Considering the deficiency of conventional environment a impacts assessment to protect bay ecosystems from unfavourable impacts of multiple human activities over the years, this paper discusses an effective approach framework to examine addictive or interactive impacts arising from the collective multiple activities of the past. There are three stages of the cumulative effects assessment process: 1) systematically selecting indicators of the ecosystem in question, 2) choosing the quantified or semi-quantified methods to assess indicators of changes, and 3) assessing the past contributions of the activities to the changes.
In a case study of Xiamen's Western Sea in China, the indicators were constructed according to their sensitivities to environmental stress and classified into three categories: physical, chemical and biological indicators. The Geography Information System and Pearson correlation analysis were applied to assess changes of the physical and chemical indicators. The case study showed that most of the indicators of Xiamen's Western Sea ecosystem have been changed greatly in the past five decades, especially in shoreline, sea area, water quality, community construction of phytoplankton and benthos, and mangrove forests. Coastal and dike construction and terrestrial pollutant input are the main causes of the changes.