[Research the biogeochemical processes of nutrients in Minjiang Estuary]

The variations in the concentration and distribution of nutrients and influencing factors in the Minjiang Estuary with a tidal cycle were investigated based on the data obtained during field observations in May 2007. The results showed the suspended sediment, dissolved inorganic nitrogen and silicate were opposite to the change of tidal, while the water level and salinity were consistent with tidal. The buffer mechanism of phosphate was controlled by suspended sand and water. The concentrations of silicate, phosphate and inorganic nitrogen were ranged 0.63-9.00 mg/L, 0.013-0.075 mg/L, 0.33-4.24 mg/L respectively. The contents of dissolved inorganic nitrogen in water mass increased remarkably comparing 1980s because of agriculture, industry and living. The research indicated that the nitrate and silicate were conservative, but phosphate was non-conservative in the biogeochemical processes of nutrients in Minjiang Estuary. The diluted water carried abundant inorganic nitrogen, silicate nutrients to Minjiang Estuary and thus phosphate was similar between diluted water and sea water. Based on the results of nutrient ratios, it was suggested that phosphate was a limiting factor for phytoplankton growth in the Minjiang Estuary.