addition (P to reach to a final concentration of 30 μg P L−1, and N to reach N:P molar ratio of 31); and (c) mixing: mixed (one rotation from surface to 3 m depth (speed of 1 m 4 min−1, total of 10 cycles)) versus static. Our findings suggest that under ambient nutrient conditions there is a synergistic effect between vertical mixing and UVR, increasing phytoplankton photosynthetic inhibition and excretion of organic carbon (EOC) from opaque lakes as compared to algae that received constant mean irradiance within the epilimnion. The opposite occurs in clear lakes where antagonistic effects were determined, with mixing partially counteracting the negative effects of UVR. Nutrient input, mimicking atmospheric pulses from Saharan dust, reversed this effect and clear lakes became more inhibited during mixing, while opaque lakes benefited from the fluctuating irradiance regime. These climate change related scenarios of nutrient input and increased mixing, would not only affect photosynthesis and production in lakes, but might also further influence the microbial loop and trophic interactions via enhanced EOC under fluctuating UVR exposure.
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Shatwell, Tom, Wim Thiery e Georgiy Kirillin. "Future projections of temperature and mixing regime of European temperate lakes". Hydrology and Earth System Sciences 23, n. 3 (18 marzo 2019): 1533–51. http://dx.doi.org/10.5194/hess-23-1533-2019.
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Abstract. The physical response of lakes to climate warming is regionally variable and highly dependent on individual lake characteristics, making generalizations about their development difficult. To qualify the role of individual lake characteristics in their response to regionally homogeneous warming, we simulated temperature, ice cover, and mixing in four intensively studied German lakes of varying morphology and mixing regime with a one-dimensional lake model. We forced the model with an ensemble of 12 climate projections (RCP4.5) up to 2100. The lakes were projected to warm at 0.10–0.11 ∘C decade−1, which is 75 %–90 % of the projected air temperature trend. In simulations, surface temperatures increased strongly in winter and spring, but little or not at all in summer and autumn. Mean bottom temperatures were projected to increase in all lakes, with steeper trends in winter and in shallower lakes. Modelled ice thaw and summer stratification advanced by 1.5–2.2 and 1.4–1.8 days decade−1 respectively, whereas autumn turnover and winter freeze timing was less sensitive. The projected summer mixed-layer depth was unaffected by warming but sensitive to changes in water transparency. By mid-century, the frequency of ice and stratification-free winters was projected to increase by about 20 %, making ice cover rare and shifting the two deeper dimictic lakes to a predominantly monomictic regime. The polymictic lake was unlikely to become dimictic by the end of the century. A sensitivity analysis predicted that decreasing transparency would dampen the effect of warming on mean temperature but amplify its effect on stratification. However, this interaction was only predicted to occur in clear lakes, and not in the study lakes at their historical transparency. Not only lake morphology, but also mixing regime determines how heat is stored and ultimately how lakes respond to climate warming. Seasonal differences in climate warming rates are thus important and require more attention.
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Bowling, LC. "Heat contents, thermal stabilities and Birgean wind work in Dystrophic Tasmanian Lakes and Reservoirs". Marine and Freshwater Research 41, n. 3 (1990): 429. http://dx.doi.org/10.1071/mf9900429.
Testo completoAbstract (sommario):
Values of whole-lake standard energy parameters (heat content, thermal stability and Birge's work of the wind) for ten dystrophic standing waters from western Tasmania were lower than expected for lakes of their depth and area. Although controlled principally by morphometric factors, the degree of shelter from wind and the extent of each lake's dystrophy also had considerable effects. These factors allowed only surface waters to contribute to the annual heat exchange cycle, thereby reducing the magnitude of each lake's heat budgets and influencing stability and wind work values. The lakes show considerable short- and long-term fluctuations in heat content, stability and wind work values in response to the capricious maritime meteorological conditions of the area. However, long periods between successive samplings may have caused some underestimation of the ranges of these three parameters. Despite this, the study reveals that these standard energy parameters are effective in describing the annual energy input and resistance to wind-induced mixing of these dystrophic Tasmanian lakes.
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Hongve, Dag. "Seasonal Mixing and Genesis of Endogenic Meromixis in Small Lakes in Southeast Norway". Hydrology Research 33, n. 2-3 (1 aprile 2002): 189–206. http://dx.doi.org/10.2166/nh.2002.0022.
Testo completoAbstract (sommario):
The inland region of Southeast Norway contains many lakes with endogenic meromixis. A synoptic study of seasonal mixing was conducted in 27 oligo- and mesotrophic lakes with surface area 0.0013 – 7.4 km2 and water colour 2-146 Hazen units. The scope was to identify properties of morphometric, optical and chemical nature that lead to development of endogenic meromixis. The summer mixing depths were found to depend on lake area and water colour. Small lakes (< 0.3 km2) were incompletely aerated during the spring circulation and had hypolimnetic temperatures near the temperature of maximum density throughout the summer stagnation. Insubstantial autumn mixing is considered the primary reason lakes in this area develop meromixis. Iron and manganese concentrations in anoxic deep waters depend on concentrations in the sediments and on accumulation of dissolved inorganic carbon in the deep waters. Development of endogenic meromixis is favoured by iron concentration in the sediment more than 5% of dry weight and manganese more than 0.5% of dry weight.
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McGuire, Shawn, e David J. Currie. "Factors Related to the Variation in Mixing Depth among Meromictic Lakes". Canadian Journal of Fisheries and Aquatic Sciences 50, n. 6 (1 giugno 1993): 1338–42. http://dx.doi.org/10.1139/f93-152.
Testo completoAbstract (sommario):
Although the factors that influence the mixing depth of holomictic lakes have been well investigated, meromictic lakes, which never mix completely, have received little attention in this regard. The purpose of the present study was to determine if the geographic variation in mixing depth of the mixolimnion is related to the same factors as is the epilimnion depth. Data on the lake morphometry, elevation, latitude, salinity in the mixo- and monimolimnia, and the depths of the epi- and mixolimnia were obtained for 56 meromictic lakes worldwide. The depth of the mixolimnion was most closely related to the maximum depth of the lake (r2 = 0.69); no other variables were significant after accounting for depth. In the same data set, epilimnetic depth was also most closely related to maximum depth, rather than fetch, as earlier studies had found. Our results suggest that wind-induced turbulence has much less effect on the depth to which both the epilimnion and the mixolimnion circulate in meromictic lakes than does morphometry.
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Scully, Norman M., e F. Vincent Warwick. "Hydrogen peroxide: a natural tracer of stratification and mixing processes in subarctic lakes". Archiv für Hydrobiologie 139, n. 1 (15 aprile 1997): 1–15. http://dx.doi.org/10.1127/archiv-hydrobiol/139/1997/1.
