Total Phosphorus Pollution Research Articles

Research on the Non-Point Source Pollution Characteristics of Important Drinking Water Sources

In recent years, freshwater resource contamination by non-point source pollution has become particularly prominent in China. To control non-point source (NPS) pollution, it is important to estimate NPS pollution exports, identify sources of pollution, and analyze the pollution characteristics. As such, in this study, we established the modified export coefficient model based on rainfall and terrain to investigate the pollution sources and characteristics of non-point source total nitrogen (TN) and total phosphorus (TP) throughout the Huangqian Reservoir watershed—which serves as an important potable water source for the main tributary of the lower Yellow River. The results showed that: (1) In 2018, the non-point source total nitrogen (TN) and total phosphorus (TP) loads in the Huangqian Reservoir basin were 707.09 t and 114.42 t, respectively. The contribution ratios to TN export were, from high to low, rural life (33.58%), farmland (32.68%), other land use types (20.08%), and livestock and poultry breeding (13.67%). The contribution ratios to TP export were, from high to low, rural life (61.19%), livestock and poultry breeding (21.65%), farmland (12.79%), and other land use types (4.38%). The non-point source pollution primarily originated from the rural life of the water source protection zone. (2) Non-point source TN and TP pollution loads and load intensities showed significantly different spatial distribution patterns throughout the water source protection area. Specifically, their load intensities and loads were the largest in the second-class protected zone, which is the key source area of non-point source pollution. (3) When considering whether to invest in agricultural land fertilizer control or rural domestic sewage, waste, and livestock manure pollution control, the latter is demonstrably more effective. Thus, in addition to putting low-grade control on agricultural fertilizer loss, to rapidly and effectively improve potable water quality, non-point source pollution should, to a larger extent, also be controlled through measures such as establishing household biogas digesters, introducing village sewage treatment plants, and improving the recovery rate of rural domestic garbage. The research results discussed herein provide a theoretical basis for formulating a reasonable and effective protection plan for the Huangqian Reservoir water source and can potentially be used to do the same for other similar freshwater resources.

Analysis on the variation of total phosphorus concentrations and loads of inflow and outflow rivers from different water resources zones around Lake Taihu

