Journal articles on the topic 'Estuarine processes'
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Silva, Alex Evaristo da, Pedro Smith Menandro, Kleverson Alencastre Do Nascimento, Valéria Da S. Quaresma, and Alex C. Bastos. "INTERPRETATION OF SEDIMENTARY PROCESSES USING ECHO-CHARACTER DISTRIBUTION: CASE STUDY OF PIRAQUÊ-AÇU AND PIRAQUÊ-MIRIM ESTUARINE SYSTEM, ARACRUZ – ES (BRAZIL)." Revista Brasileira de Geofísica 32, no. 2 (June 1, 2014): 301. http://dx.doi.org/10.22564/rbgf.v32i2.484.
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ABSTRACT. This research aimed to map distinct types of echo-character in order to recognize estuarine sedimentary processes along the Piraquê-Açu System, in Aracruz, Espírito Santo State, Brazil. Echo-character mapping was undertaken using high frequency sub-bottom profiling data. Four echo-character (EC1, EC2, EC3,EC4) patterns were recognized by combining sub-bottom and surficial sedimentological data. These EC patterns defined three distinct areas within the system that arecharacterized by the predominance of a specific echo-character and a seabed type: i) estuarine mouth, where sand beds with low penetration prevail; ii) a transitionzone, where sandy-muddy andmuddy-sandy beds are associated with a high penetration echo-character; and, iii) the rivers/estuary Piraquê-Ac¸u and Piraquê-Mirim withsandy-muddy and muddy beds with high penetration echo pattern. The interpretation showed that the association of EC and surficial sediment may represent modernsedimentary processes within the estuary. Three sedimentary processes were recognized: a) marine dominated processes showing sand transport by tidal currents;b) estuarine processes with fine sediment input, resuspension and deposition; and c) erosive estuarine processes or scour lags, exposing possibly relict deposits.Keywords: estuarine sedimentation, shallow geophysics, sub-bottom profiler. RESUMO. Esse estudo busca reconhecer os tipos de ecocaráter existentes para o melhor entendimento dos processos sedimentares do sistema estuarino do Piraquê-Açu e Piraquê-Mirim, localizado no município de Aracruz, Espírito Santo. O reconhecimento e o mapeamento dos tipos de ecocaráter foram realizados a partir deregistros de perfilador de subfundo de alta frequência. Através da associação dos dados geofísicos com dados sedimentológicos foram reconhecidos e definidos quatropadrões de ecocarácteres (EC1, EC2, EC3, EC4) associados a tipos de fundo distintos. A distribuição espacial dos tipos de eco permitiu a divisão do estuário em três áreas distintas que diferem pela predominância de diferentes tipos de ecocaráter e sedimento: i) A foz do sistema estuarino, interpretada como região de domiâancia marinha, onde predomina o fundo arenoso e a baixa penetração do sinal; ii) A zona de confluência, onde predomina sedimentos areno-lamosos a lamo-arenosos compenetração do sinal acústico; iii) Os braços Piraquê-Açu e Piraquê-Mirim de predomínio de fundo areno-lamoso a lamoso, com penetração do sinal. Estas áreas estão associadas a distintos processos sedimentares, sendo eles: a) processos marinhos com transporte de sedimentos arenosos por correntes de maré (foz do sistema até a confluência dos braços); b) processos estuarinos com aporte, resuspensão e deposição de sedimentos finos, típicos da região interna do sistema; e c) processosestuarinos erosivos ou de ravinamento, ocorrendo localmente nos braços.Palavras-chave: sedimentação estuarina, geofísica rasa, perfilador de subfundo
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Bernardino, Angelo Fraga, Paulo Roberto Pagliosa, Ronaldo Adriano Christofoletti, Francisco Barros, Sergio A. Netto, Pablo Muniz, and Paulo da Cunha Lana. "Benthic estuarine communities in Brazil: moving forward to long term studies to assess climate change impacts." Brazilian Journal of Oceanography 64, spe2 (2016): 81–96. http://dx.doi.org/10.1590/s1679-875920160849064sp2.
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Abstract Estuaries are unique coastal ecosystems that sustain and provide essential ecological services for mankind. Estuarine ecosystems include a variety of habitats with their own sediment-fauna dynamics, all of them globally undergoing alteration or threatened by human activities. Mangrove forests, saltmarshes, tidal flats and other confined estuarine systems are under increasing stress due to human activities leading to habitat and species loss. Combined changes in estuarine hydromorphology and in climate pose severe threats to estuarine ecosystems on a global scale. The ReBentos network is the first integrated attempt in Brazil to monitor estuarine changes in the long term to detect and assess the effects of global warming. This paper is an initial effort of ReBentos to review current knowledge on benthic estuarine ecology in Brazil. We herein present and synthesize all published work on Brazilian estuaries that has focused on the description of benthic communities and related ecological processes. We then use current data on Brazilian estuaries and present recommendations for future studies to address climate change effects, suggesting trends for possible future research and stressing the need for long-term datasets and international partnerships.
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Laruelle, Goulven Gildas, Nicolas Goossens, Sandra Arndt, Wei-Jun Cai, and Pierre Regnier. "Air–water CO<sub>2</sub> evasion from US East Coast estuaries." Biogeosciences 14, no. 9 (May 15, 2017): 2441–68. http://dx.doi.org/10.5194/bg-14-2441-2017.
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Abstract. This study presents the first regional-scale assessment of estuarine CO2 evasion along the US East Coast (25–45° N). The focus is on 42 tidal estuaries, which together drain a catchment of 697 000 km2 or 76 % of the total area within this latitudinal band. The approach is based on the Carbon–Generic Estuary Model (C-GEM) that allows the simulation of hydrodynamics, transport, and biogeochemistry for a wide range of estuarine systems using readily available geometric parameters and global databases of seasonal climatic, hydraulic, and riverine biogeochemical information. Our simulations, performed using conditions representative of the year 2000, suggest that, together, US East Coast estuaries emit 1.9 Tg C yr−1 in the form of CO2, which corresponds to about 40 % of the carbon inputs from rivers, marshes, and mangroves. Carbon removal within estuaries results from a combination of physical (outgassing of supersaturated riverine waters) and biogeochemical processes (net heterotrophy and nitrification). The CO2 evasion and its underlying drivers show important variations across individual systems, but reveal a clear latitudinal pattern characterized by a decrease in the relative importance of physical over biogeochemical processes along a north–south gradient. Finally, the results reveal that the ratio of estuarine surface area to the river discharge, S∕Q (which has a scale of per meter discharged water per year), could be used as a predictor of the estuarine carbon processing in future regional- and global-scale assessments.
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Le Vu, Hong, and Ron Johnstone. "Anthropogenic Impacts on Biochemical Processes in a Tropical Estuarine Lagoon." International Journal of Engineering Technology and Sciences 5, no. 2 (August 1, 2018): 102–6. http://dx.doi.org/10.15282/ijets.v5i2.1401.
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Estuaries play an invaluable role in the transformation and cycling of materials as they move between land and sea; including anthropogenic materials. Increasingly, human land use is delivering material loads that risk overwhelming the normal functions that these ecosystems provide. In this context, the objective of this study is to assess key biogeochemical processes to understand the connections of anthropogenic activities on ecosystem performance in a tropical estuarine lagoon system. This research focuses on a case study area, Dong Ho lagoon in Vietnam, which exemplifies the anthropogenic impacts and management issues facing most of the Mekong coastline and other similar areas in Vietnam. Located at the south-western edge of the Mekong delta, the Dong Ho estuary is subject to material inputs from both local and more remote sources; making it vulnerable to degradation and functional loss. This paper summarises the key findings from an assessment of the Dong Ho estuarine functions and highlights potential risks it is currently facing.
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Wei, Xi, Josette Garnier, Vincent Thieu, Paul Passy, Romain Le Gendre, Gilles Billen, Maia Akopian, and Goulven Gildas Laruelle. "Nutrient transport and transformation in macrotidal estuaries of the French Atlantic coast: a modeling approach using the Carbon-Generic Estuarine Model." Biogeosciences 19, no. 3 (February 15, 2022): 931–55. http://dx.doi.org/10.5194/bg-19-931-2022.
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Abstract. Estuaries are key reactive ecosystems along the land–ocean aquatic continuum, with significant ecological and economic value. However, they have been facing strong morphological management changes and increased nutrient and contaminant inputs, possibly leading to ecological problems such as coastal eutrophication. Therefore, it is necessary to quantify the import and export fluxes of the estuaries, their retention capacity, and estuarine eutrophication potential. The 1-D Carbon-Generic Estuary Model (C-GEM) was used to simulate the transient hydrodynamics, transport, and biogeochemistry for estuaries with different sizes and morphologies along the French Atlantic coast during the period 2014–2016 using readily available geometric, hydraulic, and biogeochemical data. These simulations allowed us to evaluate the budgets of the main nutrients (phosphorus – P; nitrogen – N; silica – Si) and total organic carbon (TOC), and their imbalance, providing insights into their eutrophication potential. Cumulated average annual fluxes to the Atlantic coast from the seven estuaries studied were 9.6 kt P yr−1, 259 kt N yr−1, 304 kt Si yr−1, and 145 kt C yr−1. Retention rates varied depending on the estuarine residence times, ranging from 0 %–27 % and 0 %–34 % to 2 %–39 % and 8 %–96 % for total phosphorus (TP), total nitrogen (TN), dissolved silica (DSi), and TOC, respectively. Large-scale estuaries had higher retention rates than medium and small estuaries, which we interpreted in terms of estuarine residence times. As shown by the indicator of eutrophication potential (ICEP), there might be a risk of coastal eutrophication, i.e., the development of non-siliceous algae that is potentially harmful to the systems studied due to the excess TN over DSi. This study also demonstrates the ability of our model to be applied with a similar setup to several estuarine systems characterized by different sizes, geometries, and riverine loads.
