Water Quality Goals Research Articles

Paradox of lake nitrogen concentration change response to watershed management: Case study of China

Human activities have caused rapid increases in lake nutrient loads over the past few decades, resulting in severe eutrophication. To mitigate eutrophication in lakes, watershed management is conducted worldwide. After decades of watershed environmental management practices, some lakes have significantly improved in water quality, whereas others continue to deteriorate. Differentiations in watershed environmental management practices have been a conundrum for watershed managers for many years. This study analyzed over 20 years of nitrogen concentration data from 13 different types of lakes in China, exploring the driving forces behind water quality changes. The results showed that agricultural nitrogen management has emerged as a predominant driver of lake nitrogen concentration changes, with the impacts of climatic factors diminishing post-transition. Two obstacles hinder the achievement of water quality goals: time lags and climate change. The time lag between agricultural management measures and water quality improvements maybe decades. Meanwhile, climate change, especially extreme weather events, introduces uncertainties that may trigger short-term deterioration. Despite the uncertainty surrounding lake nitrogen concentration changes, lakes with advanced governance structures still exhibited greater resilience to climatic changes compared to those in the early stages of environmental management. To improve water quality, more efforts and patience are required.

Disentangling the contributions of anthropogenic nutrient input and physical forcing to long-term deoxygenation off the Pearl River Estuary, China

Deoxygenation in estuarine and coastal waters worldwide has been largely attributed to the increasing anthropogenic nutrient input, whereas the contribution by long-term (decadal) changes in physical forcing is less investigated. This study aims to disentangle the impacts of three-decade changes in summer river nutrient concentration and physical forcing on the deoxygenation off a large eutrophic estuary, the Pearl River Estuary (PRE) in China. Using a coupled physical-biogeochemical model, we reproduce the observed summer oxygen conditions under the historical (the 1990s) and present (the 2020s) status of river nutrient concentration, freshwater discharge, and wind forcing. We show that the bottom hypoxic (dissolved oxygen < 2 mg/L) area off the PRE in the 2020s has increased by 73 % relative to the 1990s. The expansion is a result of the increased bottom water oxygen consumption outweighing the enhanced vertical oxygen supply, with the former driven by the sharp increase in inorganic nitrogen and phosphorus concentrations (160 %) and the latter caused by the decadal decline in both freshwater discharge (38 %) and wind speed (12.5 %) in summer. Model experiments suggest that if the observed changes in physical forcing had not occurred, the dramatic increase in anthropogenic nutrient concentrations from the 1990s to 2020s could have led to a much greater expansion of hypoxic area (249 %). On the contrary, the decadal decrease in summer freshwater discharge alone (while keeping the nutrient loading the same as in the 1990s) almost eliminates hypoxia off the PRE by weakening water column stratification and limiting the offshore spread of nutrients and organic matter, whereas the declined wind speed increases the hypoxic area by 247 % mainly through enhancing water column stability. Our results reveal that long-term changes in physical forcing are confounding the effects of anthropogenic nutrient input on deoxygenation, underlining the need to consider regional forcing changes in nutrient management to meet water quality goals.

Do farmers prefer result-based, hybrid or practice-based agri-environmental schemes?

Abstract This study examines farmers’ preferences for practice-based, result-based and hybrid agri-environmental schemes in three countries through a choice experiment conducted by the Organization for Economic Cooperation and Development, focusing on biodiversity, climate and water quality. The results reveal that, in general, farmers tend to prefer practice-based schemes for water quality or climate change mitigation goals over hybrid or result-based schemes. Moreover, the study indicates that only a limited number of hybrid schemes are both preferred by farmers and more socially beneficial compared to equivalent practice- or result-based schemes. These conclusions are further reinforced by a cost-benefit analysis.

Complex hydrology and variability of nitrogen sources in a karst watershed.

