Distribution, assessment, and sources of nutrients in river water in the headwaters of the Shule River Basin, Northeastern Qinghai-Tibet Plateau

Abstract

Nitrogen (N) and phosphorus (P) are essential nutrients and can significantly impact primary productivity of the ecosystem causing water environmental problems. However, their cycling mechanisms are not well understood in alpine mountains with climate change. Hence, 94 samples of river water were collected from 2018 to 2020 in the headwaters of the Shule River Basin to assess the nutrients spatiotemporal distribution and combined approach of water quality index to assess water quality and potential sources. The findings depict that high nutrient concentrations were found to coincide with snowmelt and glacial meltwater and rainfall recharge periods, while total flux peaked from June to September due to increased runoff. Notably, total nitrogen (TN) concentrations were significantly higher near the town, primarily attributed to the replenishment of nitrate (NO₃^‒-N) from livestock manure. The high total P (TP) was near the glacier, which was attributed to the transportation of glacial sediments into the river, and pH was another critical factor. N was the primary nutrient limiting factor for the growth of phytoplankton in river water. Although the migration and transport of nutrients have altered with climate change, river water quality is good in alpine mountains based on an overall evaluation. These findings contribute to enriching nutrient datasets and highlight the importance of water resource management and water quality assessment in sensitive and fragile alpine mountains.