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This study examines the hydrodynamic regimes in Shediac Bay, located in New Brunswick, Canada, with a focus on the breach in the Grande-Digue sand spit. The breach, which was developed in the mid-1980s, has raised concerns about its potential impacts on water renewal time and water quality in the inner bay. The aims of this study, using mathematical modeling approaches, were to evaluate the flow regimes passing through the breach and influences on the distribution of dissolved matter, providing insights into whether the breach should be allowed to naturally evolve or be artificially infilled to prevent contaminant stagnancy in the bay. The study considered three simulation scenarios to comprehend the water renewal time and the role of the breach in the environmental management of Shediac Bay. Results indicated that completely closing the breach would significantly increase the water renewal time in the inner bay, although the spatial extent of this increase is limited. However, the study identified some limitations, including the need to better define the concentration limit for considering water as renewed and the lack of consideration of dynamic factors such as wind and wave effects.

Water exchange in lake basins is a very important process in regulating the health of the aquatic environment, e.g., by shaping algal blooms. Thus, knowledge of the process is also required to develop management strategies. The paper presents a dynamic of water renewal time in the Uściwierz chain of lakes, in which the natural hydrological connectivity of the catchment areas has been altered due to human impact. Calculations of water renewal were limited to the part of the lake basin corresponding to the active (dynamic) retention layer. A comparative analysis of the rate of potential water renewal, based on the structure difference index, was used as an indicator of the degree of anthropogenic transformation of water distribution in the lake catchments. The smallest differences in the structure of the water renewal rate between the neighboring lakes in the chain system were observed in the cold period, and the largest differences were observed in the warm period. The results showed that the shorter the timescale (5-day period), the higher the similarity in the structure of the water renewal rate between the lakes. Very large differences between the structure of the potential water renewal rate in Lakes Uściwierz and Bikcze indicated a significant transformation of the water cycle down the lake chain. The water renewal rate proved to be a good indicator of the degree of anthropogenic transformation in the catchments located in close proximity.

This study examines the hydrodynamic regimes in Shediac Bay, located in New Brunswick, Canada, with a focus on the breach in the Grande-Digue sand spit. The breach, which was developed in the mid-1980s, has raised concerns about its potential impacts on water renewal time and water quality in the inner bay. The aims of this study, using mathematical modeling approaches, were to evaluate the flow regimes passing through the breach and influences on the distribution of dissolved matter, providing insights into whether the breach should be allowed to naturally evolve or be artificially infilled to prevent contaminant stagnancy in the bay. The study considered three simulation scenarios to comprehend the water renewal time and the role of the breach in the environmental management of Shediac Bay. Results indicated that completely closing the breach would significantly increase the water renewal time in the inner bay, although the spatial extent of this increase is limited. However, the study identified some limitations, including the need to better define the concentration limit for considering water as renewed and the lack of consideration of dynamic factors such as wind and wave effects. [ABSTRACT FROM AUTHOR]

The dramatic increase in the number of dams on rivers in recent years have led to a more complicated water circulation mechanism in arid regions, Capturing the impact of dams on water circulation processes is an ongoing challenge in the hydrology field. By utilizing observational isotopic data from water bodies, we conducted a comparative study on the Fyw and MTT in two inland river basins within the arid zone of Central Asia. Research findings suggest that dams amplify the damping effect and phase shift of seasonal fluctuations in river water, which in turn extends the water circulation period within inland river basins. The cascading interception of river water by dams has substantially reduced the proportion of young water (Fyw) in the river and has nearly tripled the mean transit time (MTT) of river water. This work confirms the fact that dams are profoundly influencing the water circulation processes in inland river basins from an isotopic kinetic perspective, and is useful for understanding the mechanisms driving water circulation times arid areas. [ABSTRACT FROM AUTHOR]

