Nutrient budgets (N and P) for the Nui Coc reservoir catchment (North Vietnam)

• We aim to establish the N, P budgets for the Nui Coc reservoir catchment (Vietnam).
• Different nutrient sources in the catchment to this reservoir water were considered.
• Excess of fertilizer utilization, untreated wastewater were main causes of algal blooms.
• Results are important to give better solutions for eutrophication prevention.

The Nui Coc reservoir (water surface: 25.2 km2; catchment area: 567 km2), typical of medium sized reservoirs in Vietnam and in South East Asia, was built in the 1970s to stimulate social and economic development in the surrounding area. The nitrogen and phosphorus budgets were established in this typical reservoir catchment to determine the degree of human-induced alteration of nitrogen and phosphorus cycles. The results showed that both nitrogen and phosphorus inputs are higher than their outputs in the agricultural soil system, indicating the excess of fertilizer utilization in the catchment. The budget of the hydrosystem revealed that the nitrogen and phosphorus fluxes from agricultural and forest soils accounted for 50% and 51% of the total inputs to the hydrosystem, respectively. About 66% of the annual total nitrogen and 79% of the annual total phosphorus inputs to the hydrosystem were deposited/eliminated in the reservoir.