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Abstract: We apply the three-dimensional COupled Hydrodynamical Ecological model for REgioNal Shelf seas (COHERENS) to compute water renewal time scales for Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia. Water renewal time scales are not directly observable but are derived indirectly from computational studies. Improved knowledge of these time scales assists in evaluating the water quality of coastal environments and can be utilised in sustainable marine resource management. Results from simulations with climatological September forcing are presented and compared to cruise data reported by Ribbe (2006. A study into the export of saline water from Hervey Bay, Australia. Estuarine Coastal and Shelf Science 66, 550–558). A series of simulations using idealised forcing provides detailed insight into water renewal pathways and regional differences in renewal timescales. We find that more than 85% of the coastal embayment''s water is fully renewed within about 50–80 days. The eastern and western shallow coastal regions are ventilated more rapidly than the central, deeper part of the domain. The climatological simulation yields temperature and salinity patterns that are consistent with the observed situation and water renewal time scales in the range of those derived from idealised model studies. While the reported simulations involve many simplifications, the global assessment of the renewal time scale is in the range of a previous estimate derived for this coastal embayment from a simpler model and observational data. [Copyright &y& Elsevier]

Stamou, A.I., Memos, C. and Spanoudaki, K., 2007. Estimating water renewal time in semi-enclosed coastal areas of complicated geometry using a hydrodynamic model. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 282 – 286. Gold Coast, Australia, ISSN 0749.0208 A methodology is presented to determine water renewal time in semi-enclosed coastal areas with artificial peninsulas or islands of complicated geometry. The methodology is applied in Durrat Alkhobar development in Saudi Arabia. The coastal area consists of the inner and the outer region. The inner region will be dredged and a fingerlike alignment will emerge. A hydrodynamic model was applied to illustrate the future conditions of the Bay regarding water circulation and renewal due to wind and tidal forcing. The model employs the fundamental hydrodynamic equations of continuity and momentum. The inner region of the coastal area was divided into 21 compartments. The communication of the inner region with the outer region is performed via two openings. Calculations showed that average renewal times ranged from 2.3 to 10.1 days for the wind conditions tested; in 12 compartments renewal times were less than 10 days. Furthermore, tide contributed significantly to the renewal of waters. Renewal time decreased with increasing wind velocity; southerly winds were beneficial for water renewal, because they created flow fields with relatively high exchange of flow via the openings. [ABSTRACT FROM AUTHOR]

Littoral benthic diatom communities are pivotal indicators which react to coastline sources of pollution. Littoral communities, however, may be also strongly influenced by other environmental factors: we assumed that even in lakes without anthropogenic pressure, communities could be heterogeneous. To investigate the natural causes of community heterogeneity along shoreline, we sampled 58 pristine high-altitude lakes in the French Alps. Inside each lake, three different littoral stations were sampled. Water chemical composition was measured with major environmental settings. Lakes with homogeneous communities along their shoreline were dominated by pioneer species adapted to strong physical disturbances. The water renewal time in these lakes was short (a few days) and this conveyed strong turbulences. Lakes with heterogeneous communities along their shore had longer water renewal time and were dominated by high-profile diatoms that were able to compete for light and nutrients. The within-lake heterogeneity could be explained by the variability in coastline terrestrial habitats. This study illustrates how water turbulences can limit the expression of some ecological processes like interspecific competition and reduce heterogeneity when it is an overriding stressor. Finally, implications for lake managers are given in terms of monitoring efforts. [ABSTRACT FROM AUTHOR]

The Red Sea is a deep marine basin often considered as small‐scale version of the global ocean. Hydrographic observations and ocean‐atmosphere modeling indicate Red Sea deep water was episodically renewed by wintertime open‐ocean deep convections during 1982–2001, suggesting a renewal time on the order of a decade. However, the long‐term pacing of Red Sea deep water renewals is largely uncertain. We use an annually resolved coral oxygen isotope record of winter surface water conditions to show that the late twentieth century deep water renewals were probably unusual in the context of the preceding ~100 years. More frequent major events are detected during the late Little Ice Age, particularly during the early nineteenth century characterized by large tropical volcanic eruptions. We conclude that Red Sea deep water renewal time is on the order of a decade up to a century, depending on the mean climatic conditions and large‐scale interannual climate forcing. Plain Language Summary: The Red Sea is a deep marine basin often considered as small‐scale version of the global ocean. Hydrographic observations and ocean‐atmosphere modeling indicate Red Sea deep water was episodically renewed by wintertime open‐ocean deep convections in the northern Red Sea during 1982–2001, suggesting a deep water renewal time on the order of a decade. However, the long‐term pacing of Red Sea deep water renewals is largely uncertain, due to lack of hydrographic observations. By using an annually resolved coral oxygen isotope record of winter surface water conditions in the northern Red Sea we show that the late twentieth century deep water renewals were probably unusual in the context of the preceding ~100 years. Our results suggest an absence of major deep water formation events until the 1883 Krakatau volcanic eruption. More frequent major events are detected during the late Little Ice Age, particularly during the early nineteenth century characterized by large tropical volcanic eruptions. From our long‐term perspective we conclude that Red Sea deep water renewal time is on the order of a decade up to a century, depending on the mean climatic conditions and large‐scale interannual climate forcing, which should be considered in management strategies of its unique ecosystems. Key Points: Observed frequent late twentieth century Red Sea deep water renewals were probably unusual in the context of the preceding ~100 yearsCoral proxy record suggests absence of major deep water formation events until the 1883 Krakatau volcanic eruptionMore frequent major Red Sea deep water formation events are detected during the early nineteenth century and late Little Ice Age [ABSTRACT FROM AUTHOR]

