Distribution Characteristics and Source Analysis of Nitrogen and Phosphorus in Different Rivers in Two Water Period: A Case Study of Pi River and Shiting River in the Upper Reaches of Tuo River in China

In this paper, the distribution characteristics of total nitrogen (TN), total phosphorus (TP) and fractions of nitrogen and phosphorus in water and surface sediments of the Pi and Shiting rivers in the dry and wet seasons were studied by molybdenum blue/ascorbic acid spectrophotometry and Standard Measurements and Testing (SMT). Correlation analysis, cluster analysis and principal component analysis were used to identified nitrogen and phosphorus pollution sources. The results showed that: (1) nitrogen and phosphorus in water and surface sediments in the study area were at different levels. (2) In the Pi river, the decomposition of animal and plant residues, the leachate from the accumulation of aquaculture wastewater and urban domestic sewage were the main sources of nitrogen and phosphorus pollution, while in the Shiting river, the unreasonable application of pesticides and fertilizers, the degradation of animal and plant residues, agricultural wastewater from agricultural drainage channels, industrial production wastewater and the weathering of agricultural wastes had a great impact on the nitrogen and phosphorus pollution. The results in this study provide reliable experimental data and a reference to local relevant departments for the implementation of effective control measures for the reduction of the nitrogen and phosphorus pollution load in the river basin.