Freshwater Management Research Articles

The state of knowledge of freshwater resources in the U.S. Virgin Islands: Data scarcity and implications

AbstractLike many small island communities, the U.S. Virgin Islands (USVI), an unincorporated territory of the U.S., is naturally freshwater scarce. In recent decades, rapid land development in the USVI has increased water demand considerably, exerting extra pressure on freshwater resources. Freshwater quantity and quality data for the USVI are very scarce and scattered, which limits freshwater management capabilities. We draw attention to this information deficit and discuss its implications by reviewing the current state of knowledge of surface and groundwater quantity and quality for the USVI. Our review confirms that long‐term records of surface and groundwater quantity and quality are limited and unreliable. For example, streamflow was most recently monitored in 2006, and the most extensive surface water quality records are from the 1960s and 1980s. Since 2016, mean groundwater levels have been recorded daily, but only for three wells (one on each island of the USVI). Importantly, this lack of information threatens water security for the territory and limits our understanding of how development has impacted water quality and availability over time. This could be addressed using models, such as a groundwater recharge model, in combination with remote sensing and updated field data (i.e., streamflow, groundwater, and ecohydrological characterizations of land use change).

Ecohydraulics-based environmental flow assessment in two arid North African rivers

North Africa is among the most water-stressed regions in the world; still, the habitat requirements of its freshwater biota are largely unknown. In this study, (i) we developed habitat suitability curves (HSCs) for freshwater macroinvertebrates in two poorly studied, regulated North African rivers (Ziz and Oum Er-Rbia), and (ii) assessed environmental flows downstream of each river dam by incorporating the HSCs in two-dimensional ecohydraulic models. We demonstrate a low-cost sampling methodology combined with freely distributed ecohydraulic modeling software. The results showed that macroinvertebrates in the arid-desert Ziz River could tolerate a wide range of habitats in terms of flow velocity and water depth compared to the arid-steppe Oum Er-Rbia River, probably due to their adaptation to extreme (arid-desert) environmental conditions. Optimal environmental flows downstream of the Al Hassan Addakhil (Ziz River) and the Al Massira (Oum Er-Rbia River) dams were 1 m3/s and 2 m3/s, respectively. However, environmental flows at 0.5 m3/s and 1 m3/s, respectively, could still maintain sustainable freshwater biota downstream of the dams. The results further highlight the critical status of the Ziz River, which was completely dry, and the alarming status of the Oum Er-Rbia River due to the significant reduction in the water levels of the Al Massira Dam. In a continuously changing climate, we suggest that the proposed environmental flows should be immediately delivered to prevent droughts and ensure healthy freshwater communities downstream of the dams, within a basin-wide freshwater management framework. In this water scarce region, more research is necessary to increase ecological awareness about these understudied freshwater systems and achieve a balance between human needs and ecosystem requirements.

Imprints of seawater intrusion on groundwater quality of coastal region of Pudukkottai district, India: An integrated approach

Climate change and groundwater overexploitation endanger the sustainability of groundwater in India, particularly in the coastal region of Tamil Nadu. The increasing population, agricultural and industrial development, raised the demand for groundwater in the Coastal area of Pudukottai District, Tamil Nadu. Seawater intrusion establishes a challenging environment for freshwater management in coastal areas. A total of 64 groundwater samples were collected from different places, including borewells and open wells. The seawater intrusion is evaluated using the statistical method and physiochemical analysis such as water indices, ionic ratio and hydrochemical facies. As per the results of the groundwater quality index, 93% of the samples were not suitable for drinking as the examined parameter exceeded the Indian Standards. Piper’s diagram classify the Coastal groundwater into mixed Ca<sup>2+</sup>-Na<sup>+</sup>-HCO<sub>3</sub><sup>-</sup>, Na<sup>+</sup>- HCO<sub>3</sub><sup>-</sup> and Na<sup>+</sup>-Cl<sup>-</sup> type as the dominant. As per the seawater mixing index, 78% of the groundwater samples were affected by seawater intrusion. Further, the results of the ionic ratio (Na<sup>+</sup>/Cl<sup>-</sup>, Mg<sup>2+</sup>/Cl<sup>-</sup>, Ca<sup>2+</sup>/Mg<sup>2+</sup>, Ca<sup>2+</sup>/SO<sub>4</sub>, Ca<sup>2+</sup>/HCO<sub>3</sub><sup>-</sup>) identify the salinization influence in the groundwater. The thematic maps created with the QGIS platform effectively to define the area of seawater intrusion. This study contributes to establishing a firm basis for decision-makers to enhance coastal groundwater management.

