Search Results (70)

This study focuses on a rapidly urbanizing coastal plain where river networks serve as critical pathways for pollutant transport to nearshore waters. Under frequent sluice control and sluggish hydrodynamics, pollutants accumulate in channels and are subsequently flushed during intense rainfall or sluice-opening events, increasing pollutant loads in downstream estuaries. Based on 2017–2024 water quality monitoring data, integrated multi-source environmental factor analysis and unmanned patrol boat technology, systematic water quality assessment and pollution source identification were conducted. Significant spatial heterogeneity was observed: phosphorus and nitrogen pollution dominated in the eastern region, whereas the permanganate index was more prominent in the western part of the network. Identification of abrupt water quality change sections revealed industrial wastewater as the primary contributor to phosphorus and nitrogen, whereas permanganate index pollution originated widely from aquaculture, agriculture, and industrial discharges. Atmospheric deposition likely provides a non-negligible contribution to phosphorus and nitrogen input, with fluxes strongly correlated to rainfall. Sediment release posed internal risks of carbon and phosphorus, with intensity positively linked to pollution levels. This study elucidates the water quality characteristics and multi-source pollution mechanisms in typical coastal river networks under rapid economic development. Therefore, it provides a scientific basis for precise regional water environment management and coastal water quality protection. Full article

This study examines the impact of an unintended fire at the Drava International plastic processing facility near Osijek, Croatia, on soil quality and the potential human health risks associated with agricultural soils within a 10 and 20 km radius. Surface soil samples (0–5 cm) were collected from ten locations within 10 km three days after the incident, and eight composite samples were taken from sites 10–20 km away 17 days’ post-event. Additionally, 18 control samples previously collected for soil fertility or quality monitoring were included for comparative analysis. In total, 36 agricultural soil samples were analyzed for pH, organic matter, total phosphorus, potassium, calcium, magnesium, and trace elements (Cr, Co, Ni, Cu, Zn, As, Pb). Eighteen post-fire samples were also analyzed for polycyclic aromatic hydrocarbons (PAHs), dioxins, and perfluoroalkyl substances (PFAS). Ecological risk was assessed using the pollution load index (PLI) and enrichment factor (EF), while human health risk was evaluated through the estimation of incremental lifetime cancer risk (ILCR) and individual carcinogenic risks (CRi) for As, Cr, Ni, and Pb. Results showed that concentrations of dioxins (TEQ LB and UB), dioxin-like PCBs, and non-dioxin-like PCBs in samples within 10 km were either below detection limits or present in trace amounts (4.0 × 10⁻⁶ mg/kg). PFAS compounds were not detected (<0.0005 mg/kg). The total concentration of non-dioxin-like PCBs ranged from 0.0023 to 0.0047 mg/kg, well below the maximum permissible levels. Post-fire contamination profiles revealed consistently higher PAH concentrations in the 0–10 km zone (mean 0.100 mg/kg) compared to the 10–20 km zone (mean 0.062 mg/kg). Twenty PLI values exceeded the threshold of 1 (range: 1.00–1.26), indicating moderate pollution, while the remaining values (PLI 0.82–0.99) suggested no pollution. EF values indicated minimal to moderate enrichment (EF < 2), supporting the conclusion that metal presence was predominantly geological with limited anthropogenic influence. All ILCR values for adults and children remained below the acceptable threshold of 1 × 10⁻⁴, indicating low carcinogenic risk under both pre- and post-fire conditions. CRi values followed a consistent decreasing trend across exposure pathways: ingestion > dermal absorption > inhalation. Full article

