Search Results (549)

The dairy sector produces considerable amounts of nutrient-rich effluents, which are frequently undervalued as simple by-products or waste. In particular, Second Cheese Whey (SCW), also known as scotta, exhausted whey, or deproteinized whey, represents the liquid fraction from ricotta cheese production. Despite its abundance and high organic and saline content, SCW is often improperly discharged into terrestrial and aquatic ecosystems, causing both environmental impact and resource waste. The available purification methods are expensive for dairy companies, and, at best, SCW is reused as feed or fertilizer. In recent years, increasing awareness of sustainability and circular economy principles has increased interest in the valorization of SCW. Biological treatment of SCW using microalgae represents an attractive strategy, as it simultaneously reduces the organic load and converts waste into algal biomass. This biomass can be further valorized as a source of proteins, pigments, and bioactive compounds with industrial relevance, supporting applications in food, nutraceuticals, biofuels, and cosmetics. This review, starting from analyzing the characteristics, production volumes, and environmental issues associated with SCW, focused on the potential of microalgae application for their valorization. In addition, the broader regulatory and sustainability aspects related to biomass utilization and treated SCW are considered, highlighting both the promises and limitations of microalgae-based strategies by integrating technological prospects with policy considerations. Full article

Nitrogen eutrophication represents a significant environmental challenge in Chinese aquatic ecosystems, exacerbated by rapid agricultural intensification, industrial expansion, and urban development. This review consolidates existing knowledge on the drivers and impacts of nitrogen pollution in Chinese aquatic ecosystems, with a focus on environments such as lakes, rivers, and coastal waters. The primary sources of nitrogen enrichment are excessive fertilizer application, livestock manure discharge, industrial emissions, and untreated industrial and municipal wastewater. These inputs have led to severe ecological consequences, including harmful algal blooms, hypoxia, loss of biodiversity, and deteriorating water quality, threatening ecosystem health and human well-being. The review also examines mitigation strategies implemented in China, encompassing regulatory policies such as the “Zero Growth” fertilizer initiative, as well as technological advancements in wastewater treatment and sustainable farming practices. Case studies highlighting successful interventions, such as lake restoration projects and integrated watershed management, demonstrate the potential for effective nitrogen control. However, persistent challenges remain, including uneven policy enforcement, insufficient public awareness, and gaps in scientific understanding of nitrogen cycling dynamics. This review aims to inform future efforts toward achieving sustainable nitrogen management in China by synthesizing current research and identifying key knowledge gaps. Addressing these issues is crucial for safeguarding China’s aquatic ecosystems and promoting global nutrient stewardship. Full article

Increasing demand for land and resources in Himalayan catchments is altering hydrological processes and threatening freshwater ecosystems. Sediment mobilization and nutrient fluxes, especially during monsoon rainfall events, are intensifying the degradation of water bodies. This study investigates land cover change and its effects on nutrient dynamics in the Phewa Lake catchment, Nepal. Landsat imagery from 1990 to 2021, processed through Google Earth Engine, was used to map land changes. Nutrient loading for the two time periods was estimated with the InVEST model. Surface soils were sampled across the catchment to analyze nitrogen and phosphorus distribution, while their particle-bound transport to the lake was assessed through riverbed sediments and the suspended sediments collected during monsoon rainfalls. Pre-monsoon water quality was examined to evaluate eutrophication levels across different lake zones. Results reveal forest recovery in the upper catchment, but agricultural land in the lower catchment is being rapidly converted to urban areas. While forest recovery has enhanced sediment retention, nutrient inputs to the lake, particularly nitrogen and phosphorus, have increased. Fertilizer leaching and untreated sewage emerge as key sources in rural and urban areas, respectively. Seasonal constraints of the dataset may underestimate the overall extent of water quality deterioration, as indicated by high nutrient loads in monsoon suspended sediments. Overall, this study highlights the dual effect of land cover change: forest regrowth coincides with rising nutrient discharge. Without timely interventions, growing urban populations in the region may face worsening water quality challenges. Full article