Abstract A bay's capacity to buffer fluvial fluxes between the land and sea is sensitive to hydrological changes that can affect its water renewal rates. In Cartagena Bay, Colombia, pollution issues have been associated with freshwater fluxes which are projected to increase in future years. This has led to plans to reduce freshwater flows by constructing upstream hydraulic doors. Given the influence of freshwater discharge on coastal water renewal, it is important to assess how these upstream changes will affect the bay's hydrodynamic processes. This study calibrated the 3D MOHID Water model, configured with a high-resolution mixed vertical discretization to capture the bay's characteristic processes of vertical stratification and mixing. A Lagrangian transport model was used to analyze the flow of passive particle tracers and calculate water renewal time scales. Mean residence times of 3–6 days and flushing times of 10–20 days for canal water were found, while mean residence times of 23–33 days and flushing times of 70–99 days were calculated for the bay's complete water volume. An assessment of future scenarios showed that increases in freshwater runoff would result in faster water renewal in the bay, while plans to decrease freshwater discharge would result in slower water renewal in the bay. It is therefore imperative that any plans for reducing fluvial fluxes into the bay be accompanied by the control of local pollution sources, which are abundant and could worsen the bay's water quality issues should water renewal times become longer. Highlights • 3D hydrodynamic modelling reveals anthropogenic impacts on estuarine water renewal. • Estuarine processes of vertical mixing and stratification show strong seasonality. • Estuarine circulation and water renewal exhibit dependency on freshwater discharge. • Future scenario assessment provides crucial knowledge for coastal mitigation plans. • This modelling approach is applicable to other Caribbean bays with similar issues. [ABSTRACT FROM AUTHOR]

Enrichment of redox-sensitive trace elements in ancient marine shales is conventionally believed to be controlled by marine benthic redox conditions, whereas the influence of hydrographic conditions on trace element enrichment pattern has been rarely considered. Here, we present newly obtained data sets from the Upper Pennsylvanian organicrich Cline Shale in the Midland Basin, Texas, to illustrate the influence of hydrographic circulation on the trace-element enrichment pattern and the stratigraphic record of mudrocks. Various lithofacies, including siliceous mudrocks, argillaceous mudrocks, skeletal-bearing argillaceous mudrocks, calcareous mudrocks, and wackestone, are identified in the Cline Shale. Significant changes in the trace-element enrichment pattern, mineral composition, texture of framboidal pyrite, and other bulk geochemical parameters in different lithofacies are interpreted to have been caused by high-amplitude and high-frequency glacio-eustatic sea-level oscillations in the silled Midland Basin during the late Paleozoic ice age. Specifically, glacio-eustatic sea-level falls generally resulted in the severe isolation of the Midland Basin from the Panthalassic Ocean, highly restricted hydrographic circulation, long deep-water renewal time, euxinic bottom-water conditions, depleted seawater Mo (molybdenum) in the silled basin, and low sediment Mo/TOC (total organic carbon), coupled with significant extrabasinal detrital quartz input, forming siliceous mudrocks. Enhanced phosphorus cycling and excellent preservation conditions are considered to be responsible for the high TOC observed in siliceous mudrocks. In contrast, glacio-eustatic sea-level rises substantially enhanced water exchange between the basin and the Panthalassic Ocean, created overall suboxic to anoxic bottom-water conditions, resupplied seawater Mo, elevated sediment Mo/TOC, and increased platform carbonate production in the basin, forming calcareous mudrocks and wackestone. [ABSTRACT FROM AUTHOR]

Ecological carrying capacity (ECC) indices for bivalve culture rely on key ecosystem turnover rates: 1. clearance time (CT), the time needed for the cultured bivalves to filter the entire bay volume; 2. renewal time (RT), the time required to replace the entire bay volume with external water; and 3. production time (PT), the time needed for phytoplankton biomass renewal via local primary production. These turnover rates are conceptually straightforward but lack measurement standardizations in the context of ECC assessments. This study compares simple turnover rate methods with more complex approaches designed to address key assumptions and improve accuracy. Method comparisons were performed across multiple embayments (systems) in Prince Edward Island, Canada. When crop aggregation and system-scale refiltration effects were considered, CT increased by a factor of 14 to 22 depending on the system and species under cultivation. Seasonal temperature considerations further impacted CT by a factor of 38 to 142. Regarding RT, validated hydrodynamic models and tidal prism models produced remarkably different outcomes; the tidal prism approach underestimated RT by 77–94% across the studied systems. Conversely, PT was unaffected by contrasting phytoplankton parameterization; pre-aquaculture (1969–1970) and contemporary (2011−2012) datasets led to similar PT outcomes. However, other metrics revealed a contemporary shift towards low phytoplankton biomass and smaller phytoplankton cells (picophytoplankton); these observations suggest that PT provides insufficient granularity regarding microalgae biomass replacement. Overall, the study rejects a common assumption that the bay-scale turnover rates serving the conventional CT/RT and CT/PT indices can be easily and accurately parameterized; these indices should be used cautiously in assessing the sustainability of farming activities. • Indices assessing bivalve culture sustainability rely on key ecosystem turnover rates. • Water renewal time should be assessed using full hydrodynamic models (not tidal prisms). • Bivalve clearance time should account for seasonality and refiltration effects. • Phytoplankton production time does not inform on biomass and community structure. • Interpretative caution is warranted regarding culture sustainability thresholds based on indices. [ABSTRACT FROM AUTHOR]

