Occurrence Of Organic Matter In Paddy Fields Under Fertilization, And Assessment Methodology Of Organic Pollution In Surface Water

Agricultural non-point pollution is mainly caused by the release of fertilizer, pesticide and other organic/inorganic nutrients applied in agricultural lands. Loss of organic matter from agricultural lands is one of the current agricultural and environmental issues. Release of organic matter could cause loss of soil carbon pool, bring about organic carbon pollution in ambient waters, exert risk on safe drinking water supply, and increase disinfection byproduct formation potential of raw water. Therefore, it is environmentally significant to study the source (agricultural non-point sources) and the fate (surface water) of organic matter. Because of the complexity, intermittence and dispersity of agricultural non-point sources pollution, it is quite difficult and unpracticle to study the transport of organic matter from source to fate. Therefore, this study emphasized the source of organic matter—controlling the sources of the release of organic matter; the fate of organic matter—assessing the quality of surface water polluted by organic matter from non-point sources.One of the sources of organic matter, paddy field under fertilization, was studied in this research, in order to help to source control the release of organic matter. Paddy soil and some kinds of fertilizers (eg. organic fertilizer) contain high content of organic matter, with a high potential of releasing to ambient water. First, paddy field soil organic matter was studied in this research. Field experiments were conducted to study the content and density of soil organic carbon in response to different fertilizer types and different fertilizer application amounts in Jiaxing from 2012 to 2014, to provide the scientific basis for soil carbon sequestration to mitigate greenhouse gas emission. Second, organic matter of paddy field floodwater was studied in this research. Field experiments were also conducted to study the content, reactivity and temporal change characteristics of dissolved organic carbon and disinfection byproduct precursors in the rice paddy field floodwater in Jiaxing in 2013, to provide the scientific basis to reduce the release of organic matter and disinfection byproduct precursors from agricultural non-point sources.Results showed that application of organic fertilizer (swine manure) significantly affected the content and stock of soil organic carbon. SOC content and stock of 0-20 cm soil layers increased with the amount of organic fertilizer, but their extent of increase was limited when the fertilization amount was high enough, indicating SOC might reach the saturation point. Fertilization did not affect the content and stock of SOC under 20 cm soil layers. Regression analysis of SOC stock of 0-5 cm,5-20 cm and 0-100 cm soil layers, and amount of carbon import from organic fertilizer, reflected the soil carbon sequestration rate of 10.5%,29.4% and 36.4%.The amount of DBP precursors in paddy field floodwater was not related to the amount of inorganic fertilization. Avoiding inorganic fertilizer application near a rainfall event (allowing 3 days or more between inorganic fertilizer application and a rainfall event) can minimize the risk of DOC and THMFP export via runoff. The more organic fertilizer was applied, the more content of DBP precursors was in paddy field floodwater, and the more export risk of DBP precursors via drainage and runoff. Allowing 1 or more weeks between swine manure amendment and a predicted rainfall event or irrigation event, would be the best case scenario for managing organic matter to meet crop requirements and lowering risk of DBPs precursors’ export. According to this modified irrigation-drainage pattern, paddy soil behaved as sink of DOC rather than source of DOC exporting into surrounding waterways.One of the fates of organic matter, the watershed, was studied in this research, in order to help to assess the organic matter pollution from non-point sources. In this research, the application of fluorescence excitation-emission matrix spectroscopy combined fluorescence regional integration method in water quality monitoring was studied in Yuhang, Hangzhou in 2014, to provide the scientific basis for assessment of water source safety and early warning of pollution event.Results showed that the common used water quality indicators DOC concentration and SUVA254 are not proper to be used for assessment of water quality of the watershed as the drinking water source or early warning of water source pollution event. The three hierarchical cluster analyses of fluorescence regional integration indicators of spring, summer and fall indicated that the fuorescence regional integration indicators of fluorescence excitation-emission matrix spectroscopy are proper to be used for assessment of water quality of the watershed as the drinking water source or early warning of water source pollution event.