Distribution of Nitrogen and Phosphorus in the Tidal Reach and Estuary of the Daliao River and Analysis of Potential Eutrophication

Based on the monitoring data in the tidal reach and estuary of the Daliao river in August and November, 2013, the seasonal and spatial distribution of the nitrogen and phosphorus forms were studied, and the degree of eutrophication was evaluated. The results showed that nitrate nitrogen was the main chemical species and occupied about fifty-five percent of inorganic nitrogen, and the particulate phosphorus was the main chemical species and occupied about fifty percent of total phosphorus in the tidal reach and estuary of the Daliao river in wet and dry seasons, 2013. The concentrations of nitrogen and phosphorus nutrients decreased in the direction from tidal reach to estuary of the Daliao river. Correlation analysis showed that there was a significant negative correlation between the nitrogen and phosphorus forms and salinity in most of the water body, which illustrated that physical dilution of seawater played a major role in the spatial distribution of nitrogen and phosphorus forms. The concentrations of nitrogen and phosphorus nutrients in the dry season were higher than those in the wet season, this was mainly related to the seasonal terrestrial input of the tidal reach. The concentration of the dissolved inorganic nitrogen was higher than 0.30 mg · L⁻¹, and the value of N/P was higher than 60, which indicated that PO₄³⁻-P was the nutrient limiting phytoplankton growth in the tidal reach and estuary of the Daliao river in August and November, 2013.