Integrated classification maps were produced by combining sediment grain-size and hydrological data (water renewal time, WRT) from two Mediterranean lagoons, Lesina (LL) and Varano (LV), Italy. The geophysical characteristics of the two basins, derived from detailed bathymetric charts, are quite distinct: ∼30% of LL (mean depth ∼1 m) but only 3% of LV (mean depth ∼3 m) is shallower than 1 m. The sediments of both lagoons are mainly composed of mud (∼80%). A detailed multivariate analysis of grain-size data by EntropyMax classified the lagoon beds of LL and LV into five sedimentary facies. WRT data, computed by a hydrodynamic model, indicated different hydrological conditions in the two lagoons: LL showed a sharp west-east gradient, with a basin-wide average of ∼190 days, whilst LV showed a fairly uniform distribution and a higher basin-wide average (∼260 days). The distribution of sedimentary facies and water renewal times were combined in a composite map representing the distribution of environmental patterns. The approach outlined in this study can be used to improve zonation schemes by providing a hydromorphological perspective on transitional and coastal environments. [ABSTRACT FROM AUTHOR]

Migratory fishes are one of the groups most threatened by the interruption of river connectivity caused by reservoirs and dams. The downstream displacement of eggs and larvae of these species implies overcoming the barrier presented by the reservoir and passage through the hydraulic structures of the dam. Although a low water renewal time attenuates the drift constraints on eggs and larvae in the reservoir, these organisms still require safe passage through these structures, which represents an additional challenge that demands methodological tools for impact assessment and management evaluation to subsidise operational decision making. This paper presents a protocol to help fill current gaps in knowledge of the impact of hydropower dams on the survival of fish larvae travelling through the hydraulic components of dams. A sampling and analysis design capable of in situ assessment of the effects of passage by the larvae through dams is presented and discussed along with potential alternatives to support hydraulic structure management and mortality reduction as well as inferences on the effectiveness of fish translocation strategies. The proposed approach is a new possibility for the in situ assessment of downstream ichthyoplankton passage through dams. The proposed sampling design is relatively simple, easily executed and affordable compared to those demanding more sophisticated technologies or that combine field and lab studies to associate fish injuries and mortality with the downstream passage through dams operating under different regimes. Its rapid diffusion is important given the accelerated expansion of the hydroelectric sector, especially in the main tropical basins. [ABSTRACT FROM AUTHOR]

Pyrethroid insecticides are among urban parks' most widely used and harmful insecticides. The advanced prediction method is the key to studying the pollution and diffusion risk of plant conservation insecticides in parks. A two-dimensional advection-dispersion model was established for the North Lake of Cloud Mountain Park in the subhumid area of Hebei Province. The temporal and spatial distribution of lambda-cyhalothrin pollution required by plant growth in artificial lakes under different rainfall intensities and the time of water renewal after rainfall was simulated and predicted. According to the model efficiency (E : 0.98), mean absolute error (MAE : 0.016–0.064 cm), and root mean square error (RMSE : 0.014–0.041 cm), the prediction results showed that the model fits well. The results showed that the concentration of lambda-cyhalothrin in the artificial lake was positively correlated with the increase in rainfall intensity. Under the three scenarios of moderate rain, heavy rain, and rainstorm, the variation of total pollutants into the lake over time conformed to the first-order dynamic equation (R 2 ＞0.97), and the cumulative rates were 0.013 min−1, 0.019 min−1 and 0.022 min−1, respectively. Under light rain, the accumulation rate of lambda-cyhalothrin showed a double-linear relationship, which was in accordance with the second-order kinetic equation (R 2 ＞0.97). The rapid accumulation rate of early-stage rainfall was 0.0024 min−1, and the slow accumulation rate of late-stage rainfall was 0.0019 min−1. The human health risk assessment predicted by the simulation was lower than the hazard value (R tg n (a-1) : 9.65 E−11–1.12 E−10 a-1). However, the potential risk value to aquatic species was higher (RQ : 0.33–23.05). In addition, the increase in rainfall intensity has no significant effect on the acceleration of water renewal time. The two-dimensional dispersion model of pollutants driven by water dynamics provided relevant examples for evaluating the impact of runoff on pesticide scour in parks and supplied scientific support for improving the management of artificial lakes in urban parks. [Display omitted] • Transport of pesticides in the park washed into the lake by rainfall was simulated. • A predictive model of pesticide transport based on hydrodynamics was developed. • Four rainfall intensities of pesticide washing into the lake were predicted. • Total amount of pesticides was positively correlated with rainfall intensity. • Lambda-cyhalothrin in the artificial lake shows a high ecological risk to aquatic life. [ABSTRACT FROM AUTHOR]