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Bowling, LC, e K. Salonen. "Heat uptake and resistance to mixing in small humic forest lakes in Southern Finland". Marine and Freshwater Research 41, n. 6 (1990): 747. http://dx.doi.org/10.1071/mf9900747.
Testo completoAbstract (sommario):
The annual heat budgets and maximum thermal stabilities achieved by small Finnish forest lakes are considerable for lakes of their size. Heat uptake is rapid during the brief period of vernal circulation, with the latent heat of fusion of ice contributing substantially to this. Heating then slows, with maximum heat contents and thermal stabilities occurring around early August. Absorption of solar radiation by the dystrophic waters, effective shelter from wind-induced turbulence, and considerable relative depths all combine to prevent mixing of heat much below the surface 2 m of most study lakes. Birgean wind-work values therefore remain low, and cold hypolimnetic waters occupy much of the lake volume. The lakes also respond quickly to meteorological change, which causes considerable year-to-year variation, and some short-term fluctuation, in their heat budgets and maximum stabilities. The lakes' small size and shallow thermal stratification may contribute to this.
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Sługocki, Łukasz, e Robert Czerniawski. "Trophic state (TSISD) and mixing type significantly influence pelagic zooplankton biodiversity in temperate lakes (NW Poland)". PeerJ 6 (5 ottobre 2018): e5731. http://dx.doi.org/10.7717/peerj.5731.
Testo completoAbstract (sommario):
BackgroundLake depth and the consequent mixing regime and thermal structure have profound effects on ecosystem functioning, because depth strongly affects the availability of nutrients, light, and oxygen. All these conditions influence patterns of zooplankton diversity. Zooplankton are a key component of the aquatic environment and are essential to maintaining natural processes in freshwater ecosystems. However, zooplankton biodiversity can be different regard to depth, mixing type and trophic state. Therefore, the aim of this study was to examine how depth and mixing regime affect zooplankton diversity in lakes. We also investigated the vertical distribution of diversity across a trophic gradient of lakes.MethodsA total of 329 zooplankton samples from 79 temperate lakes (36 polymictic and 43 dimictic) were collected. The biodiversity of zooplankton was calculated using species richness (SR) and the Shannon index (SI). An index based on Secchi disc visibility was used to determine the trophic state index (TSISD) of lakes. The one-way ANOVA with Duncan’s post hoc test were used to determine differences in zooplankton biodiversity between mictic lake types and thermal layers. To find the best predictors for zooplankton biodiversity a multiple stepwise regression was used. The rarefaction method was used to evaluate the impact of mixing types, thermal layers, and the TSISDon zooplankton biodiversity indices. A Sørensen similarity analysis and nonmetric multidimensional scaling (NMDS) were performed to describe the similarity patterns in species composition among lakes.ResultsWe identified a total of 151 taxa from 36 polymictic and 43 dimictic lakes. Lake depth and the TSISDwere significantly correlated with the biodiversity of lake zooplankton. The results of ANOVA and Duncan tests show that mictic type and thermal zones had a significant effect on zooplankton biodiversity. The rarefaction curve showed significant differences in zooplankton biodiversity, which was greater in lakes with lower trophic state. Ordination by NMDS showed clustering of different mictic types, thermal layers, and composition changes throughout the TSISDprofile. Moreover, we determined that polymictic lakes are more heterogeneous than dimictic lakes in regard to zooplankton similarities.DiscussionBoth mictic lake types were characterized by varying levels of zooplankton biodiversity, which is shaped by the communities’ response to lake depth, thermal layers and TSISDvalues. The zooplankton SR and SI (during daylight hours) depends greatly on the mixing type. Lake type also indicates the importance of the metalimnion in shaping zooplankton biodiversity in dimictic lakes. In addition, data from NW Polish lakes indicated that the increase of the TSISDleads to taxonomic shifts and has a negative effect on the diversity of all groups of zooplankton.
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Cortés, Alicia, e Sally MacIntyre. "Mixing processes in small arctic lakes during spring". Limnology and Oceanography 65, n. 2 (21 agosto 2019): 260–88. http://dx.doi.org/10.1002/lno.11296.
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Spigel, Robert H., e Jörg Imberger. "Mixing processes relevant to phytoplankton dynamics in lakes". New Zealand Journal of Marine and Freshwater Research 21, n. 3 (settembre 1987): 361–77. http://dx.doi.org/10.1080/00288330.1987.9516233.
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Andersen, Mikkel R., Theis Kragh e Kaj Sand-Jensen. "Extreme diel dissolved oxygen and carbon cycles in shallow vegetated lakes". Proceedings of the Royal Society B: Biological Sciences 284, n. 1862 (13 settembre 2017): 20171427. http://dx.doi.org/10.1098/rspb.2017.1427.
Testo completoAbstract (sommario):
A common perception in limnology is that shallow lakes are homogeneously mixed owing to their small water volume. However, this perception is largely gained by downscaling knowledge from large lakes to their smaller counterparts. Here we show that shallow vegetated lakes (less than 0.6 m), in fact, undergo recurring daytime stratification and nocturnal mixing accompanied by extreme chemical variations during summer. Dense submerged vegetation effectively attenuates light and turbulence generating separation between warm surface waters and much colder bottom waters. Photosynthesis in surface waters produces oxygen accumulation and CO 2 depletion, whereas respiration in dark bottom waters causes anoxia and CO 2 accumulation. High daytime pH in surface waters promotes precipitation of CaCO 3 which is re-dissolved in bottom waters. Nocturnal convective mixing re-introduces oxygen into bottom waters for aerobic respiration and regenerated inorganic carbon into surface waters, which supports intense photosynthesis. Our results reconfigure the basic understanding of local environmental gradients in shallow lakes, one of the most abundant freshwater habitats globally.
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Hanna, Micheline. "Evaluation of Models Predicting Mixing Depth". Canadian Journal of Fisheries and Aquatic Sciences 47, n. 5 (1 maggio 1990): 940–47. http://dx.doi.org/10.1139/f90-108.
