Study On The Accumulation Characteristics And Release-control Of Nitrogen And Phosphorus In The Sediments Of Aquatic-terrestrial Ecotones Of Taihulake

More and more pollutants entered into the water body and accumulated by sediment, increased the pollution load of Taihu Lake. Though the external pollution sources have been effectively controlled, eutrophication of Taihu Lake is still continuous on the basis of large number of studies. The release of nitrogen and phosphorus from the sediment in the specific environment condition of physical, chemical, biological and other factors ,causing the risk of eutrophication of Taihu Lake. Based on above, carried out the study of the pollution characteristics and release-control of nitrogen and phosphorus in the sediments of lakeside zones of Taihu Lake by on-the-spot investigation and laboratory simulation. Major conclusions were described as follows:Firstly, the distribution characteristics of nitrogen, phosphorus and organic matter were deeply researched and analyzed, and then explored the correlative relationship between organic matter and total nitrogen, total phosphorus, the correlative relationship among different nitrogen fractionation and different phosphorus fractionation in surface sediments of the inner aquatic-terrestrial ecotones of Taihu Lake; and evaluated the pollution level of the inner aquatic-terrestrial ecotones of Taihu Lake by comprehensive pollution index and organic index. The results show that: The contents of nutrients there was significant different in sediment, due to the environmental condition and human activities. Based on comprehensive pollution index and organic index, the environmental qualities of sediments in the whole lakeside zones still belonged to clean category. The serious pollution area was the sediments of Zhushan Bay.Secondly, the sediment of inner aquatic-terrestrial ecotones of Zhushan Bay, which was polluted seriously and greatly influenced by human activities, was selected to simulate the internal release of nitrogen and phosphorus under the different environmental factors by orthogonal test. The results showed that the important order of environmental factors influencing the release of nitrogen in sediments as follows: DO>pH>disturbance. And when pH=5, DO=2 mg/L as well as disturbance intensity was 0 r/min, the release of nitrogen would reach the maximum intensity; the important order of environmental factors influencing the release of phosphorous in sediments as follows: pH>DO>disturbance. And when pH=10, DO=2 mg/L as well as disturbance intensity was 60 r/min, the release of phosphorous would reach the maximum intensity. Overall, the release intensity of nitrogen in sediment decreased with the decrease of DO level. Slight disturbance may not promote the release of nitrogen; however, violent disturbance would promote nitrogen releasing. acidic or alkaline condition could all promote the release of nitrogen, while acidic condition was more beneficial to the release of nitrogen and when pH was in neutral range would promote the adsorption of nitrogen; the release intensity of phosphorous in sediment decreased with the increase of DO level, the release intensity of phosphorous in sediment increase with the increase of disturbance intensity, acidic or alkaline condition could all promote the release of phosphorous, while alkaline condition was more beneficial to the release of phosphorus. When pH was in neutral range, phosphorous was adsorbed to sediment.Thirdly, the ex situ passivation technologies with different chemicals were studied to inhibit the release of nitrogen and phosphorus in the sediments in this paper. The results show that the inhibition rates of different chemicals acting on the release of nitrogen were generally poor. The results show that the inhibition rates of different chemicals acting on the release of DIP were in decrease order as follows: Ca(NO3)2+CaO(98.1%)>FeCl3 (76.6%)>Ca(NO3)2(67.6%)>Al2(SO4)3(6.8%)>FeCl3+CaO(0%)>Al2(SO4)3+CaO(0%); The results show that the inhibition rates of different chemicals acting on the release of TP were in decrease order as follows: FeCl3(75.0%)>Ca(NO3)2(66.1%)> Ca(NO3)2+CaO(53.4%)>Al2(SO4)3(14.4%)>FeCl3+CaO(0%)>Al2(SO4)3+CaO(0%). Overall, the inhibitory effects of ex situ passivation technologies with different chemicals controlling the release of nitrogen in the sediments were generally poor, while had significant effect on controlling the release of phosphorous and Ca (NO3)2+CaO and FeCl3 could effectively inhibit the release of phosphorus than others. However, the concentration of TN in overlying water would be increased when sediments were situ-controlled by Ca (NO3)2. So using FeCl3 to passivation sediment was the best chemical in added chemical to inhibit the release of phosphorus.