Large Estuary Research Articles

Adapting to sea level rise: Emerging governance issues in the San Francisco Bay Region

San Francisco Bay, the largest estuary on the Pacific Coast of North America, is heavily encroached by a metropolitan region with over 7 million inhabitants. Urban development and infrastructure, much of which built over landfill and at the cost of former baylands, were placed at very low elevations. Sea level rise (SLR) poses a formidable challenge to these highly exposed urban areas and already stressed natural systems.“Green”, or ecosystem-based, adaptation is already on the way around the Bay. Large scale wetland restoration projects have already been concluded, and further action now often requires articulation with the reinforcement of flood defense structures, given the level of urban encroachment. While levee setback, or removal, would provide greater environmental benefit, the need to protect urban areas and infrastructure has led to the trial of ingenious solutions for promoting wetland resilience while upgrading the level of protection provided by levees.We analyzed the region’s environmental governance and planning structure, through direct observation, interviews with stakeholders, and study of planning documents and projects. We present two examples where actual implementation of SLR adaptation has led, or may lead to, the need to revise standards and practices or require uneasy choices between conflicting public interests.Among the region’s stakeholders, there is an increasing awareness of the risks related to SLR, but the institutional arrangements are complex, and communication between the different public agencies/departments is not always as streamlined as it could be. Some agencies and departments need to adapt their procedures in order to remove institutional barriers to adaptation, but path dependence is an obstacle. There is evidence that more frank and regular communication between public actors is needed. It also emphasizes the benefits of a coordination of efforts and strategies, something that was eroded in the transition from central-government-led policies to a new paradigm of local-based adaptive governance.

A dataset of molluscan fauna sampled in river estuaries of medium and small size river in Kyushu island, Japan.

BackgroundMany studies have evaluated the ecological integrity of large-scale estuaries of continental rivers using biotic indicators such as fish, phytoplankton and benthic communities. However, few studies have focused on the river estuaries of small and medium rivers. Molluscan fauna data in large estuaries or in the estuaries of large rivers have been collected by the The National Census on River Environments (conducted by the Ministry of Land, Infrastructure, Transport and Tourism) or National Survey on the Natural Environment (conducted by the Ministry of Environment). On the other hand, molluscan fauna of small and medium rivers are managed by local governments and have rarely been investigated.New informationThis paper provides basic information on the molluscan fauna of 70 rivers in Kyushu, Japan, collected with the aim of conserving estuaries of small and medium rivers. In total, 37 families, 82 species and 21,827 individuals were collected. The data are all accessible from the document “A dataset of shellfish fauna sampled in estuaries of medium and small rivers in Kyushu, Japan (http://ipt.pensoft.net/resource.do?r=shellfishes_in_kyushu)”. According to the Red Data Book published by the Japanese Ministry of Environment in 2018, 3 species were determined as Critically endangered and Endangered, 6 species were determined as Vulnerable and 13 species were determined as Near Threatened. The proportions of individuals classified as Critically endangered and Endangered from the total number of individuals were extremely low, but the proportions of Near Threatened individuals were high. Our results indicate that the risk of molluscan extinction in small- and medium-sized river estuaries in Kyushu is high and that immediate conservation is necessary.

Use of science in collaborative environmental management: Evidence from local watershed partnerships in the Puget Sound

The science-policy nexus has long puzzled scholars and managers working across diverse public policy areas, including environment. The rise of science-based management, especially in an era of big data, assumes science can improve environmental policy. At the same time, increasing attention to stakeholder engagement provides avenues for non-scientists to participate in collaborative environmental management, which might displace science in decision-making processes. Prior research points to a variety of factors thought to affect the degree to which science is used in collaborative partnerships. Drawing on such research, we examine the use of science across 9 collaborative partnerships structured and resourced from the top-down by a state government agency. All of these partnerships are working in the U.S.’s second largest estuary, the Puget Sound in Washington State. Data from partnership meeting minutes indicates that science is scarcely discussed in executive committee meetings, but is more commonly discussed in technical committee meetings. We thus might expect that the ecosystem management plans produced by these technical committees would be closely informed by science. Results indicate these plans include few citations to peer-reviewed scientific studies, but they do draw consistently on scientific information from grey literature including scientific and technical reports from federal and state agencies. These results raise important questions about government efforts to foster the use of science in collaborative partnerships, including the benefits and drawbacks of using grey literature rather than scientific articles directly, the interaction of science with other forms of knowledge, and local actors’ capacity to understand and access science.