Testo completoAbstract (sommario):
Since mixing depth affects many aspects of lake productivity, including nutrient recycling, I evaluated the predictive power of 17 empirical models that relate mixing depth to morphometric variables to identify the best predictor. These models were tested empirically by compiling data from 123 temperate lakes of differing morphometry, geometry, and trophy. Four statistical indices of precision and bias, indicate that the model published by Shuter et al. (1983) using maximum effective length of the lake was the best published model for predicting mixing depth, although it is slightly biased. I then examined the effect of alternate predictors, reflecting lake configuration, basin shape, and geographical indices, to formulate an improved model. The best single predictor of therrnodine depth (THER) was maximum effective length (MEL): Log THER = 0.336 Log MEL − 0.245. No improvement in predictive power was obtained by combining other variables. This model is statistically superior to that of Shuter et al. (1983) beause it is not biased, it represents a greater number of lakes, and it covers a broader range of lake sizes and shapes over a more extensive geographical region. Two other models, using lake area and length of shoreline are proposed as alternate predictive tools, if MEL is not readily available.
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Veillette, Julie, Marie-Josée Martineau, Dermot Antoniades, Denis Sarrazin e Warwick F. Vincent. "Effects of loss of perennial lake ice on mixing and phytoplankton dynamics: insights from High Arctic Canada". Annals of Glaciology 51, n. 56 (2010): 56–70. http://dx.doi.org/10.3189/172756411795931921.
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AbstractPerennially ice-covered lakes are well known from Antarctica and also occur in the extreme High Arctic. Climate change has many implications for these lakes, including the thinning and disappearance of their perennial ice cover. The goal of this study was to consider the effects of transition to seasonal ice cover by way of limnological observations on a series of meromictic lakes along the northern coastline of Ellesmere Island, Nunavut, Canada. Conductivity-temperature profiles during a rare period of ice-free conditions (August 2008) in these lakes suggested effects of wind-induced mixing of their surface freshwater layers and the onset of entrainment of water at the halocline. Sampling of the mixed layer of one of these meromictic lakes in May and August 2008 revealed a pronounced vertical structure in phytoplankton pigments and species composition, with dominance by cyanobacteria, green algae, chrysophytes, cryptophytes and dinoflagellates, and a conspicuous absence of diatoms. The loss of ice cover resulted in an 80-fold increase in water column irradiance and apparent mixing of the upper water column during a period of higher wind speeds. Zeaxanthin, a pigment found in cyanobacteria, was entirely restricted to the <3μm cell fraction at all depths and increased by a factor of 2–17, with the greatest increases in the upper halocline region subject to mixing. Consistent with the pigment data, picocyanobacterial populations increased by a factor of 3, with the highest concentration (1.65 × 108 cells L−1) in the upper halocline. Chlorophyll a concentrations and the relative importance of phytoplankton groups differed among the four lakes during the open-water period, implying lake-specific differences in phytoplankton community structure under ice-free conditions.
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Deshpande, Bethany N., Frédéric Maps, Alex Matveev e Warwick F. Vincent. "Oxygen depletion in subarctic peatland thaw lakes". Arctic Science 3, n. 2 (1 giugno 2017): 406–28. http://dx.doi.org/10.1139/as-2016-0048.
Testo completoAbstract (sommario):
Permafrost thawing and erosion results in the enrichment of northern lakes by soil organic matter. These allochthonous inputs favour bacterial decomposition and may cause the draw-down of dissolved oxygen to anoxic conditions that promote methanogenesis. Our objective in the present study was to determine the seasonal variations in dissolved oxygen in a set of permafrost peatland lakes in subarctic Quebec, Canada, and to relate these changes to metabolic rates, ice cover, and mixing. The lakes had high dissolved organic carbon concentrations, and their surface waters in summer had greenhouse gas concentrations that were up to one (CO2) to three (CH4) orders of magnitude above air-equilibrium values, indicating their strongly heterotrophic character. Consistent with these observations, the peatland lakes had elevated rates of bacterial production and oxygen consumption. Continuous measurements of oxygen by in situ sensors and of ice cover by automated field cameras showed that the lakes became fully anoxic shortly after freeze-up. The waters were partially re-oxygenated by mixing events in spring and fall, but in one lake, the bottom waters remained anoxic throughout the year. These observations provide a foundation for subsequent biogeochemical and modelling studies of peatland thaw lakes as an abundant class of Arctic freshwater ecosystems.
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Li, Yang, James R. Bence e Travis O. Brenden. "An evaluation of alternative assessment approaches for intermixing fish populations: a case study with Great Lakes lake whitefish". ICES Journal of Marine Science 72, n. 1 (23 aprile 2014): 70–81. http://dx.doi.org/10.1093/icesjms/fsu057.
Testo completoAbstract (sommario):
Abstract We used simulation modeling to explore how three statistical catch-at-age approaches for assessing intermixed fisheries performed in terms of assessment accuracy and management performance, under differing productivity, mixing, and harvest levels. Simulations were based on intermixing lake whitefish (Coregonus clupeaformis) populations in the upper Laurentian Great Lakes of North America. We found that with intermixing, the “separate” assessment approach, which ignored intermixing and treated mixed populations as unit stocks, produced biased estimates of spawning stock biomass (SSB); however, the “pooled” assessment approach, which lumped populations and assessed them as a single stock, was nearly unbiased in estimating SSB. The “overlap” assessment approach, which estimated the populations in one combined assessment model by incorporating actual mixing rates, was most strongly biased in estimating SSB in the absence of mixing, with bias decreasing as mixing levels increased. With high mixing levels, the overlap method had difficulty converging on unique solutions. The pooled approach provided better management performance than the separate approach with intermixing. When the overlap method could be applied, it provided the greatest SSB with little reductions in yield and the lowest inter-annual variation in yield. Relative performances of the assessment approaches were robust to assumed harvest levels.
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Boike, J., C. Georgi, G. Kirilin, S. Muster, K. Abramova, I. Fedorova, A. Chetverova, M. Grigoriev, N. Bornemann e M. Langer. "Thermal processes of thermokarst lakes in the continuous permafrost zone of northern Siberia – observations and modeling (Lena River Delta, Siberia)". Biogeosciences 12, n. 20 (19 ottobre 2015): 5941–65. http://dx.doi.org/10.5194/bg-12-5941-2015.
Testo completoAbstract (sommario):
Abstract. Thermokarst lakes are typical features of the northern permafrost ecosystems, and play an important role in the thermal exchange between atmosphere and subsurface. The objective of this study is to describe the main thermal processes of the lakes and to quantify the heat exchange with the underlying sediments. The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) were investigated using hourly water temperature and water level records covering a 3-year period (2009–2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. Lakes were covered by ice up to 2 m thick that persisted for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increased at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. Prior to ice break-up, solar radiation effectively warmed the water beneath the ice cover and induced convective mixing. Ice break-up started at the beginning of June and lasted until the middle or end of June. Mixing occurred within the entire water column from the start of ice break-up and continued during the ice-free periods, as confirmed by the Wedderburn numbers, a quantitative measure of the balance between wind mixing and stratification that is important for describing the biogeochemical cycles of lakes. The lake thermal regime was modeled numerically using the FLake model. The model demonstrated good agreement with observations with regard to the mean lake temperature, with a good reproduction of the summer stratification during the ice-free period, but poor agreement during the ice-covered period. Modeled sensitivity to lake depth demonstrated that lakes in this climatic zone with mean depths > 5 m develop continuous stratification in summer for at least 1 month. The modeled vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m−2 in summer and with heat released back into the water column at a rate of less than 1 W m−2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C.
