The determination of coastal and estuarine criteria is the most effective control tool for scientific management of eutrophication. EPA proposed six steps for the nutrient development process, including two core parts that the reference conditions and sub-areas compartmentalization. In the paper, the reference conditions in the Yangtze River estuary and adjacent water was established as a case study, which only refer to the reason variables. Candidate reference locations can be determined from compiled data with the help of regional experts familiar with the waters of the area. Base on One approach can apply a frequency distribution, known as "frequency distribution curve", the upper 75^th percentile be used as a starting point, the lower 25^th percentile is suggested. Establishing the reference condition is but one element of the criteria development process. Reference condition values are appropriately modified on the basis of examination of the historical record, expert judgment, and consideration of downstream effects.
In the present study, based on the domestic research, in which the Yangtze River estuary and adjacent waters were carved up into sub-areas, including four sea sub-areas: transitional zone, coastal zone outside of the estuary, Hangzhou Bay and Zhoushan Archipelago. As a result of the higher sediment concentration and lower transparency, in which plankton is difficult to breed, both in transitional zone and Hangzhou Bay, this tow parts would not be considered. In addition, as reason variables were referred in the paper, although a wide variety of indicator variables may be possible, the technical describes development of numerical criteria for the active phosphorus (PO₄-P) and inorganic nitrogen (DIN) as primary nutrient causal variables of eutrophication.
The established reference conditions method was applied to determine the reference condition of Yangtze River estuary and adjacent water, located in the southeast coastal zone of Shanghai city and Zhejiang Province, which is an important coastal area in China. With SPSS13.0 software, based on the monitoring data during 1992-2010, and relevant research results, as well as consulting expert experiences, the condition values that be refer the nutrient criteria values are listed in the order generally followed: in coastal zone outside area, the DIN reference condition values were 0.317mg/L in spring, 0.273 mg/L in summer, 0.211 mg/L in autumn, the PO₄-P reference condition values were 0.014mg/L in spring, 0.009 mg/L in summer, 0.018 mg/L in autumn; in Zhoushan area, the DIN reference condition values were 0.372mg/L in spring, 0.273 mg/L in summer, 0.441 mg/L in autumn, the PO₄-P reference condition values were 0.020mg/L in spring, 0.018 mg/L in summer, 0.029 mg/L in autumn. Compared to the relevant research about eutrophication in the same study area, the reference condition values, which acquired through "frequency distribution curve", were closed to the history states.