Assessing the impacts of future changes in rainfall, temperature, and land use on streamflow and nutrient loads is critical for long-term watershed management, particularly in the unglaciated Driftless Area with steep slopes, erodible soils, and karst geology. This study evaluates the Kickapoo watershed in southwestern Wisconsin to examine how projected climate change and cropland expansion may affect hydrology during the mid- (post-2050) and late century (post-2070). Climate projections suggest temperature increase, wetter springs, and drier summers over the century. Annual average streamflow is projected to decline by 5–40% relative to 2000–2020, primarily due to a 5–15% reduction in groundwater discharge. While land use changes from prairie to cropland had a limited additional impact on streamflow, it increased annual average total phosphorus (TP) by 5.67–10.08%, total nitrogen (TN) by 1.08–2.34%, and sediment by 3.11–6.07%, frequently exceeding total maximum daily load (TMDL) thresholds in comparison to the climate change scenario. These findings suggest that although land use changes exacerbate nutrient and sediment pollution, climate change remains the dominant driver of hydrologic alteration in this watershed. Instead, converting 18% (~290 km²) of cropland to grassland could enhance baseflow (0.84–14%), and reduce TP (30–45%), TN (3–5%), sediment (80–90%), and meeting TMDL 90% of the time. These findings underscore the importance of nature-based solutions, such as prairie restoration, supporting adaptive management to reduce nutrient load, sustaining low flows, and strengthening hydrologic resilience, that support key Sustainable Development Goals. This approach offers valuable insights for other unglaciated watersheds globally. Full article

Despite increasing concerns over recurrent phosphorus (P) pollution, the Ju River—a small tributary of the Yangtze River—has received limited scientific attention. To correct this, the present study integrates field-based observations with the Hydrological Simulation Program—FORTRAN (HSPF) model to comprehensively assess the conjunct effects of urban expansion and changing precipitation patterns on watershed hydrology and phosphorus dynamics at the small-catchment scale. A total of five urban expansion scenarios and three precipitation enhancement scenarios were simulated to capture both seasonal and event-driven variations in daily discharge and total phosphorus (TP) concentrations. The model was calibrated and validated using in situ water quality data, ensuring high reliability of the simulations. The results indicate that agricultural non-point sources are the primary contributor to total phosphorus (TP) loads. During the overlapping period of intensive farming and heavy rainfall (June–July), TP concentrations more than doubled compared to other months, with these two months accounting for over 70% of the annual TP load. Urban expansion significantly amplified hydrological extremes, increasing peak discharge by up to 224% under extreme rainfall, thereby intensifying flood risks. Although increased precipitation diluted TP concentrations, it simultaneously accelerated overall phosphorus export. This study offers a novel modeling–monitoring framework tailored for small watersheds and provides critical insights into how land use transitions and climate change jointly reshape nutrient cycling. The findings support the development of targeted, scenario-based strategies to mitigate eutrophication risks in vulnerable river systems. Full article

Wastewater overflows (WOs) are a growing concern for water quality and ecological health in urban estuaries. This study provides a robust water quality and ecological assessment of WOs from four pump stations discharging into the Waimea Estuary, Aotearoa, New Zealand. Using overflow scenario modelling, baseline and event-based water quality sampling, and whole effluent toxicity testing, we assessed the potential impacts under conservative (2 h) and worst-case (24 h) overflow durations. Results showed that, even under worst-case conditions, the estuary’s natural dilution capacity exceeded the median dilution required to meet the 95% ecological protection level. Ecotoxicity was site- and season-specific, with amphipods and mussels showing sensitivity at some sites, while algal assays indicated nutrient enrichment rather than toxicity. Impacts were spatially limited and unlikely to persist beyond one or two tidal cycles. The estuary’s tidal exchange and resilient biota further mitigated risks. This method provides a transferable framework for assessing intermittent discharges in other coastal systems, especially those with high ecological value and infrequent discharge events. Full article