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Escobar, Jaime, David G. Buck, Mark Brenner, Jason H. Curtis e Natalia Hoyos. "Thermal stratification, mixing, and heat budgets of Florida lakes". Fundamental and Applied Limnology / Archiv für Hydrobiologie 174, n. 4 (1 maggio 2009): 283–93. http://dx.doi.org/10.1127/1863-9135/2009/0174-0283.
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Findikakis, Angelos N., e Adrian W. K. Law. "Wind Mixing in Temperature Simulations for Lakes and Reservoirs". Journal of Environmental Engineering 125, n. 5 (maggio 1999): 420–28. http://dx.doi.org/10.1061/(asce)0733-9372(1999)125:5(420).
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MacIntyre, Sally, e José R. Romero. "Predicting upwelling, boundary mixing, and nutrient fluxes in lakes". SIL Proceedings, 1922-2010 27, n. 1 (aprile 2000): 246–50. http://dx.doi.org/10.1080/03680770.1998.11901234.
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Cossey, Heidi L., Mian Nabeel Anwar, Petr V. Kuznetsov e Ania C. Ulrich. "Biofilms for Turbidity Mitigation in Oil Sands End Pit Lakes". Microorganisms 9, n. 7 (4 luglio 2021): 1443. http://dx.doi.org/10.3390/microorganisms9071443.
Testo completoAbstract (sommario):
End pit lakes (EPLs) have been proposed as a method of reclaiming oil sands fluid fine tailings (FFT), which consist primarily of process-affected water and clay- and silt-sized particles. Base Mine Lake (BML) is the first full-scale demonstration EPL and contains thick deposits of FFT capped with water. Because of the fine-grained nature of FFT, turbidity generation and mitigation in BML are issues that may be detrimental to the development of an aquatic ecosystem in the water cap. Laboratory mixing experiments were conducted to investigate the effect of mudline biofilms made up of microbial communities indigenous to FFT on mitigating turbidity in EPLs. Four mixing speeds were tested (80, 120, 160, and 200 rpm), all of which are above the threshold velocity required to initiate erosion of FFT in BML. These mixing speeds were selected to evaluate (i) the effectiveness of biofilms in mitigating turbidity and (ii) the mixing speed required to ‘break’ the biofilms. The impact of biofilm age (10 weeks versus 20 weeks old) on turbidity mitigation was also evaluated. Diverse microbial communities in the biofilms included photoautotrophs, namely cyanobacteria and Chlorophyta (green algae), as well as a number of heterotrophs such as Gammaproteobacteria, Desulfobulbia, and Anaerolineae. Biofilms reduced surface water turbidity by up to 99%, depending on the biofilm age and mixing speed. Lifting and layering in the older biofilms resulted in weaker attachment to the FFT; as such, younger biofilms performed better than older biofilms. However, older biofilms still reduced turbidity by 69% to 95%, depending on the mixing speed. These results indicate that biostabilization is a promising mechanism for turbidity mitigation in EPLs.
28
Agbeti, Michael D., John C. Kingston, John P. Smol e Christine Watters. "Comparison of phytoplankton succession in two lakes of different mixing regimes fig: 12 tab: 4". Fundamental and Applied Limnology 140, n. 1 (13 agosto 1997): 37–69. http://dx.doi.org/10.1127/archiv-hydrobiol/140/1997/37.
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29
von Rohden, C., B. Boehrer e J. Ilmberger. "Evidence for double diffusion in temperate meromictic lakes". Hydrology and Earth System Sciences 14, n. 4 (13 aprile 2010): 667–74. http://dx.doi.org/10.5194/hess-14-667-2010.
Testo completoAbstract (sommario):
Abstract. We present CTD-measurements from two shallow meromictic mining lakes. The lakes, which differ in size and depth, show completely different seasonal mixing patterns in their mixolimnia. However, the measurements document the occurrence of similar seasonal convective mixing in discrete layers within their monimolimnia. This mixing is induced by double diffusion and can be identified by the characteristic step-like structure of the temperature and electrical conductivity profiles. The steps develop in the upper part of the monimolimnion, when in autumn cooling mixolimnion temperatures have dropped below temperatures of the underlying monimolimnion. The density gradient across the chemocline due to solutes overcompensates the destabilizing temperature gradient, and moreover, keeps the vertical transport close to molecular level. In conclusion, preconditions for double diffusive effects are given on a seasonal basis. At in general high local stabilities N2 in the monimolimnia of 10−4–10−2s−2, the stability ratio Rρ was in the range of 1–20. This quantitatively indicates that double diffusion can become visible. Between 1 and 6 sequent steps, with sizes between 1 dm and 1 m, were visually identified in the CTD-profiles. In the lower monimolimnion of the deeper lake, the steps systematically emerge at a time delay of more than half a year, which matches with the progression of the mixolimnetic temperature changes into the monimolimnion. In none of the lakes, the chemocline interface is degraded by these processes. However, double diffusive convection is essential for the redistribution of solutes in the inner parts of the monimolimnion at longer time scales, which is crucial for the assessment of the ecologic development of such lakes.
30
Fahnenstiel, G. L., R. A. Stone, M. J. McCormick, C. L. Schelske e S. E. Lohrenz. "Spring isothermal mixing in the Great Lakes: evidence of nutrient limitation and nutrient-light interactions in a suboptimal light environment". Canadian Journal of Fisheries and Aquatic Sciences 57, n. 9 (1 settembre 2000): 1901–10. http://dx.doi.org/10.1139/f00-144.
Testo completoAbstract (sommario):
During the spring isothermal mixing period (April-May) in 1993-1995, photosynthesis-irradiance and growth-irradiance experiments were conducted in Lakes Erie, Huron, Michigan, and Ontario to assess light limitation. Additionally, nutrient enrichment experiments were conducted in Lake Ontario. Results from the photosynthesis-irradiance experiments suggested that phytoplankton communities in all the lakes can be either light limited or light saturated, as the threshold parameter (Ik) was similar to mean water column irradiances (mean Iwc, ratio = 1.0). Growth-irradiance experiments also suggested the potential for light saturation; mean daily irradiance exceeded the threshold growth irradiance (Ik,g) in 95% of cases. Growth rates became light saturated at lower irradiances than photosynthetic rates. Evidence for a nutrient-light interaction in controlling in situ growth rates was also found in the nutrient enrichment experiments at incubation irradiances [Formula: see text] mean Iwc. Our results suggest that an interaction between nutrients and light is often controlling phytoplankton growth during spring mixing in the Great Lakes. The role of these nutrient-light interactions has increased in the past decade due to increased light availability in the lower lakes caused by phosphorus load reductions and the filtering activities of nonindigenous mussels.