Seasonal hydrodynamic interactions between tidal waves and river flows in the Yangtze Estuary

Estuaries are transition regions between marines and inland rivers where hydrodynamic processes are controlled by oceanic tidal waves and fluvial discharges. Moreover, human activities, such as the growing number of water conservancy projects, have an increasing impact on estuarine hydrodynamics. However, these natural variations and anthropogenic impacts are not yet fully understood, especially for large estuaries. In this study, the interactions between tidal waves and riverine flows in the Yangtze Estuary were investigated using the methods of numerical modelling and harmonic analysis. The focus of this study is on the characteristics of tides in the coastal area, seasonal variations in hydrodynamic process and impacts of reservoir regulation on tidal constituents in the tidal river. The results indicate that in the coastal area, semi-diurnal and diurnal tidal constituents propagate in different directions along the coast and that the tidal waves in the coastal area are stationary, i.e. the amplitude and phase do not change in time. However, in the tidal river, significant seasonal variations in the water surface slope, water level fluctuations and damping process can be identified. In the dry season, the tidal signal can reach Datong station, >600 km from the estuary mouth, whereas in the wet season, the signal's reach is approximately 350 km. From the dry to wet seasons, the maximum decrease in the amplitude of the dominant M2 tide is approximately 0.3 m. The amplitudes of the tidal constituents do not decrease monotonically because of the complex interactions among the bed friction, river discharge and channel width convergence as well as energy transmission between the tidal constituents. Because the Three Gorges Reservoir is used to regulate seasonal discharge, the increase in the accumulated amplitudes of the six major tides can reach up to 0.1 m in the tidal river reach.

River Discharge and Saltwater Intrusion Level Study of Yangtze River Estuary, China

The Yangtze River Estuary (YRE) is the largest estuary in China, with three-order bifurcations and four outlets into the sea. In recent years, issues of saltwater intrusions have received increased attention due to the increased levels and frequencies of the intrusions. The saltwater intrusions into the YRE resulting from river discharges were investigated in this study based on river discharge levels at the Datong station. A hydrodynamic and salinity transport model (MIKE21) was used to quantify the influences of the river discharges on the saltwater intrusions in the YRE. The model was effectively validated through observational data of the tidal and salinity levels. The 25%, 50% and 70% frequencies of the river discharges during the dry seasons were determined to be 18,112, 16,331 and 14,832 m3/s, respectively. A multi-year averaged river discharge of 27,856 m3/s was used to simulate the salinity level changes resulting from the different river discharges. The results revealed the following: (1) the salinity of the South Branch (SB) was distributed as “high–low–high”; and the changes in the salinity levels were greatly affected by the river discharges. A strong correlation was found between the salinity and flow in the North Branch (NB) and SB of between 0.917 and 1; (2) the changes in the river discharges had major impacts on the changes in the salinity levels in the SB. When the runoff was 27,856 m3/s, the salinity excessive area rate (the ratio between salinity excessive area (>0.45‰) and the SB area) less than 10%. However, when the river discharges were reduced to 16,331 m3/s, the salinity excessive area rate is more than 50%; (3) As the river discharges decreased, the amplification line (0.2‰) also rapidly decreased, and the amplification lines (0.45‰, 2‰) increased. At points far from the river’s entrance, the effects of the runoff were observed to be weakened, such as the amplification lines gradually becoming reduced; (4) the changes in the river discharges were observed to have significant impacts on the freshwater reservoir water withdrawal. When the river discharges were maintained at 27,856 m3/s, the salinity of the Baogang, Chenhang, and Qingcaosha Reservoirs remained below 0.45‰. The salinity levels of the four reservoir locations examined in this study were found to exceed the Chinese drinking water standard (0.45‰) for more than 23 days in the 14,832 m3/s river discharge scenario, which negatively affected the drinking water of the population living near the YRE.