入出湖总磷负荷变化是影响太湖湖体磷收支平衡的关键因素.基于2012-2018年水质水量监测资料，计算全湖及各水资源分区河流入出湖总磷负荷，并以水量加权计算其总磷年平均浓度，探明其时空变化规律；运用双累积曲线法分析不同分区水污关系的变化规律；以月为时间尺度，利用Pearson相关系数，揭示入湖总磷负荷分别与入湖水量、入湖总磷浓度的相关关系；通过讨论分析，明确适用于太湖的入湖总磷平均浓度计算方法、总磷负荷影响因素及控制途径.研究结果表明：（1）水量加权法比算术平均法更加适用于太湖入湖总磷平均浓度的削减管理；环太湖河流入湖总磷浓度多年平均值为0.189 mg/L，明显高于出湖的0.079 mg/L，入湖总磷负荷多年平均值为2206.51 t，也高于出湖的873.73 t；2016年丰水年入、出湖及净入湖总磷负荷均最高，分别为2993.9、1341.1、1652.8 t.（2）湖西区河流入湖总磷浓度多年平均高于所有其他分区，其值为0.226 mg/L，浙西区、武澄锡虞区河流出湖总磷浓度多年平均分别为0.114和0.109 mg/L，均高于其他分区.不同水资源分区的水污关系呈现不同的年际变化规律，但除杭嘉湖区外，其他分区均未表现出入湖总磷得到有效控制的迹象.（3）湖西区和浙西区入湖总磷年负荷多年平均值分别为1748.71和278.61 t，两区各年入湖总磷负荷占总入湖负荷的比重位居前二，湖西区的都在67.88%以上；而浙西区在7%~19%之间变化；太浦河出湖总磷年负荷多年平均值为272.27 t，自2014年起其占出湖总磷年负荷的比重均在30%以上.（4）不同水资源分区月入湖总磷负荷均与入湖水量存在较好的相关关系，且除阳澄淀泖区外，其他分区月尺度入湖总磷负荷变化主要受入湖水量控制.（5）2016年丰水年湖西区入湖河流总磷浓度较高、入湖水量大的共同作用导致了其入湖总磷负荷的显著增加.研究成果可为太湖的磷外源负荷控制提供科学依据.;The variation in inflow and outflow total phosphorus (TP) loads is a key factor affecting the balance of the phosphorus budget for Lake Taihu. Based on the monitoring data of water quality and quantity from 2012 to 2018, the TP load of the rivers in each water resources zone around Lake Taihu were calculated, the flow-weighted mean annual concentrations of TP were attained, and their spatio-temporal variations were analyzed; the double accumulation curve method was adopted to analyze the relationships between water quantity and TP load in different zones; the Pearson correlation coefficient was utilized to reveal the correlation between the TP load and water quantity as well as TP concentrations of the inflow at the monthly time scale; through discussion and analysis, the calculation method of the average TP concentration of inflow applicable to Lake Taihu, the influencing factors of TP loads and measures of controlling the TP load were investigated. The results showed that:(1) The flow-weighted mean concentration of TP is the preferred approach for calculating average concentrations of tributaries with variable flows for Lake Taihu; The average annual TP concentration of inflow rivers of Lake Taihu was 0.189 mg/L, significantly higher than that of outflow rivers (0.079 mg/L). The average annual TP load of the inflow was 2206.51 t, which was also much higher than that of the outflow (873.73 t); in the high flow year of 2016, the TP loads of the inflow, outflow and net inflow of the lake were the largest among 2012-2018, and their values were 2993.9, 1341.1 and 1652.8 t, respectively. (2) The average annual TP concentration of inflow rivers in the Huxi zone was 0.226 mg/L, which was higher than that in other zones; the average annual TP concentrations of outflow rivers in the Zhexi and Wuchengxiyu zones were 0.114 and 0.109 mg/L, which were higher than those in other zones. The interannual variation of the relationships between water quantity and TP load in different water resources zones behaved differently, suggesting that TP pollution was not effectively controlled on the whole except in the Hangjiahu zone. (3) The average annual TP load of the inflow rivers in the Huxi zone and Zhexi zone were 1748.71 and 278.61 t, respectively. The Huxi zone accounted for above 67.88% of the annual total inflow TP load, and the percentage for the Zhexi zone was between 7% and 19%; the average annual outflow TP load of Taipu River was 272.27 t and accounted for more than 30% of the total outflow TP load since 2014. (4) There were good correlations between the monthly TP load and water quantity of the inflow in different water resources zones. Moreover, except in the Yangchengdianmao zone, the variation of monthly TP load of the inflow in other zones was mainly controlled by the water quantity of the inflow. (5) In the high flow year of 2016, the combined effect of high concentration of TP and large water quantity of inflow rivers in the Huxi zone led to a significant increase in the TP load of the inflow. The research results can provide a scientific basis for external phosphorus load control for Lake Taihu.

Detection of chlorophyll fluorescence as a rapid alert of eutrophic water

Abstract An in-situ detection of chlorophyll fluorescence was used in an innovative manner to detect eutrophic water, and the results were compared with the Carlson's Trophic State Index (CTSI) indicators. Eutrophication was due to climate warming and anthropogenic activities. The turbidity and chromaticity showed a strong linear relationship (R2 = 0.85) of the Bi Lake in Taipei city. Both the swimming area and the bridge are popular with the general public and had the worst turbidity (35.80–44.00 NTU) and chromaticity (495.37–552.27 Pt). The CTSI had a stronger linear relationship with the phycocyanin (PC) concentration (R2 = 0.605) than with any other three CTSI factors like chlorophyll-a concentration, total phosphorus (TP) concentration, and transparency. The TP pollution had a potential to cause an increase in PC concentration found in this study (R2 = 0.86). The absorbances of the water samples represented that the environment is PC (cyanobacteria) dominant in winter. The PC concentration in Bi Lake ranged from 75.55 to 80.24 μg/L and was higher with lower water temperature. Measurement of in-situ chlorophyll fluorescence is similar to lab-scale spectrophotometer (R2>0.92). The real-time detection of PC concentration could be the basis of a rapid alert system for biological threats to waters.