The Mar Menor lagoon has been subjected to high anthropogenic pressures. Among them, in the early 1970s, dredging and enlargement of one of the inlets to make a navigable channel has had strong consequences on the hydrology, ecology, and fisheries of the lagoon. In recent years, changes in agricultural practices have induced an eutrophication process, leading to loss of water quality. As a solution, some management proposals have included dredging of the inlets in order to increase the water renewal. However, these proposals did not take into account the negative effects of previous experiences nor the consequences on environmental conditions of the lagoon and therefore on biological processes. The purpose of this work is to assess the effect that proposed mitigation measures, could have on the hydrodynamic conditions and discuss its possible ecological consequences. A three-dimensional (3D) numerical model has been used to simulate the lagoon under different dredging scenarios, covering different dredging depths and extensions. The simulated current fields and fluxes through the inlets, as well as water renewal times have been compared for the different scenarios. It is found that some of the considered scenarios take the system beyond the threshold of sustainability, where the modified current dynamics could affect sediment transport, beach dynamics and fishing capacities in a significant way. Water exchange with the Mediterranean is also strongly affected, with consequences for species connectivity, and a homogenization of the water renewal times that could lead to loss of ecosystem heterogeneity and structural complexity. The study demonstrates the utility of numerical models as effective tools for the management of coastal areas.

The hypothesis that local hypoxia and chlorophyll concentration are spatially tethered to local, sediment-driven nutrient release was examined in a small, nutrient-impacted estuary in the Southern Gulf of St. Lawrence, Canada. Sediment reactor core samples were taken at 10 locations between 0.25 and 100% of the estuary area in spring and fall (2019) and used to estimate nitrogen and phosphate flux. Sediment organic matter, carbonate, percent nitrogen, percent carbon, δ13C, and δ15N were measured from the reactor core stations. Oxygen was recorded continually using oxygen loggers while chlorophyll and salinity were measured bi-weekly. A hydrodynamic model was used to determine water renewal time at each station. The most severe eutrophication effects were in the upper one-fifth of the estuary. There were strong local relationships between sediment biogeochemistry, hypoxia, and chlorophyll metrics but not with water renewal time. Internal nutrient loading represented 65% and 69% of total N loading, and 98% and 89% of total P loading to the estuary in June and September, respectively. Sediment nitrogen flux was highly predictable from a range of local sediment variables that reflect either nutrient content, or organic carbon enrichment in general. Percent nitrogen and percent carbon were highly correlated but sediment P flux was poorly predicted from sediment parameters examined. The highest correlations were with percent nitrogen and percent carbon. These results indicate that incorporating internal nutrient loading into nutrient monitoring programs is a critical next step to improve predictive capacity for eutrophication endpoints and to mitigate nutrient effects. [ABSTRACT FROM AUTHOR]

In spite of its importance as regards size (volume 9.2 106 m3, max depth 151 m) and as a source of drinking water, Lake Bolsena has not been studied from a hydrochemical point of view since the second half of the 60s, when a group of researchers from the Istituto Italiano di Idrobiologia co-ordinated a complete study of the limnology of the Latium lakes Bolsena, Albano, Vico, and Bracciano. In the following years analyses were performed sporadically; since the 90s, temperature and oxygen profiles and other studies were made by the Associazione Lago di Bolsena. Based on chemical profiles made in 2001-2003, this paper discusses the present chemical composition of Lake Bolsena waters, and compares them with those of other volcanic lakes in Latium (Bracciano, Albano, Nemi and Vico). The paper briefly considers the main factors influencing the water chemistry of Lake Bolsena, the variations observed from the analyses of the 60s, and the main sources of risk to water quality.

The hydrological consequences of historical, contemporary and future human activities on a coastal system were investigated by means of numerical models. The changes in the morphology of the Lagoon of Venice during the last century result from the sedimentological response to the combined effects of human interventions on the environment and global changes. This study focuses on changes from 1927 to 2012 and includes the changes planned for the protection of the city of Venice from storm surges and exceptional tides under future sea level rise scenarios. The application of a hydrodynamic model to simulate the circulation of water masses and the transport of a passive tracer enabled the analysis of the morphodynamic effects on the lagoon circulation and the interaction with the sea. The absolute values of the exchange between the lagoon and sea increased from 1927 to 2002 (from 3900 to 4600m³ s-1), while the daily fraction of lagoon water volume exchanged decreased. At the same time, the water renewal time shortened from 11.9 to 10.8 days. Morphological changes during the last decade induced an increase of the basin-wide water renewal time (from 10.8 to 11.3 days). In the future, Venice Lagoon will evolve to a more restricted environment due to sea level rise and periodical closure of the lagoon from the sea during flooding events. Simulated scenarios of sea level rise showed that under fall-winter conditions the water renewal time will increased considerably especially in the central part of the lagoon. Furthermore, some considerations on the impact of the hydromorphological changes on the ecological dynamics are proposed. [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]

