Nutrient Speciation and Distribution between Surface Water and Sediment in the Middle Reach of the Huai River, China

The speciation and distribution of the nutrients nitrogen and phosphorus in riverbed sediment play an important role in river water quality and are the primary product for the river ecosystem. Previous research on river nutrients has not considered the relationship between nitrogen and phosphorus and their mobility effects. To investigate the role of nitrogen and phosphorus in water quality and their interactions between sediments and water, sediment and water samples were taken from 10 sites along the middle main stream of the Huai River in China from Linhuaigang to Fengtai County on December 12, 2008. Nitrogen and phosphorus concentrations in water, organic matter (OM), and different forms and contents of the elements in sediment were investigated. Results showed a positive correlation between total nitrogen in sampled sediments, primarily occupied by organic nitrogen and chlorophyll a concentrations in water (r2=0.727). Total phosphorus in sediments was primarily represented as inorganic phosphorus, accounting for 80.9–96.1% of total phosphorus. The concentrations of non-apatite inorganic phosphorus in sediment ranged from 70.85–231.27 mg/kg. Results from statistical correlation analyses showed that the non-apatite inorganic phosphorus content in sediment was obviously negatively correlated with total nitrogen concentration in water (r2=−0.875, p<0.01); inorganic nitrogen and non-apatite inorganic phosphorus contents in sediment were positively correlated with total phosphorus and resolvable phosphorus concentrations in water, respectively. Furthermore, data of May 2008 were added and analyzed. The same principles were observed between total nitrogen and non-apatite inorganic phosphorus, total phosphorus and inorganic nitrogen, but a positive correlation was found between (1) total nitrogen in water and (2) exchangeable nitrogen (p<0.01) and inorganic nitrogen (p<0.05) in sediments.