Vulnerable Waters are Essential to Watershed Resilience

Water quality improves with increased spatially surface hydrological connectivity in plain river network areas

Hydrological connectivity remarkably affects the water quality of river-lake systems, particularly in densely urbanized plain river network areas, where its impact remains unclear. The growing urbanization and rapid changes in hydrological networks make it more challenging to manage water quality effectively. Understanding how hydrological connectivity changes and the influence on key water quality variables is crucial for improving management strategies. We quantified hydrological connectivity between lakes in the northern Taihu Lake Basin using a connectivity topological model based on graph theory and landscape ecology. XG-Boost models were developed to elucidate the potential threshold effect of hydrological connectivity on key water quality parameters. These models were accompanied by linear mixed-effect (LME) models, which included land use types as a random effect to evaluate the response relationship between hydrological connectivity and water quality. Results indicated that the spatiotemporal dynamics of hydrological connectivity decreased over the last 20 years. Furthermore, changes in hydrological connectivity considerably influenced environmental variables in river-lake network areas. The XG-Boost models identified a Pij value of 0.02 as a potential threshold, at which spatial hydrological connectivity begins to impact water quality as concentrations change steadily above this threshold. The LME models confirmed that enhanced spatial hydrological connectivity was generally associated with reduced concentrations of TN, TP, NH3-N, and CODMn, and increased DO levels. In addition, hydrological connectivity was influenced by factors such as the shortest river path between lakes and hydraulic facilities along the path. This finding suggests that hydrological connectivity can be restored to improve water quality by refining river network topology, optimizing existing sluice schedules, or removing unnecessary dikes. These results highlight the potential of hydrological connectivity optimization to support water quality improvement strategies in complex urban river networks.

Factors Regulating the Potential for Freshwater Mineral Soil Wetlands to Function as Natural Climate Solutions

There are increasing global efforts and initiatives aiming to tackle climate change and mitigate its impacts via natural climate solutions (NCS). Wetlands have been considered effective NCS given their capacity to sequester and retain atmospheric carbon dioxide (CO2) while also providing a myriad of other ecosystem functions that can assist in mitigating the impacts of climate change. However, wetlands have a dual impact on climate, influencing the atmospheric concentrations of both CO2 and methane (CH4). The cooling effect associated with wetland CO2 sequestration can be counterbalanced by the warming effect caused by CH4 emissions from wetlands. The relative ability of wetlands to sequester CO2 versus emit CH4 is dependent on a suite of interacting physical, chemical, and biological factors, making it difficult to determine if/which wetlands are considered important NCS. The fact that wetlands are embedded in landscapes with surface and subsurface hydrological connections to other wetlands (i.e., wetlandscapes) that flow over and through geochemically active soils and sediments adds a new layer of complexity and poses further challenges to understanding wetland carbon sequestration and greenhouse gas fluxes at large spatial scales. Our review demonstrates how additional scientific advances are required to understand the driving mechanisms associated with wetland carbon cycling under different environmental conditions. It is vital to understand wetland functionality at both wetland and wetlandscape scales to effectively implement wetlands as NCS to maximize ecological, social, and economic benefits.

Ecological health and security of the Jazmurian Wetland Endorheic Watershed, Iran

Wetlands represent a crucial category of aquatic ecosystems that face numerous threats, such as increasing population density, alterations in land-use, climate change, excessive extraction of water resources, and inadequate construction of reservoirs. As a result of these challenges, wetlands cannot perform their essential functions, which include meeting human demands, supporting tourism, mitigating dust storms, and maintaining the biodiversity of flora and fauna. Accordingly, assessing their health and service performance is essential. However, studies on the health and security assessment of the wetland are scant. Therefore, an attempt has been made to evaluate the Jazmurian Wetland Watershed health using the cause-effect pressure (P), state (S), and response (R) conceptual approach. To this end, the problem-oriented variables were obtained through field surveying and data augmentation. Some 12 independent input variables were finalized using principal component analysis (PCA) to assess the watershed health and security at the sub-watershed scale. The study's results elucidated that P = 0.564, S = 0.368, and R = 0.643 were classified in moderate class with negative orientation, relatively desirable with negative inclination, and high with negative tendency, respectively. The overall weighted health and security indices for the Jazmurian Wetland Watershed were 0.504 and 0.446, classifying in moderate conditions with a slight positive tendency. Accordingly, an insight focused on controlling the most influential variables in the P and S indices and pertaining existing conditions on the R index-related factors in priority sub-watersheds is a vital task to take toward ecosystem sustainability. Considering the fragile health and security of the Jazmurian Wetland Watershed, management actions need to be incorporated to prevent further decline and perpetuation of situations in the region.