To investigate the variation of the biogeochemical cycle of riverine dissolved inorganic carbon (DIC) and silicon (DSi) with the cascade damming, the bicarbonate ( HCO 3 − ), dissolved silicon (DSi), and other environmental factors within the cascade reservoirs of the lower reaches of Yalongjiang River, passing through the southeastern Qinghai-Tibet Plateau, were systematically analyzed by collecting water samples during the wet season and dry season from 2018 to 2019, respectively. The results showed that the lower ratio of DSi to HCO 3 – (0.044 ± 0.001) was mainly controlled by the domination of carbonate mineral in the sedimentary rock of the Yalongjiang River drainage basin. The DSi: HCO 3 – ratio was positively correlated with discharge (P < 0.05), and negatively correlated with the water retention time (P < 0.01) and chlorophyll a, implying that the variations of DSi: HCO 3 – ratio were mainly determined by the rock chemical weathering processes and the hydrologic process outside the reservoirs and the biological processes within the cascade reservoirs. The phytoplankton photosynthetic process stoichiometrically assimilated DSi and HCO 3 – , resulted in 3.46 × 104 t·Si a−1 and 1.89 × 104 t·C a−1 sequestering in the cascade reservoirs, respectively. Compared with the situation of dam-free in the lower reaches of Yalongjiang River, the export flux of HCO 3 − and DSi at the mouth of Yalongjiang River was reduced by 11.87% and 62.50%, respectively; the ratio of DSi: HCO 3 – decreased by 36.01% for only building the Ertan dam and 53.15% for the cascade damming, respectively. The water renewal time prolonged from 45 to 126.6 days due to the regulation of the cascade reservoirs in the mainstream. Ultimately, a conceptual model on migration-transformation of DIC and DSi within the cascade reservoirs in the lower reaches of Yalongjiang River was established. These findings demonstrated that riverine cascade damming could extend the biogeochemical coupling cycle of DIC and DSi within the inland aquatic ecosystems and ensure the ecological environment security in the hot-dry valley. [ABSTRACT FROM AUTHOR]

Studying groundwater renewal time is a valuable tool to deepen the comprehension of sustainable groundwater resources specific to arid regions. Tritium is a radioactive isotope of hydrogen often used as an environmental tracer to study groundwater renewal time. The present work reports groundwater renewal times by the environmental tracer tritium to understand sustainable water resources in arid regions. First, groundwater samples were collected from wells in northeastern arid regions of Saudi Arabia. Then, an electrolysis process was employed to significantly increase the tritium level from twenty-five to thirty times the original concentration. Subsequently, the enriched water was analyzed using a liquid scintillation counter under optimized measurement conditions to determine the tritium concentration precisely. Two internationally recognized tritium laboratories conducted independent assessments to validate the estimated tritium levels. The verified tritium concentration was then used to estimate the groundwater renewal time using the Morgenstern and Pimenta curves. The results suggest that most of the monitored wells in the surveyed areas are more than a century old. Conversely, a few monitoring wells exhibit renewal times of several hundred years and may be considered nonrenewable water sources. These studies help to understand the geochemical characteristics of arid regions to ensure the sustainable management and protection of groundwater resources. [ABSTRACT FROM AUTHOR]

Evaluating and integrating local ecological knowledge held by fishers into decision-making processes has the potential to significantly enhance fisheries management. The present study aimed to collect information on fishery practices and to assess the ecological knowledge of local professional fishers through interviews, evaluating its importance in managerial design. As a case study, Polyphytos Reservoir in Greece, which supports substantial fisheries, was selected. During the summer of 2023, thirty-seven interviews were conducted to document fishing efforts, methods, catches, biological information, and fishers' perspectives on lake management, and economic/demographic details. In addition to gathering data on fishing activities, the study seeks to understand fishers' perspectives on managerial deficiencies and necessities, thereby revealing their valuable ecological knowledge. The integration of this knowledge into decision-making processes can empower stakeholders and enhance local participation in fishery management. Ultimately, this approach has the potential to address long-standing conflicts, foster inclusive processes, and ensure better collective outcomes. [ABSTRACT FROM AUTHOR]