Combined effects of layered heterogeneity and cutoff wall on groundwater salinization caused by storm surge inundation: Numerical simulations

Layered heterogeneity and cutoff wall may exacerbate storm surge-induced salinization of coastal groundwater. Earlier studies focused on the separate effects of layered heterogeneity or cutoff wall on aquifer recovery after storm surge events. However, their combined effect on aquifer recovery after a single storm surge event remains unclear. This problem was addressed numerically based on a coastal aquifer with typical stratified heterogeneity (i.e., the presence of a low-permeability layer (LPL) between two high-permeability layers). The results show that the total amount of saltwater intrusion is significantly reduced by the combined effect of LPL and cutoff wall; however, the natural recovery capacity of the aquifer will be weakened. As the depth of cutoff wall increases, the total amount of saltwater intruding into aquifer and the recovery time of aquifer (Tre) decreases stepwise, while the maximum salinized extent shows a nonmonotonic upward trend. If the base of cutoff wall locates within LPL, the salinization of aquifer changed non-monotonically as the distance between cutoff wall and ocean increases, but Tre shows an overall decreasing trend. Maximum salinized extent and saltwater intrusion mass decrease monotonically with increasing LPL thickness, but there is a non-monotonic relationship between Tre and LPL thickness. The maximum salinized extent and saltwater intrusion mass changed non-monotonically with LPL elevation, and Tre shows a non-monotonic upward trend. The study also found that a decrease in the hydraulic conductivity of LPL does not necessarily lead to an increase in Tre. This study has important implications for freshwater management and cutoff wall construction in coastal aquifers facing the risk of ocean-surge inundation.

Combined effects of river hydromorphological disturbances on macroinvertebrate communities: Multispatial scales analysis of central European rivers

Hydro-morphological threats impact the natural physical characteristics of river ecosystems, such as flow regimes, sediment transport, and channel morphology. These negative effects can occur at multiple scales, ranging from local microhabitats to geographic regions. Understanding these interactions can be useful for an integrated conservation approach and is needed for effective freshwater management. The aim of the study was to elucidate the combined effects of hydro-morphological threats on macroinvertebrates at three spatial scales: macroscale, including whole catchments, mesoscale (hydro-morphological changes in individual river sections) and the microscale, describing the microhabitat conditions of European rivers. The diversity and trophic structure of 1120 local macroinvertebrate communities in 28 catchments of various hydro-morphological disturbance levels, ranging from 0 to 2400 m asl, were analyzed. The response of macroinvertebrates to the main disturbance gradient differed between mountain and lowland communities. Random forest analysis indicated that the most important predictor of the ecological, diversity, and trophic indices was described by flow rate reduction. Generalized additive mixed models showed that decreased flow combined with river incision explained most of the variation in macroinvertebrate indices. Our results emphasize that based on multi-spatial scale analysis, hydro-morphological threats are very important factors in invertebrates biodiversity loss. Thus, to implement effective river management, we should pay more attention to the combined effects of geomorphological threats.

European water frame directive ecoregions do not adequately represent freshwater fish biogeography

The quest to understand species' distribution patterns and delineate their limits has led to the establishment of the world's ecoregions, large units of land containing a distinct assemblage of species, both for terrestrial and marine ecosystems. However, freshwaters constitute their own special case within terrestrial ecosystems, and have only recently been divided into freshwater ecoregions, primarily based on watershed limits. Freshwater ecoregions used by the European Water Frame Directive (WFD), which guides freshwater management policies in the European Union, have been criticized for not adequately representing freshwater fish biogeography. This study compares the geographic agreement between WFD ecoregions and freshwater fish distribution at the European scale. Using IUCN Red List distribution maps, we determined the composition of freshwater fish communities in major European basins. Then, we calculated a similarity matrix in order to cluster freshwater basins with more related fish assemblages. We compare our findings with WFD ecoregions and global ecoregions from the Freshwater Ecoregions of the World (FEOW) database. Our results reveal that WFD ecoregions do not sufficiently capture freshwater fish assemblage differences across Europe. Mediterranean basins exhibit high freshwater fish endemism and greater species variation, whereas central European basins harbor more similar fauna. Overall, our results align more with those of FEOW. To enhance the relevance of freshwater ecoregions in Europe for management and conservation, we propose several measures to ensure a comprehensive study involving all stakeholders in the process of defining these ecoregions accurately.