A Numerical Approach to Predict Water Levels in Ungauged Regions—Case Study of the Meghna River Estuary, Bangladesh

Quantitative flood frequency investigation in a large estuary is somewhat challenging by numerical modelling, because the model optimization depends on the appropriate physical and hydrodynamic properties of the estuarine river. This study attempts to solve the bathymetry configurations of the Meghna River estuary and the assimilation of flow data, which exposed an important role in water level prediction. Upstream flow rates and nonlinear semidiurnal tides have an impact on the instability of the flow in this estuarine river. A large amount of flow accumulates in the upstream confluence against or in favor of tides during the rainy season from the adjacent river basins and significantly moves in the Bay of Bengal. The aim of this study is to predict water levels in the un-gauged regions of the Meghna River estuary. A numerical technique was developed using Mike21 flexible mesh, comprising shallow water hydrodynamic components in the estuary. Subsequently, log-normal distribution was employed to analyze the flood magnitudes among the ungauged stations of the estuary. The calibration results comprised with the observed water levels adequately. In conclusion, these water level prediction results can be applied to alleviate the coastal land from extreme flooding and to design hydraulic structures in the narrow streams.

Community structure and biovolume size spectra of mesozooplankton in the Pearl River estuary

The Pearl River estuary is the second largest estuary in China. This study reported the species composition and size structure of mesozooplankton in the upper and lower Pearl River estuary in the dry and wet seasons. The normalized biovolume size spectrum of mesozooplankton was constructed to analyze the trophic structure of the community. Copepods were the numerically predominant mesozooplankton group at all sampling stations. However, when converted into biovolume, medusae were dominant in the upper estuary in the dry season and Chaetognatha were dominant in the lower estuary in the wet season. There were apparent seasonal and spatial variations in the normalized biovolume size spectrum characteristics in the Pearl River estuary. In the dry season, the average fitted regression line of the normalized biovolume size spectrum had a slope of −1.02 in the upper estuary and −0.88 in the lower estuary. In the wet season, the average fitted regression line of the normalized biovolume size spectrum had a slope of −0.32 in the lower estuary, and no significant regression of the normalized biovolume size spectrum was found in the upper estuary. It is suggested that the mesozooplankton community was unstable in the upper estuary due to the strong freshwater perturbation in the wet season. The size diversity and normalized biovolume size spectrum slope indicated that the strength of top-down control and trophic efficiency was highest in the lower estuary in the wet season.

Antimony in the Lot–Garonne river system: a 14-year record of solid–liquid partitioning and fluxes

Environmental contextAntimony is a trace element ubiquitously present in the environment, but data are lacking on its spatio-temporal distribution in aquatic environments. Long-term records serve as essential tools to decipher temporal patterns, historical sources and sinks and background concentrations in an area. We characterise the temporal concentrations, transport and behaviour of antimony in the Garonne River watershed, the main tributary to the Gironde Estuary, the largest estuary in south-west Europe. AbstractKnowledge of the environmental chemistry of antimony (Sb) in aquatic systems is limited, and a better understanding of its geochemical behaviour is needed. Based on a fourteen-year survey (2003–2016) with monthly measurements of dissolved and particulate Sb at five sites in the Lot–Garonne river system, combined with daily measurements of water discharge and suspended particulate matter, this work characterises Sb behaviour in the upstream major river watershed of the Gironde Estuary. The survey provides a first regional geochemical Sb background in the Garonne River watershed for dissolved (~0.2 µg L−1) and Th-normalised particulate Sb (Sbp/Thp ~0.25) concentrations. Observed decreasing temporal trends (<1 ng L−1 in dissolved and <0.02 mg kg−1 in particulate concentrations per month) at sites representing natural concentrations probably reflect global atmospheric Sb dynamics at the watershed scale. Regular seasonal cycles of solid/liquid partitioning, with higher solubility in summer (matching high dissolved and low particulate concentrations), reflect water-discharge and suspended particulate matter transport dynamics and possibly seasonal (bio)geochemical processes. Furthermore, this coefficient decreases from the river to the estuarine reaches (from average log10Kd 4.3 to minimum 3.7 L kg−1), suggesting an increased solubility of Sb in estuarine systems. Flux estimates indicate the relevance of the dissolved fraction in Sb transport (with negligible influence of the colloidal fraction) and a total flux (dissolved + particulate) entering the Gironde Estuary of 5.66 ± 2.96 t year−1 (~50 % particulate). These results highlight the importance of timescales and environmental parameters for understanding and prediction of future Sb biogeochemistry.