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Moore-Maley, Benjamin L., Debby Ianson, and Susan E. Allen. "The sensitivity of estuarine aragonite saturation state and pH to the carbonate chemistry of a freshet-dominated river." Biogeosciences 15, no. 12 (June 20, 2018): 3743–60. http://dx.doi.org/10.5194/bg-15-3743-2018.
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Abstract. Ocean acidification threatens to reduce pH and aragonite saturation state (ΩA) in estuaries, potentially damaging their ecosystems. However, the impact of highly variable river total alkalinity (TA) and dissolved inorganic carbon (DIC) on pH and ΩA in these estuaries is unknown. We assess the sensitivity of estuarine surface pH and ΩA to river TA and DIC using a coupled biogeochemical model of the Strait of Georgia on the Canadian Pacific coast and place the results in the context of global rivers. The productive Strait of Georgia estuary has a large, seasonally variable freshwater input from the glacially fed, undammed Fraser River. Analyzing TA observations from this river plume and pH from the river mouth, we find that the Fraser is moderately alkaline (TA 500–1000 µmol kg−1) but relatively DIC-rich. Model results show that estuarine pH and ΩA are sensitive to freshwater DIC and TA, but do not vary in synchrony except at high DIC : TA. The asynchrony occurs because increased freshwater TA is associated with increased DIC, which contributes to an increased estuarine DIC : TA and reduces pH, while the resulting higher carbonate ion concentration causes an increase in estuarine ΩA. When freshwater DIC : TA increases (beyond ∼ 1.1), the shifting chemistry causes a paucity of the carbonate ion that overwhelms the simple dilution/enhancement effect. At this high DIC : TA ratio, estuarine sensitivity to river chemistry increases overall. Furthermore, this increased sensitivity extends to reduced flow regimes that are expected in future. Modulating these negative impacts is the seasonal productivity in the estuary which draws down DIC and reduces the sensitivity of estuarine pH to increasing DIC during the summer season.
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Silva Junior, Milton Goncalves, Antonio Carlos Leal Castro, and Ulrich Saint-Paul. "Comparative Analysis of Distribution of Intertidal Fish Assemblages in Different Estuarine Systems on Northern Coast of Brazil." Journal of Sustainable Development 10, no. 2 (March 30, 2017): 26. http://dx.doi.org/10.5539/jsd.v10n2p26.
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The northern coast of Brazil has more than 30 estuaries distributed along 650 km of coastline. These conditions favor the presence of relatively large fish communities in estuarine environments, but published information on the fish fauna in tidal creeks in northern Brazil is only available for some mangrove systems, and comparative studies between fish estuarine communities in different tidal creeks are less common. The choice of the study area was based on the fact that it has been poorly investigated with regard to estuarine fish fauna in comparison in mangrove tidal creeks using the same fishing gear. The objective of the present study was to compare the composition of the relative biomass of taxonomic, functional and ecological guilds of fish assemblages occurring in estuarine systems along the northern coast of Brazil. The study area of the present comparative analysis extended from the southeastern edge of the Marajoara Gulf to the western edge of the Maranhense Gulf. A comparative analysis among different estuarine systems was performed using data from other studies. The abundance of juveniles was greater in the Caeté, Curuçá and Cururuca estuaries than other estuaries. Cluster analysis separated the estuaries into two distinct groups and significant differences between these groups only exist in relation to geographical proximity. The present investigation indicates that the coastal region between the states of Pará and Maranhão is characterized by high dynamics and environmental heterogeneity, particularly with regard to changes in river discharge and tidal fluctuations. The present results underscore the importance of ecological information on ichthyofauna in tropical estuaries in order to include appropriate descriptors in conservation or restoration processes of marine communities and habitats.
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Lange, Xaver, and Hans Burchard. "The Relative Importance of Wind Straining and Gravitational Forcing in Driving Exchange Flows in Tidally Energetic Estuaries." Journal of Physical Oceanography 49, no. 3 (March 2019): 723–36. http://dx.doi.org/10.1175/jpo-d-18-0014.1.
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AbstractIn straight tidal estuaries, residual overturning circulation results mainly from a competition between gravitational forcing, wind forcing, and friction. To systematically investigate this for tidally energetic estuaries, the dynamics of estuarine cross sections is analyzed in terms of the relation between gravitational forcing, wind stress, and the strength of estuarine circulation. A system-dependent basic Wedderburn number is defined as the ratio between wind forcing and opposing gravitational forcing at which the estuarine circulation changes sign. An analytical steady-state solution for gravitationally and wind-driven exchange flow is constructed, where tidal mixing is parameterized by parabolic eddy viscosity. For this simple but fundamental situation, is calculated, meaning that the up-estuary wind forcing needs to be 15% of the gravitational forcing to invert estuarine circulation. In three steps, relevant physical processes are added to this basic state: (i) tidal dynamics are resolved by a prescribed semidiurnal tide, leading to caused by tidal straining; (ii) lateral circulation is added by introducing cross-channel bathymetry, smoothly increasing from 0.47 (flat bed) to 1.3 (parabolic bed) due to an increasing effect of lateral circulation on estuarine circulation; and (iii) full dynamics of a real tidally energetic inlet with highly variable forcing, where results from a two-dimensional linear regression.
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Burchard, Hans, and Henk M. Schuttelaars. "Analysis of Tidal Straining as Driver for Estuarine Circulation in Well-Mixed Estuaries." Journal of Physical Oceanography 42, no. 2 (February 1, 2012): 261–71. http://dx.doi.org/10.1175/jpo-d-11-0110.1.
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Abstract Tidal straining, which can mathematically be described as the covariance between eddy viscosity and vertical shear of the along-channel velocity component, has been acknowledged as one of the major drivers for estuarine circulation in channelized tidally energetic estuaries. In this paper, the authors investigate the role of lateral circulation for generating this covariance. Five numerical experiments are carried out, starting with a reference scenario including the full physics and four scenarios in which specific key physical processes are neglected. These processes are longitudinal internal pressure gradient forcing, lateral internal pressure gradient forcing, lateral advection, and the neglect of temporal variation of eddy viscosity. The results for the viscosity–shear covariance are correlated across different experiments to quantify the change due to neglect of these key processes. It is found that the lateral advection of vertical shear of the along-channel velocity component and its interaction with the tidally asymmetric eddy viscosity (which is also modified by the lateral circulation) is the major driving force for estuarine circulation in well-mixed tidal estuaries.
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Grégoire, Marilaure. "Coastal and estuarine fine sediment processes." Journal of Marine Systems 37, no. 4 (November 2002): 300–302. http://dx.doi.org/10.1016/s0924-7963(02)00181-1.
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Aranda, María, Francisco Javier Gracia, and Gloria Peralta. "Estuarine Mapping and Eco-Geomorphological Characterization for Potential Application in Conservation and Management: Three Study Cases along the Iberian Coast." Applied Sciences 10, no. 13 (June 27, 2020): 4429. http://dx.doi.org/10.3390/app10134429.
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Geomorphological changes in recent decades in three estuaries along the Iberian coast were analysed using aerial orthophotographs. A hierarchical classification scheme, based on a literature review representing 26 estuarine eco-geomorphological features relevant to estuarine dynamics and functioning, is described. The estuaries selected were San Vicente de la Barquera (N Spain), Guadiana River (SW border between Spain and Portugal) and the Ebro River Delta mouth (NE Spain). For these systems, a 60-year time series of high-resolution maps was developed, analysing the changes in feature surfaces. The main subsystems analysed were beach, dunes, saltmarshes and the drainage network. The results of the cartographies showed general behaviour common to all transitional systems, relationships among main subsystems and processes inherent to each one. This work illustrates how beaches and dunes serve as a protective barrier for the tidal flats, acting as a sediment buffer for the entire system. The subsystems are connected by the drainage network responsible for the exchange of matter and energy between them. Furthermore, an accuracy assessment was performed in one of the study zones to identify the limitations of mapping with aerial photographs. The results explain the changes with time but also the processes and relationships between the estuarine features at a long-term scale. This work adds an important perspective towards a general understanding of their dependence on intrinsic and boundary conditions.
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Xu, Chaobin, Mengting Qi, Weisheng Lin, and Xiaofei Li. "Nitrous Oxide from Abiotic Processes of Hydroxylamine and Nitrite in Estuarine and Coastal Ecosystems: A Review." Journal of Marine Science and Engineering 10, no. 5 (May 2, 2022): 623. http://dx.doi.org/10.3390/jmse10050623.
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Abiotic processes of nitrogen (N) are suggested to contribute to nitrous oxide (N2O) production; however, the important role of these processes in N2O emissions is invariably ignored. This review synthesized the main abiotic processes of hydroxylamine and nitrite and associated biogeochemical controls in estuarine and coastal ecosystems. Abiotic processes of hydroxylamine and nitrite are availably detected in estuarine and coastal environments. The abiotic processes of hydroxylamine contribute more to N2O production than the abiotic processes of nitrite in estuarine and coastal environments, suggesting that hydroxylamine plays an important role in N2O production. The isotopic fractionation effects of N can occur during the abiotic processes of hydroxylamine and nitrite and are enriched with the increasing rates of N reactions. In addition, abiotic processes of hydroxylamine and nitrite are highly dependent on pH, oxygen, Fe2+, Fe3+, and Mn4+ and are also triggered by the increasing substrate contents. These results suggest that abiotic processes of hydroxylamine and nitrite have been greatly concerned for the estuarine and coastal environments, whereas the dynamics of these processes are still sparse for projecting N fates and dynamics in response to environmental factors changes. This review highlights the importance of abiotic processes of N and associated environmental implications and presents the future trend of N cycling in estuarine and coastal environments.
