Net Anthropogenic Phosphorus Inputs Research Articles

Dynamic characteristics of net anthropogenic phosphorus input to the upper Yangtze River Basin from 1989 to 2019: Focus on the phosphate ore rich area in China

Phosphorus (P), a non-renewable essential resource, faces heavy exploitation and contributes to eutrophication in aquatic environments. Assessing P input is vital for a healthier P cycle in the Upper Yangtze River (UYR), a phosphate ore rich basin, where P mining and P chemical enterprises have prominent pollution problems. This study modified the net anthropogenic phosphorus input (NAPI) model to include ore mining P input (Pore). We analyzed the evolutionary characteristics of P input in five sub-basins of UYR from 1989 to 2019 using prefecture-level data, and assessed the uncertainty of the data. NAPI in all sub-basins exhibited an upward and then downward trend during 1989–2019, with the inflection point occurring in 2015 or 2016, showing a net increase of about 1.1 times (568–1162 kg P km−2 yr−1) in the whole UYR basin. Among the components of NAPI, P fertilizer inputs (Pfer) and food/non-food and feed P inputs (Pf/nf&feed) contributed comparably, though the growth rate of Pfer was most notable basin-wide. Pore proportion increased significantly (about 3-fold), with a peak of 20%, especially in Wujiang sub-basin. The multi-year (1989–2019) average NAPI in UYR rose sequentially from west to east, with hotspot areas mainly concentrated in the Sichuan-Chongqing urban agglomeration and cities of Hubei province. The regional P input closely related to the population density and the level of agricultural development, certainly the phosphate mining was also unignorable. This study emphasizes that based on current status of NAPI development in UYR, targeted management for different regions should focus on improving agricultural P use efficiency and rational exploitation of P mineral resources.

Long-term variations in external phosphorus inputs and riverine phosphorus export in a typical arid and semiarid irrigation watershed

Excessive phosphorus (P) along with drained water from farmland in the arid and semiarid watersheds when entering into water bodies brings about serious environmental problems in the aquatic ecosystem. It is critical to explore variations in watershed P balance and the relationship between anthropogenic P input and riverine total phosphorus (TP) export in a typical irrigation watersheds. In this study, long-term anthropogenic P variations in Ulansuhai Nur watershed (UNW), a typical irrigation watershed in Yellow River basin, was investigated using a quantitative Net Anthropogenic Phosphorus Input (NAPI) budget model. The results showed that annual NAPI exhibited a significant upward trend with a multi-year average of 2541.6 kg P km−2 yr−1 in the UNW. Hotspots for watershed NAPI were discovered in Linhe and Hangjin Houqi counties. Chemical P fertilizers and livestock breeding were two dominated sources of NAPI. Annual riverine TP export showed a significantly declined trend with a net decrease of 80.6%. The export ratio of watershed NAPI was 0.6%, lower than those reported for other watersheds worldwide. There was a significant positive linear correlation between NAPI and riverine TP export from 2005 to 2009. However, after 2009, riverine TP export exhibited a decreased trend with increasing watershed NAPI, which was attributed to environmental treatment measures. By reconstructing riverine TP export without the impact of pollution treatment measures, annual average reduction amount of riverine TP export from 2009 to 2019 was estimated to be 237.2 ton, 47.2% and 52.8% of which were attributed to the point and nonpoint sources measures. This study not only widens the application scope of NAPI budget method, but also provides useful information of nutrient management and control in the arid and semiarid irrigation watershed.