Spatial characteristics and driving forces of anthropogenic phosphorus emissions in the Yangtze River Economic Belt, China

Excessive phosphorus emissions by anthropogenic activities are closely related to eutrophication in the Yangtze River. Quantitative spatial distribution of total phosphorus (TP) emissions and identifying their driving forces are important for the management of phosphorus pollution in the Yangtze River Economic Belt (YREB). In this study, anthropogenic TP emissions were estimated using emission factors in the YREB for 2017. Global and local spatial autocorrelation and multiple regression analysis were adopted to reveal the spatial agglomeration effects and driving forces of the TP emissions in 130 cities of the YREB. The TP emissions were estimated to be 155,940 t, and the agricultural TP emissions were 106,181 t, followed by domestic (46,032 t) and industrial emissions (3727 t) in 2017 in the YREB. Livestock breeding was the most significant anthropogenic source of TP emissions. The TP emissions in the middle and lower reaches were larger than those in the upper reaches. A significant spatial agglomeration effect of TP emissions was found in the YREB, with High-high aggregation in the middle reaches and Low-low aggregation in the upper reaches. The paddy land area was the most significant factor affecting TP emissions, followed by the population size and vegetable orchard area. The results provide fundamental data regarding pollution sources for subsequent research investigations. The results enhance the understanding of the TP source contributions; thus, accurate control measures could focus on the important sources and regions of TP pollution in the YREB.

Research on narrow and generalized water environment carrying capacity, economic benefit of Lake Okeechobee, USA

The water environment pollution in the Lake Okeechobee (LO) basin has caused negative impacts on lake ecology and marine ecology. In particular, total phosphorus pollution is very prominent. The two-dimensional water environment mathematical simulation method is used to calculate the narrow water environment carrying capacity (N-WECC), the comprehensive indicator evaluation method is used to calculate the generalized water environment carrying capacity (G-WECC), and the shadow price method is used to calculate the economic loss caused by water environment pollution. The total amount of TP discharged into LO is 15,611 tons in 2018. Through prediction, if the 83% pollutant emission concentration can be reduced, then the total phosphorus concentration of LO can reach the target, and its N-WECC is 2654 t/year. From the four aspects of water resources index, water environment index, water ecology index and land use index, 15 comprehensive evaluation indicators adapted to LO basin are proposed. By calculating G-WECC is 0.129, in the low load state, the most important factor is serious agricultural pollution. The largest economic loss caused by water pollution. The total economic loss caused by water pollution in the LO basin is 1,185,030,095 USD in 2018. Among them, the economic loss caused by sewage discharge was 852,546,223 USD, causing economic losses of 332,149,942 USD for human health and 612,930 USD for sewage irrigation. Martin County accounted for 42.78%, Orange County accounted for 24.79%, Osceola County accounted for 12.69%, and these three counties accounted for 80.24%.

Grey water footprint as a tool for wastewater treatment plant assessment– Hostivice case study

ABSTRACT The study evaluates the wastewater treatment plant reconstruction via the Grey Water Footprint methodology. The application was tested on a medium-size wastewater treatment plant discharging water into a small watercourse. The 6-year monitoring was assessed. The assessment included a period before and after the reconstruction when a capacity was increased and the treatment technology had been equipped with a membrane sludge separation. Ammonium nitrogen is causing the Grey Water Footprint the most often; both, before and after the reconstruction. The assessment has shown that the current setting of legal discharge limits may not cover all environmental risks even if the wastewater treatment plant meets all requirements. For environmental sustainability, it is necessary if the recipient watercourse was at least 1.4 times more watery for assimilation of total nitrogen pollution, and 3.9 times more watery for assimilation of total phosphorus pollution.

Analysis of the Effects of Local Regulations on the Preservation of Water Resources Using the CA-Markov Model

The analysis of the local regulation effects is required for sustainable and effective land utilization because land use/land cover (LULC) changes are not only determined by human activity but are also affected by national policy and regulation; however, previous studies for land use/land cover (LULC) have mainly been conducted on the LULC changes using past experience. This study, therefore, analyzed the effects of local regulations aimed at preserving the water quality in South Korea. To this end, changes in LULC were simulated using the CA-Markov model under conditions in which two local regulations, the special countermeasure area (SCA) and total maximum daily load (TMDL), were not applied and examined the differences between the simulated LULC and the actual LULC as of 2018. In addition, the differences in the generation of pollutant loads were driven for Biochemical Oxygen Demand (BOD), Total Nitrogen (TN), and Total Phosphorus (TP) using pollutant unit-load. As a result, without SCA, the agricultural area increased by 379.0 km2, the urban area decreased by 101.8 km2, and the meadow area decreased by 176.0 km2. In addition, without TMDL, the urban area increased by 169.2 km2 and the meadow area decreased to 158.8 km2.Differences in BOD, TN, and TP pollution loads without SCA applications were shown to decrease to 22,710.5 kg·km−2 day−1, 1133.9 kg·km−2 day−1, and 429.8 kg·km−2 day−1, respectively, while BOD, TN, and TP pollution loads without TMDL applications decreased to 14,435.7 kg·km−2 day−1, 2543.6 kg·km−2 day−1, and 368.2 kg·km−2 day−1, respectively. As such, this study presents a methodology for analyzing the effects of local regulations using the CA-Markov model, which can intuitively and efficiently examine the effects of regulations by predicting LULC changes.