Phosphorus (P) discharge from onsite wastewater treatment systems (OWTSs) poses a significant threat to water quality, contributing to eutrophication in nutrient-sensitive aquatic environments. In treated effluents, P predominantly exists as orthophosphate (PO₄³⁻), a highly bioavailable and reactive form that requires targeted removal. This study evaluates the performance of electrocoagulation (EC) as a polishing step for PO₄³⁻ removal from OWTS effluents using 12 anode/cathode combinations comprising aluminum (Al), iron (Fe), magnesium (Mg), and stainless steel (SS). Key operational parameters, including treatment time, mixing speed, current density, pH, and initial PO₄³⁻ concentration, were systematically investigated when synthetic denitrified effluent (20 mg P/L) was treated. Based on the performance, the four most effective electrode combinations (Al/Al, Al/Mg, Fe/Al, and Mg/Mg), along with a commercial benchmark (Fe/Fe), were further tested under extended hydraulic retention times (up to 48 h) in both synthetic and real (denitrified) wastewater. To date, none of the studies have systematically evaluated all possible anode/cathode combinations involving multiple electrode materials under uniform operational conditions. The Al/Al and Mg/Mg EC systems achieved rapid and high PO₄³⁻ removal efficiencies (>95%), while Mg-based systems demonstrated sustained performance over prolonged treatment durations, especially in real wastewater. Bimetallic pairs such as Al/Mg and Fe/Al exhibited synergistic effects through enhanced coagulant generation and pH stabilization. The results indicated that PO₄³⁻ removal efficiency was strongly influenced by electrode material selection, hydrodynamic conditions, and wastewater compositions, underscoring the need to design EC systems based on site-specific water quality conditions in OWTSs. Full article

This study describes the challenges and solutions encountered when developing a high-resolution, process-based hydrological model of the Adige River Lowland Basin (ARLB), a flat, intensively managed agricultural region in northeastern Italy. The model was based on the Soil and Water Assessment Tool (SWAT) and simulates streamflow and nutrient dynamics. Using detailed local hydrological, agricultural, and point-source data, the model robustly reproduces current conditions and projects future scenarios under climate change. Streamflow calibration demonstrated strong performance (NSE up to 0.76), with simulated monthly average discharge (192 m³/s) closely matching observed values (218 m³/s) and capturing intra- and inter-annual variability. Nutrient simulations also aligned well with observations. Total nitrogen (TN) concentrations averaged 1.08 mg/L versus 1.09 mg/L observed. Spatial TN loads were satisfactorily predicted across the subbasins, without additional nutrient calibration to prevent overfitting. Spatial analysis revealed that point sources, notably wastewater treatment plants (WWTPs) along the main river, contribute approximately 65% of the total nitrogen loads, while diffuse agricultural runoff (though secondary in load magnitude) is concentrated in the northern subbasins and is sensitive to climate variability. Climate change projections under 2 °C and 3 °C warming scenarios indicate increases in TN loadings by about 150 and 300 t/y, respectively. Phosphorus loadings exhibited weaker and more variable responses to warming than TN, reflecting model and scenario uncertainties. Overall, this work demonstrates the capability of the proposed modeling approach, based on high-resolution spatio-temporal variables, to model complex lowland hydrology and nutrient fluxes. The model can be used as a decision-support tool for regional nutrient management and climate adaptation strategies. Full article

Nutrient and carbon transport from the Mississippi River to the Gulf of Mexico have been investigated intensively. However, little is known about the direct human contribution of carbon from wastewater treatment plants (WWTPs) to this large river, a source that can be termed as Cultural Carbon. This study analyzed dissolved carbon in effluents from two municipal WWTPs on the bank of the Mississippi River in Baton Rouge, South Louisiana, USA. One of the WWTPs (WWTP North) is a conventional wastewater treatment facility with a treatment capacity of 40 million gallons per day (MGD), while the other (WWTP South) is a recently upgraded facility with a treatment capacity of 200 MGD. From September 2022 to November 2024, river water and effluent samples were collected monthly to analyze dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations and their mass transport. The study found significantly higher monthly average DIC (56.80 ± 16.51 mg/L) and DOC (29.52 ± 8.68 mg/L) concentrations in the effluent of WWTP North than in the effluent of WWTP South (DIC: 42.64 ± 10.50 mg/L and DOC: 12.93 ± 3.68 mg/L). Effluents from both WWTPs had substantially greater DOC and DIC levels than the Mississippi River water (DIC: 28.92 ± 4.91 mg/L and DOC: 5.47 ± 2.35 mg/L). WWTP North discharged, on average, 3.80 MT of DIC and 1.95 MT of DOC per day, whereas WWTP South discharged 6.27 MT of DIC and 1.92 MT of DOC per day, resulting in a total annual load of 3808 MT of DIC and 1459 MT of DOC entering the Mississippi River. Considering the large number of WWTPs within the Mississippi River Basin, these findings highlight a significant contribution of effluents to riverine carbon, suggesting that basin-wide carbon budgets and regional climate assessments must take them into account. The findings from this study can be useful for federal and state policymakers, as well as researchers and engineers involved in carbon science, climate change, and water quality assessment of the Mississippi River Basin and beyond. Full article