Dynamic spatiotemporal change of net anthropogenic phosphorus inputs and its response of water quality in the Liao river basin

The Liao river is one of the seven major rivers in China, and the process of phosphorus (P) cycling and change of water quality in this basin are influenced to a considerable extent human activities. In this work, the traditional net anthropogenic phosphorus inputs (NAPI) model was improved by considering the dynamic change of wastewater treatment capacity and P deposition (PDEP) and reclassifying the sources of phosphorus into human P consumption (PHUM), agriculture P consumption (PAGR), livestock P consumption (PANIM) and PDEP to analyze its dynamic spatio-temporal change in the Liao river basin. The results showed that the annual mean NAPI was 785.53 kg P km−2 yr−1 (2001–2020), the maximum value was 940.49 kg P km−2 yr−1 in 2009, and the minimum value was 586.04 kg P km−2 yr−1 in 2001. The temporal variation of NAPI presented an increasing-fluctuation-increasing trend and was basically in line with that of the water quality throughout the three stages, and the spatial distribution of NAPI gradually increased from upstream to downstream. During the two decades, PANIM was the predominant component of NAPI with a share of 64.32%. PHUM, PAGR, and PDEP accounted for 15.97%, 11.54%, and 8.17%, respectively, and the point source NAPI (NAPIP) contributed to 4.95% of NAPI. Further, the INAPI (Improved NAPI) -MR (Multiple Regression) -SWAT (Soil and Water Assessment Tool) model was developed to predict the spatial distribution of P flux under two scenarios. The results showed that the Liao river basin experienced a reduction in P flux to different degrees due to the improvement of the wastewater treatment system, which was more significant in its downstream area. Long-term water quality monitoring is encouraged to develop refined water quality models in the future.

Changes in net anthropogenic nitrogen and phosphorus inputs in the Yangtze River Economic Belt, China (1999–2018)

Since the industrial revolution, excess inputs of nitrogen (N) and phosphorus (P) from human activities have been the main threat of deterioration to water environmental quality. In this study, to understand the variation characteristics, evolutionary pattern, composition structure, and main influencing factors on net anthropogenic nitrogen inputs (NANI) and net anthropogenic phosphorus inputs (NAPI) in the Yangtze River Economic Belt, 20 years of data from 1999 to 2018 at the general, provincial and city scales were analyzed. The results showed that NANI and NAPI in the Yangtze River Economic Belt increased and then decreased from 1999 to 2007 and from 2008 to 2018, with average values of 7189.26 kg N km−2 yr−1 and 2169.31 kg P·km−2 yr−1. Fertilizer application constituted the largest source of contributions to NANI and NAPI, with average contribution rates of 66.31 % and 68.20 %. The spatial pattern of NANI and NAPI exhibited a decreasing trend from east to west and from north to south. Western Jiangsu, eastern Anhui, central Hubei, and western Sichuan were high-risk areas. The contribution rates of human activity factors were ranked as economic factors > land-use factors > social factors, and changes in economic factors contributed the most to changes in NANI and NAPI, with averages of 70.50 % and 70.10 %. The Yangtze River Economic Belt has crossed the Environmental Kuznets Curve (EKC) inflection point for the N/P input load and has entered the coordinated development stage of economic growth and environmental improvement. The city scale can effectively identify and optimize the control area compared with the provincial scale, and the proportions of the administrative areas for NANI and NAPI at different targets decreased by 4.11 % (5.20 %), 7.52 % (11.95 %), and 9.79 % (17.29 %), respectively.

Spatiotemporal differences in riverine nitrogen and phosphorus fluxes and associated drivers across China from 1980 to 2018

Increases in nutrient loadings to waterways over the past four decades have led to widespread eutrophication and water quality impairments across China. Understanding the spatial, interannual and long-term variations in nutrient loadings and associated drivers at the national scale is crucial for developing effective nutrient reduction strategies. However, the controls on, and spatiotemporal variations in, nutrient fluxes remain a problem from both an academic and management perspective. This study provides spatially extensive and temporally contiguous estimates of changes in riverine total nitrogen (TN), ammonia nitrogen (NH3–N) and total phosphorus (TP) fluxes for continental area of China based on machine learning stack models and empirical modeling over the period from 1980 to 2018. Results reveal considerable spatial, interannual and long-term variability in annual TN, NH3–N and TP fluxes, with spatial variations in average TN and NH3–N fluxes primarily driven by net anthropogenic nitrogen inputs. Interannual variability is dominated by precipitation across continental areas of China. Spatial variability in the estimated average annual TP flux in the undeveloped western and the developed middle east regions of China are primarily controlled by net anthropogenic phosphorus inputs and precipitation, respectively. We found that TN, NH3–N and TP fluxes increased from 1980 to 2018 in watersheds in East China; the national mean annual TN, NH3–N and TP fluxes increased before 2015 and decreased after 2015. This study illustrates the important role of precipitation and temperature variability in controlling the spatial, interannual and long-term variability of nutrient fluxes, and indicates that the influence of the meteorological conditions on annual loadings is needed when designing watershed nutrient reduction or management strategies.