Eutrophication is a major driver of the degradation of transitional waters worldwide, especially in environments with a restricted connection to the sea, such as coastal lagoons. In recent decades, intensive agriculture and urban water inputs around the Mar Menor coastal lagoon (Western Mediterranean) have disturbed this originally oligotrophic aquatic system. The nutrient input into the lagoon has triggered its eutrophication, leading to dystrophic crises and mass mortality events for aquatic biota, transforming it into one of the most eutrophication-impacted transitional waters in the Mediterranean basin. In this study, we applied a fish-based indicator to assess the ecological quality of shallow waters under different eutrophication-mediated environmental stress scenarios (from pre-eutrophic reference periods to critical eutrophic periods), as well as to explore the role of confinement (i.e., water renewal time) and shoreline anthropogenic pressure as factors modulating the indicator response. Despite the high magnitude of the eutrophication impact on the lagoon, the ecological quality of the shallow waters decreased only slightly after the mass mortality events. The level of confinement also had slight effects on the ecological quality of the most confined shallow areas in the summer during eutrophic periods. Hence, shallow waters could play a critical role as refuge habitats, both for fish assemblages and other aquatic taxa, by buffering euxinic conditions during eutrophication processes.". In fact, shallow waters could act as critical habitats, allowing for the recolonisation of aquatic biota from more impacted areas in the lagoon. This attribute further reinforces the need to properly manage and protect the shoreline areas of transitional waters, particularly under eutrophication scenarios. • A fish-based index was applied to assess the ecological quality of the Mar Menor. • No major temporal changes were found between reference and eutrophic periods. • The ecological quality of more confined areas was particularly affected in warmer seasons. • Shallow waters buffered eutrophication-mediated impacts by providing refuge habitats. • This alternative role should be considered into coastal lagoon restoration. [ABSTRACT FROM AUTHOR]

The Lagoon of Nador (Morocco) has been subject to relevant man-made changes in recent years, which consisted of closing the inlet and opening a new one, wider and deeper, with long lateral jetties. In this paper, we study some of the consequences of this modification, using a 3D hydrodynamic model that allows a comparison of the two configurations (old and new inlet). This would be not possible analysing only the observations and the approach we followed is a general method that can be applied wherever man-made or natural changes affect a coastal system. We have created two numerical grids, one with the old inlet and one with the new inlet, both covering the entire lagoon and a wide part of the coastal area. Using these two configurations, fully baroclinic simulations were run for one year. The results show a significant increase of the tidal amplitude and of the water circulation inside the lagoon, with a tidal prism four times larger. The change of the tidal asymmetry from positive to negative values (−0.7 in the inlet) causes a shift toward the ebb dominance, with implications for the mid-term morphological evolution. With the new inlet the water renewal time of the lagoon decreased from 57 to 15 days and the water temperature got warmer in winter (+1 °C) and colder in summer (−2 °C). As a consequence of this, the evaporation lowered and the salinity reduced by 0.8 PSU. The seasonal variability of the water renewal time shows that the tidal forcing, the baroclinic circulation and the wind contribute to the mixing processes. The mixing capacity of the lagoon (0.7) did not change because it is an intrinsic property of the lagoon morphology and of the atmospheric forcing. Finally, we found that the change of the water renewal time, with the new inlet, is higher than the change predicted, with the old inlet, under the RCP8.5 climate change scenario. • The opening of the new inlet lowers significantly the water renewal time, increases the exchange with sea so that the thermohaline characteristics of the lagoon are more similar to the sea. • The mixing efficiency of the lagoon did not change significantly, because it depends much more on the surface boundary conditions (wind forcing), rather than the lateral boundary conditions. • The new inlet changed the characteristic of the tidal signal from flood dominated (with the old inlet configuration) to ebb dominated. • The residual circulation is significantly influenced by the tidal jet that expands into the lagoon and the dominant N-E wind. • This anthropogenic change lowers the renewal time of the lagoon as like the climate change, but in a much shorter time and with higher magnitude. [ABSTRACT FROM AUTHOR]

Cyclonic frontal eddies are distinguishable from the surrounding water due to their unique biological and physical characteristics and have been observed in all western boundary current regions. These eddies spawn from cut-off meanders and are found on the landward side of the current. Here, we report for the first time observed frontal eddies for the intensification zone (north of 28°S) of the East Australian Current (EAC) off Southeast Queensland, Australia, by analysing remotely sensed sea surface temperature (SST) and chlorophyll-a (Chl-a) data. The frontal eddies were detected initially in the analysis of satellite tracked surface drifters. The shelf-crossing cyclonic drifter pathways indicated the presence of drifter-trapping cyclonic frontal eddies. The subsequent analysis of satellite images allows to quantify key eddy characteristics, cross-shelf volume transports associated with eddy filaments, eddy-driven shelf water renewal time scales, and export of total Chl-a and carbon per day. The observed frontal eddies have core radii of approximately 13 km and 15 km. The cold core surface SST anomaly and elevated chl-a indicates eddy entrainment of shelf water. The translational or core displacement velocity is estimated with 0.17 m s −1 or 15 km per day and the tangential velocity quantified from tracking surface drifters is 0.28 m s −1 to − 0.5 m s −1 . This results in a rotational period of 1.9 days to 3.9 days. We use maximum Chl-a and SST gradients to approximate the width of importing and exporting filaments associated with the frontal eddy to derive volume transports of 1.5 Sv and 1.9 Sv (import) and 0.3 Sv and 1.8 Sv (export), respectively. Chl-a concentrations of the exporting filaments are about 0.4 mg m −3 to 0.6 mg m −3 yielding a total export of 13–78 t of Chl-a per day. The frontal eddy induced on-shelf transport of 130 km 3 –160 km 3 per day represents between 18% and 22% of the shelf volume. Therefore, it would take approximately five days to renew all shelf water. We conclude that the observed frontal eddies of the northern intensification zone of the EAC potentially play an important role in determining cross-shelf exchanges, contribute to on-shelf marine conditions, enhancing coastal primary productivity and are possibly important to the export of shelf water properties such as the fish larvae of subtropical species via entrainment. [ABSTRACT FROM AUTHOR]

