Spatial distribution characteristics of nitrogen and phosphorus nutrients in high-altitude inland river cascade reservoirs

The spatial distribution characteristics of nitrogen and phosphorus nutrients in cascade reservoirs in high-altitude regions are crucial for water quality management. Water samples were collected from 20 typical section points in the middle and upper reaches of the Heihe River. The research focused on the nutrient concentrations in the surface, middle, and bottom layers of the cascade reservoirs. Nutrient distribution characteristics in the reservoirs were analyzed using both longitudinal and vertical sampling. The results showed significant depth-dependent variations in nitrogen and phosphorus concentrations, influenced by hydrodynamic processes, sediment dynamics, and nutrient cycling. The overall trend for TP, and TN concentrations at the selected sampling points was consistent, with bottom-layer concentrations being significantly higher than those in the surface layer. concentration was highest in the middle layer and lowest in the bottom layer, while the CODMn was highest in the surface water and lowest in the middle layer. The primary factors affecting these spatial distribution characteristics include the types and quantities of microorganisms and biological communities at different water depths, water movement and convection, sedimentation rates of suspended particles and organic matter, as well as human activities.