Dynamic characteristics of net anthropogenic phosphorus input and legacy phosphorus reserves under high human activity - A case study in the Jianghan Plain

The increase of phosphorus (P) input related to human activities is one of the main reasons for eutrophication. Notably, in areas with high population densities and intensive agricultural activities, eutrophication has occurred frequently in the Jianghan Plain, so quantitative evaluation of anthropogenic P input is of great significance for the formulation of P pollution control measures. This study estimated net anthropogenic P input (NAPI), riverine total P exports (TP exports), and the pool of P stored in the terrestrial system (legacy P reserves) at the county scale from 1990 to 2019 in the Jianghan Plain. The results showed that NAPI increased from 2645 kg·km−2·yr−1 in 1991 to 5812 kg·km−2·yr−1 in 2014, and then decreased to 4509 kg·km−2·yr−1 in 2019. Non-point sources were the main form of NAPI, of which 75–96% came from agricultural systems. Meanwhile, P fertilizer input was the largest source of NAPI. It is worth noting that the contribution of seed P input in some counties, such as Jiangling County, is relatively high, even exceeding that of net food/feed P input. The P fertilizer application and livestock density were the main drivers for NAPI change. Only 3% of NAPI was exported into rivers, so a large amount of legacy P accumulated in the terrestrial system. An empirical model incorporating NAPI components, cultivated land area ratio, and annual precipitation was established. Based on this model, the average contribution of annual NAPI and the sum of legacy P and natural background sources to TP exports were calculated to be 71% and 29%, respectively. So it is necessary to control P pollution by improving fertilizer use efficiency and enhancing manure management. The results provide a scientific basis for targeted solutions to the sources of P nutrient and its control measures in the middle reach of the Yangtze River.

Phosphorus (P) in animal diets as a driver of embodied P in animal products and net anthropogenic P inputs

AbstractOne approach to address both the environmental and scarcity issues that occur with phosphorus (P) losses from human systems is to improve understanding of the P demands of bio‐based products. Most P demand in the United States is driven by production of crops for animal feed and mineral P feed supplements for animals. In this research, we used the Commodity‐Specific Net Anthropogenic Phosphorus and Nitrogen Inputs (CSNAPNI) model to (1) assess the contributions of individual feed products such as corn, soy, and mineral P supplements to the embodied P of animal products and (2) estimate net anthropogenic phosphorus inputs (NAPIs) for the contiguous United States for two animal P‐intake scenarios. Results show that P supplements may contribute up to 30% of embodied P in pork and dairy products, up to 60% in chicken, and up to 75% in turkey. Other major contributors to animal product‐embodied P are grains, which are responsible for around 60% of embodied P in pork and dairy products, at least 30% in chicken, and at least 20% in turkey products. Results also show that animal P intake is such a significant driver of anthropogenic phosphorus that a reduction of animal P intake by 25% could reduce NAPI to the contiguous United States by 30%. Considering promising research on methods to improve digestibility of both mineral P supplements and grain P in animal diets, these results are encouraging.

