Average Total Phosphorus Concentration Research Articles

Reservoir regulation-induced variations in water level impacts cyanobacterial bloom by the changing physiochemical conditions

Gaining insight into the impact of reservoir regulation on algal blooms is essential for comprehending the dynamic changes and response mechanisms in the reservoir ecosystem. In this study, we conducted a comprehensive field investigation linking physiochemical parameters, and phytoplankton community to different water regimes in the Three Gorges Reservoir. Our aim was to explore the effects of reservoir regulation on the extinction of cyanobacterial blooms. The results showed that during the four regulatory events, the water levels decreased by 2.02–4.33 m, and the average water velocity increased 68 % compared to before. The average total phosphorus and total nitrogen concentrations reduced by up to 20 %, and the cyanobacterial biomass correspondingly declined dramatically, between 66.94 % and 75.17 %. As the change of water level decline increasing, there was a significant increase of algal diversity and a notable decrease of algal cell density. Additionally, a shift in the dominant phytoplankton community from Cyanobacteria to Chlorophyceae was observed. Our analysis indicated that water level fluctuations had a pronounced effect on cyanobacterial extinction, with hydrodynamic changes resulting in a reduction of cyanobacterial biomass. This research underlined the potential for employing hydrodynamic management as a viable strategy to mitigate the adverse ecological impacts of cyanobacterial blooms, providing a solution for reservoir's eco-environmental management.

A pilot-scale anoxic-anaerobic-anoxic-oxic combined with moving bed biofilm reactor system for advanced treatment of rural wastewater

Rural domestic poses a significant challenge to treatment technologies due to significant fluctuations in both water quality, particularly in terms of carbon concentration, and quantity. Conventional biological technology, such as anaerobic-anoxic-oxic (A2O) systems, is inefficient. In this work, a continuous pilot-scale anoxic-anaerobic-anoxic-oxic (A3O) reactor with a moving bed biofilm reactor (MBBR) system was constructed and optimized to improve the treatment efficiency of rural domestic wastewater. The sludge return ratio, volume ratio of the oxic-to-anoxic zone (Voxi/Vano), step-feeding and hydraulic retention time (HRT) at low temperature were considered the main parameters for optimization. Microbial analysis was performed on both the mixed liquor and carrier of the A3O-MBBR system under initial and post-optimized conditions. The results indicated that the A3O-MBBR improved the treatment efficiency of rural domestic wastewater, especially for total phosphorus (TP), which increased by 20 % compared with that of the A2O-MBR. In addition, the removal efficiencies of nitrogen and phosphorus were further optimized, and the average concentrations of total nitrogen (TN) and TP in the effluent reached 2.46 and 0.364 mg/L, respectively, at a sludge reflux ratio of 100 or 150 %, Voxi/Vano =200 %, step-feeding of 0.5Q/0.5Q (anaerobic/anoxic) and HRT of 15 h at low temperature in the A3O-MBBR, which met standard A of GB18918–2002, China (TN < 15 mg/L, TP < 0.5 mg/L). The average rate of attaining the standard increased by 58.63 % (post optimization). The microbial analysis showed an increase in species diversity and richness after the parameters were optimized. Moreover, compared to the microbial community structure before optimization, the post-optimization exhibited a more stable microbial structure with a significant enrichment of functional bacteria. Defluviimonas, Novosphingobium and Bifidobacterium, considered as the dominant nitrification or denitrifying bacteria, were enriched in the suspended sludge of the MBBR reactor, which the relative abundance increased by 3.11 %, 3.84 %, and 3.24 %, respectively. Further analysis of the microbial community in the carrier revealed that the abundance of Nitrospira and the denitrifying bacteria carried by the carrier were much greater than those in the suspended sludge. Consequently, the microorganism cooperation between suspended sludge and biofilm might be responsible for the improved performance of the optimized A3O-MBBR.

Effects of storm runoff on the spatial-temporal variation and stratified water quality in Biliuhe Reservoir, a drinking water reservoir.