The Source-to-Sea Landscape: A hybrid integrative territory management approach

Whether fresh or salty, water is a unique resource, a continuum interlinked by the hydrological cycle. It forms a complex system connected to the landscape. When the landscape is altered, water flows and their benefits are impacted. Degraded land compromises water resources. The governance and management of landscape and water resources are handled in a fragmented manner and in separate contexts. The Source-to-Sea approach offers an integrative vision based on systems thinking that focuses its concerns on the interaction among parts, flows, and processes. It proposes a framework for the governance and management of freshwater and marine water but does not bring the landscape into the context of the approach. This research used an analytical-deductive method to explore the interactions and connections between the Source-to-sea approach, landscape concepts and approaches, and the guidelines of the European Landscape Convention. The main objective was to identify and assess the feasibility of integrating these elements. The integration resulted in a governance and management approach termed the S2S Landscape approach. It is grounded in systems thinking, practical learning, active participation, and adaptive governance and management, providing an integrated vision between landscape and water. The approach includes four essential steps (Comprehension, Involvement, Planning, and Execution and Monitoring) that address the complex connections that freshwater and marine water maintain in the landscape, considering physical, biological, socio-environmental, and economic aspects across all segments, from the land to the open sea. This S2S Landscape approach may be the path to address the challenges of governance and sustainable management of resources in an interconnected and constantly changing world.

Identifying minimum freshwater habitat conditions for an endangered fish using life cycle analysis

AbstractIdentifying the most important factors affecting population growth in animal life cycles is an important tool of species conservation. Delta Smelt (Hypomesus transpacificus), an annual fish endemic to the San Francisco Estuary in California (USA), has been provided legal protection since 1993 but 30 years later exists in a conservation‐reliant state on the brink of extinction. Despite considerable controversies about what factors are most responsible for the species' decline, no population growth rate sensitivity comparisons between the most important factors regulating growth have been done. Nor has anyone attempted to quantitatively identify habitat conditions needed to support positive population growth. We developed a set of stage‐structured population models to link habitat indices regulating recruitment of new generations of fish as they metamorphosed into juveniles and the subsequent survival of those fish over several seasons until they reached adulthood. These models are used to quantify drivers of growth rate variation over 30 years. Several complimentary sensitivity analyses indicated freshwater outflow to the estuary during summer had the largest potential to change population growth. Multiple habitat metrics (e.g., food availability, temperature) influencing recruitment and life stage specific survival rates across different seasons interacted in nonlinear ways to determine habitat conditions and water management targets associated with positive population growth. We discuss the implications for freshwater management, Delta Smelt conservation, and the challenges climate change poses for co‐implementation of these two societal priorities.

A multifunctional desalination-osmotic energy storage (DOES) system for managing energy and water supply

Net-zero carbon emission target for mitigating climate change accelerates the exploitation of renewable energy, such as solar and wind, as power origin in utilities sector. However, the intermittency of renewable energy escalates the supply-demand mismatch in not only electricity sector but also water sector, as freshwater supply increasingly relies on unconventional, energy-intensive desalination that is increasingly powered by renewables. To enhance the energy-water resilience, we propose a desalination-osmotic energy storage (DOES) system, which alternates the operation of reverse osmosis (RO) for desalination and pressure retarded osmosis (PRO) for electricity generation, achieving multiple functions including freshwater production and storage, grid energy storage, and eventually bulk-scale management of freshwater and energy supply. Via innovative system design and operation integrating semi-closed (SC) and closed-circuit (CC) configurations in RO and PRO modes in the proposed DOES, energy loss arising from over-pressurization in RO and under-pressurization in PRO could be substantially reduced. As a result, DOES can achieve practical maximum energy efficiencies of >75 % for both RO desalination and PRO electricity generation, and a round-trip efficiency of >68 % when used as a grid-scale energy storage system (ESS). Apart from the quantitative analysis of energy performance, a qualitative comparison of various other performance metrics between DOES and other grid ESSs is also conducted. Given its various performance advantages as well as multi-functionality, the DOES system could be an important complement to, though not replacement of, existing grid-scale ESSs.