The concentration of atmospheric tracers in groundwater samples collected from springs and deep wells is, in most cases, the result of a mixture of waters with a wide range of residence times in the ground. Such is the case of an unconfined aquifer recharged over all its surface area. Concentrations greatly differ from the homogeneous residence time case. Data interpretation relies on knowledge of the groundwater flow pattern. To study relatively large systems, the conservative ion chloride and the decaying radiocarbon ( 14 C) are considered. Radiocarbon ( 14 C) activity in groundwater, after correction to discount the non-biogenic contribution, is often taken as an indication of water age, while chloride can be used to quantify recharge. In both cases, the observed tracer content in groundwater is an average value over a wide range which is related to water renewal time in the ground. This is shown considering an unconfined aquifer recharged all over its area under arid conditions, in which a period of greater recharge happened some millennia ago. The mathematical solution is given. As the solution cannot be made general, to show and discuss the changes in water reserve and in chloride and radiocarbon concentration (apparent ages), two scenarios are worked out, which are loosely related to current conditions in Northern Chile. It is shown that tracer concentration and the estimated water age are not directly related to the time since recharge took place. The existence of a previous wetter-than-present period has an important and lasting effect on current aquifer water reserves and chloride concentration, although the effect on radiocarbon activity is less pronounced. Chloride concentrations are smaller than in current recharge and apparent 14 C ages do not coincide with the timing, duration and characteristics of the wet period, except in the case in which recharge before and after the wet period is negligible and dead aquifer reserves are non-significant. The use of chloride concentration in springs as a proxy of chloride concentration in recharge to estimate recharge from atmospheric deposition leads to recharge value larger than the real one and it approaches the wet period recharge. Drawing inferences about radiocarbon data and recharge by the chloride balance method has rarely been taken into account before. It is important to consider the variable aquifer groundwater reserve. Current recharge estimation can be improved by careful selection of groundwater samples, supported by tritium and radiocarbon measurements. [ABSTRACT FROM AUTHOR]

The Black Sea is the largest euxinic seawater basin with H 2 S at depths of below 90 m. Previously found that the presence of H 2 S in water was caused by microbial sulfate reduction. Herein, we report the sulfur isotopic composition of sulfate and sulfide in seawater at stations in the central part of the Black Sea, especially from the Bottom Convective Layer (BCL) located below a water depth of 1750 m. Our study shows that the sulfur isotopic composition of sulfate (δ34S(SO 4)) in the surface layer of the oxic zone is +21.1‰ ± 0.1‰ relative to the Vienna Canyon Diablo troilite (VCDT), and does not differ from sulfate in the Mediterranean Sea. In the BCL, the average δ34S(SO 4) value is +23.0‰ ± 0.2‰, which does not change vertically or laterally owing to effective convective mixing. The sulfur isotopic composition of H 2 S varies from −40.0‰ to −41.9‰ between 200 m water depth down to the seafloor with an average δ34S(H 2 S) value of −40.6‰ ± 0.4‰ for the BCL. Based on the water mass balance and sulfur isotopic composition of sulfate in the relevant water masses affecting the BCL, we have formulated a model to calculate the sulfate reduction rate in the BCL. After evaluating the sulfate and sulfide sources in the BCL, we assumed that the only apparent sulfide source is a bacterial sulfate reduction in the water column, and the main sulfate source is a mixture of water from the Black Sea and the lower Bosporus current with an initial sulfate isotopic composition of +21‰. The weak water exchange in the BCL leads to the largest observed isotopic difference Δ SR = δ34S(SO 4) − δ34S(H 2 S) of 63.6‰ between sulfate and sulfide in the sulfidic water column of the Black Sea. To achieve a steady state with respect to the sulfate isotopic composition +23‰ in the BCL, an average sulfate reduction (SR) rate of 1.1 ± 0.1 nmol L−1 day−1 is required. A steady state relative to sulfur isotopic composition of sulfate in the BCL water was established 4200 years ago. The estimated residence time of H 2 S was 1.5 times shorter (946 years) than that of sulfate (1390 years). The latter is close to the water renewal time of the BCL (1432 years). Different residence times of sulfide and sulfate in the BCL are explained using their different fluxes from the BCL. Sulfate is mainly removed from the BCL via vertical advection, while a considerable part of the sulfide generated in the BCL (1/3 of total annual production) is probably spent on the sulfidation (FeS → FeS 2) of muddy turbidites. The estimated annual H 2 S production in the BCL is 0.78 ± 0.07 Tg. The developed model predicts that the sulfide concentration in the BCL remains practically unchanged (380 ± 5 μM) over the last 1800 years (after 5700 years from the onset of anoxia). • Due to effective convective mixing, the bottom layer of the Black Sea is homogenous. • In this layer, the only source of H 2 S is sulfate reduction. • Proposed mass balance model uses stability of water fluxes and volume of layer. • Model estimated the average sulfate reduction rate as 1.1 ± 0.1 nmol L−1 day−1. • Estimated H 2 S annual production in the bottom layer is 0.78 ± 0.07 Tg. [ABSTRACT FROM AUTHOR]