31
Woszczyk, Michał, Wojciech Tylmann, Jan Jędrasik, Tomasz Szarafin, Alfred Stach, Joanna Skrzypczak e Monika Lutyńska. "Recent sedimentation dynamics in a shallow coastal lake (Lake Sarbsko, northern Poland): driving factors, processes and effects". Marine and Freshwater Research 65, n. 12 (2014): 1102. http://dx.doi.org/10.1071/mf13336.
Testo completoAbstract (sommario):
Despite the fact that sediment dynamics in shallow coastal lakes strongly influences lake water quality and is crucial for preserving good quality paleo-records from coastal zones, the depositional processes in coastal lakes have not been thoroughly recognised so far. The present study aims at investigating the relationship between lake water circulation and the distribution of surface sediments, identifying the postdepositional physical mechanisms affecting lake deposits, and estimating the intensity of sediment mixing in a coastal lake on the Baltic coast. Our approach includes analyses of sediment grain size and chemical composition, hydrodynamic modelling and measurements of 210Pb activity in sediment short-cores from various sections of the lake. We showed that the distribution of lithofacies in the lake is explained by hydrodynamic conditions. Enhanced water dynamics reduces spatial extent of organic-rich lacustrine deposits and results in the exposure of relic marine-lagoonal sediments. A major part of the lake sediments is prone to vertical mixing by wind waves to a depth of ≥ 40 cm. Hydrodynamic modelling and 210Pb displayed overall agreement in predicting the depth of sediment mixing. At the same time the limitations of 210Pb as a geochronologic marker in shallow coastal lakes are revealed. It appears that even exponential depth-wise 210Pb distributions may be produced by storm redeposition.
32
Bouffard, Damien, e Alfred Wüest. "Convection in Lakes". Annual Review of Fluid Mechanics 51, n. 1 (5 gennaio 2019): 189–215. http://dx.doi.org/10.1146/annurev-fluid-010518-040506.
Testo completoAbstract (sommario):
Lakes and other confined water bodies are not exposed to tides, and their wind forcing is usually much weaker compared to ocean basins and estuaries. Hence, convective processes are often the dominant drivers for shaping mixing and stratification structures in inland waters. Due to the diverse environments of lakes—defined by local morphological, geochemical, and meteorological conditions, among others—a fascinating variety of convective processes can develop with remarkably unique signatures. Whereas the classical cooling-induced and shear-induced convections are well-known phenomena due to their dominant roles in ocean basins, other convective processes are specific to lakes and often overlooked, for example, sidearm, under-ice, and double-diffusive convection or thermobaric instability and bioconvection. Additionally, the peculiar properties of the density function at low salinities/temperatures leave distinctive traces. In this review, we present these various processes and connect observations with theories and model results.
33
Olefeldt, D., K. J. Devito e M. R. Turetsky. "Sources and fate of terrestrial dissolved organic carbon in lakes of a Boreal Plains region recently affected by wildfire". Biogeosciences 10, n. 10 (2 ottobre 2013): 6247–65. http://dx.doi.org/10.5194/bg-10-6247-2013.
Testo completoAbstract (sommario):
Abstract. Downstream mineralization and sedimentation of terrestrial dissolved organic carbon (DOC) render lakes important for landscape carbon cycling in the boreal region. The chemical composition of terrestrial DOC, the downstream delivery of terrestrial DOC and its processing within aquatic ecosystem may all be influenced by climate change, including increased occurrence of wildfire. Here, we assessed composition and lability (during both dark- and UV incubations) of DOC from peatland groundwater and mineral soil groundwater, and from shallow lakes within a peatland-rich region on the Boreal Plains of western Canada that was recently affected by wildfire. Wildfire was found to increase aromaticity of DOC in peat pore water above the water table, but had no effect on the concentrations or composition of peatland groundwater DOC or mineral soil DOC. Using a mixing model we estimated that on average 98 and 78% of terrestrial DOC inputs to the lakes in fine- and coarse-textured settings, respectively, originated from peatland groundwater sources. Accordingly, lake DOC composition reflected primarily a mixing of peatland and mineral soil groundwater sources, with no detectable influence of the recent wildfire. Lake and peatland DOC had low biodegradability, lower than that of mineral soil DOC. However, both mineralization and sedimentation of peatland DOC increased substantially during UV incubations through selective removal of aromatic humic and fulvic acids. Similar shifts in DOC composition as observed during the UV incubations were also observed across lakes with longer water residence times. The mixing model estimated that on average 54% (95% confidence interval: 36–64%) of terrestrial DOC had been removed in lakes as a result of mineralization and sedimentation. Meanwhile, the reduction in absorbance at 254 nm was 71% (58–76%), which suggests selective removal of aromatic DOC. Hence, incubation results, patterns of DOC composition among lakes and mixing model results were consistent with significant within-lake removal of terrestrial DOC through UV-mediated processes. Selective removal of highly aromatic DOC through UV-mediated processes implies that organic sources that are considered stabile in terrestrial ecosystems can be readily mineralized once entering aquatic ecosystems. Together, our results suggest that regional characteristics (climate, surface geology and lake morphometry) can prevent wildfire from causing pulse perturbations to the linkages between terrestrial and aquatic C cycling and also regulate the processes that dominate within-lake removal of terrestrial DOC.
34
Durán, C., J. M. Medina-Sánchez, G. Herrera, M. Villar-Argaiz, V. E. Villafañe, E. W. Helbling e P. Carrillo. "Direct and indirect effects of vertical mixing, nutrients and ultraviolet radiation on the bacterioplankton metabolism in high-mountain lakes from southern Europe". Biogeosciences Discussions 11, n. 5 (20 maggio 2014): 7291–325. http://dx.doi.org/10.5194/bgd-11-7291-2014.