Stormflow runoff is an important non-point source of pollution in drinking water reservoirs. Storm runoff is usually very turbid and contains a high concentration of organic matter, therefore affecting water quality when it enters reservoirs. In order to investigate the impact of storm runoff on spatial-temporal variation and stratification of water quality during this rainstorm event, the inflow process of the storm runoff was studied through a combination of field investigation and simulation using the Delft3D-Flow model. Water samples were collected from Biliuhe Reservoir at four different periods: before storm runoff, storm runoff flood peak period, 1week after storm runoff, and 5weeks after storm runoff. The results showed that the input of storm runoff resulted in a significant increase in the nitrogen (N) and phosphorus (P) in the reservoir water, especially in the reservoir entrance. The concentrations of total nitrogen (TN) and total phosphorus (TP) gradually decreased after the flood peak period; however, the average concentrations of TN and TP in the entire reservoir remained higher than those before the storm runoff levels for an extended duration. The storm runoff will greatly contribute to the contamination of water quality in a reservoir, and the water quality cannot be quickly restored by self-purification in the short term. During the flood peak period, under the influence of density current, the electrical conductivity (EC) and turbidity increased significantly in the water depth of 10-15m, so that the reservoir water had obvious stratification between 10 and 15m. The form of pollutants in storm runoff was mostly in particle phosphorus. Total particulate phosphorus (TPP) concentration was 0.015 ± 0.011mg/L, accounting for 44.12% of total phosphorus (TP) concentration in storm runoff flood peak period. The process of a rainstorm caused runoff, which carried high levels of turbidity, particulate phosphorus, and organic matter. The storm runoff disrupts the stratification of the reservoir water. In terms of vertical distribution, the turbidity in the reservoir area increased to 73.75 NTU. Therefore, the occurrence of significant turbidity density flow in the reservoir is frequently accompanied by intense rainfall events. Gaining insights into the impact of storm runoff on the vertical distribution of reservoir turbidity can help managers in selecting an appropriate inlet height to mitigate high turbidity outflow.

Coupled In-Situ Fermentation for Enhanced Biological Phosphorus Removal from Digested Swine Wastewater

This study demonstrated the feasibility of enhanced biological phosphorus removal coupled with in-situ fermentation (EBPR-F) to improve phosphorus removal from real digested swine wastewater. We used fermentable substrates (casein hydrolysate and glucose) as the external carbon sources to promote in-situ fermentation and enhance biological phosphorus removal. Compared with conventional EBPR dominated by Candidatus Accumulibacter, EBPR-F had significantly better phosphorus removal with enriched polyphosphate-accumulating organisms (PAOs). Under supplementation with 100 mg/L glucose, total phosphorus (TP) removal was over 95% in EBPR-F, with an average TP concentration in the effluent below 1.0 mg/L, satisfying the discharge standard (8 mg P/L) in China. The PAO activity and relative abundance of Candidatus Accumulibacter (44.7% ± 3.1%) and Tetrasphaera (18.1% ± 6.6%) in EBPR-F were much higher than those in EBPR. The improvement in phosphorus removal of EBPR-F was due to the enrichment of Tetrasphaera through the enhanced in-situ fermentation, as Tetrasphaera can efficiently ferment complex organic matter and provide bioavailable organics for phosphorus removal.

Nutrient Loadings and Exchange between the Curonian Lagoon and the Baltic Sea: Changes over the Past Two Decades (2001–2020)

The Baltic Sea faces prolonged eutrophication due to nutrient pollution, with the Nemunas River regulating nutrient input via the Curonian Lagoon. In this study, we aimed to assess the seasonal variations and changes over the past two decades in nutrient concentrations within the Curonian Lagoon–Baltic Sea transitional zone, and to identify the main factors affecting these trends. We observed slightly reduced nutrient levels in the lagoon and the Klaipėda Strait and increased nitrogen loadings in the Baltic Sea nearshore over time. Between 2007 and 2009, the average total nitrogen (TN) concentrations in the Klaipeda Strait and the Baltic Sea were 1.60 ± 0.25 and 0.54 ± 0.04 mg/L, respectively, while the average total phosphorus (TP) concentrations in the Klaipeda Strait and the Baltic Sea were 0.061 ± 0.04 and 0.03 ± 0.01 mg/L, respectively. Between 2018 and 2020, TN concentrations in the Strait and the Sea were 1.2 ± 0.36 and 0.65 ± 0.32 mg/L, respectively, while the average TP concentrations in the Klaipeda Strait and the Baltic Sea were 0.025 ± 0.002 and 0.021 ± 0.002 mg/L, respectively. The average annual amount of TN and TP entering the Curonian Lagoon from the sea was 2736 t and 162 t, respectively. Significantly higher nutrient influx to the Baltic Sea was recorded reaching 32,302 t for TN and 1278 t for TP. Nutrient concentrations correlated with water temperature, salinity, and dissolved oxygen, influenced by seasonal runoff patterns and climate change. Over time, there have been noticeable shifts in environmental conditions, including rising temperatures, decreasing oxygen levels, salinity changes, increased evaporation, and reduced precipitation.

