Variation trends of nutrient in Qinhuangdao coastal area based on statistical method

Based on data of monitoring sites inquality of seawater monitoring area,the mariculture zone,red tide monitoring area andinshore ecosystem monitoring zone in Qinhuangdao coastal area from 2003 to 2013,the long-time variation trend of nutrient(N and P)and nutrient structure were analyzed by using normal distribution method.The result showed that the mean concentration of DIN and exceeding standard of DIN in surface seawater is rising on the whole in the past 11 years,but the concentration of DIP has a remarkable fluctuation characteristic and exceeding standard of DIP has shrunk.The ratio of nitrate to DIN is decreasing initially then increasing while the ratio of ammonia to DIN is quite the contrary.It is shown that the trend of oxidizing environment in Qinhuangdao coastal areais weakening before strengthening.The primary production is limited by phosphate in this coastal area.