Inconsistent Regulatory Mapping Quietly Threatens Rivers and Streams

Even the most stringent environmental law cannot protect a river if its tributaries remain exposed to pollution and other threats upstream. Excluding a subset of watercourses from legal protection therefore threatens to alter freshwater ecosystems across entire river networks and the services they provide, such as drinking water and flood regulation. Considerable attention has been devoted to defining the scope of environmental laws protecting watercourses. Yet how these definitions are implemented through regulatory mapping, the cartography of waterbodies that legally qualify as watercourses and are thus protected, has not been examined outside of the United States. Here, we demonstrate the consequences of regulatory mapping on the extent of river networks that are protected, using France as a case study. By assembling the first map of France's watercourses protected under the Water Law, we estimate that a quarter of previously mapped hydrographic segments were excluded from protection and found stark geographical variations in the extent of protected ecosystems. Headwater and nonperennial segments are disproportionately excluded by 28% compared to their prevalence (67%) in the overall hydrographic network, with potentially far-reaching implications for biodiversity and people. We expect regulatory frameworks in most countries to be equally susceptible to local interpretation of legal definitions.

How wet must a wetland be to have federal protections in post-Sackett US?

In 2023, the US Supreme Court's majority ruled in Sackett v. Environmental Protection Agency that only wetlands that are "indistinguishable" from federally protected waters "due to a continuous surface connection" are federally protected. This study estimates the potential impact of interpretations of the ruling on federal wetlands protections, using a qualitative measure of wetland "wetness" as a proxy for the new requirement. An estimated area ranging from ~17 million acres (19%) to nearly all 90 million acres of nontidal wetlands in the conterminous United States could be without federal protections, and variability in state protections creates hotspots of risk. The high-level estimates provided here represent a first step toward understanding the long-term impacts of Sackett v. Environmental Protection Agency on federal wetlands protections and highlight the uncertainty introduced by the ruling.

Drainage network dynamics in an agricultural headwater sub-basin

Headwaters provide many ecosystems services. Currently, these vulnerable systems are subject to threats related to human activities. This work aims to analyse the spatial pattern changes (expansion/contraction) in the drainage network (DN) of a headwater sub-basin under agriculture between 1966 and 2019 in the Argentine Pampas Region. We study and discuss the hydrometeorological and land use context to understand the spatial and temporal dynamics of the DN, and propose a conceptual model that synthesizes the complex interactions between the factors involved in that dynamics. A broad (1950-2019, at the Del Azul Creek basin) and a short (1996-2019, at the sub-basin of the Videla Creek -SVC-) temporal and spatial scale analysis of data were carried out. We studied rainfall, evapotranspiration, water table depth, streamflow and land use. Temporal and spatial changes in the DN of the SVC were analysed by aerial photos and historical satellite images. Four wet and three dry periods were identified, and close surface-subsurface water interactions typical of plains, were found. The area under agriculture showed a first gradual increase (1975-2012), which turned sharp from 2012 (30,908 ha year-1), with a leading role of soybeans' sown area. The area of the DN increased 1.4699*105 m2 between 1966 and 2010, both under dry conditions, which evidenced its expansion. The study of the flatlands' particular hydrology within the current land use and management trends provided key elements to understand DN area's changes. Complex interactions between processes associated with climatic forcing and the system's sensitivity (its state to receive and process the inputs), are involved in the spatial and temporal dynamics of the DN. Our work improves the understanding of the functioning of these vulnerable systems within agricultural areas, nowadays under productive pressures associated with increasing global food demand, and threats to changes in the hydrological dynamics by global change.

Improving ecosystem health in highly altered river basins: a generalized framework and its application to the Mississippi-Atchafalaya River Basin

Continued large-scale public investment in declining ecosystems depends on demonstrations of "success". While the public conception of "success" often focuses on restoration to a pre-disturbance condition, the scientific community is more likely to measure success in terms of improved ecosystem health. Using a combination of literature review, workshops and expert solicitation we propose a generalized framework to improve ecosystem health in highly altered river basins by reducing ecosystem stressors, enhancing ecosystem processes and increasing ecosystem resilience. We illustrate the use of this framework in the Mississippi-Atchafalaya River Basin (MARB) of the central United States (U.S.), by (i) identifying key stressors related to human activities, and (ii) creating a conceptual ecosystem model relating those stressors to effects on ecosystem structure and processes. As a result of our analysis, we identify a set of landscape-level indicators of ecosystem health, emphasizing leading indicators of stressor removal (e.g., reduced anthropogenic nutrient inputs), increased ecosystem function (e.g., increased water storage in the landscape) and increased resilience (e.g., changes in the percentage of perennial vegetative cover). We suggest that by including these indicators, along with lagging indicators such as direct measurements of water quality, stakeholders will be better able to assess the effectiveness of management actions. For example, if both leading and lagging indicators show improvement over time, then management actions are on track to attain desired ecosystem condition. If, however, leading indicators are not improving or even declining, then fundamental challenges to ecosystem health remain to be addressed and failure to address these will ultimately lead to declines in lagging indicators such as water quality. Although our model and indicators are specific to the MARB, we believe that the generalized framework and the process of model and indicator development will be valuable in an array of altered river basins.