Heterogeneity in post-fire thermal responses across Pacific Northwest streams: A multi-site study

Over the past century, water temperatures in many streams across the Pacific Northwest (PNW) have steadily risen, shrinking endangered salmonid habitats. The warming of PNW stream reaches can be further accelerated by wildfires burning forest stands that provide shade to streams. However, previous research on the effect of wildfires on stream water temperatures has focused on individual streams or burn events, limiting our understanding of the diversity in post-fire thermal responses across PNW streams. To bridge this knowledge gap, we assessed the impact of wildfires on daily summer water temperatures across 31 PNW stream sites, where 10–100% of their riparian area burned. To ensure robustness of our results, we employed multiple approaches to characterize and quantify fire effects on post-fire stream water temperature changes.Averaged across the 31 burned sites, wildfires corresponded to a 0.3 – 1°C increase in daily summer water temperatures over the subsequent three years. Nonetheless, post-fire summer thermal responses displayed extensive heterogeneity across burned sites where the likelihood and rate of a post-fire summer water temperature warming was higher for stream sites with greater proportion of their riparian area burned under high severity. Also, watershed features such as basin area, post-fire weather, bedrock permeability, pre-fire riparian forest cover, and winter snowpack depth were identified as strong predictors of the post-fire summer water temperature responses across burned sites. Our study offers a multi-site perspective on the effect of wildfires on summer stream temperatures in the PNW, providing insights that can inform freshwater management efforts beyond individual streams and basins.

Investigating the occurrence of flow instabilities in coastal unconfined aquifers using sand tank experiments

Subterranean estuaries form the land-sea transition zone in coastal aquifers and are relevant for coastal freshwater management and coastal ecology. Tidal fluctuations typically lead to the formation of upper saline plumes, where denser saltwater circulates on top of the discharging, less dense freshwater. Extensive numerical simulations and only a few experimental trials previously demonstrated that these saline plumes may become unstable and exhibit salt fingering flow. This work used laboratory sand tank experiments to study the formation and evolution of tide induced flow instabilities in homogenous, unconfined coastal aquifers in a systematic manner, addressing the combined effects of relevant parameters such as sediment type, beach slope, fresh groundwater inflow, tidal amplitude, and tidal period variation. Some of these parameters have never been targeted in laboratory-based studies before and a comparable systematic and comprehensive approach has so far not been conducted. The resulting flow patterns were studied visually through the application of a colour tracer to the saltwater. The results show that the upper saline plume may be stable, unstable, or transitional, whereby the beach slope predominantly defines its state. When salt fingers form, they amplify the mixing zone between ground- and saltwater and force the freshwater to discharge at multiple locations along the beach. The processes were best visible in the coarsest sediment (1.02 × 10-2 m s−1). The finer grained the sediment was, the smaller the upper saline plume that formed. The present study further reveals the possibility of three-dimensional fingering flow, even though the physical model was intended to represent a two-dimensional cross-section. The application of a previously proposed non-dimensional stability diagram yielded reasonably accurate predictions of stability behaviour in coastal unconfined aquifers under laboratory settings. This further supports the plausibility of flow instabilities in subterranean estuaries within specific ranges of influencing hydrogeological factors.

Protecting and restoring freshwater biodiversity across urban areas in Aotearoa New Zealand: Citizens’ reporting of pollution in stormwater drains and waterways

Urbanization poses numerous challenges to freshwater biodiversity. This paper describes two studies with the joint aim of demonstrating the benefits of applying a systematic behaviour change framework and providing the foundational knowledge to inform future behavior change work to protect and restore urban freshwater biodiversity. In Study 1 we used a mixed-methods research design, involving 14 key informant interviews followed by an online survey targeting 17 freshwater biodiversity experts and another targeting a representative sample of 550 urban residents, to identify and prioritize the most promising resident behaviors to target to reduce stormwater pollution and improve natural waterway habitats in urban areas. Study 2 focused on the top-ranked short-term behavior identified in Study 1, citizen reporting of pollution in stormwater drains and waterways. We surveyed a representative sample of 1901 urban residents across Aoteraoa New Zealand to identify four main determinants influencing this behavior: awareness and uncertainty about reporting, lack of opportunity to report, social motivation and personal motivation to report, and five potential target audiences: ‘Supportive’, ‘Unaware but receptive’, ‘Motivated but lack support’, ‘Reluctant’, and ‘Not my problem’. We make recommendations for the most appropriate intervention designs to target each of these audience segments to promote the reporting of stormwater pollution in urban areas. This knowledge will allow for a more coordinated and effective approach for addressing the ‘human element’ that lies at the heart of many urban freshwater management problems.