Patterns of larval fish assemblages along the direction of freshwater input within the southern branch of the Yangtze Estuary, China: implications for conservation

ABSTRACTThe Yangtze Estuary is the largest estuary in the western Pacific Ocean, and harbors a high diversity of fish fauna. In this study, larval fish were surveyed monthly across three sections within the southern branch of the Yangtze Estuary (SBYE). A total of 49 taxa were collected, with 51.4% of the identified species being freshwater fishes. The collected numbers of larval taxa in the upper, middle, and lower sections were 22, 28, and 43, respectively. Species with differing salinity adaptations displayed different patterns along the direction of freshwater input. The collected numbers of larval taxa were 47 and 29 in the near-shore and mid-stream areas, respectively; and the abundances of larval fish in the near-shore areas tended to be higher than in the mid-stream areas in all the three sections. Larval fish occurred year-round with two peaks of abundance. Our results suggest that the freshwater input was the dominant factor shaping larval fish assemblage structure and dynamics within the SBYE. Influences of the Three Gorges Dam and South-to-North Water Transfer Project on larval fish assemblages within the SBYE should be considered with regard to conservation practices.

Sea-Level Rise and Climate Change Impacts on an Urbanized Pacific Coast Estuary

The San Francisco Bay-Delta estuary, the largest estuary on the west coast of North America, has lost over 90% of its tidal wetlands through conversion to agriculture, grazing or urban development. Accelerated sea-level rise poses an additional threat to the remaining wetlands, and keeping pace requires that they increase in relative elevation through trapping of suspended sediment or increasing organic productivity in the root zone. Suspended sediment concentrations (SSC) have been declining in rivers and deep channels, and although little is known about sediment dynamics in shallow areas, sediment supply to tidal wetlands may not be sufficient to maintain their elevations in the future. Wetlands will be constrained by existing development and mountainous terrain. Increases in tidal wetland salinity have been occurring in saline, brackish and the western edges of freshwater tidal wetlands. To mitigate for sea-level rise, considerable acreages currently are being restored, with and without active management practices. Restoration techniques are being piloted to increase shoreline protection, resiliency, and high tide refuge in adaptation to current and projected sea level rise. We recommend additional research into plant physiological responses to combinations of climate change impacts, as well as suggest potential practical policy positions.

Turning the tide: comparison of tidal flow by periodic sea level fluctuation and by periodic bed tilting in scaled landscape experiments of estuaries