Water quality in relation to land use in the Junshan Lake watershed and water quality predictions

AbstractChanges in human-dominated spatial patterns of land use are the main driving factors of water quality evolution in watersheds, and the quantitative impact of land use changes on water quality is currently a focus of lake ecology research. Using the Junshan Lake Basin as a study area, this paper quantitatively analyzes the response relationships between the water quality parameters, land use, and socio-economic factors in the study area from 2005 to 2019 and predicts the water quality in 2035 based on land and space planning scenarios. The results show the following. (1) The land use structure of the Junshan Lake Basin has changed significantly over the last 15 years. The basic trend is an increase in settlement and wetland areas in the basin and a decrease in water, cropland, forest, and grassland areas. (2) Settlement areas play the role of a ‘source’ for the total phosphorus (TP) and ammonium-nitrogen (NH3-N) pollution load, and cropland areas play the role of a ‘sink’ for the TP, NH3-N, and chemical oxygen demand (CODMn) pollution load. (3) The main land use type in the Junshan Lake Basin is cropland, which accounts for more than 40% of the total, and the water quality in the lake is affected not only by non-point source pollution but also by the regional Gross Domestic Product (GDP), total population, and per capita disposable income. According to the water quality prediction and analysis, the concentrations of TN and TP in Junshan Lake will meet the Class IV water quality standard in 2035, and the concentrations of dissolved oxygen (DO) and CODMn will meet the Class II standard. This study is significant for the management and control of the water environment in the Junshan Lake Basin.

Quantify phosphorus transport distinction of different reaches to estuary under long-term anthropogenic perturbation.

Typical diffuse pollutants such as phosphorus (P) have long been a hot topic in the surface-water research field. As the fifth-largest river in the world, the Yellow River Basin (YRB) suffers from significant soil erosion and relatively high intensity of agricultural activities, which bring large amounts of P loads. However, owing to the large drainage area, few studies have investigated the transport and attenuation dynamic processes or provided a precise calculation of the total phosphorus (TP) load for the entire YRB. In this study, the SPAtially Referenced Regressions on Watershed Attributes (SPARROW) model was used to simulate and investigate the spatial variation and transport mechanism of P in the YRB. The YRB was divided into 60 sub-basins, and the data of drainage area, spatial attribute, streamflow, and monitored flux were integrated into the model correspondingly. Calculated R2 values confirm that 84% of the spatial variability in annual TP loads can represent regional processes. The estimated YRB TP load was 41,760 tons per year, contributed by farmland (64%), construction land (27%), grassland (5%), and forest (4%). In addition, the P transport dynamic process, contribution, and sensitivity of different P flux sources in different reaches were represented and identified. Our study highlights the significance of farmland as the most significant factor exacerbating TP pollution. As the study conducted the first attempt to develop a SPARROW model, integrated management strategies that consider the spatially varying P sources and associated TP transport were proposed. Additionally, to improve the ecological health of basin, it is critical to further increase P utilization efficiency and enhance cross-regional cooperation throughout the basin.

Sediment Pollution Characteristics and Dredging in the Nanfei River Estuary, Chaohu Lake

To clarify the endogenous pollution characteristics of sediments in the Nanfei River estuary, Chaohu Lake, and provide a theoretical basis for the dredging works, the organic index, pollution index, and potential ecological risk were determined. The results show that the average total nitrogen (TN), total phosphorus (TP), and organic matter (OM) content of the sediment was 1461 mg·kg-1, 438 mg·kg-1, and 1.77%, respectively, showing enrichment in the surface layer (0-10 cm). The nutrient pollution status and TP pollution index show that the organic pollution level was moderate and the TP pollution was severe. Furthermore, the pollution risk gradually reduced with sediment depth, representing a low risk at depths below 30 cm. Static release results showed that the average release fluxes of NH4+-N and TP in the sediment were 8.04 mg·(m2·d)-1 and 0.19 mg·(m2·d)-1, respectively, and showed highest release potentials consistent with areas of sediment nutrient pollution. Except for Cr and Ni, the concentrations of six heavy metals were higher than the soil background values for Anhui Province, and the concentrations of Hg and Cd far exceeded the standards. According to the assessment of potential ecological risk from heavy metals, the 0-20 cm sediments present a high level of risk and sediments below 30 cm have a low level of risk. Heavy metal leaching toxicity indicated that the risk of heavy metal release after dredging is low and non-hazardous. These results were used to determine the key dredging area (3.93 km2) and depth (30 cm) for the Nanfei River estuary, providing an important basis for future dredging activities.

