The application of a stepwise discriminant analysis method in a marine water quality evaluation

To evaluate the marine water quality of West Guangdong Prcvince, China, an assumptive random sample comprising 400 stations (at each station there are 13 water quality indicators) is established according to the National Water Quality Standards (GB 3097-1997).The 13 indexes are filtered with a stepwise discriminant analysis method in terms of their water quality discriminant ability. Five indicators with distinguishing discriminant ability are picked out. They are a chemical oxygen demand, oil, cadmium content, total phosphorus and total nitrogen. A discriminant function and a water quality classification plate are thereafter established with these five indicators. The method avoides introducing too many indicators to have adverse impact on the water quality evaluation model. The above water quality classification plate is applied to evaluating the marine water quality of 40 stations in West Guangdong Province in 2010. Compared with the result provided by Zhanjiang Oceanic and Fishery Environmental Monitoring Station, it is found that the matching rate of 40 stations in this area is 95%. It indicates that the plate has a good application effect. It can be used as an effective way to evaluate the marine water quality by using multi-indicators.