Estimation of Total Phosphorus Concentration in Lakes in the Yangtze-Huaihe Region Based on Sentinel-3/OLCI Images

Total phosphorus (TP) concentration is a crucial parameter to assess eutrophication in lakes. As one of the most concentrated regions for freshwater lakes, the Yangtze-Huaihe region plays a significant role in monitoring TP concentrations for the sustainable utilisation of China’s water resources. In this study, a TP concentration estimation model suitable for large-sized lake groups was developed using a combination of measured and remote sensing data powered by advanced machine learning algorithms. Compared to traditional empirical models, the model developed in this study demonstrates significant accuracy in fitting (R2 = 0.53, RMSE = 0.08 mg/L, MAPE = 34.20%). Moreover, the application of this model to lakes in the Yangtze-Huaihe region from 2017 to 2022 has been conducted. The multi-year average TP concentration was 0.18 mg/L. Spatial distribution analyses showed that total phosphorus concentrations were higher in small lakes. In terms of temporal changes, the interannual decreases in total phosphorus concentrations were 0.02 mg/L, 0.01 mg/L, and 0.01 mg/L for small, medium, and large lakes, respectively. We also found that large lakes typically exhibited a “high in spring and summer, low in autumn and winter” pattern until 2020, but transitioned to a “high in summer and autumn, low in spring and winter” pattern after 2020 due to the removal of closed fish nets, which were having a significant impact on the lake ecosystem. Other lakes in the area consistently showed a pattern of “high in spring and summer, low in autumn and winter” during the six-year period. These findings may provide useful references and suggestions for the environmental protection and management of lakes in China.

Occurrence forms and environmental characteristics of phosphorus in water column and sediment of urban waterbodies replenished by reclaimed water

To illustrate the evolution process, environmental feature and phytoremediation effect of phosphorus (P) in waterbodies with long-term replenishment by reclaimed water (RW), an urban waterbody using RW as the sole supply was selected as a case study. The concentration and distribution of soluble reactive phosphate (SRP), dissolved organic P (DOP) and particulate P (PP) in water column, as well as organic P (OP), inorganic P (IP), exchangeable P (Ex-P), BD-P (redox-sensitive P), NaOH-P (P bound to Fe and Al oxyhydroxides) and HCl-P (P bound to Ca) in sediment were investigated. Results showed that the seasonal average concentrations of total phosphorus (TPw) in water column ranged from 0.048 to 0.130 mg∙L−1, with the highest in summer and the lowest in winter. P in water column was predominantly present in dissolved state, with the similar proportions of SRP and DOP. SRP decreased apparently in midstream, where the phytoremediation was applied extensively. PP content obviously increased in non-phytoremediation area in downstream, due to visitor activity and sediment resuspension. Total phosphorus (TPs) in sediments was between 352.9 and 1331.3 mg∙kg−1, with average 365.7 mg∙kg−1 of IP and 382.8 mg∙kg−1 of OP. Among IP, HCl-P had the highest proportion, followed by BD-P, NaOH-P and Ex-P. OP was significantly higher in phytoremediation areas than that in non-phytoremediation areas. Coverage of aquatic plants was positively correlated with TP, OP, BAP, while it was negatively correlated with BD-P. Hydrophyte stabilized and conserved active P in sediment and prevented release of active P. Moreover, hydrophyte increased NaOH-P and OP contents in sediment through regulating the abundance of phosphorus-solubilizing bacteria (PSB), such as Lentzea and Rhizobium. Four sources were identified through two multivariate statistical models. RW and runoff were the dominant sources of P accounting for 52.09 %, which mainly contributed to P in sediment especially IP.