This paper examines the on-shelf circulation of the eastern Australian continental shelf for a region off southeast Queensland. We identify a characteristic seasonally reoccurring wind-driven cyclonic flow. It influences the cross-shelf exchange with the East Australian Current (EAC), which is the western boundary current of the South Pacific Ocean. We refer to this cyclonic circulation as the Fraser Gyre. It is located south of Fraser Island between about 25 °S and 27 °S. The region is adjacent to the intensification zone of the EAC where the current accelerates and establishes a swift, albeit seasonally variable southward boundary flow. Through the analysis of several data sets including remotely sensed sea surface temperature and sea surface height anomaly, satellite tracked surface drifters, ocean and atmospheric reanalysis data as well as geostrophic currents from altimetry, we find that the on-shelf Fraser Gyre develops during the southern hemisphere autumn and winter months. The gyre is associated with a longshore near-coast northward flow. Maximum northward on-shelf depth averaged velocities are estimated with about 0.15–0.26 ms -1 . The flow turns eastward just to the south of Fraser Island and joins the persistent southward EAC flow along the shelf break. The annual mean net cross-shelf outward and inward flow associated with the gyre is about −1.17 ± 0.23 Sv in the north and 0.23 ± 0.13 Sv (1 Sv = 10 6 m 3 s −1 ) in the south. Mean seasonal water renewal time scales of the continental shelf are longest during austral winter with an average of about 3.3 days due to the Fraser Gyre retaining water over the shelf, however, monthly estimates range from 2 to 8 days with the longer timescale during the austral autumn and winter. The southerly wind during austral autumn and winter is identified as controlling the on shelf circulation and is the principal driver of the seasonally appearing Fraser Gyre. The conceptual model of the Fraser Gyre is consistent with general physical principals of the coastal shelf circulation. A southerly wind is associated with surface layer flow toward the coast, a near coast positive SSHa with a current in the direction of the wind, down-welling and export of shelf water. The Fraser Gyre influenced cross-shelf exchanges are possibly facilitating the offshore transport of fish larvae, sediments, nutrients, river discharges, and other properties across the shelf break and into the southward flowing EAC during the austral autumn and winter. [ABSTRACT FROM AUTHOR]

The aim of this study is to estimate the water renewal time in the Boughrara lagoon. This is a key parameter for ecological studies of the lagoon. The method used consists of the injection of a soluble tracer which has a concentration of zero at the open boundaries of the domain (C 0 = 0) and is equal to one inside the lagoon (C 1 = 1). In this study, we use numerical simulation modules developed by Deltares: the hydrodynamic Delft-Flow module and the Horizontal Large Eddy Simulation (HELS) module. We compute the horizontal advection and dispersion and get estimates, at every mesh of the computational grid, of the time needed for the tracer's concentration inside the lagoon to drop from 1 (C 1) to 0.38. This time is known as the Local Renewal Time (LRT). A spatial distribution analysis of the LRTs enables a subdivision of the domain based on the similarity of values near the LRT (at every mesh of the domain) and on the physical configuration of the domain (e.g. bay, deep/shallow zone, harbor). Then it becomes simple to compute a renewal time for each region in the domain, which is the Integral Renewal Time (IRT). If we want to take into account the whole domain, we consider the maximum value of the IRT. The numerical simulations were run taking into account the effect of the predicted tide. The computational grid has a horizontal mesh size of 150 m × 150m. The LRT under only the effect of the tidal forcing at the zone where an aquaculture farm is located is estimated at one week. Moreover, in the region of the mini-gulf of Guellala, this LRT is estimated to be one month. The encounter between the waters coming from the two channels of the lagoon occurs after a period of four months in the zone bounded to the south by the island of Djilij and to the north by the mini-gulf of Guellala. South of the fishing port of Boughrara and Djilij Island, the local water renewal time varies between 5.5 and 6.5 months. • A high-resolution tidal model is developed and validated for the Boughrara lagoon. • Water renewal in the lagoon depends on water inlet from the adjacent gulf of Gabes. • The local water renewal time varies between 5.5 and 6.5 months. • The results serve as an ecological alert in a nearly closed aquatic environment. [ABSTRACT FROM AUTHOR]

The incidence of nutrient-induced hypoxia or anoxia-related mortality of aquatic species is becoming more prevalent in coastal systems worldwide. One such instance in an estuary of New Brunswick, Canada, resulted in the loss of approximately 75% of cultured oysters in certain farms. Field observations revealed that, although the occurrence of summer hypoxia in north Tracadie Bay was linked with anthropogenic stressors, changes in the morphology of one of the bay's inlets were likely to play a significant role in escalating the eutrophic conditions. However, adequate information on the circulation dynamics of Tracadie Bay was lacking. To address this knowledge gap, a high-resolution spatially explicit hydrodynamic model was developed for Tracadie Bay to evaluate the possible physical processes involved in the generation of hypoxia leading to oyster mortality. Further, the model was coupled with a volume advection-dispersion tracer module to track the dissemination of effluent. The model showed high skill in south Tracadie Bay in simulating water level elevations and slightly lower skill in north Tracadie Bay. Residual flow estimates revealed poorly-circulated stagnant areas, consistent with hot spots in sediment organic matter content. Findings from modeling scenarios based on past, present, and future inlet morphology suggest that inlets have strong consequences on intricate circulation patterns, renewal of water, and transport. Outcomes from this study will be of relevance for managing water quality and aquaculture practices. • Bay's flushing potential responds to inlet geomorphic setting. • Long water renewal time indicates poor flushing. • Stagnant areas coincides with hot spots of sediment organic content. • Feeble outgoing fluxes likely to escalate eutrophic conditions. [ABSTRACT FROM AUTHOR]

