Research On Water Quality And Eutrophication Of Typical Bays

Qinzhou Bay, with its valuable biological resources and economic importance,is one of the most important bays of Beibu Bay and has distinctive characteristic and representativeness. Thus, the protection of water quality in Qinzhou Bay is not only the focus of the work in this bay, but also has a guiding significance and representative for the environmental protection work of the whole Beibu Bay as well as China’s coastal waters.To get a more comprehensive and deeper grasp of the water quality condition in Qinzhou Bay, this study analysised the load of nutrients into Qinzhou Bay, and then evaluated the water quality and eutrophication of this bay.Firstly, a long time series data of seawater environmental factors (DO,CODMn and chlorophyll) and nutrients (inorganic nitrogen, active phosphate and reactive silicate) from1990to2007was collected, then temporal and spatial variation of the main environmental factors and nutrients indicators in the past20years, as well as correlation of nutrients and pH and Sa were analyzed. The results showed that:Water quality in Qinzhou Bay was good; Runoff input played a leading role of DIN and SiO3-Si changes, but it had no significant effect on DIP.Secondly, based on the status of land use information, the export coefficient method was used to study the nitrogen nutrients of the non-point source pollution in2000and2007, and the more accurate total load into the sea was calculated. The results showed that: Compared with2000, the load of nitrogen nutrients into the sea had a slight increase. Non-point source pollution had the absolute percentage (86.8%) in the total load of nitrogen nutrients into the sea.Third, considering the level of water environmental pollution was interrelated with water quality classification and had ambiguity, fuzzy comprehensive evaluation method was used to evaluate the water quality of Qinzhou Bay over the years to achieve the greatest objectiviry for the first time. The results showed that:The water quality of Qinzhou Bay was fine, and the evaluation results were I level, but the inter-annual variation of a value showed a wave of down trend and the mean a was3.82. Correlation analysis between evaluation factors and a value stated that the inorganic nitrogen was the main contribution factor to the deterioration of water quality.At last, the integrated methodology for Assessment of Esutarine Trophic Status (ASSETS), one of the second generation of eutrophication assessment methods, was applied to evaluate the eutrophication level of Qinzhou Bay for the first time. The results showed that:Impact fator was rated as "Moderate", eutrophication condition was rated as "Low", future outlook was rated as "Worsen High", and finally the ASSETS evaluation of the results was rated as "Moderate".