Streams draining karst areas with rapid groundwater transit times may respond relatively quickly to nitrogen reduction strategies, but the complex hydrologic network of interconnected sinkholes and springs is challenging for determining the placement and effectiveness of management practices. This study aims to inform nitrogen reduction strategies in a representative agricultural karst setting of the Chesapeake Bay watershed (Fishing Creek watershed, Pennsylvania) with known elevated nitrate contamination and a previous documented groundwater residence time of less than a decade. During baseflow conditions, streamflow did not increase with drainage area. Headwaters and the main stem lost substantial flow to sinkholes until eventually discharging along large springs downstream. Seasonal hydrologic conditions shift the flow and nitrogen load spatially among losing and gaining stream sections. A compilation of nitrogen source inputs with the geochemistry and the pattern of enrichment of δ15N and δ18O suggest that the nitrogen in streams and springs during baseflow represents a mixture of manure, fertilizer, and wastewater sources with low potential for denitrification. The pH and calcite saturation index increased along generalized flow paths from headwaters to springs and indicate shorter groundwater residence times in baseflow during the spring versus summer. Given the substantial investment in management practices, fixed monitoring sites could incorporate synoptic water sampling to properly monitor long-term progress and help inform management actions in karst watersheds. Although karst watersheds have the potential to respond to nitrogen reduction strategies due to shorter groundwater residence times, high nitrogen inputs, effectiveness of conservation practices, and release of legacy nutrients within the karst cavities could confound progress of water quality goals.

Refining the Farm Aquaculture Resource Management Model for Shellfish Nitrogen Removal at the Local Scale

Nutrient-related environmental degradation in coastal waters is a continuing global problem. Bivalve shellfish farms show nutrient removal capabilities similar to some traditional management strategies and in some places have been incorporated into nutrient management programs to help achieve water quality goals. Bioextractive nutrient removal varies by farmed species and is influenced by environment parameters; thus, data and information for both are needed to estimate nutrient mitigation potential of shellfish farms. The Farm Aquaculture Resource Management (FARM) model, calibrated for farmed species, uses local environmental and farming practice data to simulate interactions between the farmed population and the local environment and to optimize cultivation practices for economic gain. We calibrated the model to predict nitrogen removal by Eastern oyster (Crassostrea virginica) farms with specific field and experimental data on oysters, their local environment, and farm practices in Long Island Sound, CT, USA. Previous FARM applications were not validated for nitrogen removal with local data. In the harvest when ready (HWR) model scenario (oysters are harvested when they reach harvest size), the farm removed 159 kg N ha−1 year−1 while the non-HWR scenario (all oysters are harvested at one time) removed 274 kg N ha−1 year−1. These estimates are within the range of previously reported in-water bioextraction studies in the Northeastern USA. The robust outputs from this validated model can be reliably used in marine spatial planning efforts and by nutrient managers to predict the nitrogen removal benefits that could be achieved through new or expanded eastern oyster farms in eutrophic environments.

Review of emerging technologies for nutrient removal in wastewater treatment

The burgeoning global population and industrial activities have significantly increased the generation of wastewater laden with nutrients, posing severe environmental and public health concerns. Traditional wastewater treatment methods often fall short in effectively removing nutrients like nitrogen and phosphorus, leading to eutrophication of water bodies and endangering aquatic ecosystems. In response, emerging technologies for nutrient removal in wastewater treatment have gained traction in recent years, offering innovative and efficient solutions to mitigate nutrient pollution. This comprehensive review explores the latest advancements in nutrient removal technologies, encompassing biological, physical, and chemical processes. Biological treatment methods, including activated sludge, sequencing batch reactors (SBRs), and membrane bioreactors (MBRs), have been extensively studied and optimized for nutrient removal. Novel biofilm-based systems, such as moving bed biofilm reactors (MBBRs) and integrated fixed-film activated sludge (IFAS), have demonstrated enhanced nutrient removal capabilities and resilience to fluctuations in wastewater composition. Furthermore, the integration of advanced oxidation processes (AOPs) and membrane technologies has revolutionized nutrient removal from wastewater. AOPs, such as ozonation, ultraviolet (UV) irradiation, and photocatalysis, offer effective means to degrade recalcitrant organic pollutants and disrupt nutrient cycles. Membrane-based technologies, including reverse osmosis (RO), nanofiltration (NF), and forward osmosis (FO), enable selective nutrient removal and concentration, thereby producing high-quality effluent suitable for reuse or discharge into sensitive environments. Additionally, the review delves into emerging chemical treatment strategies, such as adsorption, precipitation, and ion exchange, for targeted removal of nutrients from wastewater streams. Advanced adsorbents and nanomaterials exhibit superior adsorption capacities and selectivity for nitrogen and phosphorus compounds, paving the way for cost-effective nutrient recovery and resource recycling. Moreover, the review highlights the importance of process optimization, system integration, and environmental sustainability in the development and deployment of emerging nutrient removal technologies. Life cycle assessments (LCAs) and techno-economic analyses provide valuable insights into the environmental footprint and economic viability of these innovative solutions, guiding decision-makers towards sustainable wastewater management practices. In conclusion, the synthesis of biological, physical, and chemical processes in emerging nutrient removal technologies holds great promise for addressing the challenges of nutrient pollution in wastewater treatment. Future research directions should focus on scalability, energy efficiency, and holistic approaches towards achieving water quality goals and fostering a circular economy.