Agricultural phosphorus surplus trajectories for Ontario, Canada (1961–2016), and erosional export risk

Management strategies aimed at reducing nutrient enrichment of surface waters may be hampered by nutrient legacies that have accumulated in the landscape. Here, we apply the Net Anthropogenic Phosphorus Input (NAPI) model to reconstruct the historical phosphorus (P) input trajectories for the province of Ontario, which encompasses the Canadian portion of the drainage basin of the Laurentian Great Lakes (LGL). NAPI considers P inputs from detergent, human and livestock waste, fertilizer inputs, and P outputs by crop uptake. During the entire time period considered, from 1961 to 2016, Ontario experienced positive annual NAPI values. Despite a generally downward NAPI trend since the late 1970s, the lower LGL, especially Lake Erie, continue to be plagued by algal blooms. When comparing NAPI results and river monitoring data for the period 2003 to 2013, P discharged by Canadian rivers into Lake Erie only accounts for 12.5% of the NAPI supplied to the watersheds' agricultural areas. Thus, over 85% of the agricultural NAPI is retained in the watersheds where it contributes to a growing P legacy, primarily as soil P. The slow release of legacy P therefore represents a long-term risk to the recovery of the lake. To help mitigate this risk, we present a methodology to spatially map out the source areas with the greatest potential of erosional export of legacy soil P to surface waters. These areas should be prioritized in soil conservation efforts.

Whole process phosphorus management strategy construction with phosphorus load characteristics, driver and efficiency from the material flow perspective

End-of-pipe treatment is the main measure to control phosphorus pollution in lake watershed. Although a large number of lake watersheds have taken this measure, the lake environment has not improved significantly. Therefore, from the perspective of material flow, this study aims to put forward the whole-process lake watershed phosphorus management strategy system, including phosphorus flows characteristics, drivers analysis and phosphorus utilization efficiency from phosphorus input and discharge to entering into the lake, which is also an important way to control phosphorus pollution in lakes. Take Erhai Lake as an example, the results indicated that the phosphorus flows have stage characteristics, with the phosphorus reduction efficiency in society remained stable around 95% before 2012 then declined to 86% in 2017, the phosphorus self-purification efficiency in nature fluctuation rise from 53% to 84% before 2012, then declined to 80%. Besides, the net anthropogenic phosphorus input slowly increased before 2012, while declined 2.4-fold during 2012–2017 mainly form fertilizer and food/feed. The phosphorus discharge related to rural production and life, accounting for over 83%, mainly from the livestock and poultry farming wastewater. Phosphorus from overflow entering into the lake account for around 32% and the phosphorus from internal release of sediment keep rising to 13% from 2000 to 2012. Fertilizer application was the main driver across the phosphorus transport process, except of per capital gross domestic product. Therefore, the P management strategy optimization in Erhai lake should pay more attention on P utilization efficiency, waste management and its way into the lake, especially in the field of agriculture production and life. The constructed whole-process watershed management strategy could support the lake watershed comprehensive treatment for improving P utilization efficiency and has universality.

Variation of net anthropogenic phosphorus inputs (NAPI) and riverine phosphorus fluxes in seven major river basins in China

The riverine phosphorus (P) import resulting from human activities is always a worldwide concern for environmental management due to the effect of eutrophication. In this study, we made modification of the NAPI method to make the results closer to the actual situation. We collected the data of seven major outflow rivers in China to have a comprehensive understanding of P export and P inputs and build the quantitative relationship between them. We estimated the net anthropogenic phosphorus inputs (NAPI), including fertilizer P (Pfert), net food and feed import P and non-food P using by human (Pim+nf), in seven major river basins in China and the corresponding riverine total phosphorus (TP) fluxes. The relationship between NAPI and riverine TP flux was also explored. NAPI in seven river basins presented an obvious uneven distribution. Huaihe River basin showed the highest NAPI of 4005.09 kg P km−2 yr−1 due to its highest intensities of human-activities, and the lowest NAPI was observed in Songhua River basin as 334.36 kg P km−2 yr−1. Pim+nf occupied a larger proportion of NAPI in the Pearl River and Liaohe River basins (> 65%), while Pfert contributed more to NAPI in the other basins (nearly 60%) with an exception of the Yangtze River basin (where Pim+nf and Pfert approximately contributed the same). Different contributions of NAPI components were mainly attributed to the different land uses. The total TP flux of all the seven rivers was 117.10 × 103 t P yr−1, with the highest flux in the Yangtze River (77.42 × 103 t P yr−1), contributed 72.88% to the total TP fluxes in China. Change in riverine TP flux could be well described by NAPI, river discharge, and percentage of lake area in the basin and this provided an effective way to predict TP fluxes in rivers.

