Study of water quality and eutrophication in Sanya coastal zone

Seasonal and spatial distribution of water quality was investigated at 29 stations in the Sanya coastal zone (SYCZ). Nutrients, chlorophyll-a (Chl-a), and other physical and chemical parameters were measured in April and September from 2007 to 2009. The concentrations showed ranges of 1.22-35.93 μ mol/L for dissolved inorganic nitrogen (DIN), 0.03-1.80 μ mol/L for phosphate (PO₄-P), and 2.46-156.60 μ mol/L for silicate (SiO₄-Si). The result indicated that NO₃-N and NO₂-N were the main ingredients of DIN in most coastal zones. DIN was mainly influenced by domestic sewage coming from Sanya City and sea breed aquatics, while phosphate and silicate were generally controlled by river runoff. N/P ratios were also calculated, results suggested the restrictive nutrient was N in dry season and P in rain season. In the past two decades, concentrations of nitrogen and phosphate had markedly increased. It was too high for the natural growth of the coral and coral reef ecosystem in SYCZ.