To explore the coupling between agricultural farming models and surface water environmental in central China’s irrigation districts, this study focuses on the Four Lakes Basin within Jianghan Plain, a key grain-producing and ecological protection area. Integrating remote sensing images, statistical yearbooks, and on-site monitoring data, the study analyzed the phased characteristics of the basin’s agricultural pattern transformation, the changes in non-point source nitrogen and phosphorus loads, and the responses of water quality in main canals and Honghu Lake to agricultural adjustments during the period 2010~2023. The results showed that the basin underwent a significant transformation in agricultural patterns from 2016 to 2023: the area of rice-crayfish increased by 14%, while the areas of dryland crops and freshwater aquaculture decreased by 11% and 4%, respectively. Correspondingly, the non-point source nitrogen and phosphorus loads in the Four Lakes Basin decreased by 11~13%, and the nitrogen and phosphorus concentrations in main canals decreased slightly by approximately 2 mg/L and 0.04 mg/L, respectively; however, the water quality of Honghu Lake continued to deteriorate, with nitrogen and phosphorus concentrations increasing by approximately 0.46 mg/L and 0.06 mg/L, respectively. This indicated that the adjustment of agricultural farming models was beneficial to improving the water quality of main canals, but it did not bring about a substantial improvement in the sustainable development of Honghu Lake. This may be related to various factors that undermine the sustainability of the lake’s aquatic ecological environment, such as climate change, natural disasters, internal nutrient release from sediments, and the decline in water environment carrying capacity. Therefore, to advance sustainability in this basin and similar irrigation districts, future efforts should continue optimizing agricultural models to reduce nitrogen/phosphorus inputs, while further mitigating internal nutrient release and climate disaster risks, restoring aquatic vegetation, and enhancing water environment carrying capacity. Full article

The soft drink industry generates effluents with high organic loads and contaminants such as nitrogen and phosphorus, requiring sequential secondary and tertiary treatments to meet international discharge standards. Moving beyond traditional monocultures, this study developed a microbial consortium (forming microalga–fungus pellets), demonstrating a synergistic combination due to the resistance of the pellets, enhancing the treatment efficiency, and facilitating the recovery of the microbial sludge produced. Specifically, the treatment of anaerobic effluents (tertiary treatment) from the soft drink industry using consortia of the fungus Penicillium gravinicasei and the microalgae Tetradesmus obliquus and Chlorella sp. in aerated reactors was evaluated, analyzing the impact of aeration rates (0.5–3.5 vvm) on pollutant removal and microbial sludge production. The results showed that moderate aeration rates (1.5 vvm) optimized the removal of COD (up to 92.5%), total nitrogen (TN) (up to 79.3%), and total phosphorus (TP) (up to 83.4%) in just 2.5 h. Furthermore, excessive aeration reduced treatment efficiency due to microbial stress and difficulty in forming microalga–fungus pellets. The Chlorella sp. consortium showed greater stability, while T. obliquus was more sensitive to the aeration rate. Microbial sludge production was also optimized at around 1.5 vvm, consequence of the pollutant removal, with the formation of pellets that facilitated biomass harvesting. Full article

Lake eutrophication is governed by persistent anthropogenic nutrient inputs, primarily nitrogen (N), phosphorus (P) and cryptic internal nutrient cycling processes that sustain bioavailable nutrient pools. While the impact of external nutrient loads on lake eutrophication has been extensively studied, the role of internal nutrient cycling in lake ecosystems remains underexplored. In this study, the hierarchical bootstrap generalized linear model (HBGLM) to long-term summer water quality data (1999–2020) from Lake Dianchi, China, to explore the relative importance of nitrogen (N), phosphorus (P), as well as the limitations of N and P on the growth of phytoplankton. The results revealed that from 1999 to 2020, the Chla and TP concentrations decreased by 49% and 78%, respectively, and that internal nutrient cycling significantly influenced changes in nutrient concentrations, reflecting the relationships among N, P, and chlorophyll a (Chla). Particularly in 2007, 2013, and 2017, the long-term trends of the TN:TP ratio, an indicator of potential nutrient limitation in the lake, were consistent with changes in the distributions of the average slopes of TN and TP across different periods, indicating that these years primarily exhibited patterns of colimitation by N and P or P limitation, indirectly confirming that Lake Dianchi will transition from N and P colimitation to being limited primarily by P. This study reveals that N is typically the primary limiting element, while P is a key element promoting water eutrophication. To further validate improvements to existing eutrophication mitigation models, conducting carefully de-signed experiments at different scales is recommended. Full article

