[Effect of Rainfall Intensity on the Content of Nitrogen and Phosphorus Components in Plateau Areas: A Case Study of the Fengyu River Watershed].

The runoff formed by rainfall carrying various land surface materials into rivers and lakes is an important factor leading to a change in water quality, and the characteristics of nitrogen and phosphorus output of rivers under different rainfall intensities are different. This study explores the impact of rainfall intensity on the water quality of the Fengyu River Watershed in the plateau agricultural region, based on the water quality monitoring data of the export section of the Fengyu River Watershed from 2011 to 2013, combined with local rainfall monitoring. The effects of four rainfall intensities (light rain, moderate rain, heavy rain, and torrential rain) on the content of different nitrogen and phosphorus components in water were analyzed. The results show that the rainfall intensity has a significant effect on the nitrogen and phosphorus emissions of the Fengyu River Watershed. The average nitrogen and phosphorus concentrations of all components are lower in light rain (<10 mm) and moderate rain (10-25 mm), and higher in heavy rain (25-50 mm) and torrential rain (50-100 mm). The percentage of NH4+-N (57.14%-76.85%) to TN is larger than that of PN (23.15%-42.86%), and the percentage of TDP (22.73%-28.00%) to TP is smaller than that of PP (72.00%-77.27%). The nitrogen concentration of different forms is:TN > NH4+-N > PN; the phosphorus concentration of different forms is:TP > PP > TDP.

[Impact of Human Activities on Net Anthropogenic Nitrogen Inputs (NANI) at Township Scale in Erhai Lake Basin].

Excessive nitrogen inputs from human activities have become the main cause of water eutrophication and related ecological hazards. In order to study the impact of human activities on nitrogen in the basin, and based on statistical data of administrative units in 16 towns and villages, this study used the NANI model to calculate net anthropogenic nitrogen inputs (NANI) at township scale in Erhai Lake basin. Results show that the total amount of NANI in Erhai Lake basin was 29.81×103 t in 2014, and nitrogen input intensity per unit area was 10986 kg·(km2·a)-1, significantly higher than the national average. The input of nitrogen from food by the local tourist population was 0.26×103 t, accounting for 8% of local food nitrogen input. Nitrogen input from chemical fertilizer is the largest NANI input source, accounting for 47% of net nitrogen input in the basin, followed by net nitrogen input of food and feed. The spatial distribution of NANI at township scale shows evident regionalization, with higher values in the north and lower values in the south of the basin. The intensity of NANI in towns with cropland or population is high. The corresponding risk of nitrogen pollution in Erhai Lake basin is therefore a primary concern, and will remain so in the near future.

[Seasonal Changes of the Pathways of Nitrogen Export from an Agricultural Watershed in China].

Nonpoint source pollution has become a major factor influencing the water quality. Identifying the pathway of nitrogen (N) transport from the source to the watershed mouth is a critical step in taking measures to control this pollution. However, it is difficult to identify the pathway of N transport because the transport pathway varies among different watersheds depending on the difference in the terrain, hydrology, and land cover etc and changes over time. Additionally, there is little knowledge about the major pathway of N transport through agricultural watersheds in the Yunnan Plateau lake area. The pathways of N export and their temporal variations over time were investigated in this study based on a typical agriculture-dominated watershed in a plateau lake area, Yunnan Province, and two-year monitoring data (June 2011-May 2013) in combination with a base flow separation program. The results show that the base flow accounts for most of the streamflow discharge (80.0%) and N export (71.1%). The proportion of the stream flow discharge via storm flow increases significantly with increasing rainfall. Therefore, the percentage of total N (TN) export via storm flow increases with increasing storm flow, which is closely related to rainfall. The major pathway of N export shifts toward storm flow when the storm flow proportion of the stream flow discharge increases up to 40%. During the monitoring period, the proportion of the TN export via storm flow increases up to 65.6% in the rainy season. This study provides important information for the improvement of the management of nonpoint source pollution at the watershed scale.