Output response of non‐point source pollutants and its driving mechanisms of different arable land use patterns

AbstractThe irrational use of arable land has caused increased nutrient loss and aggravated non‐point source (NPS) pollution. This natural process has a significant socioeconomic origin. However, because of the inconsistency between the simulation scale of NPS pollution mechanism models and the statistical calibre of socioeconomic factors, the quantitative expression of the relationship between socioeconomic development, arable land use, and NPS pollutant output needs further exploration. We improved the mechanism model using a flow accumulation algorithm to construct a measure of the NPS pollutant output response at the administrative region scale. The mediating effect test confirmed that socioeconomic factors such as labour transfer, farmland property rights, large‐scale operations, agricultural technological progress and risk aversion were also fundamental drivers that affected the NPS pollutant output by changing the arable land use form factors. The mediating drivers included endowment, landscape morphology, management system, planting mode and production capacity. The average total phosphorus concentrations per unit area in townships with various arable land use patterns were grain and economical crop extensive operations (0.83 mg/L); grain and economical crop scale operations (0.54 mg/L); grain, oil, and cotton scale operations (0.45 mg/L); and suburban compound operations (0.44 mg/L). We found that the degree of influence and path of each fundamental and mediating driver on NPS pollutant output concentrations showed clear differences between townships with different patterns, which were the primary reasons for the significant differences in NPS pollutant output responses.

Filtration columns containing waste iron shavings, loofah, and plastic shavings for further removal of nitrate and phosphate from wastewater effluent

A novel pilot-scale advanced treatment system combining waste products as fillers is proposed and established to enhance the removal of nitrate (NO3−-N) and phosphate (PO43−-P) from secondary treated effluent. The system consists of four modular filter columns, one containing iron shavings (R1), two containing loofahs (R2 and R3), and one containing plastic shavings (R4). The monthly average concentration of total nitrogen (TN) and total phosphorus (TP) decreased from 8.87 to 2.52 mg/L and 0.607 to 0.299 mg/L, respectively. Micro-electrolysis of iron shavings produces Fe2+ and Fe3+ to remove PO43−-P, while oxygen (O2) consumption creates anoxic conditions for subsequent denitrification. Gallionellaceae, iron-autotrophic Microorganisms, enriched the surface of iron shavings. The loofah served as a carbon source to remove NO3−-N, and its porous mesh structure facilitated the attachment of biofilm. The plastic shavings intercepted suspended solids and degraded excess carbon sources. This system can be scaled up and installed at wastewater plants to improve the water quality of effluent cost-effectively.

Effects of river input flux on spatiotemporal patterns of total nitrogen and phosphorus in the Pearl River Estuary, China

The increasing riverine nutrient sources have significantly affected the ecological environment of estuaries and coastal waters, resulting in deteriorating land-sea water quality and intensified eutrophication. However, the effects of river input flux on spatiotemporal patterns of total nitrogen (TN) and total phosphorus (TP) were poorly understood in the Pearl River Estuary (PRE). In this study, the spatiotemporal patterns of TN and TP concentrations and river input flux of PRE were studied based on the seasonal nutrients monitoring data obtained for the rivers and estuary in 2019. The results showed the spatiotemporal patterns of the TN and TP concentrations in the eight rivers of the PRE were different, and the annual average concentrations of TN and TP in the rivers entering the PRE were 207.18 ± 105.13 and 3.51 ± 1.70 μmol/L, respectively. The annual river TN and TP fluxes discharged into the PRE were 8.61 × 1010 and 1.55 × 109 mol/year, respectively. In addition, the significantly decreasing trends in of TN and TP concentrations from upper estuary to offshore seawater were observed in the PRE, which implied TN and TP showed conservative behaviour in all season and only the dry season, respectively. Moreover, the annual average concentrations of TN and TP in the estuary were 70.64 ± 10.10 and 1.67 ± 0.78 μmol/L, respectively. The annual average ratios of TN/TP for rivers, freshwater, mixed and seawater were 59.31 ± 5.98, 59.45 ± 3.75, 45.73 ± 21.27 and 330.94 ± 434.71 respectively, which were higher than the Redfield ratios. These results indicated that the water quality in most areas of the PRE is significantly polluted and that the TN and TP in seawater were significantly influenced by river inputs. Therefore, monitoring and management of unified TN and TP nutrient indicators discharge from rivers entering the sea can be strengthened in the PRE, and eutrophication mitigation strategy should be established and implemented across river-estuary-coast continuum systems in the Great Bay Area.