Distribution of Nitrogen and Phosphorus in Lake Chaohu Sediments and Pollution Evaluation

We investigated the spatial distribution and storage of nitrogen and phosphorus in Lake Chaohu sediments and evaluated the sediment nitrogen and phosphorus pollution index. Results show that the average total nitrogen (TN) and total phosphorus (TP) content in the surface-layer sediments of Lake Chaohu were 1088 mg·kg-1 and 585 mg·kg-1, respectively, and 666 mg·kg-1 and 509 mg·kg-1 in the bottom-layer sediments, respectively. TN content in the surface layer was significantly higher than in the bottom layer (P<0.01). Spatially, TN, TP, and sediment thickness were ranked in the order western lake area > eastern lake area > middle lake area, and the TN and TP contents were significantly different in the surface sediments from the middle and eastern areas of the lake (P<0.05, P<0.01). TN and TP storage in the lake sediments was 1.58×105 t and 0.98×105 t, respectively. TN and TP were significantly correlated in both the western and middle parts of the lake (P<0.01). In addition, TN was significantly correlated with sediment thickness in middle area of the lake, which indicated that TN may have the same pollution sources as TP and both were affected by sediment thickness. TN pollution index (STN), TP pollution index (STP), and comprehensive pollution index (FF) values were 1.09, 1.39, and 1.32, respectively, indicating light-to-moderate levels of pollution. Specifically, the western lake surface sediments were heavily polluted with respect to TP, the eastern lake surface sediments were moderately polluted, and the middle lake surface sediments were slightly polluted. Nutrient pollution varied widely between different areas of the lake, with sediments in the western part of the lake presenting a higher safety risk. Overall, these observations indicate that Lake Chaohu is threatened by internal nutrient loading.

Modeling and Prioritizing Interventions Using Pollution Hotspots for Reducing Nutrients, Atrazine and E. coli Concentrations in a Watershed

Excess nutrients and herbicides remain two major causes of waterbody impairment globally. In an attempt to better understand pollutant sources in the Big Sandy Creek Watershed (BSCW) and the prospects for successful remediation, a program was initiated to assist agricultural producers with the implementation of best management practices (BMPs). The objectives were to (1) simulate BMPs within hotspots to determine reductions in pollutant loads and (2) to determine if water-quality standards are met at the watershed outlet. Regression-based load estimator (LOADEST) was used for determining sediment, nutrient and atrazine loads, while artificial neural networks (ANN) were used for determining E. coli concentrations. With respect to reducing sediment, total nitrogen and total phosphorus loads at hotspots with individual BMPs, implementing grassed waterways resulted in average reductions of 97%, 53% and 65% respectively if implemented all over the hotspots. Although reducing atrazine application rate by 50% in all hotspots was the most effective BMP for reducing atrazine concentrations (21%) at the gauging station 06883940, this reduction was still six times higher than the target concentration. Similarly, with grassed waterways established in all hotspots, the 64% reduction in E. coli concentration was not enough to meet the target at the gauging station. With scaled-down acreage based on the proposed implementation plan, filter strip led to more pollutant reductions at the targeted hotspots. Overall, a combination of filter strip, grassed waterway and atrazine rate reduction will most likely yield measureable improvement both in the hotspots (&gt;20% reduction in sediment, total nitrogen and total phosphorus pollution) and at the gauging station. Despite the model’s uncertainties, the results showed a possibility of using Soil and Water Assessment Tool (SWAT) to assess the effectiveness of various BMPs in agricultural watersheds.

