Biogeochemical Controls on C, N, and P Stoichiometry and Nutrient Cycling in Bedkot Lake, Chure Region of Far-Western Nepal

Abstract

This study evaluates the controlling factors of carbon-nitrogen-phosphorus (C-N-P) and nutrient dynamics of a freshwater ecosystem, Bedkot Lake in far-western Nepal. Lake water samples were collected from eight different locations during two sampling events (dry summer period and wet monsoon season) for a total of sixteen samples, characterizing spatiotemporal variation of major chemical parameters and water quality. Key chemical parameters such as dissolved organic carbon (DOC), total dissolved nitrogen (TDN), dissolved inorganic nitrogen (DIN), and phosphorus were measured alongside other hydrochemical variables with the application of correlation analysis and advanced statistical approaches. The nutrient dynamics showed distinct spatial variations with chemical limitations within the lake. DOC and TDN showed very stable tight relationship with exceptionally low spatial variability. In contrast, the DIN concentrations were vastly different, indicating significant change between inorganic and organic nitrogen control across the lake ecosystem. Importantly, high nutrient ratio showed a high concentration of nitrogen over dissolved phosphorus. Such significant imbalance between nitrogen and phosphorus clearly indicates dissolved phosphorus appears as a limiting nutrient which controls overall productivity and the chemical equilibrium of the Bedkot Lake. Biogeochemical dynamics of Bedkot Lake are primarily controlled by internal nutrient cycling based on our analysis. Three most important environmental gradients, such as reactive nutrient dynamics, hydrochemical/phosphorus regulation, and internal organic nutrient coupling, were observed based on correlation modeling. The highly synchronized relationship between dissolved organic carbon and nitrogen reflects the close linkage in organic matter processing within the lake. Dissolved inorganic nitrogen and ammonium show strong relationships, indicating internal microbial cycling and reflecting active internal transformation pathways of nitrogen dynamics. The lake functions as a stable ecosystem during the summer-monsoon season, although the lake is exposed to significant evaporation, and nutrient dynamics are controlled by complex interacting biogeochemical processes based on exploratory regression. Overall, water is safe for domestic and agricultural use with no clear evidence of widespread trace metal contamination.