Improvement of soil fertility and rice yield after long-term application of cow manure combined with inorganic fertilizers

Fertilization is an effective technique to improve soil fertility and increase crop yield. The long-term effects of different fertilizers on soil considerably vary. Over 38 consecutive years of different fertilization positioning experiments in a double cropping rice field of Qiyang Red Soil Experimental Station, seven different fertilization treatments including CK (no fertilization), NPK (nitrogen, phosphorus, and potassium fertilizer), M (cow manure), NPKM (nitrogen, phosphorus, and potassium with cow manure), NPM (nitrogen and phosphorus with cow manure), NKM (nitrogen and potassium with cow manure), and PKM (phosphorus and potassium with cow manure) were applied to study the effects on rice yield, soil fertility, and nutrient apparent balance in a paddy field. The results showed that the annual average yields of rice in NPKM, NPM, NKM, PKM, M, NPK and CK treatments ranged from 6 214 to 11 562 kg ha–1. Yields under long-term organic and inorganic treatments (NPKM, NPM, NKM and PKM) were 22.58, 15.35, 10.53 and 4.41%, respectively, greater than under the NPK treatment. Soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN) and available potassium (AK) concentration with long-term organic and inorganic treatment (NPKM, NPM, NKM and PKM) were significantly higher than in inorganic fertilizer (NPK) treatments. Soil total phosphorus (TP) and available phosphorus (AP) contentration with organic fertilizer combined with inorganic N and P fertilizer treatment (NPKM, NPM and PKM) were significantly higher than with inorganic fertilizer alone (NPK treatments). The average annual rice yield (11 562 kg ha–1), SOC (20.88 g kg–1), TN (2.30 g kg–1), TP (0.95 g kg–1), TK (22.50 g kg–1) and AP (38.94 mg kg–1) concentrations were the highest in the NPKM treatment. The soil AN concentration (152.40 mg kg–1) and AK contentration (151.00 mg kg–1) were the highest in the NKM treatment. N and P application led to a surplus of nitrogen and phosphorus in the soil, but NPKM treatment effectively reduced the surplus compared with other treatments. Soils under all treatments were deficient in potassium. Correlation analysis showed that SOC, TN, AN, TP, and AP contentration was significantly correlated with rice yield; the correlation coefficients were 0.428, 0.496, 0.518, 0.501, and 0.438, respectively. This study showed that the combined application of N, P, and K with cow manure had important effects on rice yield and soil fertility, but balanced application of N, P, and K with cow manure was required.

Optimization of a compact on-site stormwater runoff treatment system: Process performance and reactor design

Stormwater runoff has become a major anthropogenic urban pollution source that threatens water quality. In this study, coagulation-sedimentation, and ammonium ion exchange and regeneration (AIR) modules were coupled as a CAIR system to efficiently treat stormwater runoff. In the coagulation module, 99.3%, 91.7%, and 97.0% of turbidity, total phosphorus, and chemical oxygen demand could be removed at an optimized poly-aluminum ferric chloride dosage of 30 mg/L, and the continuous experiment confirmed that the full load mode was more suitable for its rapid start-up. In the AIR module, dynamic ammonium removal indicated that the breakthrough time decreased with the rising initial concentration and superficial velocity. The Modified Dose Response (MDR) model described the ammonium exchange behavior better than the Thomas and the Bohart-Adams models. Then, a design flow of the ion exchange reactor was constructed by correlating constants in the MDR model with engineering parameters, and the ion exchange reactor was designed for continuous operation of the CAIR system. The average concentrations of chemical oxygen demand, total phosphorus, ammonium nitrogen, and total nitrogen in the effluent of the CAIR system were 7.22 ± 2.26, 0.17 ± 0.05, 1.49 ± 0.01, and 1.62 ± 0.02 mg/L, respectively. The almost unchanged exchange capacity and physicochemical properties after the multicycle operation confirmed the durability of zeolite for ion exchange. Techno-economic analysis suggested that the CAIR system is practically promising for stormwater management with efficient pollutants removal, small footprint, and acceptable operating cost.