Spatial Distribution and Pollution Evaluation of Carbon, Nitrogen, and Phosphorus in Sediments of Zhushan Bay at Taihu Lake

To reveal the distribution characteristics of carbon, nitrogen and phosphorus in the sediments of Zhushan Bay at Taihu Lake, sedimentary columns were collected and sliced by 2 cm vertically from ten sampling points in three sections of Zhushan Bay. The content of total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) were determined for each slice to reveal their horizontal and vertical distribution. The results showed that:spatially, the content of TN, TP, and TOC increased in the surface sediments of Zhushan Bay from the open lake area to the bay, and inside the bay these indexes were significantly higher than in the open lake area (P<0.01). The content of TN, TP, and TOC in the surface sediments in the bay (section A) were 1.53 mg·g-1, 1.55 mg·g-1, and 11.31 mg·g-1, respectively, while in the surface sediments near the open lake (section C) they were only 0.75 mg·g-1, 0.57 mg·g-1, and 6.70 mg·g-1, respectively. Vertically, a feature of surficial enrichment was shown, and the contents of carbon, nitrogen and phosphorus in all three sections showed a decreasing trend with increase of depth. The contents of TN, TP and TOC in the surface sediments are 2-3 times, 2-5 times, and 2-3 times those in the bottom sediments, respectively. Generally, the average TP content in the sediment of Zhushan Bay is 0.93 mg·g-1, suggesting an apparent heavy pollution, while the average TN content is 1.11 mg·g-1 as slight pollution. According to the organic nitrogen index and comprehensive pollution index, the northern part of Zhushan Bay is suffering from heavy pollution, where the organic pollution is relatively strong. The TP pollution index is between 1.03 and 3.87, indicating heavy pollution in Zhushan Bay.

Risk Assessment Based on Nitrogen and Phosphorus Forms in Watershed Sediments: A Case Study of the Upper Reaches of the Minjiang Watershed

In order to achieve effective eutrophication control and ecosystem restoration, it is of great significance to investigate the distribution characteristics of nutrient elements in sediments, and to perform ecological risk assessments. In the current grading criteria for nutrient elements in sediments, only the overall or organic components of carbon, nitrogen and phosphorus are considered, while the specific species distributions and bioavailability characteristics are rarely taken into account. Hence, using the current grading criteria, the differences in the release, migration and biological activity of nutrient elements in sediments cannot be accurately reflected. Taking the upper reaches of the Minjiang River watershed as an example, we analyzed the overall distributions and the ratio of nutrient elements in sediments, the spatial changes of nitrogen and phosphorus forms, the bioavailability, and the environmental significance. The ecological risk of nitrogen and phosphorus in sediments was assessed using an evaluation method based upon the biological effective parameter. The results were compared with the results of the evaluation methods based on the single pollution index, and then these evaluation methods were confirmed accordingly. From the results, the following conclusions can be obtained: (1) The spatial distributions of nutrient elements in sediments in the upper reaches of the Minjiang River Watershed (including the Jianxi Basin, Futunxi Basin, and Shaxi Basin) were significantly affected by the local ecology and the urban sewage discharge system. (2) The maximum average contents of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) in sediments were observed in the Jianxi Basin, the Futunxi Basin and the Shaxi Basin, respectively. (3) According to the contents of nitrogen and phosphorus in sediments, the bioavailable nitrogen (TTN) accounted for 35.49% of the total contents of TN. The components of TTN can be sorted from high to low as follows: Nitrogen in organic sulfide form (SOEF-N) &gt; nitrogen in iron-manganese oxide form (SAEF-N) &gt; nitrogen in ion exchange form (IEF-N) &gt; nitrogen in weak acid leaching form (WAEF-N). Inorganic phosphorus (IP) was the main component of TP. The components of IP can be sorted from high to low as follows: Metal oxide bound phosphorus (NaOH-P) &gt; calcium bound phosphorus (HCl-P) &gt; reduced phosphorus (BD-P) &gt; weakly adsorbed phosphorus (NH4Cl-P). Meanwhile, bioavailable phosphorus (BAP, BAP = NH4Cl-P + BD-P + NaOH-P) accounted for 36.94% of TP. According to the results of the single pollution index method, the risk level of TOC pollution in the sediments was relatively low in the whole area, while the risk level of TN pollution was low or moderate in most zones, and severe in certain ones. The risk level of TP pollution was low to moderate. (4) From the results of the bioavailability index evaluation method, based on the total amounts and forms of N and P, the risk level of N pollution was moderate, while the risk of P pollution was negligible. In addition, the results of the bioavailability index evaluation method were more consistent with the actual situation and reflected the overall environmental effects of nitrogen and phosphorus.