Although the sediment–water interface of deep and large reservoirs is recognized as a dominant source of internal phosphorus (P) loading, the quantitative hierarchy of environmental drivers and their interaction thresholds remains poorly resolved. Here, we integrate 512 studies to provide the first process-based synthesis that partitions P release fluxes among temperature, pH, dissolved oxygen, salinity, sediment properties, and microbial activity across canyon, valley, and plain-type reservoirs. By deriving standardized effect sizes from 61 data-rich papers, we show that (i) a 1 °C rise in bottom-water temperature increases soluble reactive P (SRP) flux by 12.4% (95% CI: 10.8–14.0%), with sensitivity 28% lower in Alpine oligotrophic systems and 20% higher in warm monomictic basins; (ii) a single-unit pH shift—whether acid or alkaline—stimulates P release through distinct desorption pathways,; and (iii) each 1 mg L⁻¹ drop in dissolved oxygen amplifies release by 31% (25–37%). Critically, we demonstrate that these drivers rarely act independently: multi-factor laboratory and in situ analyses reveal that simultaneous hypoxia and warming can triple the release rate predicted from single-factor models. We further identify that >75% of measurements originate from dam-proximal zones, creating spatial blind spots that currently limit global P-load forecasts to ±50% uncertainty. To close this gap, we advocate coupled metagenomic–geochemical observatories that link gene expression (phoD, ppk, pqqC) to real-time SRP fluxes. The review advances beyond the existing literature by (1) establishing the first quantitative, globally transferable framework for temperature-, DO-, and pH-based management levers; (2) exposing the overlooked role of regional climate in modulating temperature sensitivity; and (3) providing a research agenda that reduces forecasting uncertainty to <20% within two years. Full article

The construction of cascade reservoir systems (CRSs) is increasing globally, providing reliable energy and water resources for human social development, while also having significant impacts on the watershed water environment, particularly in terms of nitrogen and phosphorus distribution in the rivers and lakes of these areas. Watershed management authorities urgently need model tools that can comprehensively analyze the sources of nitrogen and phosphorus in CRSs and the nitrogen and phosphorus cycling in lakes and reservoirs. Therefore, this study establishes a model framework that includes a watershed nutrient load model and a hierarchical reservoir nutrient cycling model, validating and analyzing this framework in the Water Diversion Basin from the Luanhe River to Tianjin (WDBLT) in North China, which yields nitrogen and phosphorus substance flows over different time scales. The conclusions show that banning cage culture and curbing point sources improved reservoir water quality, and the internal TP flux serves as a key environmental indicator. This model framework is scientifically sound, easy to operate, and does not require high data demands, demonstrating high practical value for similar water environmental management in CRS. Full article

Phosphorus (P) release from reservoir sediments critically influences water quality and ecosystem stability. This study analyzed surface sediments from four representative zones to investigate phosphorus fraction distribution, key influencing factors, and implications for water quality. Results showed that total phosphorus (TP) content in sediments from main and tributary inflow zones was significantly higher than in open-water and transition zones. Inorganic phosphorus (IP) was the dominant form, with iron-bound phosphorus (Fe-P) accounting for 33.2–42.0% of IP. A strong correlation existed between P release and the Fe/P molar ratio; notably, when the ratio approached 10, phosphorus desorption increased significantly, indicating a shift from sink to source. Sediments with grain sizes <0.01 mm had the highest P release rates, suggesting particle size, Fe content, and hydrodynamics jointly regulate P mobilization. Using the Diffusive Gradients in Thin Films (DGT) technique, phosphorus release in inflow zones exceeded 1 g/m² in all hydrological periods, contributing substantially to internal loading. Sediment-derived P primarily influenced bottom water, while surface water was more affected by external inputs. These findings highlight the spatial heterogeneity of P release and underscore the need for zone-specific management strategies in reservoir systems. Full article

Lake Winona, a 129 ha eutrophic urban lake comprised of two interconnected basins, exceeds state water quality standards for total phosphorus. Historical lake nutrient data and traditional watershed modeling for the lake’s two basins highlighted multiple major pathways (e.g., municipal stormwater discharges, watershed runoff, internal loading, and wetland discharges) for total phosphorus (P) loading, with >900 kg P/year estimated entering the water columns of each basin. Updated data sources and newer watershed modeling resulted in significantly different (both higher and lower) P loading estimates for the various P sources, especially watershed runoff and internal loading. Overall, basin-specific loading estimates using the updated model were significantly lower (28–40%) than previous estimates: 680 and 546 kg P/year mobilized in the western and eastern basins, respectively. To achieve state water quality standards (<60 ppm P for the western basin, <40 ppm for the eastern basin), watershed and internal P loading each would need to be reduced by approximately 120 kg P/year across the two basins. Reductions could be achieved by a combination of alum treatments to reduce internal loading, removal of common carp (Cyprinus carpio) to prevent interference with alum treatments and nutrient releases via excretion and defecation, and six engineered structures to intercept P before it enters the lake. The different P reduction projects would cost USD 119 to 7920/kg P removed, totaling USD 5.2 million, or USD 40,310/hectare of lake surface area. Full article