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Lawson, Stephan Korblah, Hitoshi Tanaka, Keiko Udo, Nguyen Trong Hiep, and Nguyen Xuan Tinh. "Morphodynamics and Evolution of Estuarine Sandspits along the Bight of Benin Coast, West Africa." Water 13, no. 21 (October 21, 2021): 2977. http://dx.doi.org/10.3390/w13212977.
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It is well known that estuarine systems are significantly affected by hydrodynamic conditions such as river discharge, storm surges, waves and tidal conditions. In addition to this, human interferences through developmental projects have the capability of disrupting the natural morphological processes occurring at estuaries. In West Africa, the goal to improve standards of living through large-scale dam construction, offshore ports and coastal erosion countermeasures has triggered alarming changes in the morphodynamics of estuarine systems. The estuaries at the Volta River mouth (Ghana) and “Bouche du Roi” inlet (Benin), located along the Bight of Benin coast, West Africa, were selected as two case study sites to examine their long-term morphodynamics and sandspit evolution. In this study, we primarily analyzed estuarine morphology using remotely sensed images acquired from 1984 to 2020. We further estimated the longshore sediment transport for this region using results from the image analysis and the depth of active sediment motion. Our results reveal that the longshore sediment transport rates for this region are in the magnitude of 105–106 m3/year. Comparative analysis with other estuaries and sandy coasts suggests that the longshore sediment transport along this coast has one of the largest rates estimated in the world.
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Santos, Sindiany Suelen Caduda dos, Edilson Divino de Araújo, and Rosemeri Melo e Souza. "Análise dos Tensores Antropogênicos dos Mangues no Complexo Estuarino Real- Piauí-Fundo, sul de Sergipe." Revista Brasileira de Geografia Física 14, no. 3 (July 20, 2021): 1690. http://dx.doi.org/10.26848/rbgf.v14.3.p1690-1706.
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Os mangues do litoral sul de Sergipe sobrevivem em meio à presença de tensores antropogênicos comprometedores da existência do ecossistema manguezal. Objetiva-se analisar os tensores antropogênicos que afetam os mangues Avicennia schaueriana Stapf. & Leech, Laguncularia racemosa (L.) Gaertn.f. e Rhizophora mangle L. e os níveis de vulnerabilidade decorrentes da tensão, no complexo estuarino Real-Piauí-Fundo/ Sergipe. Mediante adaptações na metodologia de Laranjeira e de Oliveira com Melo e Souza, foram determinadas características definidoras da transformação dos mangues. Os tensores foram observados sistematicamente nos estuários inferior, médio e superior, com base na definição prévia de atributos de tensão. Para avaliação conjunta dos tensores, foram determinados pesos e calculado o reescalonamento da vulnerabilidade. Os dados expressos em quadros, gráficos e mapa produzido no ArcGis, revelam: o estuário médio constitui a área de menor tensão antrópica; e o superior a área de maior vulnerabilidade, com a maior parte da faixa de mangues fora dos limites do polígono da Área de Proteção Ambiental do Litoral Sul, quando visualizados os limites da APA e as localidades da pesquisa. A sensibilidade dos estuários inferior e médio, que estão dentro da APA, foi classificada como elevada e moderada, respectivamente, revelando que os mangues do complexo estuarino estão sujeitos aos riscos das ações humanas. Mesmo dentro de um complexo estuarino, os mangues apresentam capacidade de resposta distinta aos tensores antropogênicos e chances significativas de desaparecimento. Analysis of Mangrove Anthropogenic Tensors in the Real- Piauí-Fundo Estuarine Complex, south of Sergipe, Brasil ABSTRACTThe mangroves on the south coast of Sergipe survive amid the presence of anthropogenic tensors that compromise the existence of the mangrove ecosystem. The objective is to analyze the anthropogenic tensors that affect the Avicennia schaueriana (Stapf & Leech), Laguncularia racemosa (L.) C.F. Gaertn and Rhizophora mangle (L.) and the levels of vulnerability resulting from tension, in the Real-Piauí-Fundo/ Sergipe estuarine complex. The tensors were systematically observed in the lower, middle and upper estuaries, based on the previous definition of tension attributes. For the joint assessment of the tensors, weights were determined and the rescheduling of the vulnerability was calculated. The data expressed in charts, graphs and maps produced in ArcGis, reveal: the average estuary constitutes the area with the lowest anthropogenic tension; and the upper one, the most vulnerable area, with most of the mangrove strip outside the limits of the polygon of the Environmental Protection Area of the South Coast, when viewing the APA limits and the research locations. The sensitivity of the lower and middle estuaries, which are within the APA, was classified as high and moderate, respectively, revealing that the mangroves of the estuarine complex are subject to the risks of human actions. Even within an estuarine complex, the mangroves have a different response capacity to anthropogenic tensors and significant chances of disappearance.Keywords: mangrove vulnerability. environmental stressor. mangrove. anthropic actions.
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Gomes, Vando J. C., Nils E. Asp, Eduardo Siegle, José Diego Gomes, Ariane M. M. Silva, Andrea S. Ogston, and Charles A. Nittrouer. "Suspended-Sediment Distribution Patterns in Tide-Dominated Estuaries on the Eastern Amazon Coast: Geomorphic Controls of Turbidity-Maxima Formation." Water 13, no. 11 (June 1, 2021): 1568. http://dx.doi.org/10.3390/w13111568.
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In tide-dominated estuaries, maximum-turbidity zones (MTZs) are common and prominent features, characterized by a peak in suspended-sediment concentration (SSC) associated with estuarine processes. The Brazilian Amazon coast includes many estuaries, experiencing macrotidal conditions. MTZs are expected to occur and are crucial for sediment delivery to the longest continuous mangrove belt of the world. The area is under influence of the Amazon River plume (ARP), the main SSC source, as local rivers do not deliver substantial sediment supply. To assess the processes that allow the ARP to supply sediment to the estuaries and mangrove belt along the Amazon coast, the results from previous individual studies within five Amazon estuaries (Mocajuba, Taperaçu, Caeté, Urumajó and Gurupi) were compared with regards to SSC, salinity, morphology and tidal propagation. This comparison reinforces that these estuaries are subject to similar regional climate and tidal variations, but that their dynamics differ in terms of distance from the Amazon River mouth, importance of the local river sediment source, and morphology of the estuarine setting. The Urumajó, Caeté and Gurupi are hypersynchronous estuaries where perennial, classic MTZs are observed with SSC > 1 g·L−1. This type of estuary results in transport convergence and MTZ formation, which are suggested to be the main processes promoting mud accumulation in the Amazonian estuaries and therefore the main means of mud entrapment in the mangrove belt. The Mocajuba and the Taperaçu estuaries showed synchronous and hyposynchronous processes, respectively, and do not present classic MTZs. In these cases, the proximity to the ARP for the Mocajuba and highly connected tidal channels for the Taperaçu estuary, assure substantial mud supply into these estuaries. This study shows the strong dependence of the estuaries and mangrove belt on sediment supply from the ARP, helping to understand the fate of Amazon River sediments and providing insights into the mechanisms providing sediment to estuaries and mangroves around the world, especially under the influence of big rivers.
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Nayak, Ganapati Narayan. "Changing Tropical Estuarine Sedimentary Environments with Time and Metals Contamination, Cest Coast of India." Journal of The Indian Association of Sedimentologists 38, no. 2 (December 31, 2021): 63–78. http://dx.doi.org/10.51710/jias.v38i2.141.
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Estuaries are one of the major sub-environments of the coastal zone wherein freshwaters interact and mix with saline waters, and facilitate deposition of finer sediments, organic matter, and metals. Intertidal mudflat and mangrove sediment cores collected from estuaries along the central west coast of India were investigated for various sedimentological and geochemical parameters to understand the changes in the sedimentary depositional environments and various factors influencing the processes. Additionally, estuarine biota was examined to understand the bioaccumulation of metals with respect to bioavailability. The results indicated considerable changes in the depositional environments with time owing to sea-level changes; geomorphology of the estuaries; rainfall and river runoff; anthropogenic activities including construction of dams and bridges. The sediments in the estuaries are considerably polluted by metals and pose toxicity risks to the estuarine biota due to high metal bioavailability. Marine gastropods and mangrove plants act as prospective bio-indicators, and the bioremediation potential of mangroves for contaminated sediments was identified. Metal bioaccumulation in edible benthic biota can be harmful to the human health.
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Huang, Weihao, Wenping Gong, Heng Zhang, Zhengbo Jia, Zhenyu Huang, Lei Zhu, and Jiahuan Liu. "Stochasticity in the estuarine sediment erosion processes." Continental Shelf Research 225 (August 2021): 104479. http://dx.doi.org/10.1016/j.csr.2021.104479.
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Ortega, T., J. M. Forja, and A. Gómez-Parra. "Teaching Estuarine Chemical Processes by Laboratory Simulation." Journal of Chemical Education 78, no. 6 (June 2001): 771. http://dx.doi.org/10.1021/ed078p771.
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Bernhard, Anne E., and Annette Bollmann. "Estuarine nitrifiers: New players, patterns and processes." Estuarine, Coastal and Shelf Science 88, no. 1 (June 2010): 1–11. http://dx.doi.org/10.1016/j.ecss.2010.01.023.