Abstract: Tidal and wind renewal of water in the coastal zone is important in the transport of natural and anthropogenic particles and solutes. Models of these systems require detailed parameterization of exchange processes. Renewal of seston food supplies for cultured suspension-feeding shellfish is one such application. This study examines the sensitivity of food limitation estimates of an inshore region for shellfish aquaculture to the methods used in calculating the region''s water renewal time. The region is the Indian Island oyster culture site in the Richibucto estuary, New Brunswick, Canada, and the methods considered are the volume advection and the local conservative tracer methods. In both cases, water renewal is calculated from field time series measurements of hydrodynamic parameters and outputs of coupled hydrodynamic and advection–dispersion three-dimensional (3D) numerical models. A comparison of oyster food demand and supply is then made to estimate the food limitation risk in the region using field measurements of biological parameters and the renewal times previously estimated. It is found that water renewal by tides is efficient but it can be cancelled altogether by meteorological forcing. Contrary to the conservative tracer method, the tidal prism method proves to be inadequate when estimating water renewal in estuarine tidal channels and was replaced by another volume advection method. The preliminary results obtained using the depletion index estimates indicate that the Indian Island region could sustain a high oyster biomass. These simple calculations also show the importance of water renewal estimate for carrying capacity studies. Hence, the tidal prism method or other volume advection estimates should be used with great caution or be avoided altogether in such studies. [Copyright &y& Elsevier]

The Arctic Ocean likely impacts global climate through its effect on the rate of deep-water formation and the subsequent influence on global thermohaline circulation. Here, the renewal of the deep waters in the isolated Canadian Basin is quanitified. Using hydraulic theory and hydrographic observations, the authors calculate the magnitude of this renewal where circumstances have thus far prevented direct measurements. A volume flow rate of Q = 0.25 ± 0.15 Sv (Sv ≡ 106 m3 s-1) from the Eurasian Basin to the Canadian Basin via a deep gap in the dividing Lomonosov Ridge is estimated. Deep-water renewal time estimates based on this flow are consistent with 14C isolation ages. The flow is sufficiently large that it has a greater impact on the Canadian Basin deep water than either the geothermal heat flux or diffusive fluxes at the deep-water boundaries. [ABSTRACT FROM AUTHOR]

To estimate the water-renewal time of the Gulf of Finland, a numerical-model simulation comprising the years 1987–1992 was carried out for realistic meteorological forcing. The results concerning water age as well as renewal index proved to reflect properties of the mean circulation system. The highest water ages (of around 2 yr) were found in the south-eastern part of the Gulf. The water-age distribution after the 5-yr simulation proved to be almost identical to that obtained after 3 yr, indicating that the circulation in the Gulf may be rather stable. The analysis of the renewal-index results showed that it takes around 5 yr to renew 98% of the water masses of the Gulf. When local maxima of the renewal index are found in conjunction with high water ages, this may indicate that the region is particularly vulnerable to eutrophication. [ABSTRACT FROM AUTHOR]

A temporally and spatially detailed historical (1985–2018) analysis of cyanobacteria blooms was performed in the Curonian Lagoon (Lithuania, Russia), the largest coastal lagoon in the Baltic Sea. Satellite data allowed the mapping of cyanobacteria surface accumulations, so-called "scums", and of chlorophyll-a concentration. The 34-year time series shows a tendency towards later occurrence (October–November) of the cyanobacteria scum presence, whereas the period of its onset (June–July) remains relatively constant. The periods when scums are present, "hot moments", have been consistently increasing in duration since 2008. The differences in the starting, ending and annual duration of cyanobacteria blooms have been significantly altered by hydro-meteorological conditions (river discharge, water temperature, and wind conditions) and their year-round patterns. The most important environmental factors that determined the temporal changes of the scum presence and area were the standing stock of cyanobacteria and the ambient wind conditions. The "hotspots", the areas where the blooms most likely occur, were distributed in the south-southwestern and central parts of the lagoon. The least affected areas were the northern part, which is connected to the coastal waters of the Baltic Sea, and the Nemunas River delta region. The longstanding, well-established spatial patterns of cyanobacteria blooms were linked to hydrodynamic features, namely water renewal time and current patterns, and to potential nutrient sources that included muddy sediments and the locations of colonies of piscivorous birds. Our findings confirmed that the annual and seasonal variations of cyanobacteria blooms and their regulation are a complex issue due to interactions between multiple factors over spatially and temporally broad scales. Despite great progress in the prevention and control of eutrophication and cyanobacteria blooms, the lagoon is still considered to be in a poor ecological status. This work provides a new and missing understanding on the spatial and temporal extent of cyanobacteria blooms and the factors that govern them. Such an understanding can help in planning management strategies, forecasting the magnitude and severity of blooms under changing nutrient loads and potential climate scenarios. Unlabelled Image • Landsat data showed potential for long-term algal bloom records in the Curonian Lagoon. • Spatial-temporal patterns of cyanobacteria 'hotspots' were revealed from satellite data. • Blooms 'hot moments' occur annually, their span is getting longer in the recent decade. • Hydrodynamics and potential nutrient sources explained >45% of blooms spatial patterns. • 'Hotspots' mapping is important for monitoring efficacy of eutrophication measures. [ABSTRACT FROM AUTHOR]