Upstream water management and its role in estuary health, evaluation of freshwater management and subtropical estuary function

In highly modified and managed systems the balance of freshwater inputs discharged to estuarine systems are important to maintain salinity balances and thus estuarine function. However, the availability of freshwater is highly dependent on upstream water management to provide flood protection whilst meeting freshwater demand for people and the environment. In South Florida, water is managed by a water control plan with Lake Okeechobee at the center. Currently, water levels within the lake are managed based on the Lake Okeechobee Regulation Schedule of 2008. The new regulation schedule, Lake Okeechobee System Operating Manual (LOSOM), updates water management rules while attempting to balance the needs of downstream systems; salinity and water quality in the Caloosahatchee and Saint Lucie (northern) estuaries; and more water for the southern Everglades. This study evaluates LOSOM relative to ecologically significant performance measures for the northern estuaries. Overall, the proposed regulation schedule is expected to provide a more sustainable flow regime to the estuaries by reducing stressful and damaging discharge events. Moreover, new management rules combined with new infrastructure are expected to reduce low discharge events to the Caloosahatchee estuary and reduce stress on key indicator species such as Vallisneria americana during the wet season. This regulation schedule provides improved conditions for the estuaries at the expense of higher Lake Okeechobee stages. Future restoration and water management will maintain the benefits afforded to the estuaries while at the same time reducing the impacts to Lake Okeechobee resulting in a more sustainable and resilient system.

Fresh water management in coastal Bangladesh: preparedness and adaptation

Water management is very significant because of changing the pattern of rainfall, seasonal variation of rainfall, sea level rising, water consumption pattern, acceleration of water quality and unavailability of fresh water in the coastal areas of Bangladesh due to adverse impacts of natural calamities. The aims were to investigate fresh water management with preparedness and adaptation strategies. Household data were collected from respective union parisad and total 338 households (out of 2789) were determined considering 95% significance level from three shoreline (Bagerhat), interim (Khulna) and inland (Satkhira) coastal regions of Bangladesh which distributed proportionately. Data were collected with self-administrated semi-structured questionnaire and three FGDs and analyzed with SPSS. Map was drawn by Arc GIS software. The study resulted that plastic bottle was dominantly used as conservation system for drinking (58.28%) and rainwater (44.08%). Besides, plastic drum, silver pots, earthen and ferro cement container were also used to conserve water. The mean weighted average index of preparedness of household and homestead agriculture is moderate (0.332) in inland and poor in shoreline (0.313) and interim (0.309) area. About 25.15% households satisfied with current water supply system. Individually, about 65.76% respondents adopted pond sand filter technology in the shoreline, followed by 16.90% (interim) and 37.35% (inland) area. Other adaptation strategies (rainwater harvesting, pond water conservation, potable jar water use, re-excavation of pond, boiling pond/canal water) were adopted by households and institutions with seasonal variations. Proper adaptation strategies should be taken with involving the local stakeholders for better performance in the study area.

Freshwater conservation: Lost in limnology?

Abstract Although scientific research has identified the causes of undesirable ecological changes in fresh waters, translating the results of research into practical conservation and management, and raising awareness of the need for action, is often inadequate. This Viewpoint considers the present coverage of conservation‐related freshwater research, the application of science to conservation, the extent of collaboration between international organizations, and the level of awareness of freshwater ecosystems and the need for their conservation. Far greater attention has been given to conservation in marine than freshwater areas. This is illustrated by the respective number of publications in the scientific literature, an imbalance in the UN Sustainable Development goals, and, until recently, the lack of an explicit reference to freshwater ecosystems in the UN Global Biodiversity Framework. Four case studies are presented as examples of how freshwater conservation can be made more effective: involving local communities in applying nature‐based solutions; bringing scientists and stakeholders together to discuss how to improve freshwater management; collaborating at a global scale in freshwater protection and restoration; and demonstrating how scientists and government can work together to reconcile the competing needs of nature and human society. Producing and implementing effective conservation and management plans needs a recognition of the extensive diversity of freshwater habitats and species, as well as a systematic evaluation of how scientific information can be translated into action at local, regional and global scales. Data on freshwater ecosystems need to be accessible, comprehensible, unambiguous and available to all those working on practical conservation projects. Many international organizations are already active in this field, but greater collaboration would make their work more effective. Raising awareness needs education and training, carefully targeted at a wide range of audiences, and communicated using the full range of media now available.