Abstract. Analogue models or scale experiments of estuaries and short tidal basins are notoriously difficult to create in the laboratory because of the difficulty to obtain currents strong enough to transport sand. Our recently discovered method to drive tidal currents by periodically tilting the entire flume leads to intense sediment transport in both the ebb and flood phase, causing dynamic channel and shoal patterns. However, it remains unclear whether tilting produces periodic flows with characteristic tidal properties that are sufficiently similar to those in nature for the purpose of landscape experiments. Moreover, it is not well understood why the flows driven by periodic sea level fluctuation, as in nature, are not sufficient for morphodynamic experiments. Here we compare for the first time the tidal currents driven by sea level fluctuations and by tilting. Experiments were run in a 20 × 3 m straight flume, the Metronome, for a range of tilting periods and with one or two boundaries open at constant head with free inflow and outflow. Also, experiments were run with flow driven by periodic sea level fluctuations. We recorded surface flow velocity along the flume with particle imaging velocimetry and measured water levels along the flume. We compared the results to a one-dimensional model with shallow flow equations for a rough bed, which was tested on the experiments and applied to a range of length scales bridging small experiments and large estuaries. We found that the Reynolds method results in negligible flows along the flume except for the first few metres, whereas flume tilting results in nearly uniform reversing flow velocities along the entire flume that are strong enough to move sand. Furthermore, tidal excursion length relative to basin length and the dominance of friction over inertia is similar in tidal experiments and reality. The sediment mobility converges between the Reynolds method and tilting for flumes hundreds of metres long, which is impractical. Smaller flumes of a few metres in length, on the other hand, are much more dominated by friction than natural systems, meaning that sediment suspension would be impossible in the resulting laminar flow on tidal flats. Where the Reynolds method is limited by small sediment mobility and high tidal range relative to water depth, the tilting method allows for independent control over the variables flow depth, velocity, sediment mobility, tidal period and excursion length, and tidal asymmetry. A periodically tilting flume thus opens up the possibility of systematic biogeomorphological experimentation with self-formed estuaries.

Massive Upland to Wetland Conversion Compensated for Historical Marsh Loss in Chesapeake Bay, USA

Sea level rise leads to coastal transgression, and the survival of ecosystems depends on their ability to migrate inland faster than they erode and submerge. We compared marsh extent between nineteenth-century maps and modern aerial photographs across the Chesapeake Bay, the largest estuary in North America, and found that Chesapeake marshes have maintained their spatial extent despite relative sea level rise rates that are among the fastest in the world. In the mapped region (i.e., 25% of modern Chesapeake Bay marshland), 94 km2 of marsh was lost primarily to shoreline erosion, whereas 101 km2 of marsh was created by upland drowning. Simple projections over the entire Chesapeake region suggest that approximately 100,000 acres (400 km2) of uplands have converted to wetlands and that about a third of all present-day marsh was created by drowning of upland ecosystems since the late nineteenth century. Marsh migration rates were weakly correlated with topographic slope and the amount of development of adjacent uplands, suggesting that additional processes may also be important. Nevertheless, our results emphasize that the location of coastal ecosystems changes rapidly on century timescales and that sea level rise does not necessarily lead to overall habitat loss.

Marsh persistence under sea-level rise is controlled by multiple, geologically variable stressors

ABSTRACTIntroduction: Marshes contribute to habitat and water quality in estuaries and coastal bays. Their importance to continued ecosystem functioning has led to concerns about their persistence.Outcomes: Concurrent with sea-level rise, marshes are eroding and appear to be disappearing through ponding in their interior; in addition, in many places, they are being replaced with shoreline stabilization structures. We examined the changes in marsh extent over the past 40 years within a subestuary of Chesapeake Bay, the largest estuary in the United States, to better understand the effects of sea-level rise and human pressure on marsh coverage.Discussion: Approximately 30 years ago, an inventory of York River estuary marshes documented the historic extent of marshes. Marshes were resurveyed in 2010 to examine shifts in tidal marsh extent and distribution. Marsh change varied spatially along the estuary, with watershed changes between a 32% loss and an 11% gain in marsh area. Loss of marsh was apparent in high energy sections of the estuary while there was marsh gain in the upper/riverine section of the estuary and where forested hummocks on marsh islands have become inundated. Marshes showed little change in the small tributary creeks, except in the creeks dominated by fringing marshes and high shoreline development.Conclusions: Differential resilience to sea-level rise and spatial variations in erosion, sediment supply, and human development have resulted in spatially variable changes in specific marsh extents and are predicted to lead to a redistribution of marshes along the estuarine gradient, with consequences for their unique communities.