Global circulation models predict that global warming caused by greenhouse gases will be particularly marked at high latitudes. Possibly so, but lower latitudes do not escape unscathed. Researcher P. Verburg et al. demonstrate a pro-found effect of global warming on Lake Tanganyika, just south of the equator in tropical Africa. Lake Tanganyika is one of the oldest and deepest lakes in the world. Its great mass of water gains and loses so little through rivers that its water renewal time is measured in millennia rather than years or decades. One might expect the great thermal inertia of so much water to buffer the lake against the vagaries of climate change. The work of Verburg et al. contradicts that expectation. Many animal species that live nowhere else are endemic to Lake Tanganyika. The lake contains two genera of small herrings, and many of its gastropod molluscs have spiny shells like those found on tropical seashores. Because of its great depth, Lake Tanganyika is perennially stratified. Dead organic matter sinks from the illuminated surface zone and decays as it falls, releasing nutrient materials such as silica and phosphorus. More intense stratification has led to drastic changes in water chemistry. Dissolved oxygen does not penetrate to the depth it once did, and one of the endemic snails. Tiphohia horei, which in 1890 was collected to a depth of 300 m, is now restricted to the upper 100 m of the water column.

Abstract: Since advection and diffusion are the main physical processes that influence the cleaning capacity of coastal transitional waters, the 3-D spatial distribution of the water renewal times was used to delineate a physically-based zonation scheme. The temporal and spatial variations of the hydrodynamics are assessed using a validated three dimensional hydrodynamic finite element model. The developed methodology was applied to the Cape Peloro system, a coastal protected area located in the Messina Strait (Italy) consisting of two connected small brackish basins: the shallow Lake Ganzirri and the deep meromictic Lake Faro. The hydrodynamics of the two coastal lakes shows strong seasonal and spatial variation. The 3-D distribution of the water renewal times suggests a horizontal partition of the Lake Ganzirri into two sub-basins and a vertical zonation of the Lake Faro, with the mixolimnion extending till 10m depth and the presence of a persistent bottom stagnant layer. The derived physically-based zonation scheme helps in explaining the highly heterogeneous spatial distribution of many biogeochemical variables in the Cape Peloro coastal system. [Copyright &y& Elsevier]

We calculated average aquatic dissolved organic carbon (DOC) age (the time span from soil discharge to observation) in water from the inlets and outlets of two unproductive Swedish lakes at different times during an annual cycle. Bacterial production (BP) and bacterial growth efficiency (BGE) determined during 7-d bioassays decreased with increasing average aquatic DOC age. Parallel to the declines in BP and BGE there was a rise in specific ultraviolet absorbance at the wavelength of 254 nm (SUVA254), which indicates that decreasing BP and BGE were connected to a shift to a more aromatic and recalcitrant DOC pool. The relationships between bacterial metabolism and DOC age were stronger after a Q10 correction of the DOC age, showing that temperature affected rates of DOC quality changes over time and should be taken into account when relating lake bacterial growth to substrate aging in natural environments. We propose that hydrological variability in combination with lake size (water renewal time) have a large influence on pelagic BP in lakes with high input of terrigenous DOC. [ABSTRACT FROM AUTHOR]

New observations of physical, biological, and chemical parameters were obtained between July 2003 and February 2005 in Nitinat Lake, British Columbia, a permanently anoxic seawater fjord. These observations include continuous profiles of nitrate and bisulfide using a new instrument for in situ ultraviolet spectrophotometry. Anoxic seawaters in this 200-m-deep basin can be found as shallow as 7 m. However, Nitinat Lake is surprisingly dynamic, with a deep-water renewal time of only about 5 yr and significant spatial and temporal variability. Exchange with the ocean is limited by the size of the linking channel, and during low tides the outflow is subject to an hydraulic control. This nonlinearity causes a relatively large fortnightly cycle in water level and explains flooding events associated with heavy rainstorms. In addition, the restricted flow makes deep-water renewal gradual so that anoxic conditions are preserved. Intermediate waters (5-40 m in depth) are renewed alternately by oxygenation from surface mixing in winter and by upwelling of anoxic water and horizontal inflow of subducted ocean water in summer. The horizontal inflow results in a subsurface region of suboxic water in mid-fjord during summer. No suboxic regime is evident at either the river end of Nitinat Lake (where oxygen and sulfide-rich regions adjoin in a nitrate-depleted water column) or at the ocean end of Nitinat Lake (where oxygen and nitrate-rich regions sometimes overlap with sulfide-rich regions). Maximum phytoplankton levels near the surface are high in both winter and summer. A second peak in biological activity appears near the anoxic boundary, possibly as a result of sulfur-oxidizing bacteria. Sulfate-reducing bacteria are also present in anoxic water in both seasons and just above the oxic/anoxic interface in winter and just above the suboxic/anoxic interface in summer. [ABSTRACT FROM AUTHOR]