Long-term (1980–2015) changes in net anthropogenic phosphorus inputs and riverine phosphorus export in the Yangtze River basin

Quantitative information on long-term net anthropogenic phosphorus inputs (NAPI) and its relationship with riverine phosphorus (P) export are critical for developing sustainable and efficient watershed P management strategies. This is the first study to address long-term (1980–2015) NAPI and riverine P flux dynamics for the Yangtze River basin (YRB), the largest watershed in China. Over the 36-year study period, estimated NAPI to the YRB progressively increased by ∼1.4 times, with NAPIA (chemical fertilizer input + atmospheric deposition + seed input) and NAPIB (net food/feed imports + non-food input) contributing 65% and 35%, respectively. Higher population, livestock density and agricultural land area were the main drivers of increasing NAPI. Riverine total phosphorus (TP), particulate phosphorus (PP) and suspended sediment (SS) export at Datong hydrological station (downstream station) decreased by 52%, 75% and 75% during 1980–2015, respectively. In contrast, dissolved phosphorus (DP) showed an increase in both concentration (∼7-fold) and its contribution to TP flux (∼16-fold). Different trends in riverine P forms were mainly due to increasing dam/reservoir construction and changes in vegetation/land use and NAPI components. Multiple regression models incorporating NAPIA, NAPIB, dam/reservoir storage capacity and water discharge explained 84% and 92% of the temporal variability in riverine DP and PP fluxes, respectively. Riverine TP flux estimated as the sum of DP and PP fluxes showed high agreement with measured values (R2 = 0.87, NSE = 0.84), indicating strong efficacy for the developed models. The model forecasted an increase of 50% and 7% and a decrease of 15% and 22% in riverine DP flux from 2015 to 2045 under developing, dam building, NAPIA and NAPIB reduction scenarios, respectively. This study highlights the importance of including enhanced P transformation from particulate to bioavailable forms due to river regulation and changes in land-use, input sources and legacy P pools in development of P pollution control strategies.

Impact of human activities on phosphorus flows on an early eutrophic plateau: A case study in Southwest China

The net anthropogenic phosphorus inputs (NAPI) model has been used extensively to assess changes in phosphorus (P) inputs and cycling in the environment. However, temporary populations have generally been unconsidered in these assessments. In this study, the NAPI model was used to estimate P loads from the 16 towns and villages in the Erhai Lake Basin (ELB), Southwest China and to evaluate the potential impact from temporary residents (tourism). The results showed that the average value P inputs in the basin (estimated at 2384 kg P km−2 year−1) were 5 times the national average level, and that temporary residents contributed 1%. Agriculture accounted for most of the net P, with chemical fertilizers (55% of the inputs) as the main source, followed by food and animal feed. Only 9.54% of the P inputs to the basin were exported. River water quality and NAPI were significantly correlated (P < 0.01). Tourism industry contributes significantly to regional economic growth and prosperity, but its beneficial effects on the economy does not equate with the adverse impact on environment. This study illustrates what is happening in Southwest China and provides scientific evidence that shows we need to find novel ways to reduce nutrients.

Nitrogen and phosphorus retention budgets of a semiarid plain basin under different human activity intensity