[Characteristics of Nitrogen Variation and Its Response to Rainfall:A Case Study in Wuxi Port at Taihu Lake Basin].

Based on monitoring data of the water quality in the Wuxi port estuary of Taihu Lake from 2010 to 2015, we studied the temporal variation characteristics of nitrogen and its response to rainfall in Wuxi port. The results showed that the pollution level in Wuxi port is serious, with an average annual total nitrogen (TN) concentration of (4.41-5.92 mg·L-1), worse than the water environment quality grade Ⅴ standard (2 mg·L-1). The ammonia nitrogen (NH4+-N) concentration was 1.09-1.72 mg·L-1. The concentrations of TN and NH4+-N showed obvious seasonal variations, with the concentration of TN and NH4+-N in summer and autumn higher than in spring and winter. The concentration of TN in 2015, 2012, and 2011 was 5.92, 5.82, and 5.47 mg·L-1, respectively, which was significantly higher than in 2013 and 2014. The concentration of NH4+-N in 2011 (1.72 mg·L-1) was higher than in 2013 and 2015. With the increase of rainfall intensity, the TN concentration showed an increase after the first downward trend and then a decrease, while the NH4+-N concentration increased first and then decreased. In addition, the nitrogen concentration in the non-flood season was higher than in the flood season.

[Characteristics of Nitrogen and Phosphorus Emissions in the Gufu River Small Watershed of the Three Georges Reservoir Area].

To study the seasonal change characteristics and form composition of nitrogen and phosphorus output concentration and pollutant discharge load with rainfall characteristics at the outlet of Gufu river small watershed,the quality and quantity of water combined with natural rainfall events were monitored from January to December 2014.The results showed that the annual runoff volume of the Gufu river small watershed was 0.6×108 m3.The runoff was concentrated in raining season (from July to September),accounting for 63.9%.There was significant (P<0.01) positive correlation between the runoff flow and the annual rainfall.The annual emission of total nitrogen (TN) was 1432 t·a-1,and the emission was 853 t·a-1 during the raining season,accounting for 59.6% of annual TN emission content.The dissolved nitrogen was the main form of nitrogen emission,and the emission load of each month accounted for 55.4%-91.3% of TN.The positive correlation between the nitrate nitrogen concentration and rainfall was significant (P<0.05).The annual emission of total phosphorus (TP) was 563.1 t·a-1,and the content during the raining season accounted for 78.6% of TP annual emission content.The particle phosphorus (PP) was the main form of phosphorus emission,and the emission load of each month accounted for 41.9%-79.5% of TP.There was significant (P<0.01) positive correlation between the annual rainfall,sediment and TP,PP.The correlation between the total dissolved phosphorus concentration and rainfall was significant (P<0.05).

[Analysis of Spatial Variability of Water Quality and Pollution Sources in Lihe River Watershed, Taihu Lake Basin].

The source of pollutants in the Tai Lake basin and the characteristics of spatiotemporal variations were studied by conducting water quality monitoring in the Lihe River watershed to the west of Tai Lake in 2014. The dynamic changes in total phosphorus (TP), ammonia nitrogen (NH4+-N), and chemical oxygen demand (COD) were studied in flood and non-flood seasons at five monitoring points from upstream to downstream. The average concentrations of TP, NH4+-N, and COD were 0.176 mg·L-1, 1.075 mg·L-1, and 10.626 mg·L-1 respectively, and the water quality was lower than the grade Ⅳ standard. From upstream to downstream, the concentrations of TP and NH4+-N gradually increased. The water quality downstream was poor, worse than the gradeⅤstandard; however, COD was low and met the grade Ⅳ standard. During the non-flood season, the pollutant concentrations gradually increased from upstream to downstream. There was no obvious trend in flood season. Concentrations of pollutants gradually increased with the increase in the area of inhabited land and decrease in the area of forest land. The population density, livestock, and poultry production were significantly correlated with the concentrations of pollutants in the river. The pollutants in the Lihe River watershed mainly originated from human activities, and livestock and poultry breeding activities.