Physicochemical Characteristics of Riverine Water and Sediments Association with Primary Productivity in Selected Sites of North Bihar, India

Abstract

Riverine sediment and water chemistry together influence nutrient availability and primary production, yet the spatial variability of these factors is not well understood for many small and seasonal rivers in the Indo-Gangetic plain. This research assessed certain physicochemical characteristics of bottom sediment and the water above it at three locations within the Saryu river system in north Bihar, exploring their relationship with gross primary productivity (GPP). Sediments were taken from the top 15 cm, processed, and analyzed for physicochemical properties, organic carbon, and micronutrients. GPP and net primary productivity (NPP) were measured using the light–dark bottle method, with dissolved oxygen estimated through the Winkler technique. At the three sites, sediment pH rose from 5.6-6.2 at Site 1 to 6.3-7.2 at Site 3, while mineralizable nitrogen increased from 56.24-63.32 to 124.3-156.22 mg kg-1, and available phosphorus rose from 25.13-31.24 to 48.21-53.62 mg kg^-1. The pH of the water column increased from 5.9-6.5 to 6.6-7.5, and dissolved nitrogen rose from 10.32-12.23 to 24.31-27.22 mg L^-1. GPP increased from 32.13-33.22 to 56.62-57.71 mg/cm^-3h^-1 across the sites. Pearson correlations from the original data indicated positive relationships between GPP and sediment pH (r=0.3241), mineralizable nitrogen (r=0.3180), available phosphorus (r=0.4164), and available potassium (r=0.2842), with stronger positive correlations for water-column nitrogen (r=0.5264) and potassium (r=0.5161). These findings suggest that nutrient availability and sediment-water interactions may lead to spatial variations in riverine primary production. This study offers a foundational framework for nutrient-sensitive river management, emphasizing the need for seasonally detailed monitoring and more robust statistical designs before recommending site-specific nutrient enrichment.