Excessive nitrogen (N) and phosphorus (P) runoff from human activities results in degraded water quality. It is, therefore, crucial to quantitatively assess nutrient inputs over time and their impact on riverine nutrient exports. In this study, we estimated the long-term (1995–2015) nutrient inputs at the county scale by integrating Net Anthropogenic Nitrogen Input (NANI) and Net Anthropogenic Phosphorus Input (NAPI) methods, and nutrient exports into rivers by the Export Coefficient Model (ECM) for a semiarid plain basin, the Baiyangdian (BYD) Basin, China. The results showed that N and P input intensities in the year 2015 reached 18852 kg N km2 yr−1 and 2073 kg P km−2 yr−1, showing a 35% and 11% increase in comparison with 1995, respectively. About 60% of these nutrients were derived from fertilizer application. The multi-year averaged N and P exported to rivers was 548 kg N km−2 yr−1 and 79 kg P km−2 yr−1, respectively. Hotspots for nutrient budgets were found in the southeastern counties. Hotspots covered about 12% of the total land, but contributed by 38–52% of total nutrient budgets. The nutrient export ratios showed no significantly temporal variations, and only about 2.15–2.89% of NANI and NAPI were exported into rivers. The low nutrient export ratio was due to the low water discharge that limited the nutrient transportation in the semi-arid plain basin. As most of anthropogenic nutrient inputs were retained in the basin, their impacts on the pollution of soils and aquifers need to be considered and adequately addressed in the future. This study constructs the spatial quantitative nutrient budgets, which can provide effective information for region policy formulation.

Spatial dstribution of the net anthropogenic phosphorus input (NAPI) to the Dongting Lake basin, China.

Based on the net anthropogenic phosphorus input (NAPI) model, we estimated the NAPI of the Dongting Lake basin and its sub-basins from 1985 to 2015, and analyzed the spatio-temporal distributions and variations. The results showed that there was an increasing trend at first and then a decrease in the Dongting Lake basin. The NAPI values in the area in 1985, 1995, 2005 and 2015 were 7.00, 9.20, 10.33, 10.01 kg·hm-2·a-1, respectively. The largest input source changed from the net food and feed import in 1985 to phosphorus fertilizer during 1995-2015. The mean annual input of phosphorus fertilizer, with an average value of 6.01 kg·hm-2·a-1 accounting for 65.8% of NAPI; followed by the food and feed import, the annual average value was 2.65 kg·hm-2·a-1, accounting for 29.0%, and the least was non-food phosphorus, with an average annual value of 0.47 kg·hm-2·a-1, accounting for 5.2%. Spatially, the distribution of NAPI in the Dongting Lake basin showed the characteristics of high in the northeast region and low in the west, which was mainly consistent with distribution of local agriculture. The average annual NAPI values in sub-basin from high to low ranked as following: Dongting Lake area, Xiangjiang River downstream, Zijiang River upstream, Xiangjiang River upstream, Lishui River area, Yuanjiang River upstream, Yuanjiang River downstream and Zijiang River downstream. The highest NAPI was found in the Dongting Lake area, increasing from 13.01 kg·hm-2·a-1 in 1985 to 24.14 kg·hm-2·a-1 in 2015. Agricultural production and population growth were the main contributors to the current input of net phosphorus, and the negative ecological effects of which could not be ignored.

Opportunities to reduce nutrient inputs to the Baltic Sea by improving manure use efficiency in agriculture

While progress has been made in reducing external nutrient inputs to the Baltic Sea, further actions are needed to meet the goals of the Baltic Sea Action Plan (BSAP), especially for the Baltic Proper, Gulf of Finland, and Gulf of Riga sub-basins. We used the net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) nutrient accounting approach to construct three scenarios of reduced NANI-NAPI. Reductions assumed that manure nutrients were redistributed from areas with intense animal production to areas that focus on crop production and would otherwise import synthetic and mineral fertilizers. We also used the Simple as Necessary Baltic Long Term Large Scale (SANBALTS) model to compare eutrophication conditions for the scenarios to current and BSAP-target conditions. The scenarios suggest that reducing NANI-NAPI by redistributing manure nutrients, together with improving agronomic practices, could meet 54–82% of the N reductions targets (28–43 kt N reduction) and 38–64% P reduction targets (4–6.6 kt P reduction), depending on scenario. SANBALTS output showed that even partial fulfillment of nutrient reduction targets could have ameliorating effects on eutrophication conditions. Meeting BSAP targets will require addressing additional sources, such as sewage. A common approach to apportioning sources to external nutrients loads could enable further assessment of the feasibility of eutrophication management targets.