Testo completoAbstract (sommario):
Abstract. As a consequence of global change, modifications in the interaction among abiotic stressors on aquatic ecosystems have been predicted. Among other factors, UVR transparency, nutrient inputs and shallower epilimnetic layers could alter the trophic links in the microbial food web. Currently, there are some evidences of higher sensitiveness of aquatic microbial organisms to UVR in opaque lakes. Our aim was to assess the interactive direct and indirect effects of UVR (through the excretion of organic carbon – EOC – by algae), mixing regime and nutrient input on bacterial metabolism. We performed in situ short-term experiments under the following treatments: full sunlight (UVR + PAR, >280 nm) vs. UVR exclusion (PAR only, >400 nm); ambient vs. nutrient addition (phosphorus (P; 30 μg PL−1) and nitrogen (N; up to final N : P molar ratio of 31)); and static vs. mixed regime. The experiments were conducted in three high-mountain lakes of Spain: Enol [LE], Las Yeguas [LY] and La Caldera [LC] which had contrasting UVR transparency characteristics (opaque (LE) vs. clear lakes (LY and LC)). Under ambient nutrient conditions and static regimes, UVR exerted a stimulatory effect on heterotrophic bacterial production (HBP) in the opaque lake but not in the clear ones. Under UVR, vertical mixing and nutrient addition HBP values were lower than under the static and ambient nutrient conditions, and the stimulatory effect that UVR exerted on HBP in the opaque lake disappeared. By contrast, vertical mixing and nutrient addition increased HBP values in the clear lakes, highlighting for a photoinhibitory effect of UVR on HBP. Mixed regime and nutrient addition resulted in negative effects of UVR on HBP more in the opaque than in the clear lakes. Moreover, in the opaque lake, bacterial respiration (BR) increased and EOC did not support the bacterial carbon demand (BCD). In contrast, bacterial metabolic costs did not increase in the clear lakes and the increased nutrient availability even led to higher HBP. Consequently, EOC satisfied BCD in the clear lakes, particularly in the clearest one [LC]. Our results suggest that the higher vulnerability of bacteria to the damaging effects of UVR may be particularly accentuated in the opaque lakes and further recognizes the relevance of light exposure history and biotic interactions on bacterioplankton metabolism when coping with fluctuating radiation and nutrient inputs.
35
Boike, J., C. Georgi, G. Kirilin, S. Muster, K. Abramova, I. Fedorova, A. Chetverova, M. Grigoriev, N. Bornemann e M. Langer. "Physical processes of thermokarst lakes in the continuous permafrost zone of northern Siberia – observations and modeling (Lena River Delta, Siberia)". Biogeosciences Discussions 12, n. 8 (30 aprile 2015): 6637–88. http://dx.doi.org/10.5194/bgd-12-6637-2015.
Testo completoAbstract (sommario):
Abstract. The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) have been investigated using hourly water temperature and water level records covering a three year period (2009–2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. The data were used for numerical modeling with FLake software, and also to determine the physical indices of the lakes. The lakes vary in area, depths and volumes. The winter thermal regime is characterized by an ice cover up to 2 m thick that survives for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increase at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. The effects of solar radiation return prior to ice break-up, effectively warming the water beneath the ice cover and inducing convective mixing. Ice break-up starts the beginning of June and takes until the middle or end of June for completion. Mixing occurs within the entire water column from the start of ice break-up and continues during the ice-free periods, as confirmed by the Wedderburn numbers. Some of the lakes located closest to the Lena River are subjected to varying levels of spring flooding with river water, on an annual basis. Numerical modeling using FLake software indicates that the vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m−2 in summer and with heat released back into the water column at a~rate of less than 1 W m−2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C. The data are available in the Supplement for this paper and through the PANGAEA website (http://www.pangaea.de/).
36
Borowiak, Magdalena, Dariusz Borowiak e Kamil Nowiński. "Spatial Differentiation and Multiannual Dynamics of Water Conductivity in Lakes of the Suwałki Landscape Park". Water 12, n. 5 (30 aprile 2020): 1277. http://dx.doi.org/10.3390/w12051277.
Testo completoAbstract (sommario):
Water conductivity in 23 lakes of the Suwałki Landscape Park (SLP) was tested in the years 2012–2014. Conductivity profiles were made at the deepest place every two months between spring and autumn water mixing. The collected measurement data, supplemented with historical data, were used to identify factors that shape the spatial variability of water conductivity and to reconstruct its multiannual changes. The range of variability of the mean conductivity of surface water of the SLP lakes ranged from 178 to 522 µS cm−1. The strong negative relationship between conductivity and lake elevation (R = 0.816, p < 0.000) suggests that in the territorially compact complex of the SLP lakes, conductivity is a consequence of the location of the lake in the catchment, which, in turn, affects the structure of its water supply. However, the physical and environmental parameters of the catchment and morphometric parameters of lake basins are of secondary importance. In dimictic lakes and in those showing signs of “spring meromixis”, the magnitude of conductivity differences in the water column is determined by the lakes’ susceptibility to wind mixing expressed by the exposure index value. The developed climate models have also shown that conductivity, an indicator of water quality, is very sensitive to climate change. The analysis of the reconstructed chronological conductivity sequences shows that the deterioration of the quality of the waters of the SLP lakes first occurred at the beginning of the 21st century and a clear increasing trend has been maintained over the last decade.
37
Imberger, J., e G. N. Ivey. "Boundary mixing in stratified reservoirs". Journal of Fluid Mechanics 248 (marzo 1993): 477–91. http://dx.doi.org/10.1017/s0022112093000850.
Testo completoAbstract (sommario):
We consider the steady flow driven by turbulent mixing in a benthic boundary layer along a sloping boundary in the general case of a non-uniform background density gradient. The velocity and density fields are decomposed into barotropic and baroclinic components, and a solution is obtained by taking an expansion in the small parameter A, the aspect ratio of the boundary layer defined as the thickness divided by the alongslope length. The flow in the boundary layer is governed by a balance between alongslope baroclinic and barotropic density fluxes. A number of flow regimes can exist, and we show that in the regimes relevant to lakes and reservoirs, the barotropic flow is divergent and drives an exchange flow between the boundary layer and the interior. This leads to changes in the interior density gradient which are significant when compared to field observations.
38
Radke, L. C., K. W. F. Howard e Peter A. Gell. "Chemical diversity in south-eastern Australian saline lakes. I: geochemical causes". Marine and Freshwater Research 53, n. 6 (2002): 941. http://dx.doi.org/10.1071/mf01231.
Testo completoAbstract (sommario):
This study re-examined hydrochemical data for south-eastern Australian saline lakes using graphical techniques and reaction path models generated by PHRQPITZ. Results showed that the lakes are more diverse than previous studies have implied. Cyclic solute matrices are modified in catchments by rock–water interactions, mineral dissolution, seawater intrusion and cation-exchange reactions, and within the lakes by sulfate reduction, mixing, brine reflux, mineral precipitation and the recycling of the most soluble salts. Three different pathways of the Eugster–Jones–Hardie models are identified. The study is important because the described variations of water chemistry influence the composition of lake biota.
