Characteristics of nutrients in the Jiulong River and its impact on Xiamen Water, China

Water samples were collected at 20 sites on 4 occasions in 2009 (twice in May, and once in both August and November) along the Jiulong River, South China to examine how nutrient inputs from the Jiulong River could affect the nutrient status of the Xiamen Water. Samples were analyzed for nitrite (NO 2 -N), nitrate (NO 3 -N), ammonium (NH 4 -N), phosphate (PO 4 -P), silicate (SiO 3 -Si), salinity, and temperature, to determine the nutrient and trophic status of the river. The results indicate that nutrients are derived mainly from river runoff. NO 3 -N was the main form of DIN in most parts of the river. In addition, NO 3 -N, DIN, and SiO 3 -Si behave conservatively. There is a surplus of DIN and SiO 3 -Si in the river, and PO 4 -P is a limitation on phytoplankton growth. The concentration of DIN is typically above 0.60 mg/dm 3 , and higher than 1.00 mg/dm 3 in most parts of the river. The concentration of PO 4 -P is typically above 0.02 mg/dm 3 , while the concentration of SiO 3 -Si is higher than 1.00 mg/dm 3 . Between 2003 and 2008, samples were collected 3 times per year (May, August and November) at 27 sites in the Xiamen Water and analyzed for NO 2 -N, NO 3 -N, NH 4 -N, PO 4 -P, salinity, and temperature. We discovered that the Jiulong River was the key source of DIN into the Xiamen Water, but not PO 4 -P, indicating the reason of the N/P molar ratio imbalance in the Xiamen Water. In the future, the effects of high DIN concentrations on the phytoplankton communities and marine ecosystems of the Xiamen Water shall be studied.