Phycoremediation - A Clean Technology for Water Pollution Abatement

Phycoremediation has been utilised to remediate wastewater and successfully lower nutrient levels. There isn’t many research, though, on how well phycoremediation works to lower nitrogen levels in eutrophic lakes. This review concentrates on the process and variables involved in using algae. Before considering the possibility of algal-based approaches in remediating lake eutrophication, to remove nutrients and contaminants from wastewater. Algal biofilm, algal grass scrubbers, high-rate algal ponds (HRAP), and immobilised algae are methods used in phycoremediation of wastewater. A wastewater treatment method based on microalgae lowers BOD, prevents coli forms, eliminates pollutants and nutrients, and removes heavy metals. The sixth sustainable development target of the UNDP cannot be attained without phytoremediation. Microalgae can effectively treat wastewater at a very low cost, and the biomass they produce can be used to produce biofuels. The cost-effective growing of microalgae and contaminants with wastewater can be replaced by the successful coupling of microalgae with wastewater, which can also scale up production of high-value products. This review mainly focused on the potential of algae and their specific mechanisms involved in wastewater treatment and energy recovery systems leading to important industrial precursors. The review is highly beneficial for scientists, wastewater treatment plant operators, freshwater managers, and industrial communities to support the sustainable development of natural resources. Keywords: Algae, Biodegradation, Pollutant removal, Phycoremediation, Wastewater treatment.

Sustainable Water Management with Design and Economic Evaluation of Recycling Greywater at Abu Dhabi University—A Case Study on Decentralization

Wastewater can be segregated as greywater and blackwater separately. The greywater generated in malls, restaurants, and university buildings is generally dilute, while it will later become concentrated when it is merged into the main sewage collection line. It would be more economical and environmentally friendly if the greywater is treated locally using a modular wastewater treatment facility that produces treated water amenable for other uses such as irrigation or horticulture. The objective of this article is to study the economic feasibility and design a decentralized plant that produces fresh water from greywater generated at the Abu Dhabi university campus located in the United Arab Emirates. The proposed unit will consist of a compact design of filtration, chemical treatment and disinfection processes that would generate treated wastewater that can be used for horticulture in and around the local campus or can be stored and supplied for irrigation purposes. Several parameters such as total suspended solids, biological oxygen demand, and chemical oxygen demand are measured and monitored throughout the entire process and are regulated by appropriate operations performed for each unit. This study shows that decentralization of greywater treatment is not only economical but also essential for the management of fresh water, which in turn assures environmental sustainability. By using coagulation, flocculation and chlorination with a 30 mg/L alum dosage, 0.6 mg/L of polyacrylamide and 0.12 mg/L of sodium hypochlorite, respectively, greywater is treated to meet the water specification for reusing it for horticulture. Further, a modular plant with an investment of USD 8 M is proved to process 90,000 tons of greywater with a 34% discounted rate of return.

Dark waters: Evaluating seagrass community response to optical water quality and freshwater discharges in a highly managed subtropical estuary