39
Anderson, Robert F., Sherry L. Schiff e Raymond H. Hesslein. "Determining Sediment Accumulation and Mixing Rates Using 210Pb, 137Cs, and Other Tracers: Problems Due to Postdepositional Mobility or Coring Artifacts". Canadian Journal of Fisheries and Aquatic Sciences 44, S1 (18 dicembre 1987): s231—s250. http://dx.doi.org/10.1139/f87-298.
Testo completoAbstract (sommario):
Sediment profiles of 137Cs in 12 lakes and of radionuclides (60Co, 134Cs, 226Ra) added experimentally to four lakes at the Experimental Lakes Area, northwestern Ontario, were inconsistent with sediment chronologies derived from 210Pb distributions. Peaks in the 37Cs profiles were sometimes shallower than the depth corresponding to the 1963 fallout maximum (based on 210Pb chronology) and sometimes 137Cs peaks were not observed at all. Expected peaks in the profiles of experimentally added nuclides were similarly absent in three of four lakes. The absence of these peaks at depths corresponding to their time of maximum input to the lakes probably resulted from the initial uptake of the nuclides by littoral sediments followed by the winnowing over periods of several years of nuclide-tagged fine particles to the deeper parts of the basins where the cores were collected. Sediment focussing is manifested by 210Pb sediment inventories at the coring sites greatly exceeding inventories that can be supported by atmospheric deposition of 210Pb in this area.137Cs and the experimentally added nuclides were found much deeper in the cores than the depths corresponding to the time of their initial inputs to the lakes based on 210Pb chronologies. Diffusion of the nuclides in the pore waters could explain some of their downward penetration. However, in some cases, the profiles could only be fit if the effective diffusion coefficient increased with depth. This situation might reflect mixing of these high porosity sediments during core collection or extrusion.Distributions of 137Cs and of the experimentally added nuclides do not provide valid chronologies which can be used to date other features recorded in the sediments of these lakes. Although unsupported 210Pb profiles in these lakes provided excellent fits to classical steady-state sediment accumulation models, 210Pb profiles too may have been affected by sediment mixing or core disturbance. Further studies are necessary to test the reliability of 210Pb-based sediment chronologies in high porosity sediments such as those studied at ELA.
40
Zagarese, Horacio E., Barbara Tartarotti, Walter Cravero e Pablo Gonzalez. "UV damage in shallow lakes: the implications of water mixing". Journal of Plankton Research 20, n. 8 (1998): 1423–33. http://dx.doi.org/10.1093/plankt/20.8.1423.
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41
Gu, Ruochuan, e Heinz G. Stefan. "Mixing of Temperature‐Stratified Lakes and Reservoirs by Buoyant Jets". Journal of Environmental Engineering 114, n. 4 (agosto 1988): 898–914. http://dx.doi.org/10.1061/(asce)0733-9372(1988)114:4(898).
Testo completo
42
Stemberger, Richard S. "The influence of mixing on rotifer assemblages of Michigan lakes". Hydrobiologia 297, n. 2 (febbraio 1995): 149–61. http://dx.doi.org/10.1007/bf00017481.
Testo completo
43
De Crop, Wannes, e Dirk Verschuren. "Mixing regimes in the equatorial crater lakes of western Uganda". Limnologica 90 (settembre 2021): 125891. http://dx.doi.org/10.1016/j.limno.2021.125891.
Testo completo
44
Riera, Joan L., John E. Schindler e Tim K. Kratz. "Seasonal dynamics of carbon dioxide and methane in two clear-water lakes and two bog lakes in northern Wisconsin, U.S.A." Canadian Journal of Fisheries and Aquatic Sciences 56, n. 2 (1 febbraio 1999): 265–74. http://dx.doi.org/10.1139/f98-182.
Testo completoAbstract (sommario):
We investigated carbon dynamics in the water column and CO2 and CH4 exchange across the air-water interface in four closed-basin lakes in northern Wisconsin: two with clear, low dissolved organic carbon (DOC) waters and two bog lakes with stained, high-DOC waters. Clear-water lakes quickly became undersaturated following ice-out and remained undersaturated until fall turnover. Bog lakes were supersaturated in CO2 throughout the ice-free season, although surface CO2 concentrations dropped sharply following ice-out and increased again during autumn turnover. Differences in seasonal patterns of CO2 were attributed to morphometry and the timing and intensity of mixing events. Ice-free season fluxes of CO2 were 6.7 and 10.0 mol·m-2 in the bog lakes and 1.2 and 0.09 mol·m-2 in the clear-water lakes. Fluxes of CH4 were significant only immediately after ice-out and during autumn turnover and were <0.4 mol·m-2 in the bog lakes and <0.05 mol·m-2 in the clear-water lakes. Compared with changes in carbon pools in the lakes, our results indicate rapid carbon turnover rates in bog lakes, as opposed to clear-water lakes. We suggest that allochthonous inputs of CO2 may be responsible for this rapid turnover.
45
Blair, Jennifer M., Ilia Ostrovsky, Brendan J. Hicks, Robert J. Pitkethley e Paul Scholes. "Growth of rainbow trout (Oncorhynchus mykiss) in warm-temperate lakes: implications for environmental change". Canadian Journal of Fisheries and Aquatic Sciences 70, n. 5 (maggio 2013): 815–23. http://dx.doi.org/10.1139/cjfas-2012-0409.
Testo completoAbstract (sommario):
To predict potential effects of climate and anthropogenic impacts on fish growth, we compared growth rates of rainbow trout (Oncorhynchus mykiss) in nine closely located warm-temperate lakes of contrasting morphometry, stratification and mixing regime, and trophic state. Analyses of long-term mark–recapture data showed that in deep oligotrophic and mesotrophic lakes, trout growth rates increased with increasing indices of lake productivity. In contrast, in shallow eutrophic lakes, where fish habitat volume is constrained by temperature and dissolved oxygen, trout growth rates declined with increasing productivity. Growth rates were higher in lakes with greater volumes of favourable habitat (i.e., dissolved oxygen > 6.0 mg·L−1 and temperature < 21 °C) and lower in lakes with increased turbidity, chlorophyll a, and nitrogen concentrations. Our findings suggest that increases in lake productivity and temperatures as a result of global climatic change are likely to be more detrimental to salmonid habitat quality in shallower, productive lakes, while salmonids will better endure such changes in deeper, oligotrophic lakes. Fishery managers can use this information to aid future stocking decisions for salmonid fisheries in warm-temperate climates.