Modeling phosphorus sources and transport in a headwater catchment with rapid agricultural expansion

Increasing riverine phosphorus (P) levels in headwaters due to expanded and intensified human activities are worldwide concerns, because P is a well-known limiting nutrient for freshwater eutrophication. Here we adopt the conceptual framework of the SPAtially Referenced Regressions On Watershed attributes (SPARROW) model to describe total phosphorus (TP) sources and transport in a headwater watershed undergoing rapid agricultural expansion in the upper Taihu Lake Basin, China. Our models, which include variables for land cover, river length, runoff depth, and pond density, explain 94% of the spatio-temporal variability in TP loads. Agricultural lands contribute the largest percentage (61%) of the TP loads delivered downstream, followed by forestland (21%) and urban land (18%). Future agricultural expansion to 15% of the total basin area is possible, which could lead to a 50% increase in TP loads. According to our analysis, an average of 24% of the total P export from the watershed landscape was intercepted in ponds. The exported amount was subsequently retained by tributaries and along the mainstem river, accounting for 14% and 43% of their inflowing loads, respectively. The remaining ∼6 tons yr−1 of TP was eventually transported into Tianmu Lake, in Southeastern China. The model identified several sub-catchments as hotspots of TP loss and thus logical sites for targeted management. Our study underscores the significance of agricultural expansion as a factor that can exacerbate headwater TP pollution, highlighting the importance of landscapes to buffer TP losses from sensitive hilly catchments. This also points to a need for an integrated management strategy that considers the spatial-varying P sources and associated transport of TP in precious headwater resources.

Analysis of the Characteristics of Nitrogen and Phosphorus Emissions from Agricultural Non-point Sources on Hanfeng Lake Basin

To understand the status of agricultural non-point source pollution and to find out the primary pollution sources and the key control areas in the Hanfeng Lake Basin, the discharges of total nitrogen (TN) and total phosphorus (TP) from farming, livestock and poultry breeding, and rural living in thirty-two counties in 2015 were estimated using the pollutant discharge coefficient method. The spatial distribution characteristics of the quality and intensity of the TN and TP emissions from these sources were investigated using the GIS spatial analysis method. Pollution evaluation and source analysis were also carried out using the equivalent pollution load method. The results show that the total loads of TN and TP in the Hanfeng Lake Basin are 2721.42 t and 492.04 t, respectively. The discharge of pollutants is the largest in the Nanhe Basin and the smallest in the area around Hanfeng Lake. The total pollutant loads from the agricultural non-point sources varied greatly, with fertilizer application and livestock and poultry breeding being the main sources. The contribution from fertilizer application is 76.92%, which represents the primary source of TN and TP pollution in the Hanfeng Lake Basin. Among the townships, the equivalent pollution loads of Dunhao, Tieqiao, and Baiqiao are higher than 350 m3·a-1; thus, these are the key control towns. According to the results of the equivalent pollution method and cluster analysis, the 32 counties were divided into four types of pollution areas. These areas are planting-livestock breeding dominant area, fertilizer-livestock breeding dominant area, fertilizer dominant area, and heavily polluted planting dominant area.

The Transport Process of Total Suspended Substance and Its Influence on TN and TP Fluxes in Urban River: A Case Study of Baoxiang River, Yunnan China

To reveal the characteristics of solid phase TSS (Total suspended substance) distribution and transported flux in urban river, and explore its effect on TN (Total nitrogen) and TP (Total phosphorus) transported fluxes. The TSS concentrations and flux, TN flux and TP flux, river runoff flux were be monitored and calculated systematically in Baoxiang River, the results shows that: (1) the annual TSS quantity transported by Baoxiang River into Dianchi Lake was 578.86t. Urban areas were the major transported areas of TSS, and summer and autumn were the main transported periods. (2) TSS has a certain correlation with TN (R2=0.28, P<0.01, n=72) and TP (R2=0.34, P<0.01, n=72), but there correlations were not significant. However, the correlations of river runoff flux with TN and TP were significant, it indicated that liquid phase was the main factor affecting TN TP fluxes, priority should be given to liquid phase when dealing with TN and TP pollution. The results can provide a basis for eutrophication control of urban rivers and nonpoint pollution management of Dianchi Lake River basin.

A Bayesian modeling approach for phosphorus load apportionment in a reservoir with high water transfer disturbance.

