Saltwater Intrusion Induced by a Complete Neap Tide and Its Effect on Nutrients Variation in the Estuary of Pearl River, China

Temporal and spatial variations of water temperature, salinity, dissolved oxygen (DO), and dissolved inorganic nutrients (NO3-,NO2- SiO42-) were investigated over a complete neap tide in the estuary of Pearl River, China. Obvious saltwater intrusion was observed at the lower reaches of our survey section: surface water salinity varied from 2.00 parts per thousand to 17.80 parts per thousand, and bottom water salinity varied from 5.59 parts per thousand to 22.13 parts per thousand. The calculated stratification index indicated that the lower reaches had intense stratification during the present neap tide. Obvious dilation of and SiO24- was observed in the course of saltwater intrusion. Due to intensive decomposition and desorption-releasing action, NO(3)and PO4 concentration increased with increasing water salinity. Investigation results revealed that saltwater intrusion had a significant effect on nutrient structure and probably alleviated a phosphorus-limiting situation in the estuary ecosystem. All these changes were induced to some degree by tidal currents and their associated sediment-agitation process and had a profound effect on the estuary ecosystem.