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Ji, Z. G., M. R. Morton, and J. M. Hamrick. "Wetting and Drying Simulation of Estuarine Processes." Estuarine, Coastal and Shelf Science 53, no. 5 (November 2001): 683–700. http://dx.doi.org/10.1006/ecss.2001.0818.
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Dijkstra, Yoeri M., and Henk M. Schuttelaars. "A Unifying Approach to Subtidal Salt Intrusion Modeling in Tidal Estuaries." Journal of Physical Oceanography 51, no. 1 (January 2021): 147–67. http://dx.doi.org/10.1175/jpo-d-20-0006.1.
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AbstractThe salinity structure in estuaries is classically described in terms of the salinity structure as well mixed, partially mixed, or salt wedge. The existing knowledge about the processes that result in such salinity structures comes from highly idealized models that are restricted to either well-mixed and partially mixed cases or subtidal salt wedge estuaries. Hence, there is still little knowledge about the processes driving transitions between these different salinity structures and the estuarine parameters at which such a transition is found. As an important step toward a unified description of the dominant processes driving well-mixed, partially mixed, and salt wedge estuaries, a subtidal width-averaged model applicable to all these salinity structures is developed and systematically analyzed. Using our model, we identify four salinity regimes, resulting from different balances of dominant processes. It is shown that each regime is uniquely determined by two dimensionless parameters: an estuarine Froude and Rayleigh number, representing freshwater discharge and tidal mixing, respectively, resulting in a classification of the regimes in terms of these two parameters. Furthermore, analytical expressions to approximate the salt intrusion length in each regime are developed. These expressions are used to illustrate that the salt intrusion length in different regimes responds in a highly different manner to changes in depth and freshwater discharge. As one of the key results, we show that there are only very weak relations between the process-based regime of an estuary and the salt intrusion length and top–bottom stratification. This implies that the salinity structure of an estuary cannot be uniquely matched to a regime.
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Volta, C., S. Arndt, H. H. G. Savenije, G. G. Laruelle, and P. Regnier. "C-GEM (v 1.0): a new, cost-efficient biogeochemical model for estuaries and its application to a funnel-shaped system." Geoscientific Model Development 7, no. 4 (July 4, 2014): 1271–95. http://dx.doi.org/10.5194/gmd-7-1271-2014.
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Abstract. Reactive transport models (RTMs) are powerful tools for disentangling the complex process interplay that drives estuarine biogeochemical dynamics, for assessing the quantitative role of estuaries in global biogeochemical cycles and for predicting their response to anthropogenic disturbances (land-use change, climate change and water management). Nevertheless, the application of RTMs for a regional or global estimation of estuarine biogeochemical transformations and fluxes is generally compromised by their high computational and data demands. Here, we describe C-GEM (Carbon-Generic Estuary Model), a new one-dimensional, computationally efficient RTM that reduces data requirements by using a generic, theoretical framework based on the direct relationship between estuarine geometry and hydrodynamics. Despite its efficiency, it provides an accurate description of estuarine hydrodynamics, salt transport and biogeochemistry on the appropriate spatio–temporal scales. We provide a detailed description of the model, as well as a protocol for its set-up. The new model is then applied to the funnel-shaped Scheldt estuary (BE/NL), one of the best-surveyed estuarine systems in the world. Its performance is evaluated through comprehensive model–data and model–model comparisons. Model results show that C-GEM captures the dominant features of the biogeochemical cycling in the Scheldt estuary. Longitudinal steady-state profiles of oxygen, ammonium, nitrate and silica are generally in good agreement with measured data. In addition, simulated, system-wide integrated reaction rates of the main pelagic biogeochemical processes are comparable with those obtained using a high-resolved, two-dimensional RTM. A comparison of fully transient simulations results with those of a two-dimensional model shows that the estuarine net ecosystem metabolism (NEM) only differs by about 10%, while system-wide estimates of individual biogeochemical processes never diverge by more than 40%. A sensitivity analysis is carried out to assess the sensitivity of biogeochemical processes to uncertainties in parameter values. Results reveal that the geometric parameters LC (estuarine convergence length) and H (water depth), as well as the rate constant of organic matter degradation (kox) exert an important influence on the biogeochemical functioning of the estuary. The sensitivity results also show that, currently, the most important hurdle towards regional- or global-scale applications arises from the lack of an objective framework for sediment and biogeochemical process parameterization. They, therefore, emphasize the need for a global compilation of biogeochemical parameter values that can help identify common trends and possible relationships between parameters and controlling factors, such as climate, catchment characteristics and anthropic pressure.
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Souza, José Francisco Almeida de, José Luiz Lima de Azevedo, Leopoldo Rota de Oliveira, Ivan Dias Soares, and Maurício Magalhães Mata. "INCORPORATION OF NEW TURBULENT CLOSURE SCHEMES IN THE PRINCETON OCEAN MODEL (POM)." Revista Brasileira de Geofísica 31, no. 1 (March 1, 2013): 17. http://dx.doi.org/10.22564/rbgf.v31i1.243.
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One of the most challenging issues in oceanography is the simulation of the mixing processes, which are responsible for diffusion of momentum, heat, salt, sediments etc. In the modeling of flow, the hydrodynamic model simulates the properties of the mean flow while the turbulence model, coupled to the first, is responsible for simulating the mixing processes. In this article it is used the Princeton Ocean Model (POM), which includes the well known turbulent closure model q2 − q2L of Mellor & Yamada (1982), level 2.5. To add flexibility to the modeling, the k − ε and k − ω models, which belong to the same class of models, are incorporated into the POM and two test cases, one involving the deepening of the oceanic mixed layer and the other addressing the estuarine circulation, are carried out to allow the quality assessment of the models implementation in the computer code. The tests indicated that the model implementation was adequate. Comparing with the original model available in the Princeton Ocean Model, the results showed that the model k − ε tends to overestimate the mixed layer, while the model k − ω underestimates it, within an acceptable range of tolerance. In terms of estuarine circulation, the k − ε and k − ω models showed a greater capacity of mixing at the bottom of the estuarine mixing zone and also at the surface layer.RESUMO: Uma das questões mais desafiadoras em oceanografia é a simulação dos processos de mistura, responsáveis pela difusão de momentum, calor, sal, sedimentos etc. Na modelagem de escoamentos, o modelo hidrodinâmico simula as propriedades do escoamento médio, enquanto o modelo de turbulência, acoplado ao primeiro, é o responsável por simular os processos de mistura. Nesse artigo é utilizado o Princeton Ocean Model (POM), o qual traz acoplado o conhecido esquema de fechamento turbulento q2 − q2L de Mellor & Yamada (1982), n´ıvel 2.5. Para adicionar flexibilidade à modelagem, os modelos k − ε e k − ω, da mesma categoria de modelos, são incorporados ao POM e dois casos-teste, um envolvendo o aprofundamento da camada de mistura oceânica e o outro a circulação estuarina, são realizados para permitir a avaliação da qualidade da implementação dos modelos no código computacional. Os testes indicaram que a implementação dos modelos foi adequada. Tendo como referência o modelo original do POM, os resultados mostraram que o modelo k − ε tende a superestimar a camada de mistura, enquanto o k − ω a subestima, numa faixa aceitável de tolerância. Em termos de circulação estuarina, os modelos k − ε e k − ω apresentaram uma maior capacidade de mistura tanto no fundo da zona de mistura estuarina como na camada superficial.Palavras-chave: modelos de turbulência, processos de mistura, modelos a duas equações, camada de mistura, circulação estuarina.
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De Oliveira, Allan De Oliveira. "CARACTERIZAÇÃO SEDIMENTAR E APLICAÇÃO DO DIAGRAMA DE PEJRUP PARA INTERPRETAÇÃO DA DINÂMICA EM UMA ENSEADA ESTUARINA NA LAGOA DOS PATOS/BRASIL / Sedimentary Characterization and Application of Pejrup Diagram to Interpret the Dinamics in a Small Cove of The Lagoa dos Patos/Brazil." Geographia Meridionalis 1, no. 2 (December 18, 2015): 363. http://dx.doi.org/10.15210/gm.v1i2.6232.
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A partir da análise dos parâmetros estatísticos dos sedimentos de fundo de uma enseada estuarina e da aplicação do diagrama de Pejrup, foi possível caracterizar os processos dinâmicos e sedimentares que ocorrem em uma pequena enseada da Lagoa dos Patos. Os sedimentos que recobrem o fundo da área estudada são formados por areias finas a muito finas, com presença de material lamoso, preferencialmente silte, em direção à região central e margens da enseada. A hidrodinâmica da área é dominada pela circulação estuarina e correntes fluviais, bem como pela ação dos ventos que influenciam estas correntes. Esses fatores são responsáveis pelo transporte, redistribuição e deposição dos sedimentos na área de estudo.ABSTRACTFrom statistical parameters of the bottom morphology and of the application of the diagram of Pejrup it was possible to characterize the dynamic and sedimentary processes that occur in a small cove of the Lagoa dos Patos. The sediments that recover the bottom of the studied area are formed by fine to very fine sands, with the presence of muddy (silt) in the central region and marginal area. The hydrodynamic of the area is dominated by the estuarine circulation and fluvial currents as well, partly due the action of winds which influence these currents. These factors are responsible for the transport, redistribution and deposition of the sediments in the study area.Keywords: sedimentary characterization; hydrodinamics; estuarine cove.
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Dolby, Greer A., Ryan Hechinger, Ryan A. Ellingson, Lloyd T. Findley, Julio Lorda, and David K. Jacobs. "Sea-level driven glacial-age refugia and post-glacial mixing on subtropical coasts, a palaeohabitat and genetic study." Proceedings of the Royal Society B: Biological Sciences 283, no. 1843 (November 30, 2016): 20161571. http://dx.doi.org/10.1098/rspb.2016.1571.