Challenges to quantifying glass eel abundance from large and dynamic estuaries

Abstract European eel Anguilla anguilla recruitment into the rivers of the northeastern Atlantic has declined substantially since the 1980s. Monitoring of recruiting juveniles, or glass eels, is usually undertaken in small estuaries and rivers. Sampling of large-scale estuaries is rare, due to the size of the sampling area and the resources needed to provide adequate sampling levels. Here we describe surveys for glass eels in the UK’s largest estuarine system, the Severn Estuary/Bristol Channel. We sampled across a 20 km-wide stretch of the estuary in 2012 and 2013, using a small-meshed net deployed from a commercial fishing trawler, and the surveys yielded over 2500 glass eels. Eels were more abundant in the surface layer (0–1.4 m depth) than at depth (down to 8.4 m depth), were more abundant close to the south shore than along the north shore or middle of the estuary, and were more abundant in lower salinity water. Numbers were higher in the second year than in the first and eels were more abundant in February than April. The difficulties and logistics of sampling in such a large estuary are discussed, along with the level of resources required to provide robust estimates of glass eel abundance.

Low-cost device for retrieval of moorings deployed with underwater remote release systems

Underwater acoustic and timed-release systems are commonly deployed with sensors and other equipment for ecological and oceanographic research in aquatic environments. These systems allow equipment deployed at depth to be remotely released from their moorings for retrieval. However, a current limitation is that most systems do not incorporate mechanisms for retrieval of the mooring anchor and attachments (e.g. shackles, cable). Herein we provide a detailed description and evaluation of a ‘retrieval pod’ that can be attached directly to remotely released underwater devices to facilitate mooring retrieval. The system was tested using acoustic release telemetry receivers under field conditions in a large estuary in the Northern Territory, Australia. Six receivers fitted with pods were retrieved from the field after two consecutive 6-month deployments (12 retrievals in total) with no failed mooring retrievals. Although our tests were confined to shallow depths (<8m), it should be straightforward to modify the system for use in deeper water by increasing the spool capacity. The retrieval pods are reusable, require minimal construction skills and can be assembled from basic equipment available at most hardware or boating stores, making them a convenient and low-cost option for the retrieval of moorings deployed with remote release systems.

Evaluation of water quality during successive severe drought years within Microcystis blooms using fish embryo toxicity tests for the San Francisco Estuary, California

In the San Francisco Estuary, California, the largest estuary on the Pacific Coast of North America, the frequency and intensity of drought and associated cyanobacteria blooms are predicted to increase with climate change. To assess the impact of water quality conditions on estuarine fish health during successive severe drought years with Microcystis blooms, we performed fish embryo toxicity testing with Delta Smelt and Medaka. Fish embryos were exposed to filtered ambient water collected from the San Francisco Estuary during the Microcystis bloom season in 2014 and 2015, the third and fourth most severe recorded drought years in California. Medaka embryos incubated in filtered ambient waters exhibited high mortality rates (>77%), which was mainly due to bacterial growth. Medaka mortality data was negatively correlated with chloride, and positively correlated with water temperature, total and dissolved organic carbon, and ambient and net chlorophyll a concentration. Delta Smelt embryo mortality rates were lower (<42%) and no prominent seasonal or geographic trend was observed. There was no significant correlation between the Delta Smelt mortality data and water quality parameters. Aeromonas was the dominant bacteria that adversely affected Medaka. The growth of Aeromonas was suppressed when salinity was greater than or equal to 1psu and resulted in a significant reduction in mortality rate. Bacterial growth test demonstrated that the lysate of Microcystis cells enhanced the growth of Aeromonas. Toxin production by Microcystis is a major environmental concern, however, we conclude that dissolved substances released from Microcystis blooms could result in water quality deterioration by promoting growth of bacteria. Furthermore, a distinctive developmental deformity was observed in Medaka during the toxicity tests; somite formation was inhibited at the same time that cardiogenesis occurred and the functional heart was observed to be beating. The exact cause of the embryonic developmental deformity is still unknown.

