Research On Agricultural Diffuse Pollution And Pre-reservoir Controlling Technology In The Upper Stream Basin Of Yi River

With the effective control of industry point source pollution, the agricultural non-pointsource pollution has already become the main pollution source in water environment nowdays,because of dispersion, random occurrence, spatial variability features and lack of effectivecontrol measures. The occurrence mechanism and control measures of the non-point sourcepollution received widely attention. In the upper stream basins of the Yi River, soil erosion andagricultural development activities were serious and the non-point source pollution induced bysoil erosion and agricultural development activities severely threatened the water environmentquality. Based on the former research results, supported by the remote sensing (RS) andgeographic information system (GIS), helped by simulated experiment in the lab and fieldstudy with the guidance of such theories as environment science, botany, soil conservation,statistics, and remote sensing, this thesis ananlyzed transportation characteristics of nitrogen (N)and phosphorus (P) of the Menglianggu watershed located in the upper stream of Yi River,selected plants which can effectively remove plants, and designed pre-reservior. The mainresearch progress and conclusions are as following:(1) The variation characteristics of nitrogen and phosphorus varied in different processes.In the non-rain state, dissolved nitrate nitrogen (DNN) was the main form, whichperformed a step variation. The phosphorus contents were much beyond warning concentrationfor eutrophication and the contents of dissolved reactive phosphorus (DIP) and total phosphorus(TP) were significantly different. In the precipitation process, total nitrogen (TN) andparticulate nitrogen (PN) contents reached rapidly the maximum before the runoff peak andthen declined quickly, while dissolved nitrogen (DN)and dissolved nitrate nitrogen increasedgradually and became stable. Different forms of phosphorus contents increased sharply andparticulate phosphorus (PP) played main role in total phosphorus. What's more, the dischargeweighted concentration (DWEC) and the average loss rates of nitrogen and phosphorus varieddifferently. DN and PP was the main form of nitrogen and phosphorus loss and DNN was the main form of DN. Besides, the average loss rates of nitrogen and sediment were both positivelyco-related to rainfall intensity.(2) Aquatic plants could purify nitrogen and phosphorus, but the purification efficienciesvaried a lot.Nine kinds of hydrophytes, such as calamus, iris pseudoacorus, ceratophyllum demersum,scirpus tabernaemontani, typha orientalis presl, canna indica Lin., thalia dealbata, pontederiacordata and lythrum Salicaria growed well in the sewage and the removal rates were higherthan other hydrophytes. Take ceratophyllum demersum for example, the removal rates of TN,DHN, TP and DIP were85.53%,99.07%,76.09%and82.43%, respectively. Furthermore, thecontents of TN and TP presented a short rise trend and then decreased constantly, while thecontent of DNN was very low in the early stage, reached the maximum after fifteen days,andthen declined in different degrees.Besides, in the contabescence, the mean releasing rates of Nand P for most species were generally higher in25°C environment than that in15°C condition.The content of TN varied differently with training the extension of time while the content of TPreached the maximum in the third day, declined sharply, and the became stable after six days.So the hydrophytes could be harvested in a week after the hydrophytes died.(3) The controlling technology of pre-reservoir can manage agricultural diffuse pollutionobviously.Based on the research results showed above, pre-reservoir technology has been establishedin the Menglianggu watershed, including subsystem of runoff collecting and regulating, settlingtank, flood ditch and headwaters area of pre-reservoir. Futhermore, the N and P mean releasingrates of the soil were less than zero, so the soil could remove pollutants. The removal rates of Nand P presented different variation characteristics. What's more, the variation of TN removalrate showed the same trend and the mean removal rate of TN was17.23%.The law of DNN andDIP removal rate were not obvious, with an average of10.87%and16.85%, respectively. Theremoval rates of DHN and TP showed decreasing trends, with an average rate of43.46%and28.07%, respectively. In a word, the removal rate of the pre-reservoir achieved the desiredeffect.