| To enhance water exchange and alleviate eutrophication in Lake Taihu, the second largest freshwater lake in China, it has been implemented or planned to flush pollutants out of Lake Taihu by transporting freshwater from the Yangtze River since 2002. Along the water diversion route, twenty surface water samples were collected in the Yangtze River, Wangyu River and Gonghu Bay during water diversion(August and December 2013) and after water diversion(April 2014), respectively. To clarify the pollution characteristics of nitrogen and phosphorus during the water diversion on the main sources of drinking water in the Gonghu Bay, they were analyzed to research the form composition, seasonal and spatial distribution of nitrogen and phosphorus in surface water and that of phosphorus in the suspended particles in three different periods. The main results were as follows:(1) The percentages of various N species showed that NO3--N was the major N species in the Yangtze River and Wangyu River during the 2 water transfer processes, meanwhile DON was the major N species in the Gonghu Bay in August and they were TPN and DON that took the main percentage of N species in Gonghu Bay in December, respectively. TP contents in samples collected from the Yangtze river displayed constant trend compared with the Wangyu River. However, the percentages of various P species were different with each other during the2 water transfer processes. In general, TPP and PO43--P were still the major P species. The concentrations of DON and TP in surface water in August were higher than those in December and the contents of NO3--N and TDP were lower in August than those in December.(2) NO3--N was the main composition of TN in April 2014. However, NH4+-N content in the Wangyu River was higher than that in the Yangtze River and Gonghu Bay, due to pollution input in the west of the Wangyu River. And PO43--P and TPP were the main compositions of TP in the Yangtze River, Wangyu River and Gonghu Bay in April 2014. Except TP content was above the national environmental quality standards for surface water(GB 3838-2002,grade V), TP contents of other samples were classified as IV~V in the Yangtze River, Wangyu River and Gonghu Bay.(3) Because G7 and G15 were closer to the entrance to Gonghu Bay than G9, the water quality of G7 and G15 were better than that of G9. And main input N and P forms to G7, G9 and G15 during water diversion were as follows: NO2--N, NO3--N, TN and PO43--P, TP. Due to water diversion, NH4+-N concent was diluted obviously. NO2--N content of G15 was the highest in the Yangtze River, Wangyu River and Gonghu Bay in April 2014. Meanwhile,NO3--N, DON, TN, TPP and TP contents were also the highest in the Gonghu Bay, except G14. The government should pay attention to G15.(4) The contents of six forms of P were different in three different periods. But the main compositions were still Org-P, Fe-P, De-P and Res-P. The spatial characteristic of Ca-P, De-P and Res-P concentrations was Wangyu River > Gonghu Bay. From the point of seasonal change, PTP, Ex-P and Org-P contents in August 2013 in the Wangyu River and Gonghu Bay were lower than those in December 2013. Compared with PTP, Ex-P and Org-P, opposite feature of seasonal characteristic existed in Ca-P, De-P and Res-P contents. Seasonal characteristic of PTP, Ex-P and Fe-P contents in the Wangyu River was December 2013 <April 2014, similar to Fe-P, Ca-P and De-P in the Gonghu Bay. Because of alage bloom,Org-P content was always higher than others in the Gonghu Bay. The contents of Org-P and Fe-P were the highest in the Wangyu River.(5) The main forms of P in the suspended particles of G7, G9 and G15 were Org-P and Fe-P, no matter what during and after water diversion. It indicated that they were polluted by human activity and P.(6) All in all, water diversion is good for Gonghu Bay to improve the water quality,especially for G15. It is the best period in April, August and December to water diversion for the Gonghu Bay. |
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