Aquaculture is the fastest-growing food production sector and plays a pivotal role in global food security. However, the reliance on conventional fishmeal and fish oil in aquafeeds raises sustainability concerns due to overfishing, high costs, and ecological burden. This review explores the valorisation of microalgae as a sustainable and functional alternative for aquafeed development. Microalgae are rich in proteins, polyunsaturated fatty acids, bioactive compounds, and pigments that support aquatic animal growth, immunity, and product quality. We critically examine the integration of green technologies, including cultivation systems, biomass harvesting, and eco-friendly extraction methods for optimising microalgal biomass and bioactive recovery. The review also discusses recent innovations in bioremediation and circular aquaculture systems, highlighting the role of microalgae in reducing nutrient discharge, carbon footprint, and operational cost. Challenges such as scalability, digestibility, and economic feasibility are also addressed, providing insight into pathways toward industrial adoption. This review aims to provide an updated and holistic perspective on microalgae-based aquafeeds in advancing sustainable aquaculture practices. Full article

With the rapid development of urbanization and the economy in recent years, increased human activities along the Yinghe River in Fuyang City and industrial expansion have degraded the water quality. Various sewage discharges have elevated nitrogen and phosphorus levels in the water body, disrupting its original ecological balance and exacerbating environmental issues. Therefore, studying the water purification capacity of the Fuyang region is particularly important. Using the InVEST model, this paper analyzes temporal changes and spatial differences in water purification capacity by quantifying nitrogen and phosphorus retention. The results show the following: The water purification capacity of Fuyang exhibits a spatial pattern of higher effectiveness in the north and lower effectiveness in the southwest. This study represents the strength of water purification capacity as the sum of regional output of nitrogen and phosphorus nutrients, based on which different types of areas are divided into water purification capacity deficit areas and water purification capacity control areas, and then combined with the different impacts of different land use types on the regional water purification capacity, corresponding countermeasures are proposed to optimize the water purification capacity of Fuyang City. Full article

The erosion plot method (EPM) is the most accurate method for measuring total runoff and soil loss in the field, but it is expensive, time-consuming, and tedious to use, thereby limiting the scope of soil erosion research. Alternatively, the fractional method (FM) involves measuring a portion of total runoff and soil loss to estimate the total erosion. Although the FM may be easier to use in rainforest agroecology, it has not been evaluated under vetiver grass technology (VGT). Thus, a 2-year field study was conducted to verify the efficacy of the FM under VGT by comparing soil nutrient erosion between the FM and the EPM on two slopes (5% and 10%). Three piped drums (left, central, and right) were used to collect total runoff under the EPM, while only a central piped drum was used under the FM (usual practice). The FM’s runoff and soil loss values were similar to those under the EPM (R² = 0.98–0.99; p < 0.001). Runoff nutrients (R² = 0.90; p < 0.001) and eroded nutrients (R² = 0.97; p < 0.001) from the FM were highly similar to those of the EPM on the 5% slope. Similarly, runoff nutrients (R² = 0.86; p < 0.001) and eroded nutrients (R² = 0.95; p < 0.001) from the FM were strongly similar to those of the EPM on a 10% slope. The FM accounted for 92% of the total nutrient erosion measured by the EPM under VGT management. Thus, the FM will make research more efficient, cost-effective, and attractive, particularly in large-scale water erosion studies. Full article