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Using a novel combination of palaeohabitat modelling and genetic mixture analyses, we identify and assess a sea-level-driven recolonization process following the Last Glacial Maximum (LGM). Our palaeohabitat modelling reveals dramatic changes in estuarine habitat distribution along the coast of California (USA) and Baja California (Mexico). At the LGM (approx. 20 kya), when sea level was approximately 130 m lower, the palaeo-shoreline was too steep for tidal estuarine habitat formation, eliminating this habitat type from regions where it is currently most abundant, and limiting such estuaries to a northern and a southern refugium separated by 1000 km. We assess the recolonization of estuaries formed during post-LGM sea-level rise through examination of refugium-associated alleles and approximate Bayesian computation in three species of estuarine fishes. Results reveal sourcing of modern populations from both refugia, which admix in the newly formed habitat between the refuges. We infer a dramatic peak in habitat area between 15 and 10 kya with subsequent decline. Overall, this approach revealed a previously undocumented dynamic and integrated relationship between sea-level change, coastal processes and population genetics. These results extend glacial refugial dynamics to unglaciated subtropical coasts and have significant implications for biotic response to predicted sea-level rise.
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Leal Filho, Walter, Gustavo J. Nagy, Filipe Martinho, Mustafa Saroar, Mónica Gómez Erache, Ana Lígia Primo, Miguel A. Pardal, and Chunlan Li. "Influences of Climate Change and Variability on Estuarine Ecosystems: An Impact Study in Selected European, South American and Asian Countries." International Journal of Environmental Research and Public Health 19, no. 1 (January 5, 2022): 585. http://dx.doi.org/10.3390/ijerph19010585.
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It is well-known that climate change significantly impacts ecosystems (at the macro-level) and individual species (at the micro-level). Among the former, estuaries are the most vulnerable and affected ecosystems. However, despite the strong relations between climate change and estuaries, there is a gap in the literature regarding international studies across different regions investigating the impacts of climate change and variability on estuaries in different geographical zones. This paper addresses this need and reviews the impacts of climate change, variability and extreme weather on estuaries. It emphasises the following: (i) a set of climate parameters governing estuarine hydrology and processes; and (ii) a sample of countries in Asia (Bangladesh), Europe (Portugal) and South America (Uruguay). We reviewed the influences of the climatic drivers of the estuarine hydrology, ecological processes and specific species in estuarine communities across the selected geographical regions, along with an analysis of their long-term implications. The key results from the three estuaries are as following: (i) Hilsa fish, of which the catches contribute to 10% of the total earnings of the fishery sector (1% of GDP), are affected by climate-forced hydrological and productivity changes in the Meghna; (ii) extreme droughts and short-term severe precipitation have driven the long-term abundance and spatial distribution of both fish larvae and juveniles/adults in the Mondego; and (iii) the river inflow and fluctuations increases since the early 1970s have contributed to variations in the salinity, the stratification, the oxygen, nutrient and trophic levels and the spatial pattern for the life stages of planktonic species, fish biomass and captures in the Rio de la Plata. The results suggested that immediate action is needed to reduce the vulnerability of estuaries to climate stressors, mainly the changing river flows, storms and sea-level rise. As a contribution to addressing current problems, we described a set of adaptation strategies to foster climate resilience and adaptive capacity (e.g., early-warning systems, dam management to prevent overflows and adaptive fisheries management). The implications of this paper are two-fold. Firstly, it showcases a variety of problems that estuaries face from changing climate conditions. Secondly, the paper outlines the need for suitable adaptive management strategies to safeguard the integrity of such vital ecosystems.
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Seriani, Robson, Lucas Buruaem Moreira, Denis Moledo de Souza Abessa, Laís D. Abujamara, Natashy S. B. de Carvalho, Luciane Alves Maranho, Aline A. Kirschbaum, and Maria José T. Ranzani-Paiva. "Hematological analysis of Micropogonias Furnieri, Desmarest, 1823, Scianidae, from two estuaries of Baixada Santista, São paulo Brazil." Brazilian Journal of Oceanography 58, spe3 (June 2010): 87–92. http://dx.doi.org/10.1590/s1679-87592010000700011.
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Hematological alterations in fish are considered a useful tool to evaluate pathological processes resulting from the exposure to environmental pollutants. The whitemouth croaker Micropogonias furnieri is a common species in estuarine areas and potentially exposed to many contaminants. In the present study, the hematological characteristics of fish collected at two sites in Baixada Santista (Santos Estuarine System - SES, a polluted site; and the Estuary of Itanhaém River - EIR, unpolluted site) del was analysed. The following blood descriptors were analyzed: number of Erythrocytes (Er), Hematocrit (Ht), Hemoglobin (Hb), Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin concentration (MCHC). Fish from SES exhibited significant lower levels of Ht and increase on MCHC and Hb. Such differences are likely related to the different contamination levels found in these estuaries.
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R., Anusiya, and Sukumaran M. "Assessment of Seasonal Variation (2020 to 2021) in Physico-Chemical Parameters of Nandalar Estuary in East Coast of Tamil Nadu, India." International Journal of Zoological Investigations 08, special issue (2022): 254–58. http://dx.doi.org/10.33745/ijzi.2022.v08i0s.030.
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Estuaries are defined as the areas between rivers and the ocean that have unique ecological characteristics, a wealth of flora and fauna, and are essential to both biodiversity and hydrological processes. Aquatic ecosystems depend on their biological traits as well as their physical and chemical qualities. The objective of the current study was to identify seasonal variations in the physico-chemical parameters of Tamil Nadu's Nandalar Estuary. The physico-chemical characteristics of the Nandalar Estuary were recorded which have an impact on the estuarine environment. Future analyses of the ecological, biological, and cultural elements of estuarine species as well as the allowable limit of fisheries and aquatic life would benefit from preliminary data on the physico-chemical parameters in this Nandalar estuary area.
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Kleinhans, Maarten G., Lonneke Roelofs, Steven A. H. Weisscher, Ivar R. Lokhorst, and Lisanne Braat. "Estuarine morphodynamics and development modified by floodplain formation." Earth Surface Dynamics 10, no. 2 (April 29, 2022): 367–81. http://dx.doi.org/10.5194/esurf-10-367-2022.
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Abstract. Rivers and estuaries are flanked by floodplains built by mud and vegetation. Floodplains affect channel dynamics and the overall system's pattern through apparent cohesion in the channel banks and through filling of accommodation space and hydraulic resistance. For rivers, effects of mud, vegetation and the combination are thought to stabilise the banks and narrow the channel. However, the thinness of estuarine floodplain, comprised of salt marsh and mudflats, compared to channel depth raises questions about the possible effects of floodplain as constraints on estuary dimensions. To test these effects, we created three estuaries in a tidal flume: one with recruitment events of two live vegetation species, one with mud and a control with neither. Both vegetation and mud reduced channel migration and bank erosion and stabilised channels and bars. Effects of vegetation include local flow velocity reduction and concentration of flow into the channels, while flow velocities remained higher over mudflats. On the other hand, the lower reach of the muddy estuary showed more reduced channel migration than the vegetated estuary. The main system-wide effect of mudflats and salt marsh is to reduce the tidal prism over time from upstream to downstream. The landward reach of the estuary narrows and fills progressively, particularly for the muddy estuary, which effectively shortens the tidally influenced reach and also reduces the tidal energy in the seaward reach and mouth area. As such, estuaries with sufficient sediment supply are limited in size by tidal prism reduction through floodplain formation.
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Groeneveld, Johan C., Jorge Santos, Fiona MacKay, and Cosmas N. Munga. "A regional assessment of seasonal-to-decadal changes in estuarine socio-ecological systems in the Western Indian Ocean." Western Indian Ocean Journal of Marine Science, no. 1/2021 (December 23, 2021): 131–61. http://dx.doi.org/10.4314/wiojms.si2021.1.9.
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Estuarine socio-ecological systems (SES) in the Western Indian Ocean (WIO) region face mounting pressures from overexploitation, habitat degradation, impacts of climate change and governance inadequacies. A regional assessment of seasonal-to-decadal change in SES of three estuaries (Bons Sinais in Mozambique, Ruvu in Tanzania and Tana in Kenya) was undertaken along 2000 km of tropical coastline (3°-18°S), using a systems-oriented approach and information collected during the Estuarize-WIO project (2016-2019). All three estuaries were open and tidal, but differed along gradients of geomorphology, annual precipitation, exposure to tropical storms, drought, sea level rise, and rural to urban development. Despite physical differences, similar marine species, mangrove assemblages, seasonality in fish-based farming systems and cultivated crops, and fishing methods were apparent across the region. Key differences were related to the scale of anthropogenic disturbance, discerned from land use / land cover (LULC) change analysis, which showed decadal increases in developed-, cultivated- and grasslands, at the expense of wetlands and forests, and seasonal transformation of wetlands to agriculture and grasslands. The three estuaries represented a gradient along urban-production-conservation dimensions, brought about by rural to urban transformation, and by freshwater and sediment diversion for economic development in upstream catchment areas. Household surveys indicated strongly seasonal livelihood strategies, with highest diversity in peri-urban settings, and reliance on different combinations of ecosystem goods and services in coastal and upstream rural settings. Estuarine fisheriesranged from unselective, low trophic-level fisheries using fine-mesh nets at the urbanized and most-disturbed Bons Sinais Estuary, to a more complex organized fishery at the least-disturbed Tana. At Ruvu, fisheries and agriculture production exit the system to distant markets. The systems-oriented approach demonstrated that human-induced processes affected WIO estuaries and dependent livelihoods more deeply than inherent physical differences. A key conclusion is that research, management and governance will benefit from regional cooperation, given the similarities of the systems and the different levels of disturbance.