Effects of urbanization and accessibility to sanitation services on water quality in urban streams in Uruguay

The world's urban population is growing rapidly, and threatening natural ecosystems, especially streams. Urbanization leads to stream alterations, increased peak flow frequencies, and reduced water quality due to pollutants, morphological changes, and biodiversity loss, known as the urban stream syndrome. However, a shift towards recognizing urban streams as valuable natural systems is occurring, emphasizing green infrastructure and nature-based solutions. This study in Uruguay examined water quality in various watersheds with different urbanization levels and socio-environmental characteristics along a precipitation gradient. Using Geographic Information Systems (GIS) and in situ data, we assessed physicochemical parameters, generated territorial variables, and identified key predictors of water quality. We found that urbanization, particularly urban areas, paved areas, and populations without sanitation, significantly influenced water quality parameters. These factors explained over 50% of the variation in water quality indicators. However, the relationship between urbanization and water quality was non-linear, with abrupt declines after specific urban intensity thresholds. Our results illustrate that ensuring sanitation networks and managing green areas effectively are essential for preserving urban stream water quality. This research underscores the importance of interdisciplinary teams and localized data for informed freshwater resource management.

Towards implementing precision conservation practices in agricultural watersheds: A review of the use and prospects of spatial decision support systems and tools

Agricultural nonpoint source (NPS) pollution leads to water quality degradation. While agriculture is faced with the challenge of feeding a growing population in a changing climate, farmers must also strive to minimize adverse impacts of agriculture on the environment. As a result, policies, and agri-environmental programs to promote agricultural conservation practices for controlling NPS pollution have been emerging. Despite progress, reducing NPS is a complex challenge that requires ongoing innovation and investment. A major challenge is to achieve an optimal spatial trade-off between the economic costs and positive environmental outcomes of conservation practices on complex agricultural landscapes. Geospatial systems and tools can help to address this challenge and enhance the effectiveness and efficiency of conservation efforts. However, using these tools for precision conservation is underexamined. This review paper aims to address this gap through a critical exploration of spatial decision support systems and tools to provide synthesized knowledge for implementing precision conservation practices. This paper proposes a conceptual framework to guide the implementation of precision conservation and identifies areas for further development of geospatial systems and tools on planning and assessment of precision conservation efforts. All of which will be helpful for decision-makers and watershed managers in determining the most effective approaches for precision conservation. Furthermore, this review highlights the need for further research and development towards establishing an integrated spatial decision support system framework, which can improve socio-economic, environmental, and ecological outcomes.

Mapping global non-floodplain wetlands

Non-floodplain wetlands - those located outside the floodplains - have emerged as integral components to watershed resilience, contributing hydrologic and biogeochemical functions affecting watershed-scale flooding extent, drought magnitude, and water-quality maintenance. However, the absence of a global dataset of non-floodplain wetlands limits their necessary incorporation into water quality and quantity management decisions and affects wetland-focused wildlife habitat conservation outcomes. We addressed this critical need by developing a publicly available "Global NFW" (Non-Floodplain Wetland) dataset, comprised of a global river-floodplain map at 90 m resolution coupled with a global ensemble wetland map incorporating multiple wetland-focused data layers. The floodplain, wetland, and non-floodplain wetland spatial data developed here were successfully validated within 21 large and heterogenous basins across the conterminous United States. We identified nearly 33 million potential non-floodplain wetlands with an estimated global extent of over 16×106 km2. Non-floodplain wetland pixels comprised 53% of globally identified wetland pixels, meaning the majority of the globe's wetlands likely occur external to river floodplains and coastal habitats. The identified global NFWs were typically small (median 0.039 km2), with a global median size ranging from 0.018-0.138 km2. This novel geospatial Global NFW static dataset advances wetland conservation and resource-management goals while providing a foundation for global non-floodplain wetland functional assessments, facilitating non-floodplain wetland inclusion in hydrological, biogeochemical, and biological model development. The data are freely available through the United States Environmental Protection Agency's Environmental Dataset Gateway (https://gaftp.epa.gov/EPADataCommons/ORD/Global_NonFloodplain_Wetlands/, last access: 24 May 2023) and through https://doi.org/10.23719/1528331 (Lane et al., 2023a).