Blackwater rivers are enriched in humic acids and impoverished in nutrients, sometimes discharging into oceans. Brazil has a coastal zone of about 8700 km, with several blackwater rivers discharging into the Atlantic Ocean, in addition to the Rio Negro of the northern Amazon basin, which is the largest (about 1700 km long) and best-known tropical backwater river. On the other hand, only a few attempts have been made to deal with their hydrochemical composition and how it is related to the hydrochemistry of different water bodies nearby. This paper focuses on a sector of the Atlantic Ocean shore occurring in São Paulo State, enclosing two important Ecological Reserves, i.e., the Restinga State Park of Bertioga and the State Park of Serra do Mar–São Sebastião Nucleus, located at Bertioga and São Sebastião cities, respectively. Physicochemical parameters such as pH and electrical conductivity, as well as the composition of major constituents like sodium, potassium, calcium, magnesium, bicarbonate, chloride, sulfate, nitrate, etc., have been evaluated in two blackwater rivers and one blackwater stream to compare their relative inputs into the Atlantic Ocean. Traditional hydrogeochemical diagrams such as the Piper, Schoeller, Gibbs, van Wirdum, and Wilcox graphs were utilized for investigating the major features of the blackwater’s composition, revealing in some cases that they suffer an accentuated influence of the constituents occurring in the Atlantic Ocean waters, due to backward currents (coastal upwelling or tidal currents). Another highlight of this paper is the measurement of an enhanced concentration of dissolved iron in one blackwater sample analyzed, reaching a value of 1.9 mg/L. Such a finding has also been often reported in the literature for blackwater rivers and streams, as humic and fulvic acids are used to bind Fe³⁺, keeping it in solution. Nowadays, iron in solution has been considered a very important element acting as a natural fertilizer of the coastal ocean because it is an essential nutrient to marine phytoplankton. Full article

Global climate changes impact the Arctic seas by decreasing the sea ice area and changing the inorganic and organic matter supply via rivers and coastal permafrost thawing. Therefore, climate change may affect biogeochemical processes in the Kara Sea (KS) and Laptev Sea (LS), which form the Arctic Transpolar Drift. This study explores the effect of the KS shelf water supply on seawater parameters in the LS in late summer and early fall 2007, 2008, 2018, 2019, and 2024 using ship-borne (temperature, salinity, dissolved oxygen, nutrients, and pH), satellite-derived (sea surface heights, geostrophic current velocities), and model (current velocities) data. The results demonstrate that an inflow of KS shelf water with salinity of 33.0–34.5, high Apparent Oxygen Utilization values (50–110 µM), and increased concentrations of the dissolved inorganic phosphorus (DIP~ 0.7–1.2 µM), dissolved inorganic nitrogen (DIN~ 4–12 µM) and silicic acid (DSi~ 10–18 µM) enriches the subsurface layer of the LS with nutrients. The distributions of Atlantic—derived water (ADW) and KS shelf water in the LS from August to October depend on water dynamics caused by wind and river discharge. High Lena River discharge and westerly (downwelling favorable) winds promoted the supply of the KS shelf water to the LS through Vilkitsky Strait. In the area of the central trough of the LS, the KS shelf water can be modified by mixing with ADW. Mixing ADW with high DIN/DIP ratios (DIN~ 10 µM at DIP of 0.80 µM) and KS shelf water with low DIN/DIP ratios (DIN~ 8 µM at DIP of 0.80 µM) leads to changes in the DIN vs. DIP ratio in the subsurface layer of the LS. Full article

The paper presents the results of investigations into the relationship between selected water quality parameters and hydrological streamflow drought in a small river situated in the Mazovian Lowlands in Poland. As hydrological streamflow drought periods become more frequent in Poland, investigations about the relationship between flow and water quality parameters can be an essential contribution to a better understanding of the impact of low flow on the status of water rivers. Data from a three-year study of a small lowland river along with significant agricultural land management was used to analyze the connection between low flows and specific water quality indicators. The separation of low-flow data from water discharge records was achieved using two criteria: Q90% (the discharge value from a flow duration curve) and a minimum low-flow duration of 10 days. During these periods, the concentration of water quality indicators was determined based on collected water samples. In total, 30 samples were gathered and examined for pH, suspended sediments, dissolved substances, hardness, ammonium, nitrates, nitrites, phosphates, total phosphorus, chloride, sulfate, calcium, magnesium, and water temperature during sampling. The study’s main aim was to describe the relation between hydrological streamflow droughts and chosen water quality parameters. The analysis results demonstrate an inverse statistically significant relationship between concentration and low-flow values for total hardness and sulfate. In contrast, there was a direct relationship between nutrient indicators, suspended sediment concentration, and river hydrological streamflow drought. Statistical tests were applied to compare the datasets between years, revealing statistical differences only for nutrient indicators. Full article