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Volta, C., S. Arndt, H. H. G. Savenije, G. G. Laruelle, and P. Regnier. "C-GEM (v 1.0): a new, cost-efficient biogeochemical model for estuaries and its application to a funnel-shaped system." Geoscientific Model Development Discussions 6, no. 4 (November 14, 2013): 5645–709. http://dx.doi.org/10.5194/gmdd-6-5645-2013.
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Abstract. The first part of this paper describes C-GEM (Carbon – Generic Estuary Model), a new, one-dimensional, generic reactive-transport model for the biogeochemical dynamics of carbon and associated bio-elements (N, P, Si) in estuaries. C-GEM is computationally efficient and reduces data-requirements by using an idealized representation of the estuarine geometry to quantitatively predict the dominant features of the estuarine hydrodynamics, salt transport and biogeochemistry. A protocol for the set-up of C-GEM for an estuarine system is also described. The second part of this paper presents, as a proof of concept, the application of C-GEM to the funnel-shaped Scheldt estuary (Belgium, the Netherlands), one of the best-surveyed system in the world. Steady-state and transient simulations are performed and the performance of C-GEM is evaluated through model-data and model-model comparison, using integrated measures of the estuarine biogeochemical functioning, such as system-wide estimates of the Net Ecosystem Metabolism (NEM). A sensitivity analysis is also carried out to identify model parameters that exert the most important control on biogeochemical processes and to assess the sensitivity of the NEM to uncertainties in parameter values. The paper ends by a short discussion of current model limitations with respect to local, regional and global scale applications.
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Silva, Janaina Barbosa da, Josiclêda Domiciano Galvíncio, Antonio Carlos De Barros Corrêa, Danielle Gomes da Silva, and Célia Cristina Clemente Machado. "Classificação Geomorfológica dos Estuários do Estado de Pernambuco (Brasil) com Base em Imagens do LANDSAT 5/TM (Geomorphologic Classification of Estuaries of the State of Pernambuco (Brazil) Based on Landsat 5 TM Images)." Revista Brasileira de Geografia Física 4, no. 1 (July 17, 2011): 118. http://dx.doi.org/10.26848/rbgf.v4i1.232689.
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O presente estudo visou classificar os quinze estuários do Estado de Pernambuco, adotando como base as características geomorfológicas. A base de dados utilizada para a classificação foram imagens de satélites do Landsat 5-TM. Foram realizadas análises visuais das imagens de satélite e posteriormente efetuados trabalhos de campo com o intuito de validar as interpretações realizadas. Na zona costeira pernambucana os estuários classificam-se como: Planície Costeira (vale inundado), Formado por Barras e por Outros Processos. As interações espaço-temporal dos processos ambientais durante o Quaternário foram de fundamental importância para a atual configuração das áreas estuarinas classificadas, tendo em vista que tectonismo, erosão e sedimentação recorrente das regressões e transgressões marinhas foram processos recursivos durante a formação dos estuários e que deixaram registros na paisagem. Foram definidos como planície costeira os estuários do Goiana/Megaó, Jaguaribe, Paratibe, Maracaípe, Sirinhaém e Formoso. Do tipo construído pro barra tem-se o Timbó, Beberibe, Jaboatão/Pirapama, Mamucabas/Ilhetas e Una. Estuários tipo ria são os de Itapessoca e Canal de Santa Cruz, enquanto os de laguna costeira são o Ipojuca e o Capibaribe. Palavras-chave: Estuários, Zona Costeira Pernambucana, Quaternário Geomorphologic Classification of Estuaries of the State of Pernambuco (Brazil) Based on Landsat 5 TM Images ABSTRACT This study aimed to classify the fifteen estuaries of the State of Pernambuco-Brazil, using as base the geomorphological characteristics. The database used for the classification were satellite images of Landsat-5 TM. Were performed visual analysis of satellite images and were later made field work to validate the interpretations made. In the coastal zone of Pernambuco are found three classifications of estuaries: coastal plain (the flood plain), formed by bars and other processes. The space-time interactions of environmental processes during the Quaternary were of fundamental importance to the current configuration of estuarine areas classified in order to tectonics, erosion and sedimentation of the applicant marine transgressions and regressions were recursive processes during the formation of estuaries and left records in the landscape. Were defined as the coastal plain estuaries of Goiana/Megaó, Jaguaribe, Paratibe, Olinda, Sirinhaém and Formoso. Type built by bar has the Timbó, Beberibe, Jaboatão/Pirapama, Mamucaba/Ilhetas and Una. Estuaries are the kind of laughed Itapessoca and Channel and Santa Cruz, while the coastal lagoon and are Ipojuca and Capibaribe. Key-words: Estuary, coastal Pernambuco, quaternary
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Burchard, Hans. "A Universal Law of Estuarine Mixing." Journal of Physical Oceanography 50, no. 1 (January 2020): 81–93. http://dx.doi.org/10.1175/jpo-d-19-0014.1.
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AbstractA universal law of estuarine mixing is derived here, combining the approaches of salinity coordinates, Knudsen relations, total exchange flow, mixing definition as salinity variance loss, and the mixing–exchange flow relation. As a result, the long-term average mixing within an estuarine volume bounded by the isohaline of salinity S amounts to M(S) = S2Qr, where Qr is the average river runoff into the estuary. Consequently, the mixing per salinity class is m(S) = ∂SM(S) = 2SQr, which can also be expressed as the product of the isohaline volume and the mixing averaged over the isohaline. The major differences between the new mixing law and the recently developed mixing relation based on the Knudsen relations are threefold: (i) it does not depend on internal dynamics of the estuary determining inflow and outflow salinities (universality), (ii) it is exactly derived from conservation laws (accuracy), and (iii) it calculates mixing per salinity class (locality). The universal mixing law is demonstrated by means of analytical stationary and one-dimensional and two-dimensional numerical test cases. Some possible consequences for the salinity distribution in real estuaries are briefly discussed. Since the mixing per salinity class only depends on the river runoff and the chosen salinity, and not on local processes at the isohaline, low-mixing estuaries must have large isohaline volumes and vice versa.
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Lonthair, Joshua, Rasmus Ern, and Andrew J. Esbaugh. "The early life stages of an estuarine fish, the red drum (Sciaenops ocellatus), are tolerant to high pCO2." ICES Journal of Marine Science 74, no. 4 (January 8, 2017): 1042–50. http://dx.doi.org/10.1093/icesjms/fsw225.
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Ocean acidification (OA) and other climate change induced environmental alterations are resulting in unprecedented rates of environmental deterioration. This environmental change is generally thought to be too fast for adaptation using typical evolutionary processes, and thus sensitivity may be dependent on the presence of existing tolerant genotypes and species. Estuaries undergo natural pCO2 fluctuations over a variety of time scales, and levels regularly exceed the predicted end of the century values. Interestingly, estuarine fish species have been overlooked in reference to the impacts of OA. Here, we use the estuarine red drum (Sciaenops ocellatus) as a model to explore the hypothesis that early life stages of estuarine species have intrinsic tolerance to elevated pCO2. Our sensitivity endpoints included: survival, growth, yolk consumption, heart rate, and scototaxis. Survival was significantly decreased when exposed to 1300 μatm and 3000 μatm, and coincided with a significant increase in heart rate at the 3000 μatm exposure. However, these effects were less pronounced than the findings of previous studies on other marine fish species. Yolk depletion rate and standard length were not significantly affected by pCO2. Scototaxis behaviour was also not significantly affected by exposure to elevated levels of pCO2 under both acute and acclimated exposure scenarios. Overall, these results support the hypothesis that estuarine life history and habitat usage may play a critical role in determining sensitivity of fish species to OA. Furthermore, estuarine species may provide present-day insight into the physiological and ecological foundation of OA tolerance.
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Hughes, Brent B., Kerstin Wasson, M. Tim Tinker, Susan L. Williams, Lilian P. Carswell, Katharyn E. Boyer, Michael W. Beck, et al. "Species recovery and recolonization of past habitats: lessons for science and conservation from sea otters in estuaries." PeerJ 7 (December 10, 2019): e8100. http://dx.doi.org/10.7717/peerj.8100.
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Recovering species are often limited to much smaller areas than they historically occupied. Conservation planning for the recovering species is often based on this limited range, which may simply be an artifact of where the surviving population persisted. Southern sea otters (Enhydra lutris nereis) were hunted nearly to extinction but recovered from a small remnant population on a remote stretch of the California outer coast, where most of their recovery has occurred. However, studies of recently-recolonized estuaries have revealed that estuaries can provide southern sea otters with high quality habitats featuring shallow waters, high production and ample food, limited predators, and protected haul-out opportunities. Moreover, sea otters can have strong effects on estuarine ecosystems, fostering seagrass resilience through their consumption of invertebrate prey. Using a combination of literature reviews, population modeling, and prey surveys we explored the former estuarine habitats outside the current southern sea otter range to determine if these estuarine habitats can support healthy sea otter populations. We found the majority of studies and conservation efforts have focused on populations in exposed, rocky coastal habitats. Yet historical evidence indicates that sea otters were also formerly ubiquitous in estuaries. Our habitat-specific population growth model for California’s largest estuary—San Francisco Bay—determined that it alone can support about 6,600 sea otters, more than double the 2018 California population. Prey surveys in estuaries currently with (Elkhorn Slough and Morro Bay) and without (San Francisco Bay and Drakes Estero) sea otters indicated that the availability of prey, especially crabs, is sufficient to support healthy sea otter populations. Combining historical evidence with our results, we show that conservation practitioners could consider former estuarine habitats as targets for sea otter and ecosystem restoration. This study reveals the importance of understanding how recovering species interact with all the ecosystems they historically occupied, both for improved conservation of the recovering species and for successful restoration of ecosystem functions and processes.
