Spatio-Temporal Variation in Nutrient Profiles and Exchange Fluxes at the Sediment-Water Interface in Yuqiao Reservoir, China

Nutrients released from sediments have a significant influence on the water quality in eutrophic lakes and reservoirs. To clarify the internal nutrient load and provide reference for eutrophication control in Yuqiao Reservoir, a drinking water source reservoir in China, pore water profiles and sediment core incubation experiments were conducted. The nutrients in the water (soluble reactive P (SRP), nitrate-N (NO(3)(−)-N), nitrite-N (NO(2)(−)-N), and ammonium-N (NH(4)(+)-N)) and in the sediments (total N (TN), total P (TP) and total organic carbon (TOC)) were quantified. The results show that NH(4)(+)-N was the main component of inorganic N in the pore water. NH(4)(+)-N and SRP were higher in the pore water than in the overlying water, and the concentration gradient indicated a diffusion potential from the sediment to the overlying water. The NH(4)(+)-N, NO(3)(−)-N, and SRP fluxes showed significant differences amongst the seasons. The NH(4)(+)-N and SRP fluxes were significantly higher in the summer than in other seasons, while NO(3)(−)-N was higher in the autumn. The sediment generally acted as a source of NH(4)(+)-N and SRP and as a sink for NO(3)(−)-N and NO(2)(−)-N. The sediments release 1133.15 and 92.46 tons of N and P, respectively, to the overlying water each year.