Response of regional agricultural soil phosphorus status to net anthropogenic phosphorus input (NAPI) determined by soil pH value and organic matter content in subtropical China

Exploring the relationship between net anthropogenic phosphorus input (NAPI) and soil available P (SAP) content could inform applied issues related to environmental quality and agronomic productivity and increase our knowledge of element biogeochemical cycles. Here, the NAPI was estimated and the SAP content determined in eight counties in subtropical China from 1980 to 2010. It is suggested that the NAPI ranging 318-924 km−2 yr−1 in 1980 had increased substantially to 865–3601 km−2 yr−1 in 2010 across the eight counties, in which the P fertilizer application was estimated to represent the largest individual source of NAPI, accounting for an average of 36.1–74.6% of the NAPI. The NAPI in agricultural land (NAPIa) was the largest component of the NAPI, and 60.7–77.1% of the NAPIa accumulated in the upper 20 cm layer of agricultural soils, which significantly increased soil total–P (TP) and SAP contents. The increases in SAP, resulting from 10,000 kg P km−2 of the NAPIa (IOPNAPI), were estimated to be 1.61–4.36 mg P kg−1 in the counties. Both the correlation and variation partitioning analyses (VPAs) suggested that the soil pH and organic matter content (SOM) were the most important factors influencing the variations of IOPNAPI (determination coefficient: 72.5%). Therefore, the contribution of soil pH and SOM should be considered in enriching soil SAP levels and implementing optimal P management strategies to improving the agronomic effectiveness of P fertilization and further reduce the environmental risk of P loss in subtropical region.

Deteriorated Water Quality of Agricultural Catchments in South China by Net Anthropogenic Phosphorus Inputs

Improper anthropogenic phosphorus (P) management is considered a major cause of water quality deterioration, however the relationship between anthropogenic P input and catchment water quality is rarely quantified in China. The study area encompassed eight small catchments with areas ranging from 58.6 to 13,442.4 ha in the subtropical region of South China. On-site observations of P concentrations, stream fluxes, and social investigation of P input were conducted over a 3-year period. The regional variations of net anthropogenic phosphorus inputs (NAPI) and responses of riverine P export were quantitatively analyzed. Results showed that the total NAPI of catchments varied from 11.04 to 40.52 kg P ha−1 year−1, where cropland systems (NAPIc) were the largest P sources, accounting for 47.7–67.7% in total. Meanwhile, net food and feed P input varied from 3.87 to 30.73 kg P ha−1 year−1, accounting for 35.0–75.8% in total, followed by fertilizer and non-food P input with 4.65–10.48 and 0.63–2.89 kg P ha−1 year−1, respectively. Riverine P export and the soil total P and Olsen–P contents in croplands were all positively related to NAPI (p &lt; 0.05). A simple empirical model was simulated to predict the annual riverine total P fluxes using NAPIc with greater accuracy than with using NAPI or NAPI for residential land (NAPIr). Gray relational analysis suggested that livestock density was the most important influencing factor for NAPI. It is concluded from these results that, although the livestock accounted for the largest part of the NAPI, the cropland contributed the greatest to catchment riverine P export. This probably due to recycling of animal manure for plant cropping systems. Therefore, maintaining a reasonable scale of livestock production, and reducing the internal cycle of manure or replacing part of the chemical fertilizer should be a major approach in reducing NAPI and corresponding riverine P export in the study area.

Factors controlling phosphorus export from agricultural/forest and residential systems to rivers in eastern China, 1980–2011