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Bange, Hermann W., Chun Hock Sim, Daniel Bastian, Jennifer Kallert, Annette Kock, Aazani Mujahid, and Moritz Müller. "Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo." Biogeosciences 16, no. 22 (November 15, 2019): 4321–35. http://dx.doi.org/10.5194/bg-16-4321-2019.
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Abstract. Nitrous oxide (N2O) and methane (CH4) are atmospheric trace gases which play important roles in the climate and atmospheric chemistry of the Earth. However, little is known about their emissions from rivers and estuaries, which seem to contribute significantly to the atmospheric budget of both gases. To this end concentrations of N2O and CH4 were measured in the Rajang, Maludam, Sebuyau and Simunjan rivers draining peatland in northwestern (NW) Borneo during two campaigns in March and September 2017. The Rajang River was additionally sampled in August 2016 and the Samunsam and Sematan rivers were additionally sampled in March 2017. The Maludam, Sebuyau, and Simunjan rivers are typical “blackwater” rivers with very low pH (3.7–7.8), very high dissolved organic carbon (DOC) concentrations (235–4387 mmol L−1) and very low O2 concentrations (31–246 µmol L−1; i.e. 13 %–116 % O2 saturation). The spatial and temporal variability of N2O and CH4 concentrations (saturations) in the six rivers or estuaries was large and ranged from 2.0 nmol L−1 (28 %) to 41.4 nmol L−1 (570 %) and from 2.5 nmol L−1 (106 %) to 1372 nmol L−1 (57 459 %), respectively. We found no overall trends of N2O with O2 or NO3-, NO2- or NH4+, and there were no trends of CH4 with O2 or dissolved nutrients or DOC. N2O concentrations showed a positive linear correlation with rainfall. We conclude, therefore, that rainfall is the main factor determining the riverine N2O concentrations since N2O production or consumption in the blackwater rivers themselves seems to be low because of the low pH. CH4 concentrations were highest at salinity = 0 and most probably result from methanogenesis as part of the decomposition of organic matter under anoxic conditions. CH4 in the concentrations in the blackwater rivers showed an inverse relationship with rainfall. We suggest that CH4 oxidation in combination with an enhanced river flow after the rainfall events might be responsible for the decrease in the CH4 concentrations. The rivers and estuaries studied here were an overall net source of N2O and CH4 to the atmosphere. The total annual N2O and CH4 emissions were 1.09 Gg N2O yr−1 (0.7 Gg N yr−1) and 23.8 Gg CH4 yr−1, respectively. This represents about 0.3 %–0.7 % of the global annual riverine and estuarine N2O emissions and about 0.1 %–1 % of the global riverine and estuarine CH4 emissions. Therefore, we conclude that rivers and estuaries in NW Borneo – despite the fact their water area covers only 0.05 % of the global river/estuarine area – contribute significantly to global riverine and estuarine emissions of N2O and CH4.
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Hodgkin, Ernest P., and Patrick Hesp. "Estuaries to salt lakes: Holocene transformation of the estuarine ecosystems of south-western Australia." Marine and Freshwater Research 49, no. 3 (1998): 183. http://dx.doi.org/10.1071/mf96109.
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When the estuaries of south-western Australia were first flooded by the Holocene marine transgression about 7000 years before present (BP), most were enclosed by limestone barrier dunes. Coastal sand drift built bars and flood-tide deltas in the narrow entrances, but until about 3500 years BP the estuaries remained tidal-dominated systems with a diverse marine–estuarine fauna. Now the bars/deltas so obstruct the small tides that estuary water is fresh in winter and marine to hypersaline in summer; the estuaries are river-flow-dominated systems and the ecosystems are characterised by a restricted euryhaline estuarine biota. Some estuaries are still permanently open, their bars/deltas never close, and some are seasonally open, their bars open with river flow in winter and close in summer. Other estuaries are normally closed, their bars remain closed for several years and break with episodic flood flow, or are permanently closed coastal salt lakes with bars that never or rarely break: they can become grossly hypersaline and may dry up altogether. An hypothesis to explain this Holocene transformation of the estuaries attributes it principally to sedimentary processes in an environment where river flow is highly seasonal, tides are microtidal, there was a fall in sea level, and there are differences in the volume and periodicity of flow and the degree of shelter to the entrances from the prevailing south-west winds and swell.
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Windom, Herbert L., and Thomas M. Church. "Second international symposium on the biogeochemistry of model estuaries: Estuarine processes in global change." Marine Chemistry 43, no. 1-4 (July 1993): 1–2. http://dx.doi.org/10.1016/0304-4203(93)90211-6.
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Conroy, Ted, David A. Sutherland, and David K. Ralston. "Estuarine Exchange Flow Variability in a Seasonal, Segmented Estuary." Journal of Physical Oceanography 50, no. 3 (March 2020): 595–613. http://dx.doi.org/10.1175/jpo-d-19-0108.1.
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AbstractSmall estuaries in Mediterranean climates display pronounced salinity variability at seasonal and event time scales. Here, we use a hydrodynamic model of the Coos Estuary, Oregon, to examine the seasonal variability of the salinity dynamics and estuarine exchange flow. The exchange flow is primarily driven by tidal processes, varying with the spring–neap cycle rather than discharge or the salinity gradient. The salinity distribution is rarely in equilibrium with discharge conditions because during the wet season the response time scale is longer than discharge events, while during low flow it is longer than the entire dry season. Consequently, the salt field is rarely fully adjusted to the forcing and common power-law relations between the salinity intrusion and discharge do not apply. Further complicating the salinity dynamics is the estuarine geometry that consists of multiple branching channel segments with distinct freshwater sources. These channel segments act as subestuaries that import both higher- and lower-salinity water and export intermediate salinities. Throughout the estuary, tidal dispersion scales with tidal velocity squared, and likely includes jet–sink flow at the mouth, lateral shear dispersion, and tidal trapping in branching channel segments inside the estuary. While the estuarine inflow is strongly correlated with tidal amplitude, the outflow, stratification, and total mixing in the estuary are dependent on the seasonal variation in river discharge, which is similar to estuaries that are dominated by subtidal exchange flow.
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Wei, Xiaoyan, Henk M. Schuttelaars, Megan E. Williams, Jennifer M. Brown, Peter D. Thorne, and Laurent O. Amoudry. "Unraveling Interactions between Asymmetric Tidal Turbulence, Residual Circulation, and Salinity Dynamics in Short, Periodically Weakly Stratified Estuaries." Journal of Physical Oceanography 51, no. 5 (May 2021): 1395–416. http://dx.doi.org/10.1175/jpo-d-20-0146.1.
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AbstractAsymmetric tidal turbulence (ATT) strongly influences estuarine health and functioning. However, its impact on the three-dimensional estuarine dynamics and the feedback of water motion and salinity distribution on ATT remain poorly understood, especially for short estuaries (estuarine length ≪ tidal wavelength). This study systematically investigates the abovementioned interactions in a short estuary for the first time, considering periodically weakly stratified conditions. This is done by developing a three-dimensional semi-analytical model (combining perturbation method with finite element method) that allows a dissection of the contributions of different processes to ATT, estuarine circulation, and salt transport. The generation of ATT is dominated by (i) strain-induced periodic stratification and (ii) asymmetric bottom-shear-generated turbulence, and their contributions to ATT are different both in amplitude and phase. The magnitude of the residual circulation related to ATT and the eddy viscosity–shear covariance (ESCO) is about half of that of the gravitational circulation (GC) and shows a “reversed” pattern as compared to GC. ATT generated by strain-induced periodic stratification contributes to an ESCO circulation with a spatial structure similar to GC. This circulation reduces the longitudinal salinity gradients and thus weakens GC. Contrastingly, the ESCO circulation due to asymmetric bottom-shear-generated turbulence shows patterns opposite to GC and acts to enhance GC. Concerning the salinity dynamics at steady state, GC and tidal pumping are equally important to salt import, whereas ESCO circulation yields a significant seaward salt transport. These findings highlight the importance of identifying the sources of ATT to understand its impact on estuarine circulation and salt distribution.
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Prandle, David, Andrew Lane, and Andrew J. Manning. "New typologies for estuarine morphology." Geomorphology 81, no. 3-4 (November 2006): 309–15. http://dx.doi.org/10.1016/j.geomorph.2006.04.017.
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Smith, Jansen A., Daniel A. Auerbach, Karl W. Flessa, Alexander S. Flecker, and Gregory P. Dietl. "Fossil clam shells reveal unintended carbon cycling consequences of Colorado River management." Royal Society Open Science 3, no. 9 (September 2016): 160170. http://dx.doi.org/10.1098/rsos.160170.
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Water management that alters riverine ecosystem processes has strongly influenced deltas and the people who depend on them, but a full accounting of the trade-offs is still emerging. Using palaeoecological data, we document a surprising biogeochemical consequence of water management in the Colorado River basin. Complete allocation and consumptive use of the river's flow has altered the downstream estuarine ecosystem, including the abundance and composition of the mollusc community, an important component in estuarine carbon cycling. In particular, population declines in the endemic Colorado delta clam, Mulinia coloradoensis , from 50--125 individuals m −2 in the pre-dam era to three individuals m −2 today, have likely resulted in a reduction, on the order of 5900–15 000 t C yr −1 (4.1–10.6 mol C m −2 yr −1 ), in the net carbon emissions associated with molluscs. Although this reduction is large within the estuarine system, it is small in comparison with annual global carbon emissions. Nonetheless, this finding highlights the need for further research into the effects of dams, diversions and reservoirs on the biogeochemistry of deltas and estuaries worldwide, underscoring a present need for integrated water and carbon planning.
