Spatial variation characteristics and influencing factors of nitrogen and phosphorus ecological stoichiometry in the Yangtze River system

The nitrogen (N) and phosphorous (P) ecological stoichiometry characteristics reflected the coupling relationship between N and P in ecosystem process. However, there was a short of the insights in the spatial and temporal evolution law of the mole ratio of N and P (N:P) in the Yangtze River watershed, as well as its response mechanism to anthropogenic activities, which was difficult to satisfy the demands in the governance theory and management practice. Based on the water quality monitoring data and river water and sediment data of the Yangtze River system, the spatial-temporal distribution characteristics of N:P in the Yangtze River system were illustrated from the whole basin scale, and the critical impact factors on N:P variations were identified. The results showed that there was a decreased tendency of N:P in the mainstream from upstream to downstream with the average of 92±78. The N:P ratio of the export of Datong station was 47±16. The spatial variations of N:P in the Yangtze River system were influenced by inputs from tributaries, non-point sources input along the way, urban sewage input, phosphate mining activities, and reservoirs interception. Temporal patterns of N:P depended on the inputs and retention of particulate P and dissolved N in the river system. The impacts from human activities on the nutrient transportation and transformation in the Yangtze River system were preliminarily revealed on the view of ecological stoichiometry and a certain theoretical support was offered for future ecological restoration, management and protection of the Yangtze River watershed.