Biodegradation Kinetics of Organic Matter in Water from Sludge Dewatering after Autothermal Thermophilic Aerobic Digestion

The study presents the research results on the rejected water generated in dewatering sludge stabilised in Autothermal Thermophilic Aerobic Digestion (ATAD) technology. The research was carried out in three municipal wastewater treatment plants (WWTPs), with a capacity of 1500 to 3260 m3 d−1 and a sludge node capacity of 835 to 2000 kg DM d−1. The mean content of Kjeldahl nitrogen (TKN) in the rejected water samples taken from each object ranged from 485 to 1573 mg N L−1, ammonium nitrogen 318 to 736 mg N L−1, and the average concentration of total phosphorus ranged from 96 to 281 mg P L−1. The average content of organic matter expressed as five-day biological oxygen demand (BOD5) ranged from 205 to 730 mg O2 L−1, while chemical oxygen demand (COD) ranged from 767 to 4884 mg O2 L−1. The study determined the kinetics of the biochemical decomposition of organic matter, assuming that it follows the first-order equation. The average reaction rate constant k in subsequent treatment plants was estimated at 0.424, 0.513 and 0.782 d−1. The R2 coefficient determining the model’s adjustment to empirical values was not lower than 0.952. The organic matter biodegradability index average values ranged from 0.17 to 0.26.

Changes in water chemical composition in Lake Vedlozero and one of its bays as a result of anthropogenic eutrophication

Lake Vedlozero is an accumulating system of a variety of anthropogenic impacts. Since the 1970s, significant changes have occurred in the landscape structure of stream catchments in the southeastern and western parts of the lake’s drainage basin. Deforestation, conversion to arable land and drainage have enriched the lake water with nutrients and organic matter. The northeastern bay of the lake receives substantial amounts of wastewater from the village of Vedlozero and water from the River Vokhtozerka, affected by agriculture in the catchment. High average annual concentrations of total phosphorus (47–173 μg/l) in the water of the bay cause continuous blooming during the open water period. Blooming intensively in the bay, blue-green algae (cyanobacteria) release toxic substances (neuro-, hepato-, and dermatotoxins) dangerous for humans and animals. Massive development of cyanobacteria in the northeastern bay of Lake Vedlozero in summer now causes skin disorders, specifically allergic dermatitis, in Vedlozero village inhabitants (especially children) who swim in the lake.

Cyanobacterial blooms in Ontario, Canada: Continued increase in reports through the 21st century

Favot EJ, Holeton C, DeSellas AM, Paterson AM. 2023. Cyanobacterial blooms in Ontario, Canada: Continued increase in reports through the 21st century. Lake Reserv Manage. XX:XXXXXX. The Ontario Ministry of the Environment, Conservation and Parks samples algal composition in response to public reports of suspected algal blooms, which have been tracked since 1994. In a previous analysis, Winter et al. noted a significant increase in the number of reports of confirmed algal blooms dominated by cyanobacteria from 1994 to 2009. Here, we determined that this increasing trend in the yearly number of confirmed cyanobacterial bloom reports (CCBRs) has persisted in Ontario over the intervening decade, to 2019. More than half of CCBRs were from waterbodies on the Precambrian Shield, in the Georgian Bay (5E) ecoregion, known for cottaging and water-based tourism. Data from the Ontario Lake Partner Program (LPP) was used to investigate total phosphorus (TP) concentrations in waterbodies with CCBRs. Approximately 44% of the waterbodies with a CCBR (mean TP 12.99 µg/L, n = 135) had average spring TP concentrations less than 10 µg/L, compared to 64% for LPP waterbodies with no reported or confirmed cyanobacterial blooms (mean TP 9.79 µg/L, n = 918). The most common taxon of cyanobacteria dominating bloom samples in inland waterbodies was Dolichospermum, followed by Aphanizomenon in waterbodies on the Precambrian Shield, and Microcystis in the Mixedwood Plains ecozone in southern Ontario. While an increase in public awareness cannot be ruled out in contributing to the rise in CCBRs across Ontario, the high proportion of cyanobacterial blooms occurring in oligotrophic waterbodies suggests that there may be a link to climate warming, rendering conditions more favorable for these blooms to occur.

Characteristics analysis of water pollutants in Cihu Lake, China, based on a multivariate statistical analysis method