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Dinauer, Ashley, and Alfonso Mucci. "Spatial variability in surface-water <i>p</i>CO<sub>2</sub> and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)." Biogeosciences 14, no. 13 (July 6, 2017): 3221–37. http://dx.doi.org/10.5194/bg-14-3221-2017.
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Abstract. The incomplete spatial coverage of CO2 partial pressure (pCO2) measurements across estuary types represents a significant knowledge gap in current regional- and global-scale estimates of estuarine CO2 emissions. Given the limited research on CO2 dynamics in large estuaries and bay systems, as well as the sources of error in the calculation of pCO2 (carbonic acid dissociation constants, organic alkalinity), estimates of air–sea CO2 fluxes in estuaries are subject to large uncertainties. The Estuary and Gulf of St. Lawrence (EGSL) at the lower limit of the subarctic region in eastern Canada is the world's largest estuarine system, and is characterized by an exceptional richness in environmental diversity. It is among the world's most intensively studied estuaries, yet there are no published data on its surface-water pCO2 distribution. To fill this data gap, a comprehensive dataset was compiled from direct and indirect measurements of carbonate system parameters in the surface waters of the EGSL during the spring or summer of 2003–2016. The calculated surface-water pCO2 ranged from 435 to 765 µatm in the shallow partially mixed upper estuary, 139–578 µatm in the deep stratified lower estuary, and 207–478 µatm along the Laurentian Channel in the Gulf of St. Lawrence. Overall, at the time of sampling, the St. Lawrence Estuary served as a very weak source of CO2 to the atmosphere, with an area-averaged CO2 degassing flux of 0.98 to 2.02 mmol C m−2 d−1 (0.36 to 0.74 mol C m−2 yr−1). A preliminary analysis revealed that respiration (upper estuary), photosynthesis (lower estuary), and temperature (Gulf of St. Lawrence) controlled the spatial variability in surface-water pCO2. Whereas we used the dissociation constants of Cai and Wang (1998) to calculate estuarine pCO2, formulations recommended for best practices in open ocean environments may underestimate pCO2 at low salinities, while those of Millero (2010) may result in overestimates.
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BRÜCKNER, MURIEL Z. M., WILLIAM J. MCMAHON, and MAARTEN G. KLEINHANS. "MUDDYING THE WATERS: MODELING THE EFFECTS OF EARLY LAND PLANTS IN PALEOZOIC ESTUARIES." PALAIOS 36, no. 5 (May 31, 2021): 173–81. http://dx.doi.org/10.2110/palo.2020.073.
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ABSTRACT The Paleozoic evolution of vegetation transformed terrestrial landscapes, facilitating novel sedimentary processes and creating new habitats. This transformation left a permanent mark on the sedimentary record, perhaps most strikingly via an upsurge in preserved terrestrial mudrock. Whereas feedbacks between evolving vegetation and river structure have been widely studied, Paleozoic estuaries have so far received scant attention. Located at the interface between the land and sea, the co-adjustment of estuarine morphology and plant traits are fundamentally tied to a varied range of geochemical cycles, and determine how global silicate weathering patterns may have varied over time. Here we employ an eco-morphodynamic model with an in-built vegetation code to simulate estuarine morphology through five key stages in plant evolution. An abiotic model (early Precambrian?) saw mud deposition restricted to fortuitous instances of limited erosion along bar-flanks. Estuaries colonized by microbial mats (Precambrian onwards) facilitated mud accretion that sufficiently stabilized bar surfaces to promote extensive mudflat development. Small-stature, rootless vegetation (Silurian–Early Devonian) introduced novel above-ground baffling effects which led to notable mud accumulation in lower-energy environments. The incorporation of roots (Early Devonian) strengthened these trends, with root structures decreasing the mortality of the occupying plants. Once the full complement of modern vascular plant architectures had evolved (Middle Devonian), dense colonization promoted the formation of in-channel islands accompanied with system-wide mud accumulation. These simulations suggest estuaries underwent profound change during the Paleozoic, with the greening of the continents triggering processes and feedbacks which render all previous source-to-sink sediment pathways non-uniformitarian.
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Zhang, Bing, Jing Lv, Peng Huo, and Shao Xiong Zhang. "Application of EFDC to Density Stratified Flow." Applied Mechanics and Materials 256-259 (December 2012): 2486–89. http://dx.doi.org/10.4028/www.scientific.net/amm.256-259.2486.
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Environmental Fluid Dynamics Code (EFDC) was developed by Hamrick at Virginia Institute of Marine Science for estuarine and coastal applications. EFDC is a general-purpose modeling package for simulating three-dimensional flow, transport, and biogeochemical processes in surface water systems such as rivers, lakes, reservoirs, estuaries, wetlands and coastal regions. Use the 3-D numerical model EFDC simulated the density stratified flow in a slut. Compared the simulation and experimental data, the results showed that EFDC could accurately simulated the density stratified flow.
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Nidzieko, Nicholas J. "Allometric scaling of estuarine ecosystem metabolism." Proceedings of the National Academy of Sciences 115, no. 26 (June 11, 2018): 6733–38. http://dx.doi.org/10.1073/pnas.1719963115.
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There are still significant uncertainties in the magnitude and direction of carbon fluxes through coastal ecosystems. An important component of these biogeochemical budgets is ecosystem metabolism, the net result of organismal metabolic processes within an ecosystem. In this paper, I present a synthesis of published ecosystem metabolism studies from coastal ecosystems and describe an empirical observation that size-dependent patterns in aquatic gross primary production and community respiration exist across a wide range of coastal geomorphologies. Ecosystem metabolism scales to the 3/4 power with volume in deeper estuaries dominated by pelagic primary production and nearly linearly with area in shallow estuaries dominated by benthic primary production. These results can be explained by applying scaling arguments for efficient, directed transport networks developed to explain similar size-dependent patterns in organismal metabolism. The main conclusion from this synthesis is that the residence time of new, nutrient-rich water is a fundamental organizing principle for the observed patterns. Residence time changes allometrically with size in pelagic ecosystems because velocities change by only an order of magnitude across systems that span more than ten orders of magnitude in size. This nonisometric change in velocity with size requires lower specific metabolic rates at larger ecosystem sizes. This change in transport may also explain a shift from predominantly net heterotrophy to net autotrophy with increasing size. The scaling results are applied to the total estuarine area in the continental United States to estimate the contribution of estuarine systems to the overall coastal budget of organic carbon.
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Ricci, SW, DB Eggleston, DR Bohnenstiehl, and A. Lillis. "Temporal soundscape patterns and processes in an estuarine reserve." Marine Ecology Progress Series 550 (May 25, 2016): 25–38. http://dx.doi.org/10.3354/meps11724.
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Thrush, Simon F., Judi E. Hewitt, Alf Norkko, Vonda J. Cummings, and Greig A. Funnell. "MACROBENTHIC RECOVERY PROCESSES FOLLOWING CATASTROPHIC SEDIMENTATION ON ESTUARINE SANDFLATS." Ecological Applications 13, no. 5 (October 2003): 1433–55. http://dx.doi.org/10.1890/02-5198.
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Telesh, Irena V., and Vladislav V. Khlebovich. "Principal processes within the estuarine salinity gradient: A review." Marine Pollution Bulletin 61, no. 4-6 (2010): 149–55. http://dx.doi.org/10.1016/j.marpolbul.2010.02.008.
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Chant, Robert J., Wayne R. Geyer, Robert Houghton, Elias Hunter, and James Lerczak. "Estuarine Boundary Layer Mixing Processes: Insights from Dye Experiments*." Journal of Physical Oceanography 37, no. 7 (July 1, 2007): 1859–77. http://dx.doi.org/10.1175/jpo3088.1.
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Abstract A series of dye releases in the Hudson River estuary elucidated diapycnal mixing rates and temporal variability over tidal and fortnightly time scales. Dye was injected in the bottom boundary layer for each of four releases during different phases of the tide and of the spring–neap cycle. Diapycnal mixing occurs primarily through entrainment that is driven by shear production in the bottom boundary layer. On flood the dye extended vertically through the bottom mixed layer, and its concentration decreased abruptly near the base of the pycnocline, usually at a height corresponding to a velocity maximum. Boundary layer growth is consistent with a one-dimensional, stress-driven entrainment model. A model was developed for the vertical structure of the vertical eddy viscosity in the flood tide boundary layer that is proportional to u2*/N∞, where u* and N∞ are the bottom friction velocity and buoyancy frequency above the boundary layer. The model also predicts that the buoyancy flux averaged over the bottom boundary layer is equal to 0.06N∞u2* or, based on the structure of the boundary layer equal to 0.1NBLu2*, where NBL is the buoyancy frequency across the flood-tide boundary layer. Estimates of shear production and buoyancy flux indicate that the flux Richardson number in the flood-tide boundary layer is 0.1–0.18, consistent with the model indicating that the flux Richardson number is between 0.1 and 0.14. During ebb, the boundary layer was more stratified, and its vertical extent was not as sharply delineated as in the flood. During neap tide the rate of mixing during ebb was significantly weaker than on flood, owing to reduced bottom stress and stabilization by stratification. As tidal amplitude increased ebb mixing increased and more closely resembled the boundary layer entrainment process observed during the flood. Tidal straining modestly increased the entrainment rate during the flood, and it restratified the boundary layer and inhibited mixing during the ebb.