Water Quality Trade-offs for Risk Management Interventions in a Green Building.

Premise plumbing water quality degradation has led to negative health impacts from pathogen outbreaks (e.g., Legionella pneumophila and non-tuberculous mycobacteria), as well as chronic effects from exposure to heavy metals or disinfection by-products (DBP). Common water quality management interventions include flushing, heat shock (thermal disinfection), supplemental disinfection (shock or super chlorination), and water heater temperature setpoint change. In this study, a Legionella pneumophila- colonized Leadership in Energy and Environmental Design (LEED) certified building was monitored to study health-relevant water quality changes before and after three controlled management interventions: (1) flushing at several points throughout the building; (2) changing the water heater set point; and (3) a combination of interventions (1) and (2) by flushing during a period of elevated water heater set point (incompletely performed due to operational issues). Microbial (culturable L. pneumophila, the L. pneumophila mip gene, and cATP) and physico-chemical (pH, temperature, conductivity, disinfectant residual, disinfection by-products (DBPs; total trihalomethanes, TTHM), and heavy metals) water quality were monitored alongside building occupancy as approximated using Wi-Fi logins. Flushing alone resulted in a significant decrease in cATP and L. pneumophila concentrations (p = 0.018 and 0.019, respectively) and a significant increase in chlorine concentrations (p = 0.002) as well as iron and DBP levels (p = 0.002). Copper concentrations increased during the water heater temperature setpoint increase alone to 140°F during December 2022 (p = 0.01). During the flushing and elevated temperature in parts of the building in February 2023, there was a significant increase in chlorine concentrations (p = 0.002) and iron (p = 0.002) but no significant decrease in L. pneumophila concentrations in the drinking water samples (p = 0.27). This study demonstrated the potential impacts of short term or incompletely implemented interventions which in this case were not sufficient to holistically improve water quality. As implementing interventions is logistically- and time-intensive, more effective and holistic approaches are needed for informing preventative and corrective actions that are beneficial for multiple water quality and sustainability goals.

Linking Sediment and Water Column Phosphorus Dynamics to Oxygen, Temperature, and Aeration in Shallow Eutrophic Lakes

AbstractWater quality improvements in shallow eutrophic lakes are commonly delayed due to loading from legacy phosphorus (P)‐enriched sediments, even with reduced external nutrient loads. It is critical to understand the drivers of internal P loading to suppress or remove this source of P and meet water quality goals. We contrast the drivers of internal P loading in two shallow eutrophic systems (Lake Carmi and Missisquoi Bay). Legacy P dynamics in the unmanipulated systems were compared to Lake Carmi during aeration. In‐situ high frequency water column monitoring along with water and sediment sampling was used to study P dynamics in response to changing lake conditions and aeration. Despite both systems exhibiting P mobility controlled by iron redox cycling, we observed distinct differences in the spatial extent and drivers of internal P loading. Legacy P loading was controlled by seasonal drivers in Lake Carmi, but by spatially variable and highly transient wind driven forcing of hydrodynamics in Missisquoi Bay. Aeration altered the mixing regime of Lake Carmi and shifted loading dynamics to frequent wind‐driven pulses of legacy P to surface waters akin to those of Missisquoi Bay. Mean hypolimnetic dissolved oxygen increased with aeration, but greater oxygen demand rates and periods of anoxia under transient stratification still resulted in internal P loading. Surface P concentrations were higher in summer months with aeration compared to previous years. This research illustrates the dynamic nature of legacy P behavior within and between shallow eutrophic lakes and the challenges in addressing this common water resources threat.