Phosphorus loading from external and internal sources poses a potential risk to eutrophication of lakes or reservoirs. However, the relative contribution of external and internal sources to eutrophication is still unclear especially for reservoirs with water transfer disturbance. The objective of this paper is to estimate the phosphorus loading from external (water transfer and diffusing emission) and internal sources (sediment release) in Yuqiao Reservoir (YQR) and compare their relative contribution of external and internal sources. In this study, we estimated the phosphorus loading considering both external (water transfer and diffusing source emission) and internal (release from sediment) sources of YQR. The phosphorus loading from water transfer was estimated by total phosphorus (TP) concentration × monthly flow of inflow. The phosphorus loading from nonpoint source emission was estimated using a generalized watershed loading function (GWLF). The phosphorus loading from internal sources was estimated with a Bayesian phosphorus budget model. Our result showed that water transfer TP load is the biggest (45.2%) source of TP load in YQR and internal TP load (20.5%) accounts for a comparable proportion of TP load as nonpoint source (34.3%) in YQR and dominates the total loading in some months. Analysis of seasonal total phosphorus load apportionment indicated that water transfer TP load takes the largest proportion in winter (60.8%), spring (60.2%), and autumn (47.8%). Nonpoint source TP load takes the largest proportion in summer (60.1%), and internal TP load is the second source of YQR in summer (22.4%). Our study indicates that water transfer may be the major driver of eutrophication for some reservoir systems, and sediment release may prevent recovery of many eutrophic lakes and reservoirs. Our analysis suggests that TP pollution control strategies in YQR should be preferentially focused on the improvement of water quality in the upstream reservoir, and nonpoint source TP load reductions should be focused on summer. Compared with conventional nutrient apportionment model applications, this paper provides a new approach to estimate external and internal TP loads simultaneously. Graphical abstract ᅟ.

Evolution Characteristics of Surface Water Quality Due to Climate Change and LUCC under Scenario Simulations: A Case Study in the Luanhe River Basin.

It is of great significance to study the effects and mechanisms of the key driving forces of surface water quality deterioration—climate change and LUCC (land use and land cover change). The Luanhe River Basin (LRB) in north-eastern China was examined for qualitatively and quantitatively assessing the responses of total nitrogen (TN) and total phosphorus (TP) loads on different climate scenarios and LUCC scenarios. The results show that from 1963 to 2017, the TN and TP loads basically presented a negative correlation with the temperature change (except for winter), while showing a significant positive correlation with the precipitation change. The incidence of TN pollution is sensitive to temperature increase. From 2020 to 2050, the annual average loads of TN and TP were slightly lower than from 1963 to 2017. The contribution of rising temperature was more significant on nutrient loads. Also, the incidence of TN pollution is sensitive to the future climate change. Under LUCC scenarios, the TN and TP loads and pollution incidence increased correspondingly with the decrease of natural land. The evolution characteristics analysis can provide support for the effect and adaptation-strategies study of climate change and LUCC on surface water quality.

Distribution of Phosphorus Fractions in Surface Sediments of Minjiang Mainstreams

In recent years, the total phosphorus pollution in Minjiang River was serious, and the surface sediments of the Minjiang River also threatened water quality. To study the spatial distributions of phosphorus in the surface sediments of the Minjiang River, samples of surface sediments were collected upstream (Aba District) and downstream (Yibin District) of the Minjiang River in December, 2016. The sediments were analyzed with the modified sequential extraction method (SEDEX) to obtain six forms of phosphorus, including exchangeable phosphorus (Ex-P), exchangeable organic phosphorus (Org-P), iron-bound phosphorus (Fe-P), authigenic phosphorus (Ca-P), detrital phosphorus (De-P), and refractory phosphorus (Res-P). The results indicated that the contents of total phosphorus (TP) in surface sediments ranged from 522.17 μg ·g-1 to 979.22 μg ·g-1, which were far more than the soil phosphorus background values (700 μg ·g-1). The spatial distribution characteristics of the TP of surface sediments indicated that the TP concentrations in sediments at the Meishan sections (the middle reach of the Minjiang River) were higher than those in the other sections. This was related to the smaller particle size and higher OM contents in sediments in the Meishan sections. The main phosphorus forms in the sediments in the Minjiang River were Ca-P and De-P, with their concentrations accounting for 75% of TP in the sediments. The bio-available phosphorus, which included Ex-P, Org-P, and Fe-P, accounted for 0.31%-29.62% of TP in the sediments of the Minjiang River. The concentrations of bio-available phosphorus in sediments at the Meishan sections and Leshan sections (the middle reach) were highest, indicating that bio-available phosphorus in the surface sediments was high, and its potential environmental impact risks were higher.