In order to understand the sources of pollutants and the temporal and spatial distribution characteristics of the water quality in Cihu Lake, China, the monitoring data of seven water quality indicators from 12 sampling sites from 2015 to 2019 were selected, and the temporal and spatial variation laws of the water quality and pollution sources were analyzed by the use of the multivariate statistical analysis method. The results show that nitrogen and phosphorus pollution in the lake is dominant. The average concentrations of total nitrogen (TN) and total phosphorus (TP) exceed the surface water quality Class III standards by 1.6 and 2.2 times, respectively. Spatially, the results of the cluster analysis showed that the water quality in Cihu Lake can be categorized into three regions: the northern half of the lake, the southern half of the lake, and the canal entering the lake. Temporally, the water quality in these three regions can be classified into three categories: March to May (the northern half of Cihu Lake), September to November (the southern half of Cihu Lake), and September (the canal entering Cihu Lake). The discriminant analysis results showed that NH3-N, TN, CODCr, and BOD5 are the main factors that affect the uneven spatial distribution of the water quality of Cihu Lake, while TN, DO, and CODMn are the main factors that affect the temporal difference in the northern half of Cihu Lake, and NH3-N, TP, CODCr, DO, CODMn, TN, and TP are the main factors affecting the temporal difference in the southern half of Cihu Lake and the canal entering Cihu Lake. It was found that the water pollution in the study area can be mainly attributed to the incoming water and urban domestic pollution. The main pollution sources for the canal entering Cihu Lake and the southern half of Cihu Lake are the water from the sewage treatment plant and the domestic sewage that has not been intercepted, while the northern half of Cihu Lake is mainly affected by surface runoff, mixed rainwater and sewage, and internal pollution.

Variation Characteristics of Surface Water Quality in China in Recent Years

Based on data from 839 comparable sections (sites) of the national surface water environmental quality monitoring network from 2012 to 2020, the variation tendency of surface water environmental quality over the past nine years was analyzed. The results showed that the environmental quality of surface water in China has continuously improved, the proportion of Grade Ⅰ-Ⅲ water quality increased steadily, and the proportion of inferior Grade Ⅴ water quality decreased in succession. The annual average concentration of ammonia nitrogen, total phosphorus, and permanganate index all showed a decreasing trend annually; compared with those in 2012, the three indicator concentrations respectively declined 75.9%, 48.2%, and 17.5% by 2020. In Guangxi, Hainan, and Ningxia, the proportion of Grade Ⅰ-Ⅲ water quality sections was maintained at 100%, whereas Hubei and Jiangxi showed a consecutive decreasing trend, and the other provinces showed a consecutive increasing trend. In Guangxi, Hainan, Ningxia, Hunan, and Fujian, the proportion of inferior Grade Ⅴ water quality sections remained at 0, and the other provinces showed a decreasing trend yearly. The annual average concentration of total phosphorus in Guangxi and Jiangxi and the permanganate index in Hubei, Hainan, and Liaoning increased annually, whereas that in the other provinces decreased to varying degrees. The proportion of Grade Ⅰ-Ⅲ water quality sections in Ten Major basins showed a fluctuating upward trend. The proportion of inferior Grade Ⅴ water quality in the Zhejiang and Fujian Slice Rivers was maintained at 0, and the other river basins showed a fluctuating and declining trend. The annual average of the main pollution indicators all decreased to varying degrees. In 2020, 53% of 32 important lakes were eutrophic, which increased 12% compared to that in 2012. On the whole, surface water quality has generally improved in China during the past nine years; especially since the 13th Five-Year Plan period, remarkable achievements have been made in the prevention and control of water pollution. However, there are differences among various provinces and basins, the improvement in water environmental quality is unbalanced and uncoordinated, water resources are distributed unevenly, and the eutrophication trend of lakes and reservoirs is not optimistic. In the future, water resources, water environment, and water ecology should be overall managed, and great attention should be focused on precise pollution control and ecological restoration of surface water.

Water Purification Effect of Ecological Floating Bed Combination Based on the Numerical Simulation

