Occurrence of nutrients in riverine runoff of the Pearl River Delta, South China

Water samples were collected monthly from the eight riverine outlets of the Pearl River Delta (PRD), South China, from March 2005 to February 2006, and were analyzed for total nitrogen (TN), dissolved inorganic nitrogen (DIN), particulate nitrogen (PN), dissolved organic nitrogen (DON), total phosphorus (TP), and dissolved inorganic phosphorus (DIP) to examine spatial and temporal variations of nutrient species and nutrient fluxes. The annual mean concentrations of TN, DIN, PN, DON, TP, and DIP were 164.4, 113.8, 19.1, 31.4, 3.2, and 0.7 μM. The annual fluxes of the same substances from the PRD to the coastal ocean were 4.1 × 1010, 2.9 × 1010, 5.1 × 109, 6.9 × 109, 7.7 × 108, and 1.8 × 108 mol yr−1, respectively. The significant seasonality in rainfalls and the riverine discharge were the key hydrologic factors controlling nutrient fluxes. Spatial variability in nitrogen and phosphorus implies that local drainage from the PRD is a main factor impacting nutrient concentration at different outlets.