Study on water quality and eutrophication level in the coastal area of Dapeng Bay

Based on the monitoring data in the coastal area of Dapeng Bay in 2012-2016, the water quality of survey region was evaluated by using methods of single factor index and the organic pollution index. Furthermore, the eutrophication index and potential eutrophication index were applied to assess the eutrophication level, and the correlations between eutrophication level and environmental factors (salinity) also investigated. The results suggested that the water quality in the whole study area was generally good in 2012-2016, meeting Class Ⅱ seawater quality standards in Sea Water Quality Standard (GB 3097-1997), and the interannual changes were fluctuating without obvious rules. In the spatial distribution, only the Sha Tau Kok area was significantly polluted. The results of eutrophication level basically showed low-nutrient, and the interannual changes showed an upward trend. In the spatial distribution, only the Sha Tau Kok and Nan’ao Bay showed eutrophic and high eutrophic states, respectively. The potential eutrophication was mainly concentrated in grade Ⅰ (poor-nutrition). The correlation analysis showed that the eutrophication index was negatively correlated with salinity, suggesting that the surveyed sea area was greatly affected by low-salinity and high-concentration pollutants from estuarine flushing water and land-based pollution.