Application of an integrated methodology for eutrophication assessment: a case study in the Bohai Sea

An integrated methodology for eutrophication assessment, which integrates both water quality indicators (causative factors) and ecological response indicators (effect factors), is described. It is then applied to rank the eutrophication status of the years 2007 and 2008 in the southwest Bohai Sea. The assessment model identified that north Bohai Bay and west Laizhou Bay were the two areas with the most serious eutrophication problems in the southwest Bohai Sea. In addition, compared to that in the west Laizhou Bay, the eutrophication conditions in the north Bohai Bay was more serious in both years. Eutrophication problems such as harmful algal blooms (HABs) and low dissolved oxygen (DO) events in north Bohai Bay were frequent. The integrated method outmatched the currently used Chinese nutrient index method by definitely identifying areas with the most serious eutrophication problems, while the nutrient index method gave ambiguous results between the two years. Inclusion of both causative factors and effect factors, combining concentration, spatial coverage and frequency of indicators, as well as use of multi-season monitoring datasets in the methodology result in a more accurate, representative and useful assessment.