Longevity of rain gardens in Minnesota (US) as a stormwater solution: a question of homeowner motivation and satisfaction

Rain gardens are gardens with a specific purpose. Designed as a shallow depression that captures stormwater runoff from impervious surfaces, rain gardens are planted with deep-rooted, wet/dry-cycle tolerant plants that enable the water to slowly permeate and be filtered by the soil. They are used as stormwater best management practices by municipalities and organizations as part of their overall plans to meet water quality goals as mandated by the United States (US) Clean Water Act. City and watershed administrators are counting on these rain gardens to be durable, effective solutions for managing stormwater runoff. But when the rain gardens are installed in the yards of privately owned homes, control of these solutions lands on the homeowners' shoulders. How effective are the rain gardens years after installation? How do the social factors of motivation and satisfaction relate to the longevity of the rain gardens? The objective of this case study was to determine the perceived performance of residential rain gardens as well as homeowner motivation and satisfaction with them over time. Data was collected via an email survey from homeowners located in the Twin Cities of Minneapolis and St. Paul, MN, US that had installed a rain garden. Key findings include (1) almost all rain gardens performed effectively, though some were not seen as successful, (2) motivations for installing rain gardens differ widely for successful vs. challenged gardens and (3) satisfaction with the rain gardens decreases over time.

Leveraging machine learning to automate regression model evaluations for large multi-site water-quality trend studies

Large multi-site trend studies provide an opportunity to evaluate progress of waterbodies towards water-quality goals across broad geographic areas. Such studies often aggregate the results of site-specific models and thus contend with evaluating each model for appropriate fit and statistical assumptions. We explored the use of four traditional machine learning models (logistic regression, linear and quadratic discriminant analysis, and k-nearest neighbors) to perform these checks and estimate probabilities that an analyst would publish or reject a site-specific trend model from a multi-site study. We trained these “model-checking models” (MCMs) using a national study of over 6000 trend models and tested the MCMs using a smaller set of novel trend models. Although the MCMs did not perform well enough to bypass analyst review entirely, we found incorporating an MCM into a larger evaluation workflow can reduce the number of trend models needing an analyst review by more than half.

Impact of Ecological Factors on Water quality goals

A deeper knowledge of the processes that influence environmental elements in areas such as water management, consumer services, water reuse acceptability, and risk communication, among others. Also, as a result of the unique climate, soil features, and agricultural idiosyncrasies, water quality and water management for human welfare and the natural environment. Also, various kinds of contamination may also have an impact on aquatic habitats across the world. Trace metals are one of the most major pollutants that have harmed marine environments. Its release into the marine environment is caused by both natural and human activities. Erosion and pollution are two of the negative repercussions of agricultural operations on soil quality. Pollution from nutrient leaching and intrusion is one of the consequences for water resources. To choose the best long-term solutions for mitigating these effects, researchers should focus on developing an accurate water and soil quality monitoring system at many scales based on a functional evaluation. On the other hand, the review focuses on the influence of metals and nutrients on water quality for water usage and its impact on agricultural output. Its mean water quality great impact on natural and human on the other hand effect on environment and ecosystem. finally this review indicated that many ecological factors positive effects on water quality goals.

A century of nitrogen dynamics in agricultural watersheds of Denmark

Intensive agriculture has been linked to increased nitrogen loads and adverse effects on downstream aquatic ecosystems. Sustained large net nitrogen surpluses have been shown in several contexts to form legacies in soil or waters, which delay the effects of reduction measures. In this study, detailed land use and agricultural statistics were used to reconstruct the annual nitrogen surpluses in three agriculture-dominated watersheds of Denmark (600–2700 km2) with well-drained loamy soils. These surpluses and long-term hydrological records were used as inputs to the process model ELEMeNT to quantify the nitrogen stores and fluxes for 1920–2020. A multi-objective calibration using timeseries of river nitrate loads, as well as other non-conventional data sources, allowed to explore the potential of these different data to constrain the nitrogen cycling model. We found the flux-weighted nitrate concentrations in the root zone percolate below croplands, a dataset not commonly used in calibrating watershed models, to be critical in reducing parameter uncertainty. Groundwater nitrate legacies built up in all three studied watersheds during 1950–1990 corresponding to ∼2% of the surplus (or ∼1 kg N ha yr−1) before they went down at a similar rate during 1990–2015. Over the same periods active soil nitrogen legacies first accumulated by approximately 10% of the surplus (∼5 kg N ha yr−1), before undergoing a commensurate reduction. Both legacies appear to have been the drivers of hysteresis in the diffuse load at the catchments’ outlet and hindrances to reaching water quality goals. Results indicate that the low cropland surpluses enforced during 2008–2015 had a larger impact on the diffuse river loads than the European Union’s untargeted grass set-aside policy of 1993–2008. Collectively, the measures of 1990–2015 are estimated to have reset the diffuse load regimes of the watersheds back to the situation prevailing in the 1960s.