Summary This study quantified long-term response of riverine total phosphorus (TP) export to changes in land-use, climate, and net anthropogenic phosphorus inputs to agricultural/forest (NAPIAF) and residential (NAPIR) systems for the upper Jiaojiang watershed in eastern China. Annual NAPIAF rose by 73% in 1980–1999 followed by a 41% decline in 2000–2011, while NAPIR continuously increased by 122% over the 1980–2011 period. Land-use showed a 63% increase in developed land area (D%) and a 91% increase in use of efficient drainage systems on agricultural land area (AD%) over the study period. Although no significant trends were observed in annual river discharge or precipitation, the annual number of storm events rose by 90% along with a 34% increase in the coefficient of variation of daily rainfall. In response to changes of NAPIAF, NAPIR, land-use and precipitation patterns, riverine TP flux increased 16.0-fold over the 32-year record. Phosphorus export via erosion and leaching was the dominant pathway for P delivery to rivers. An empirical model incorporating annual NAPIAF, NAPIR, precipitation, D%, and AD% was developed (R2 = 0.96) for apportioning riverine TP sources and predicting annual riverine TP fluxes. The model estimated that NAPIAF, NAPIR and legacy P sources contributed 19–56%, 16–67% and 13–32% of annual riverine TP flux in 1980–2011, respectively. Compared to reduction of NAPIAF, reduction of NAPIR was predicted to have a greater immediate impact on decreasing riverine TP fluxes. Changes in anthropogenic P input sources (NAPIAF vs. NAPIR), land-use, and precipitation patterns as well as the legacy P source can amplify P export from landscapes to rivers and should be considered in developing P management strategies to reduce riverine P fluxes.

Net anthropogenic phosphorus inputs and riverine phosphorus fluxes in highly populated headwater watersheds in China

Riverine phosphorus (P) levels in headwaters are a worldwide concern for environmental management due to the sensitivity of freshwater ecosystems to phosphorus loads. Here, we evaluate P in the Huai River Basin of China, a watershed with one of the highest intensities of human-activity in the world. Estimates of net anthropogenic phosphorus inputs (NAPI) were obtained by accounting for the main anthropogenic phosphorus inputs in each watershed of the basin, including fertilizer application, net food and feed import, non-food P and seeding P. Multi-year average (2003–2010) anthropogenic inputs of P to the entire basin were 2700 kg P km−2 year−1, with an average amount of 1800 kg P km−2 year−1 entering its 17 headwater watersheds. Fertilizer application was the largest source of new P across the headwater watersheds (about 70 % of NAPI), followed by P content of imported food and feed (24 %) and non-food P (6 %). Riverine total phosphorus (TP) fluxes showed a significant linear relationship with NAPI, with an average 3.2 % of NAPI exported as riverine TP flux. Our result indicates that NAPI could be a good indicator for assessing the risk of regional P loss, as well as an excellent potential predictor of riverine TP flux. A comparison of our results with other similar analyses suggests that around 3 % of NAPI would be exported as riverine TP loads, although fractional export of P may vary significantly regionally. Corresponding P management should be targeted at the main anthropogenic sources and hot-spot areas.

Net anthropogenic phosphorus inputs (NAPI) index application in Mainland China

This study provides a new understanding on sources of P, which may serve as a foundation for further exploration of anthropogenic effects on P input. Estimation of net anthropogenic phosphorus input (NAPI) was based on an inventory of phosphorus (P) fertilizer use, consumption of human food and animal feed, seeding phosphorus and non-food phosphorus net flux. Across Mainland China, NAPI had an upward trend from 1981 to 2009, which reflects development trend of the population and economic. NAPI for years 1981, 1990, 2000 and 2009 are 190kgPkm−2yr−1 (1.8kg P per person yr−1), 295kgPkm−2yr−1 (2.5kgP per person yr−1), 415kgPkm−2yr−1 (3.1kg P per person yr−1) and 465kgPkm−2yr−1 (3.4kgP per person yr−1), respectively. On a geographical basis, NAPI per unit area is lower in northwest Mainland China than in southeast Mainland China with the largest NAPI of 3101kgPkm−2 yr−1 in Shanghai, while NAPI per person is in reverse with the largest NAPI 7.7kg P per person yr−1 in Tibet. P input of fertilizer is the largest source of NAPI, accounting for 57.35–83.73% (109–390kgPkm−2yr−1) of the total NAPI, followed by non-food P and P in human food and animal feed. Year 2000 was a critical point where P changed almost from net input to output. Grain production rate per unit mass of fertilizer showed an obvious downward trend. The primary factor in relation to the change in NAPI is total population.