The Wuqing urban section of the North Canal Basin, Tianjin, is a significant gathering place for multisource pollution, showing the characteristics of a stagnant water body supplied by unconventional water sources. With the development of the economy and society, the water quality of the Wuqing urban section of the North Canal Basin, Tianjin, has been seriously polluted due to the discharge of sewage outlets and the influx of nonpoint source pollution from farmland. In this study, based on the results of special water experiments, a two-dimensional hydrodynamic water quality model was constructed. The concentrations of ammonia nitrogen (NH3-N), total phosphorus (TP), and chemical oxygen demand (COD) in the study area were simulated, and the model parameters were calibrated and verified with the measured values. Based on the model verification, the water quality improvement scheme of the ecological floating bed with different plant ratios was set up to simulate the water quality. The research results showed that the average concentrations of NH3-N, TP, and COD decreased by 10.4%, 15.7%, and of d 26.3%, respectively, after the ecological floating bed was arranged. During model parameter calibration and validation, the RMSE ranges of NH3-N, TP, and COD were 0.09~0.22 mg/L, 0.00~0.02 mg/L, and 0.37~2.42 mg/L, respectively. Other statistical indicators are also within a reasonable range, and the model accuracy and reliability are high. The simulation results of different scenarios showed that the optimal ratio of ecological floating bed plants was 700 m2 of Scirpus validus Vahl and 700 m2 of Canna in zone 1 of the floating bed combination, 430 m2 of Scirpus validus Vahl, and 170 m2 of Iris in zone 2 of the floating bed combination, and 200 m2 of Iris and 200 m2 of Lythrum salicaria in zone 3 of the floating bed combination. This study can provide a theoretical basis for the sustainable development of water purification in the North Canal. It can also provide a model approach for the implementation of river water purification schemes, exemplified by the North Canal.

Multi-Level Control and Utilization of Stormwater Runoff

This study proposes the technology of “runoff storage and seepage utilization” for achieving purification of road rainfall–runoff and presents a multi-level series purification system (PBT-GR) comprising porous asphalt pavement (PAP), a bioretention system (BS), a storage tank (T) and a hydroponic green roof (GR). The operation parameters of each component unit were optimized and the contribution of each unit to pollution was analyzed. The results showed that under typical simulated rainfall, the suspended solids (SS), total nitrogen (TN), total phosphorus (TP), Pb, Zn and Cu removal rates by filtration and interception of porous pavement were 62.26 ± 3.19%, 16.29 ± 1.74%, 29.27 ± 1.37%, 37.61 ± 2.58%, 35.57 ± 4.64% and 31.17 ± 3.27%, respectively. The average concentrations of SS, TN, TP, Pb, Zn and Cu in the effluent of the PBT-GR system were 14.70 ± 2.21 mg/L, 1.52 ± 0.24 mg/L, 0.14 ± 0.04 mg/L, 0.09 ± 0.04 mg/L, 0.11 ± 0.03 mg/L and 0.04 ± 0.01mg/L, respectively, which met the water quality standards recommended in the Chinese guidelines and showed a high adaptability to pollution load. The contents of pesticide residues and heavy metals in cultivated vegetables met the national standards. The period required to recoup the investment in the system was approximately 3 years, indicating its good economic feasibility. The present study can provide a valuable reference of the construction of an efficient, low consumption and sustainable urban stormwater treatment system and can contribute to the improvement in the quality of the urban water environment.

Release of Endogenous Nutrients Drives the Transformation of Nitrogen and Phosphorous in the Shallow Plateau of Lake Jian in Southwestern China

Eutrophication remediation is an ongoing priority for protecting aquatic ecosystems, especially in plateau lakes with fragile ecologies and special tectonic environments. However, current strategies to control the phosphorus (P) and nitrogen (N) levels in eutrophication sites have been mainly guided by laboratory experiments or literature reviews without in-field analyses of the geochemical processes associated with the hydrological and eutrophic characteristics of lakes. This study analyzed the water quality parameters of 50 sites at Lake Jian in May 2019, a moderate eutrophication shallow plateau lake, based on dissolved/sedimentary nitrogen, phosphorous and organic matter, grain size, C/N ratios and stable isotope ratios of δ13C or δ15N in sediments. The results showed that the average total nitrogen (TN) and total phosphorus (TP) concentrations in the lake water were 0.57 mg/L and 0.071 mg/L, respectively. The TN and TP contents of surface sediment ranged from 2.15 to 9.55 g/kg and 0.76 to 1.74 g/kg, respectively. Stable isotope and grain source analysis indicated that N in sediments mainly existed in organic matter form and P mainly occurred as inorganic mineral adsorption. Endogenous pollution contributed to &gt;20% of TN. Furthermore, our findings showed that phosphorus was the nutrient that limited eutrophication at Lake Jian, unlike other eutrophic shallow lakes. In contrast, the nutrient levels in the sediment and input streams belonged entirely to the N-limitation state. The distinctness in release intensity of N and P could modify the N/P limitation in the lake, which affects algae growth and nutrient control. These results demonstrated that reducing exogenous nutrients might not effectively mitigate lake eutrophication due to their endogenous recycling; thus, detailed nutrient monitoring is needed to preserve aquatic ecosystems.