Looking back to move forward: Restoring vegetated canals to meet missing Water Framework Directive goals in agricultural basins

Nitrate pollution and eutrophication remain pressing issues in Europe regarding the quality of aquatic ecosystems and the safety of drinking water. Achieving water quality goals under the Water Framework Directive (WFD) has proven to be particularly challenging in agricultural catchments, where high nitrate concentrations are the main reason for the failure of many water bodies to meet a good ecological status. Canals and ditches are common man-made features of irrigated and drained landscapes and, when vegetated, have recently been identified as denitrification hotspots.By combining experimental data and GIS-based upscaling estimation, the potential capacity of the canal network to reduce nitrate loads was quantified in several scenarios differing in the level of nitrate pollution and in the extent of the canal network length where conservative management practices are implemented. The analysis was carried out in the irrigated lowlands of the Po River basin, which is the largest hydrographic system in Italy and a global hotspot for nitrogen inputs and eutrophication.Scenario simulations showed that maintaining aquatic vegetation in at least 25 % of the canal network length, selecting sites with high nitrate availability (>2.4 mg N L−1), would promote a greater potential for permanent N removal. The increased denitrification capacity would meet the load reduction target required to achieve a WFD good ecological status in waters draining into the Adriatic Sea during the spring-summer months, when the eutrophication risk is higher. Promoting denitrification in the canal network by postponing the mowing of in-stream vegetation to the end of the growing season could be an effective mitigation strategy to improve water quality in agricultural basins and contribute to achieving the WFD goals.

Integrated assessment for Sustainable Development Goals of metropolitan regions: A case study of the Pearl River Delta region, China

Achieving Sustainable Development Goals (SDGs) at the sub-national scale requires contextual insights and localized implementation. This study utilizes Driver-Pressure-State-Impact-Response (DPSIR) framework to assess SDG progress and interactions in the Pearl River Delta (PRD) metropolitan region of China. Population growth, economic development, and rapid urbanization are key drivers, exerting pressures on energy and water consumption, pollutant discharges, transportation, environmental degradation, and disaster management. The results reveal varied progress in nine goals intrinsic to this metropolitan context, with notable progress in energy and water consumption, and employment (Goals 7, 8, and 3). While moderate progress is evidenced in poverty reduction, economic growth, healthcare services, social security, access to potable water, water quality (Goals 1 and 6), challenges remain in transportation, waste generation, air quality, forest management, and disaster response (Goals 9, 11, and 15). Furthermore, target interaction analysis suggests that initiatives in high-leverage areas - ecosystem and environmental protection, equal access to resources and basic services, and climate change response - can yield substantial systemic impacts. However, poverty reduction, access to resources and basic services, ecosystem protection, and economic growth appear more dependent on system-wide efforts. By leveraging the DPSIR model, this context-sensitive SDG assessment accentuates priority zones and offers valuable perspective for cohesive SDG strategy formation and policy-making in dynamically growing metropolitan areas globally.

Simulating the effect of perennialized cropping systems on nitrate-N losses using the SWAT model

Several newly released crop varieties, including the perennial intermediate wheatgrass (grain marketed as Kernza®), and the winter hardy oilseed crop camelina, have been developed to provide both economic return for farmers and reduced nutrient losses from agricultural fields. Though studies have indicated that these crops could reduce nitrate-nitrogen (N) leaching, little research has been done to determine their effectiveness in reducing nitrate-N loading to surface waters at a watershed scale, or in comparing their performance to more traditional perennial crops, such as alfalfa. In this study, nitrate-N losses were predicted using the Soil and Water Assessment Tool (SWAT) model for the Rogers Creek watershed located in south-central Minnesota, USA. Predicted looses of nitrate-N under three perennialized cropping systems were compared to losses given current cropping practices in a corn (Zea mays L.)-soybean (Glycine max L. Merr.) rotation. The perennialized systems included three separate crop rotations: intermediate wheatgrass (IWG) in rotation with soybean, alfalfa in rotation with corn, and winter camelina in rotation with soybean and winter rye. Model simulation of these rotations required creation of new crop files for IWG and winter camelina within SWAT. These new crop files were validated using measured yield, biomass, and nitrate-N data. Model results show that the IWG and alfalfa rotations were particularly effective at reducing nutrient and sediment losses from agricultural areas in the watershed, but smaller reductions were also achieved with the winter camelina rotation. From model predictions, achieving regional water-quality goals of a 30% reduction in nitrate-N load from fields in the watershed required converting approximately 25, 34, or 57% of current corn-soybean area to the alfalfa, IWG, or camelina rotations, respectively. Results of this study indicate that adoption of these crops could achieve regional water quality goals.