Lake eutrophication, often driving harmful algal blooms (HABs) and ecosystem degradation, involves complex biogeochemical shifts within sediments. Changes in the sedimentary dissolved organic matter (DOM) composition during transitions from macrophyte to algal dominance are thought to critically regulate internal phosphorus (P) loading, yet the underlying mechanisms, especially in vulnerable plateau lakes like Qilu Lake, require further elucidation. This study investigated the coupled cycling of carbon (C) and P in response to historical ecosystem succession and anthropogenic activities using a 0–24 cm sediment core from Qilu Lake. We analyzed the total organic carbon (TOC), total phosphorus (TP), sequential P fractions, and DOM fluorescence characteristics (EEM-PARAFAC), integrated with chronological series data. The results revealed an asynchronous vertical distribution of TOC and TP, reflecting the shift from a submerged macrophyte-dominated, oligotrophic state (pre-1980s; high TOC, low TP, stable Ca-P dominance) to an algae-dominated, eutrophic state. The eutrophication period (~1980s–2010s) showed high TP accumulation (Ca-P and NaOH85 °C-P enrichment), despite a relatively low TOC (due to rapid mineralization), while recent surface sediments (post-2010s) exhibited a high TOC, but a lower TP following input controls. Concurrently, the DOM composition shifted from microbial humic-like dominance (C1) in deeper sediments to protein-like dominance (C3) near the surface. This study demonstrates that the ecosystem shift significantly regulates P speciation and mobility by altering sedimentary DOM abundance and chemical characteristics (e.g., protein-like DOM correlating negatively with Ca-P), reinforcing a positive feedback mechanism that sustains internal P loading and potentially exacerbates HABs. DOM molecular characteristics emerged as a key factor controlling the internal P cycle in Qilu Lake, providing critical insights for managing eutrophication in plateau lakes. Full article

Phosphorus plays a key role in water eutrophication. The release of endogenous phosphorus from sediments maintains eutrophication in Dianchi Lake. This study aimed to summarize and analyze the research trends, occurrence characteristics, adsorption and release characteristics, influencing factors, and prospects of internal phosphorus pollution control in Dianchi Lake based on a literature search and data integration. The results revealed that sediment phosphorus in Dianchi Lake has been widely studied. From previous studies, the total phosphorus (TP) content and various forms of phosphorus in the Dianchi Lake sediments have decreased since 2010. The TP contents measured in Dianchi Lake in previous research were considerably different owing to the influence of sampling depth and dredging projects. The TP content in the sediments of Dianchi Lake was higher but its release risk was lower than those in other lakes in China. The risk of release was higher in Caohai and North Waihai than that in Central Waihai and South Waihai. In addition to environmental factors at the sediment–water interface, sediment characteristics, and ecosystem degradation are important factors that affect phosphorus migration and transformation. Over the past 30 years, sediment dredging has been the primary measure for reducing the internal pollution load in Dianchi Lake. However, more accurate sediment dredging and systematic vegetation–algae–sediment co-management measures are needed for water ecosystem restoration in Dianchi Lake. This study provides new insights into the study of internal phosphorus pollution. Full article

The internal nutrient load of natural and artificial lakes is a worldwide problem. To minimize its potential risks, the dredging of the highly eutrophic shallow first reservoir of Kis-Balaton (Lake Hídvégi) is planned in the near future. Our study aimed to evaluate the potential effects of dredging and desiccation on water and sediment quality. Experimental dredging was carried out in the northernmost part of Lake Hídvégi (2023). The physical and chemical characteristics of the sediment and nutrient loss during desiccation were examined in a column experiment. The relationships between the properties of leachate and sediment were identified using principal component analysis (SPSS). Spatial variations in sediment particle size distribution, nutrient content, and other chemical parameters (e.g., organic matter) suggest that deeper core sampling than the depth of preliminary dredging is necessary for a more comprehensive assessment of potential impacts. We found that spatiotemporally varying the dominance of chemical and biological processes affects the amount of and changes in phosphorus fractions under lake-/sediment-specific conditions. The readily available calcium- and iron-bound phosphorus, texture, and organic matter content of the sediment play an important role in phosphorus fixation/release. Based on our results, dredging and desiccation are feasible within the intended operating parameters. The sediment’s composition does not preclude potential agricultural disposal. Full article