46
Fee, E. J., e R. E. Hecky. "Introduction to the Northwest Ontario Lake Size Series (NOLSS)". Canadian Journal of Fisheries and Aquatic Sciences 49, n. 12 (1 dicembre 1992): 2434–44. http://dx.doi.org/10.1139/f92-269.
Testo completoAbstract (sommario):
The rationale, design, and limitations of the Northwest Ontario Lake Size Series (NOLSS) research program are described. The primary purpose of NOLSS is to discover how lake size per se influences limnological and fisheries phenomena, so that conclusions drawn from studies of particular lakes can be rigorously scaled and applied to lakes of other sizes. NOLSS consists of six lakes located in a remote wilderness region of Northwest Ontario. These lakes were chosen for their geological, hydrological, and morphological similarity (Canadian Shield geology; water renewal time> 5 yr; fully stratified in summer), but they form an exponential gradient in surface area (from 89 to 34 700 ha.) Associated with this gradient of lake size are gradients of physical properties (turbulent energy, mixing depth, thermal behaviour) to which biological communities must adapt. NOLSS fills the conspicuous gap in size that separates two well-studied groups of lakes in Northwest Ontario: the Experimental Lakes Area (ELA), where whole-lake manipulation experiments are performed, and the Laurentian Great Lakes (Nipigon, Superior), where these experiments find some of their most important applications.
47
Cahill, Kendra L., John M. Gunn e Martyn N. Futter. "Modelling ice cover, timing of spring stratification, and end-of-season mixing depth in small Precambrian Shield lakes". Canadian Journal of Fisheries and Aquatic Sciences 62, n. 9 (1 settembre 2005): 2134–42. http://dx.doi.org/10.1139/f05-127.
Testo completoAbstract (sommario):
From a 3-year study of 21 northern Ontario lakes, models were developed to determine the duration of ice cover, predict the timing of spring stratification, and predict the end-of-season mixing depth. The model to determine lake freeze and thaw dates was based on the daily variability of water temperature measured with a data logger suspended 1 and 2 m below the surface. The model to predict the duration of time (days) from lake thaw to lake stratification was developed using the mean May air temperature (degrees Celsius), dissolved organic carbon, and lake surface area (r2 = 0.79). The end-of-season mixing depth was best predicted using days to stratification and dissolved organic carbon concentration (r2 = 0.72). By applying a simple climate change scenario model, we were able to show that increased air temperature, rather than increased water clarity, was the most important factor affecting the timing of stratification. In contrast, lake clarity was the most important factor affecting end-of-season mixing depth in small Shield lakes.
48
Patalas, K., e A. Salki. "Spatial Variation of Crustacean Plankton in Lakes of Different Size". Canadian Journal of Fisheries and Aquatic Sciences 50, n. 12 (1 dicembre 1993): 2626–40. http://dx.doi.org/10.1139/f93-286.
Testo completoAbstract (sommario):
The patterns of spatial distribution of planktonic crustaceans changed with increasing lake size. Greatest abundances were often found offshore in smaller lakes but nearshore in larger lakes. Interstation similarity of plankton, measured with Jaccard's and Renkonen's indices, was higher in small- to middle-sized lakes and lower in very small and very large lakes, indicating that mechanisms existed at both ends of the size spectrum which prevented plankton from mixing horizontally. The information content of a single central lake sample was evaluated against a lake average from 9–10 stations. To capture at least 80% of the species present, one station was sufficient only in smaller lakes, three to six stations were needed in the smallest and medium-sized lakes, and more than nine stations were needed in the largest lake. The single central station in small- and medium-sized lakes represented average total plankton abundance and dominant species relatively well but underestimated rare species. In larger lakes, lake average plankton was not well characterized by a single station. In Lake Superior, the central station reflected the offshore but not the nearshore community. Neither plankton abundance nor the number of species appeared related to lake size in the series of lakes investigated.
49
Gawad, S. T. Abdel, J. A. McCorquodale e H. Gerges. "Near-field mixing at an outfall". Canadian Journal of Civil Engineering 23, n. 1 (1 febbraio 1996): 63–75. http://dx.doi.org/10.1139/l96-007.
Testo completoAbstract (sommario):
The near-field mixing of effluent from buoyant and nonbuoyant flows from outfalls discharging into a cross-flowing ambient current in trapezoidal channels has been investigated. A physical model was scaled to represent a typical large outfall into one of the connecting channels of the Great Lakes system. The discharged jet was measured in detail to determine the velocity and concentration fields. The excess velocities and concentrations were found to follow the Gaussian distribution. Empirical expressions for the jet trajectories, minimum dilutions, and plume widths were derived. A correction factor has been introduced to the concentration distribution to ensure mass conservation. The calibrated model was verified by comparison with field data and the results of other near-field models (PDS, MIT, and CORMIX). Key words: mixing, near field, pollutant transport, outfall, buoyant flow, non-buoyant flows.
50
Blanchette, Melanie L., e Mark A. Lund. "Aquatic Ecosystems of the Anthropocene: Limnology and Microbial Ecology of Mine Pit Lakes". Microorganisms 9, n. 6 (3 giugno 2021): 1207. http://dx.doi.org/10.3390/microorganisms9061207.
Testo completoAbstract (sommario):
Mine pit lakes (‘pit lakes’) are new aquatic ecosystems of the Anthropocene. Potentially hundreds of meters deep, these lakes are prominent in the landscape and in the public consciousness. However, the ecology of pit lakes is underrepresented in the literature. The broad goal of this research was to determine the environmental drivers of pelagic microbe assemblages in Australian coal pit lakes. The overall experimental design was four lakes sampled three times, top and bottom, in 2019. Instrument chains were installed in lakes and measurements of in situ water quality and water samples for metals, metalloids, nutrients and microbe assemblage were collected. Lakes were monomictic and the timing of mixing was influenced by high rainfall events. Water quality and microbial assemblages varied significantly across space and time, and most taxa were rare. Lakes were moderately saline and circumneutral; Archeans were not prevalent. Richness also varied by catchment. Microbial assemblages correlated to environmental variables, and no one variable was consistently significant, spatially or temporally. Study lakes were dominated by ‘core’ taxa exhibiting temporal turnover likely driven by geography, water quality and interspecific competition, and the presence of water chemistry associated with an artificial aquifer likely influenced microbial community composition. Pit lakes are deceptively complex aquatic ecosystems that host equally complex pelagic microbial communities. This research established links between microbial assemblages and environmental variables in pit lakes and determined core communities; the first steps towards developing a monitoring program using microbes.