Study On Agricultural Non-point Pollution Potential Index (APPI) Model And Its Application In Yixing

This thesis focuses on the agriculture non-point pollution at the river network area of Taihu Lake A combination method of field monitoring, field survey, sediment loss estimation and a GIS platform were used and an agricultural non-point pollution potential index (APPI) model were optimized and calibrated. The model was used to quantify the rural non-point source nitrogen and phosphorus in Dapu Town and Yixing City. The distribution pattern of discharge loads and potential indexes was obtained and major pollution factor and priority controlling area were defined, which can be used as a tool for the management and control of non-point pollution.At the same time, combining with researches on biological toxicity assessment of selected pollutants, toxicity threshold of non-point pollution was obtained.Main findings are listed as following:1. Nitrogen and phosphorus loads of agriculture non-point pollution in Dapu townAfter optimizing the model parameters based on soil loss equation and GIS platform, the nitrogen load from rural non-point sources was quantitatively estimated i n Dapu Town. Results showed that the non-poi nt discharge of nitrogen from Dapu Town were about 207 t·a-1, which was composed of 8016 tons of farmland,61.1 tons of living sewage,4913 tons of fishery,1015 tons of garbage and 514 tons of sediment production per year, which occupied 39.10%,29.15%,23.18%,5.11% and 2.16%, respectively. The critical control factors of the five nitrogen sources were farmland, living sewage and fishery. The average nitrogen discharge from four villages, Fangqiang, Dapu, Pubei and Punan, were 8014,7310,6014and 5213 kg·ha-2·a-1, which were much higher than that from other villages. Therefore the four villages were priority controlling areas.The contribution of phosphorus from rural non-point source pollution was investigated. About 30.1 tons phosphorus per year was discharged into environment of Dapu Town, in which 10.9 tons were from people sewage loading,1.9 tons from garbage,11.3 tons from livestock &.fishery sewage,4.1 tons from farmland,1.89 tons from rain runoff, corresponding to 36.1%,6.4%,37.5%,.13.7% and 6.3%, respectively. The key factors were people sewage and livestock and fishery sewage. More attention should be paid to Fangqian, Dapu and Punan sincethar phosphorus loading were relatively high. The critical area identified for NFS control in Dapu town were Fangqian, Dapu, Pubei and Punan for their average loss loadingwere 21.7,17.1,10.9 and 8.7 kg·hm-2·a-1,much higher than the others.2. Non-point pollution potential index in DapuThe APPI model was applied and validated in Dapu Town, Yixing city through field experiments and local investigation with geographical information system, for identifying and ranking agricultural non-point source pollution potential and qualification of the key facts in critical areas. Result from the model showed that the critical area identified for NPS control in Dapu Town was Fangqian, Pubei and Dapu. The nitrogen and phosphorus polIution from Iivestock of ait kinds pollution bigger scale in critical areas. It showed that the nitrogen and phosphorus pol lution from livestock should be one of the key facts.3. Non-point pollution potential index in Yixing cityThe APR model developed in Dapu town was introduced into Yixing city using a new normalized method to estimate the non-point pollution load and potential index. Results showed that total N load of Yixing was 7276.95 t·a-1,including 5.29% runoff, 31.19% fertilizer lost,3.67% garbage,21.3% domestic sewage and 38.56% livestock raising and total P load was 99.77 t·a-1, including 13.58%,11.84%,9.82%,21.89% and 42.86%, respectively. APPI index showed that Fangzhuang, Xinqian, Heqiao, Fuxiangqiao are the priority controlling areas.4. Development of agriculture non-point pollution loading and potential index softwareUsing Mapbasic, visual Basic, Mapinfo and known study results, based on the APPI model, we developed a non-point pollution assessment software It can assess, edit, search and compare pollution loads and densities in different areas, which can be used as a tool for the management and control of non-point pollution.5. Toxicological effects of lanthanum ions on Vicia faba L. seedlingsRare earth elements were widely used as microcomponent fertilizer in agriculture, inducing potential risk to ecology. Vicia faba L. seedlings were hydroponically cultivated in 0-12 mg/L of extraneous lanthanum (La) for 15 days to investigate ecotoxicological effects and risk assessment of rare earth elements (REEs). The results showed that reactive oxygen species (ROS) production such as superoxide radical (O2-) and hydrogen peroxide (H2O2) were overproduced at higher concentrations of La, resulting in oxidatively modified proteins and shoot growth retardation. The threshold dose range was firstly delimited as 1-2 mg/L of extraneous La, corresponding to 7.34-9.37 ?g/g dry weight in the leaves. These results would be helpful to further understand the toxicological effects and possible mechanisms of REE(s) on crop seedlings.