Numerical Research For Export Of Non-point Nitrogen Of Dagu Watershed And Its Impact On Water Quality Of Jiaozhou Bay

Numerical Research for Export of Non-point Nitrogen of Dagu Watershed and its Impact on Water Quality of Jiaozhou BayJiaozhou bay is a typical semi-enclosed bay affected by human activities in China. During a long time people have paid their most attention on point-source pollution and thus resulted in the ignorance of the great impact of non-point source(NPS) pollution of watersheds on water quality of Jiaozhou bay. In this paper, watershed NPS pollution model was used combining with export coefficient method to quantitatively estimate the long-time NPS nitrogen export of Dage watershed. In addition, a coastal water dynamic /water quality model was used to estimate the impact of such NPS nitrogen on the water quality of Jiaozhou bay.The calculation result of the annual NPS total nitrogen yield in Dagu watershed from 1973 to 2001 showed that the value increased rapidly since 1970s'period though it had a interannual variation. Through the research of landuse maps, it was found that the landuse type in research area was not under a rapidly changing period, so the most important reasons for the growth of NPS pollution are animal husbandry and fast growing use of fertilizer. In another aspect, the ration of all types of NPS pollution accounting for total NPS pollution were varied significantly in the past several decades. The ration of soil and water loss decreased from about 80% in 1973 to about 50% in 2001 while the rations of fertilizer utility and animal husbandry increased to 35% and 13% in 2001. Meanwhile, rural living was not the major source of NPS pollution despite of its continuous growth. To sum up, while formulating policies for solving NPS pollution in Dagu watershed, several aspects should be token into account, firstly: decrease the use of fertilizer and enhance the availability, increase the treatment rate of excrement of animal husbandry and apply new treatment technologies.The distribution of total nitrogen which drained by Dagu watershed NPS pollution was simulated in Jiaozhou bay, results showed that the concentration was comparatively low in months of 1~6 because of the low discharge of pollutant in this period, and just a small area surround the estuary of Dagu river was affected significantly. July to September was the peak period for the discharge of NPS pollutants, major area of Jiaozhou bay even including some places outside would be affected by the strong drainage of Dagu river. The TN concentration in this period was high surround Dagu estuary and gradually decreased from northwest to southeast part of Jiaozhou bay. It was the recover period for water quality from October to December in this coastal area. Because of the water exchange effect, the concentration of TN in Jiaozhou bay gradually decreased to the normal level. What's more, the water quality in this area was in deterioration trend year by year by reason of increasing intensity of NPS pollution discharge.