Redox reactions and weak buffering capacity lead to acidification in the Chesapeake Bay

The combined effects of anthropogenic and biological CO2 inputs may lead to more rapid acidification in coastal waters compared to the open ocean. It is less clear, however, how redox reactions would contribute to acidification. Here we report estuarine acidification dynamics based on oxygen, hydrogen sulfide (H2S), pH, dissolved inorganic carbon and total alkalinity data from the Chesapeake Bay, where anthropogenic nutrient inputs have led to eutrophication, hypoxia and anoxia, and low pH. We show that a pH minimum occurs in mid-depths where acids are generated as a result of H2S oxidation in waters mixed upward from the anoxic depths. Our analyses also suggest a large synergistic effect from river–ocean mixing, global and local atmospheric CO2 uptake, and CO2 and acid production from respiration and other redox reactions. Together they lead to a poor acid buffering capacity, severe acidification and increased carbonate mineral dissolution in the USA’s largest estuary.

Effects of hydrocarbon pollution in the structure of macrobenthic assemblages from two large estuaries in Brazil

Changes in the structure of benthic macrofauna and its relationship with hydrocarbon contamination were determined at different spatial scales in sublittoral sediments of two large estuaries in Brazil. Guanabara Bay (GB) is a heavily polluted estuary due to the presence of a large industrial complex and high demographic density. Laranjeiras Bay (LB) lies in an Environmental Protection Area and can still be considered as preserved from human activities. Despite some spatial differences within each bay, the PAHs concentrations were significantly and consistently higher in GB, with values generally above the threshold effect levels. No signs of hydrocarbon contamination were observed in LB. Macrofauna abundance, diversity and overall assemblage structure were largely different between bays. Canonical analysis of principal coordinates (CAP), used to model the relationship between macrofauna and PAHs levels, indicated that this class of hydrocarbons is the main structuring factor of soft-bottom assemblages in both bays.

A trophic flow model of the Golfo de Nicoya, Costa Rica

The Golfo de Nicoya is among the largest tropical estuaries (1530km2) in Central America and the main. and already overexploited. fishing area of Costa Rica. It can be separated into a shallow (25m) interior part fringed by mangroves and mud flats and a deeper part that extends to the shelf edge to about 200m. In order to integrate available information on biomass. catches. food spectrum and dynamics of the main species populations of the system. a trophic model of 21 compartments was constructed by the use of tile ECOPATH II software. The larger portion of system biomass is confined to the benthic domain (18.4 gm-2, mangroves excluded, compared to 13.8 gm-2 for the pelagic domain). Mangroves, although only covering 1% of tile gulf area, contribute 76% to the system biomass, but only about 1%, to the system's primary production. Through their root system, their provide surface area for about 90% of the gulfs biomass of epifauna (12 gm-2), the second largest group of the model. It serves as food source for commercially important species and also fuels the system by the production of large amounts of pelagic larvae and faecal material. Based on these findings, it is emphasized that mangroves, even if they cover only small areas of an estuarine system. have a fundamental role in biomass distribution and flow pattern. and must be considered when constructing a trophic model of the system. Most of !he system's energy throughput is achieved from the trophic levels I to II (62%) and II to III (34%) as expected for coastal phytoplankton/detritus based systems. Total catch amounts to 3.38 gm-2. which is considered intermediate for tropical coastal systems. A high gross efficiency of the fishery (catch/ primary production) of 0.3% confirms the known high level of fisheries exploitation in the Golfo de Nicoya As shown by the model, shrimps occupy a central role within the gulf as converters of detritus and other food into prey biomass for many predators, that seem to be simultaneously affected by the overexploitation of this resource. The network summary stadistics computed for the model suggest an overall picture of!he Golfo de Nicoya as a system of a low degree of maturity, which seems to be characteristic for tidally driven. tropical estuarine systems. The results are compared and discussed with other published trophic models of coastal systems. Among these, is Golfo Dulce, a further Costarrican gulf system about 200km south of the Golfo de Nicoya.

Spatial variability in surface-water &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and gas exchange in the world's largest semi-enclosed estuarine system: St. Lawrence Estuary (Canada)

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.