Spatial and seasonal variations in nutrient load and trophic status of Ganga and Yamuna rivers in Uttar Pradesh, India

Nutrient loading in aquatic systems from anthropogenic sources is a worldwide concern. The Ganga is the most important river in India, but pollution is currently severely threatening its biodiversity and long-term environmental viability. Water samples were taken from 36 locations along the length of the Ganga and Yamuna rivers in Uttar Pradesh and analysed for nutrient concentration to evaluate the nutrient load, eutrophication danger, and river trophic status. The average concentration of NO3-N, PO4-P, NH4-N, and SiO2-Si exceeded the values in unpolluted rivers, indicating the contribution of anthropogenic sources. The concentration of NO3-N and NH4-N showed significant spatial variation, and PO4-P showed significant seasonal variation in the study area. The DIN/DIP ratio in the study area exceeded 16:1, indicating a phosphate-limiting condition for phytoplankton development. The DSi/DIN value showed a declining trend in the downstream region of both rivers with average values <1, indicating nitrate pollution leading to eutrophic conditions. The Indicator for Coastal Eutrophication Potential (ICEP) showed a positive value, indicating that the Ganga and Yamuna rivers in Uttar Pradesh were eutrophic due to nitrogen pollution. Trophic State Index (TSI) values indicated that super-eutrophic conditions existed in the Ganga River (65.62) and hypereutrophic conditions existed in the Yamuna River (75.55) in Uttar Pradesh.