The Time Series Analysis Of Nutrient Elements And To Forecast Risk Of Eutrophication In Suzhou Creek

Suzhou Creek, the largest branch of Huangpu River, the connect channel between Tai Lake and Huangpu River and also the important natural water of Shanghai, is being confronted with the risk of eutrophication. Based on the nutrient date in Suzhou Creek during 1983-2002 and date mining by Time Series Analysis, then coupled the analysis of four times' monitoring results(NH₃-N NO₂-N NO₃-N TN PO₄-P TP chla)in 2005 to make an prediction of eutrophic risk.Through the time series analysis of nutrient historical data in upriver and lower reaches of Suzhou Creek, it is conclued that the nitrogen and phosphorus loading in Suzhou Creek is very high, the 20 years' average value of ammonium-N in upriver is more two times than that in lower reaches and the increasing of nitrogen in upriver has becoming the character of water quality in Suzhou Creek. The concentration of nitrite is no space fluctuation in creek. The average value of nitrate in lower reaches (0.68mg/L) is one fifth of that in upriver (3.24mg/L) because of the unstable dissolved oxygen;The total phosphorus in upriver falls from0.926mg/L to 0.283mg/L around 1991,while that in lower reaches has keep high level (0.86mg/L).The rate of dissolved nutrient salts is more than 60% in whole creek.Though analysis on space-temporal variation and correlation to nutrient factors of chlorophyll-α in Suzhou Creek, the paper found that the amount of nutrient element and chlorophyll-α showed clear seasonal variation. The variation of chlorophyll-α content correlated obvious negatively with nitrogen. The addition of nitrogen can't improve the growth of algal.The variation of chlorophyll-α content correlated obvious positively with phosphorus. The high concentration of chlorophyll-α and large nitrogen and phosphorus loadings are clear potential of eutrophication in Suzhou Creek and lead to biological effect, it is possible of water bloom to take place, Wuninglu, lower of the creek, has the highest risk. Based on the analysis of N/P and correlation between TN TP and PO₄-P, to conclude that Suzhou Creek is alternation control between nitrogen and phosphorus, it is phosphorus control in early spring and winter, but the lower temperature and weak light went against the algal growth. In the opposite, the N/P is fit for the nutrient absorption of algal in summer and autumn, coupled with the proper temperature and light, it is possible for water bloom to break out. The main controlling factor of euthophication in Suzhou creek is phosphrus.The algal stimulation test shows that when the input of nitrogen andphosphorus are below 21.6mg/L and 2.88mg/L, the algal growth will be promoted in early spring in Suzhou Creek;When the input of nitrogen and dissolved silicon in upriver are below 10.8mg/L and 14.4mg/L, the algal growth will be promoted in summer in upriver. While the nitrogen n phophorus and silicon input in lower reach are 43.2mg/L^ 5.76mg/L and 7.2mg/L. When in winter, the phophorus input below 0.48mg/L in upriver, while the nitrogen in lower reach is 8.4mg/L, but the temperature and light may limit the algal growth.The detection of microcystin was conducted in the research. The microsystin content is below the WHO safety lever.It shows that toxic blue-green algal is not the major component in community. The research provide the manager with scientific proofs for the control of eutrophication.