Water availability and seasonality shape elemental stoichiometry across space and time

The interaction of climate change and increasing anthropogenic water withdrawals is anticipated to alter surface water availability and the transport of carbon (C), nitrogen (N), and phosphorus (P) in river networks. But how changes to river flow will alter the balance, or stoichiometry, of these fluxes is unknown. The Lower Flint River Basin (LFRB) is part of an interstate watershed relied upon by several million people for diverse ecosystem services, including seasonal crop irrigation, municipal drinking water access, and public recreation. Recently, increased water demand compounded with intensified droughts have caused historically perennial streams in the LFRB to cease flowing, increasing ecosystem vulnerability. Our objectives were to quantify how riverine dissolved C:N:P varies spatially and seasonally and determine how monthly stoichiometric fluxes varied with overall water availability in a major tributary of LFRB. We used a long-term record (21-29 years) of solute water chemistry (dissolved organic carbon, nitrate/nitrite, ammonia, and soluble reactive phosphorus) paired with long-term stream discharge data across six sites within a single LFRB watershed. We found spatial and seasonal differences in soluble nutrient concentrations and stoichiometry attributable to groundwater connections, the presence of a major floodplain wetland, and flow conditions. Further, we showed that water availability, as indicated by the Palmer Drought Severity Index (PDSI), strongly predicted stoichiometry with generally lower C:N and C:P and higher N:P fluxes during periods of low water availability (PDSI < -4). These patterns suggest there may be long-term and significant changes to stream ecosystem function as water availability is being dramatically altered by human demand with consequential impacts on solute transport, in-stream processing, and stoichiometric ratios.

National hydrologic connectivity classification links wetlands with stream water quality

Wetland hydrologic connections to downstream waters influence stream water quality. However, no systematic approach for characterizing this connectivity exists. Here using physical principles, we categorized conterminous US freshwater wetlands into four hydrologic connectivity classes based on stream contact and flowpath depth to the nearest stream: riparian, non-riparian shallow, non-riparian mid-depth and non-riparian deep. These classes were heterogeneously distributed over the conterminous United States; for example, riparian dominated the south-eastern and Gulf coasts, while non-riparian deep dominated the Upper Midwest and High Plains. Analysis of a national stream dataset indicated acidification and organic matter brownification increased with connectivity. Eutrophication and sedimentation decreased with wetland area but did not respond to connectivity. This classification advances our mechanistic understanding of wetland influences on water quality nationally and could be applied globally.

Modeling the Territorial Structure Dynamics of the Northern Part of the Volga-Akhtuba Floodplain

The subject of our study is the tendency to reduce the floodplain area of regulated rivers and its impact on the degradation of the socio-environmental systems in the floodplain. The aim of the work is to create a new approach to the analysis and forecasting of the multidimensional degradation processes of floodplain territories under the influence of natural and technogenic factors. This approach uses methods of hydrodynamic and geoinformation modeling, statistical analysis of observational data and results of high-performance computational experiments. The basis of our approach is the dynamics model of the complex structure of the floodplain. This structure combines the characteristics of the frequency ranges of flooding and the socio-environmental features of various sites (cadastral data of land use). Modeling of the hydrological regime is based on numerical shallow water models. The regression model of the technogenic dynamics of the riverbed allowed us to calculate corrections to the parameters of real floods that imitate the effect of this factor. This made it possible to use digital maps of the modern topography for hydrodynamic modeling and the construction of floods maps for past and future decades. The technological basis of our study is a set of algorithms and software, consisting of three modules. The data module includes, first of all, the cadastres of the territory of the Volga-Akhtuba floodplain (VAF, this floodplain is the interfluve of the Volga and Akhtuba rivers for the last 400 km before flowing into the Caspian Sea), satellite and natural observation data, spatial distributions of parameters of geoinformation and hydrodynamic models. The second module provides the construction of a multilayer digital model of the floodplain area, digital maps of floods and their aggregated characteristics. The third module calculates a complex territorial structure, criteria for the state of the environmental and socio-economic system (ESES) and a forecast of its changes. We have shown that the degradation of the ESES of the northern part of the VAF is caused by the negative dynamics of the hydrological structure of its territory, due to the technogenic influence the hydroelectric power station on the Volga riverbed. This dynamic manifests itself in a decrease in the stable flooded area and an increase in the unflooded and unstable flooded areas. An important result is the forecast of the complex territorial structure and criteria for the state of the interfluve until 2050.