Salinization and sedimentation drive contrasting assembly mechanisms of planktonic and sediment-bound bacterial communities in agricultural streams.

Agriculture is the most dominant land use globally and is projected to increase in the future to support a growing human population but also threatens ecosystem structure and services. Bacteria mediate numerous biogeochemical pathways within ecosystems. Therefore, identifying linkages between stressors associated with agricultural land use and responses of bacterial diversity is an important step in understanding and improving resource management. Here, we use the Mississippi Alluvial Plain (MAP) ecoregion, a highly modified agroecosystem, as a case study to better understand agriculturally associated drivers of stream bacterial diversity and assembly mechanisms. In the MAP, we found that planktonic bacterial communities were strongly influenced by salinity. Tolerant taxa increased with increasing ion concentrations, likely driving homogenous selection which accounted for ~90% of assembly processes. Sediment bacterial phylogenetic diversity increased with increasing agricultural land use and was influenced by sediment particle size, with assembly mechanisms shifting from homogenous to variable selection as differences in median particle size increased. Within individual streams, sediment heterogeneity was correlated with bacterial diversity and a subsidy-stress relationship along the particle size gradient was observed. Planktonic and sediment communities within the same stream also diverged as sediment particle size decreased. Nutrients including carbon, nitrogen, and phosphorus, which tend to be elevated in agroecosystems, were also associated with detectable shifts in bacterial community structure. Collectively, our results establish that two understudied variables, salinity and sediment texture, are the primary drivers of bacterial diversity within the studied agroecosystem, whereas nutrients are secondary drivers. Although numerous macrobiological communities respond negatively, we observed increasing bacterial diversity in response to agricultural stressors including salinization and sedimentation. Elevated taxonomic and phylogenetic bacterial diversity likely increases the probability of detecting community responses to stressors. Thus, bacteria community responses may be more reliable for establishing water quality goals within highly modified agroecosystems that have experienced shifting baselines.

Navigating or adding to complexity? Exploring the role of catchment partnerships in collaborative governance

An enduring challenge for environmental governance is how to coordinate multiple actors to achieve more collaborative and holistic management of complex socio-ecological systems. Catchment partnerships are often thought able to achieve this, so here we ask: do such partnerships actually help navigate complexity, or merely add to it? We answer this question by analysing the experiences of four voluntary UK catchment partnerships. Our data combined a structured desk-based analysis of partnership documents, with semi-structured interviews with partnership coordinators, chairs and partner representatives. These data were analysed using a qualitative thematic approach informed by the literatures on catchment management and collaborative governance of complexity. We found that partnerships both add to and help navigate the complexity of holistic and inclusive environmental management. Maintaining partnerships entails costs for partners, and partnerships connect messily and multitudinously to other initiatives. However, the partnerships were all judged as worthwhile, and made progress towards goals for water quality, biodiversity and river restoration. They were especially valued for envisioning and initiating complex activities such as Natural Flood Management. Communication and networking by partnership coordinators and partners underpinned these achievements. Aspects of pre-existing governance systems both enabled and constrained the partnerships: in particular, statutory agencies responsible for policy delivery were always important partners, and delivering partnership plans often depended on public-sector grants. This draws attention to the pervasive effect of governmentality in collaborative governance. More attention to analysing—and supporting—such partnerships is worthwhile, complemented by reflection on the limits to environmental governance in the face of complexity.

Factors in homeowners' willingness to adopt nitrogen-reducing innovative/alternative septic systems.