In Finland, municipal wastewater treatment has significantly improved in recent decades, leading to a substantial reduction in nutrient loads from wastewater discharged into water bodies. For example, in the marine area off Turku in the Archipelago Sea, located in the northern Baltic Sea, the total phosphorus load from wastewater has decreased to approximately one-eighth of its level in the early 1990s. Simultaneously, the total nitrogen load has been reduced to one-fifth, and the ammonium nitrogen load is now less than 5% of its peak in 1994. This study examines in detail how water quality parameters and phytoplankton indicators in wastewater-affected areas have changed during the same period in which wastewater loads have significantly decreased. This reduction has contributed to positive developments in the marine area off Turku, although the goal of achieving good ecological status remains unmet. In Raisio Bay, chlorophyll a concentrations decreased by 68% following the relocation of wastewater discharge. In Rauvola Bay, the reduction was estimated to be 36%. Over the past 15 years, the biomass of nitrogen-fixing cyanobacteria has increased in northern Airisto. This trend appears to be driven by a decrease in external nitrogen loading in combination with increased internal phosphorus loading. Water bodies in the inner archipelago continue to receive excessive nutrient inputs from the surrounding catchment area, while internal loading significantly delays the restoration process. Full article

The natural process of lake and reservoir eutrophication through nutrient accumulation within sediments has been accelerated through anthropogenic sources of nitrogen and, especially, phosphorus (P). Stored nutrients can result in significant internal loading (during periods of low sediment redox potential or elevated pH), which may drive poor water quality despite best practices in catchment management. Internal P loading can promote proliferation of cyanobacterial and algal taxa responsible for harmful algal blooms (HABs), as well as taste and odour (T&O) and cyanotoxin events. Here, we investigate the sediment and water column P content of eight reservoirs by analysing iron-bound (Fe-P), calcium-bound (Ca-P), and labile P fractions. We find that all but one reservoir demonstrated high iron (Fe) content (27–52 g Fe/kg sediment), suggesting a high Fe-P binding capacity and hence a potentially high susceptibility to redox-mediated internal loading. However, we found no correlation between Fe-P and Fe content in sediments, suggesting the Fe pool was not saturated with P and thus has capacity for further storage. All sites had low levels of labile P (up to 0.14 mg P-PO₄/g dry sediment), with the highest pool of P being Ca-bound, which would be expected based on catchment geology and the presence of Ca-minerals which bind P. Currently, within industry, emphasis falls on controlling the external loading of nutrients from the surrounding catchment, often ignoring the critical role of internal loading. However, here, we demonstrate the need to continually monitor sediment P content and potential internal loading as part of the standard monitoring regime used by water companies to inform reservoir management strategies. Full article

In eutrophic aquatic ecosystems like the Archipelago Sea in the northern Baltic, the role of the sediment as a sink and source of nutrients is especially important. Based on previous research on the Archipelago Sea, it can be concluded that the amount of stored phosphorus that can be released with time from sediments is large, and internal phosphorus recycling processes may thus play a key role in phosphorus fluxes in the coastal zone. The release of nutrients from the sediment has been suggested as an explanation for the fact that a substantial reduction in the external nutrient load does not always result in a corresponding reduction in nutrient concentrations and phytoplankton biomass in recipient waters. However, the magnitude of the actual internal phosphorus load in the Archipelago Sea has not been successfully estimated, or the estimates have been evidently too high. In this study, calculations were performed based on the measured water quality data to estimate how much phosphorus has been transported from the bottom water layer to the surface layers during the biological production season for use in algal production. In other words, the magnitude of the effective internal phosphorus load in the Archipelago Sea was determined. The calculations resulted in a summer internal net phosphorus load in the surface layer of approximately 270 tons over 5 months. The other total phosphorus load in the Archipelago Sea, which mainly (60%) originates from the catchment area, was 575 t/a. A permanent way to mitigate internal loading has been thought to be to reduce external loading. However, a decrease in internal loading occurs with an unknown delay, making it impossible to predict the recovery rate. Full article