Seagrass communities are vitally important ecosystems that support and foster organisms across trophic levels. Understanding the drivers of seagrass distribution and extent in estuary systems is valuable for conservation and restoration efforts. A critical driver of seagrass distribution is how light moves through the water column (i.e. light attenuation) and the availability of light to reach the estuary bottom. Light attenuation combined with the depth of seagrass colonization is used to estimate the percent surface irradiance and is an indicator of seagrass light requirements The objective of this study was to evaluate optical water quality parameters within the Caloosahatchee River Estuary (CRE) relative to changes in freshwater discharge conditions. During the study period, freshwater discharge significantly increased resulting in an increase of annual stressful and damaging discharge events to marine seagrass species. Concurrent with changes in freshwater discharge conditions, changes to optical water quality parameters including color, chlorophyll-a, total suspended solids, and light attenuation were detected along the estuary. Using photo-interpreted seagrass coverage data combined with bathymetric data, the depth of colonization was estimated for three survey years (2008, 2014, and 2020). This information combined with a spatial and temporal light attenuation generalized additive model percent surface irradiance (%SI) was estimated. Over the study period, %SI significantly increased across the lower CRE indicating an improvement in light attenuation. The current freshwater management plan has increased stressful and damaging discharge events, however recent changes in operations has minimized these damaging events which could be linked to the precipitous increase in %SI across the lower CRE. Seagrass density data collected from transects within the estuary suggest that prolonged stress and damaging (>5.13 hm3d−1) has significantly reduce species density. Future water management strategies are expected to reduce the frequency and volume of discharges to the CRE, effectively reducing stress and damaging freshwater discharge event.

Detecting changes in fish behaviour in real time to alert managers to thresholds of potential concern

AbstractFish behaviour is one biological organisational level regularly used to assess the state of freshwater ecosystems and can be monitored using fish telemetry methods. The development of activity sensors incorporated into fish telemetered tags allows for non‐spatial movement to be detected and is increasingly used to understand the energy budgets and response and fine‐scale behaviour of fishes. In addition, detecting tagged fish remotely and in real time highlights the need to process fish activity data in near real time to make it relevant to managers in the water resource sector. Our study on Labeobarbus natalensis, a cyprinid, in the uMngeni River in KwaZulu‐Natal, South Africa, adapted and then tested the exponentially weighted moving average (EWMA), as developed for financial predictive modelling, using activity data from fish. To determine changes in behaviour, we compared the EWMA‐predicted fish behaviour against the present fish behaviour. We showed that the EWMA could adequately detect changes in behaviour on both individual and population levels. Changes in behaviour are potentially indicative of a change in environmental conditions and thus were developed into management alerts. We conducted further analyses using generalised additive mixed models (GAMM) to determine the relationship between fish activity and the environmental data collected. The GAMMs helped determine the potential drivers for changes in behaviour where the EWMA could detect these in real time. Detecting changes in behaviour in real time as a result of environmental variables can identify thresholds of potential concern influencing management decisions and allow managers to respond, contributing to improving effective freshwater management.

Nitrate prediction in groundwater of data scarce regions: The futuristic fresh-water management outlook

Nitrate contamination in groundwater poses a significant threat to water quality and public health, especially in regions with limited data availability. This study addresses this challenge by employing machine learning (ML) techniques to predict nitrate (NO3−-N) concentrations in Mexico's groundwater. Four ML algorithms—Extreme Gradient Boosting (XGB), Boosted Regression Trees (BRT), Random Forest (RF), and Support Vector Machines (SVM)—were executed to model NO3−-N concentrations across the country. Despite data limitations, the ML models achieved robust predictive performances. XGB and BRT algorithms demonstrated superior accuracy (0.80 and 0.78, respectively). Notably, this was achieved using ∼10 times less information than previous large-scale assessments. The novelty lies in the first-ever implementation of the ‘Support Points-based Split Approach’ during data pre-processing. The models considered initially 68 covariates and identified 13–19 significant predictors of NO3−-N concentration spanning from climate, geomorphology, soil, hydrogeology, and human factors. Rainfall, elevation, and slope emerged as key predictors. A validation incorporated nationwide waste disposal sites, yielding an encouraging correlation. Spatial risk mapping unveiled significant pollution hotspots across Mexico. Regions with elevated NO3−-N concentrations (>10 mg/L) were identified, particularly in the north-central and northeast parts of the country, associated with agricultural and industrial activities. Approximately 21 million people, accounting for 10 % of Mexico's population, are potentially exposed to elevated NO3−-N levels in groundwater. Moreover, the NO3−-N hotspots align with reported NO3−-N health implications such as gastric and colorectal cancer. This study not only demonstrates the potential of ML in data-scarce regions but also offers actionable insights for policy and management strategies. Our research underscores the urgency of implementing sustainable agricultural practices and comprehensive domestic waste management measures to mitigate NO3−-N contamination. Moreover, it advocates for the establishment of effective policies based on real-time monitoring and collaboration among stakeholders.