When environmental mitigation requires individual adoption, engagement approaches centered on cost effectiveness and technological efficiency alone are often insufficient. Through focus groups with adopters and prospective adopters, this research identifies factors influencing homeowners' willingness to adopt Innovative/Alternative (I/A) septic systems for nitrogen reduction. We apply concepts from technology adoption and behavior change models as a framework for illustrating the homeowner decision-making process around I/A adoption. The perceived needs to replace an old/failing septic system, comply with local regulations, and protect local water quality synergistically catalyzed adoption. Adoption was further influenced by the larger context within which it is taking place, perceived characteristics of I/A systems and the installation process, system aesthetics concerns, and homeowners' attitudes and beliefs. Considering how these factors affect adoption could enable resource managers to design more targeted interventions to encourage adoption through behavior change strategies such as social marketing, and to improve how these systems are communicated. If I/A systems are to be used as a tool to achieve water quality goals, the considerations influencing homeowners' willingness to install these systems will be critical to incentivizing voluntary adoption. Many of these factors are relevant to the adoption of other individual-level environmental management strategies, which are being increasingly deployed in response to complex, nonpoint source pollution issues.

Modification of exploration of long‐term nutrient trajectories for nitrogen (ELEMeNT-N) model to quantify legacy nitrogen dynamics in a typical watershed of eastern China

Legacy nitrogen (N) is recognized as a primary cause for the apparent failure of watershed N management strategies to achieve desired water quality goals. The ELEMeNT-N (exploration of long‐term nutrient trajectories for nitrogen) model, a parsimonious and process-based model, has the potential to effectively distinguish biogeochemical and hydrological legacy effects. However, ELEMeNT-N is limited in its ability to address long-term legacy N dynamics as it ignores temporal changes in soil organic N (SON) mineralization rates. This work represents the first use and modification of ELEMeNT-N to quantify legacy effects and capture spatial heterogeneity of legacy N accumulation in China. An exponential function based on mean annual temperature was employed to estimate yearly changes in SON mineralization rate. Based on a 31 year water quality record (1980–2010), the modified model achieved higher efficiency metrics for riverine N flux in the Yongan watershed in eastern China than the original model (Nash–Sutcliff coefficient: 0.87 vs. 0.72 and R 2: 0.80 vs. 0.71). The modified ELEMeNT-N results suggested that the riverine N flux mainly originated from the legacy N pool (88.2%). The mean overall N lag time was 11.9 years (95% confidence intervals (CIs): 8.3–21.3), of which biogeochemical lag time was 9.7 years (6.3–18.4) and hydrological lag time was 2.2 years (2.0–3.0). Legacy N accumulation showed considerable spatial heterogeneity, with 219–239 kg N ha−1 accumulated in soil and 143–188 kg N ha−1 accumulated in groundwater. The ELEMeNT-N model was an effective tool for addressing legacy N dynamics, and the modified form proposed here enhanced its ability to capture SON mineralization dynamics, thereby providing managers with critical information to optimize watershed N pollution control strategies.

Computational fluid dynamics modeling of floating treatment wetland retrofitted stormwater pond: Investigation on design configurations

Floating Treatment Wetland (FTW) is a cost-effective and easy-to-retrofit device for stormwater treatment. Its treatment efficiency largely depends on the fraction of inflow entering FTW and the residence time within it. Thus hydrodynamics play a crucial role, which is affected by the design configurations of FTW and stormwater pond. Despite a spike in research on FTWs, very little is known about how various design configurations affect treatment efficiency by an FTW. Our study hypothesizes that relative positions of FTW geometry, FTW position and pond inlet–outlet have impact on the hydrodynamics and as a consequence, treatment efficiency. To explore these design features, we employed computational fluid dynamics (CFD) modeling conducted in ANSYS Fluent, validated by experimental data to examine the impact of the aforementioned design features. The results revealed that circular FTW geometry positioned near inlet coupled with center inlet–side outlet configuration achieved the highest removal (94.8%) for a non-dimensional removal rate of krtHRT = 20 (kr is the first order removal rate in per day, tHRT is the nominal hydraulic residence time of the pond in days). Far side inlet–side outlet configuration performed the worst due to profound promotion of short-circuiting. FTW positioned near inlet performed better (61.8% mass removal on an average) than center (42.7%) and near outlet positions (54.1%) for krtHRT = 20. Sensitivity analysis revealed that the treatment efficiency is most sensitive to inlet–outlet configurations. The design implications of this study will help practitioners achieving better water quality and ecological improvement goals.