The spatial and temporal variation of submarine groundwater discharge (SGD) has been a topic of interest for researchers in recent years. However, the study of SGD is limited within the scope of Zhanjiang Bay. The Zhanjiang Bay is located in western Guangdong Province, known for its high temperatures and typhoon vulnerability. The present study examined the fluctuation patterns of seawater 222Rn in Zhanjiang Bay during the period from June 2021 to March 2022. This investigation employs the 222Rn tracing technique to establish a mass balance model to compute the SGD rate, and assess the significance of SGD in translocating nutrients into the bay. We conducted a four-month sampling, observing the differences between the rainy and dry seasons. Precipitation exerts a significant influence on the seasonal variations of SGD. The SGD rates of Zhanjiang Bay ranged from 7.14 to 10.75 cm·d-1 in the dry season and from 13.38 to 14.61 cm·d-1 in the rainy season. SGD-derived nutrients also exhibited seasonal fluctuations, the annual input of nutrients it supplies may be comparable to the quantity delivered by rivers, which significantly impacted the trophic status of the bay. [ABSTRACT FROM AUTHOR]

Bivalve culture is know to affect some interactions between the water column and the benthic environment with the organic enrichment. An in situ mesocosms experiment was used to determine the influence of mussel biodeposition on the benthic ecosystem in St. Peters Bay, Prince Edward Island, eastern Canada. Eight mussel densities (0 to 2266 mussels m-2) were placed above mesocosms to reproduce the organic enrichment from a mussel farm over 12 weeks. The experimental procedure created an accumulation of organic matter on the seafloor with increasing mussel densities. Some benthic parameters had the predicted response to organic enrichment, with the presence of anoxic sediment in sediment profile images, increased water and organic matter content, and reduced infaunal abundance and species richness. Other parameters, including redox potential, total free sulfides, and the response of the biotic index AMBI, had inconsistent responses to mussel biodeposition-related organic enrichment. Given that other studies done in other locations have observed varying results, results suggest that measurement of various parameters is important to interpret the influence of deposition from mussel farms. The conditions of the site and the study duration are also parameters to consider when evaluating the results from mesocosm studies. Results from this study also suggest that St. Peters Bay is likely impacted by biodeposition from the mussels farmed there. [ABSTRACT FROM AUTHOR]

Harmful algal bloom events occur in salt, brackish, and fresh water. In bodies of water such as oceans and estuaries, diatoms or dinoflagellates form "tides" that produce toxins associated with seafood poisoning, including paralytic shellfish poisoning, or respiratory distress from inhalation of aerosolized toxins. Cyanobacteria predominantly bloom in fresh water; they can produce microcystins; cylindrospermopsin; and other toxins that humans or animals might be exposed to through water contact, inhalation, or ingestion. Animals that become ill or die can be sentinels for harmful algal bloom events. In a One Health approach, information about harmful algal bloom exposures and health effects support efforts to detect these events and mitigate and prevent associated illnesses. Human, animal, and environmental health partners can work together to document the occurrence and impacts of harmful algal bloom events and characterize associated illnesses. [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]

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]

This work presents an experimental evaluation of a Venturi and Venturi-Vortex microbubble aeration system, taking as input variables the water-air flow ratio, water renewal time and area-volume ratio of the water tank. The aeration process response variables are defined in terms of oxygen transfer and aeration efficiency through the standard volumetric mass transfer coefficient (KLa20), standard oxygen transfer rate (SOTR), and standard aeration efficiency (SAE). Two methods of air injection were analyzed: 1. Air injection in the throat chamber of the Venturi generator; 2. air supplying in the suction side of the hydraulic pump of the aeration system. Experimental results indicate that the water renewal time variable (RT) is a statistically significant factor with respect to the KLa20, which can be maximized by decreasing RT. The effects of the variable flow ratio (FR) are greater than the effects of renewal time and area-volume ratio (AVR) concerning SOTR and SAE, indicating a maximum response with a minimum flow ratio, using the Venturi-Vortex microbubble generator. When the flow ratio decreases, the air flow increases, generating and transferring a greater amount of microbubbles (MB) into the water. It was found that increasing the air flow produced an increase in the standard oxygen transfer rate SOTR and standard aeration efficiency SAE. Results allow concluding that the injection of the air flow from the suction side of the pump promotes the generation of microbubbles (MB) for a maximum air flow allowed by the system. SOTR and SAE could be maximized whit the flow ratio factor and the Venturi-Vortex generator, supplying air flow from the suction side of the hydraulic pump.