Influence Of Urban Garbage Landfill Leachate On Tidal Environment And Its Decontamination Mechanism

In recent years, the coastal environment in our country is getting worse: red tide breaks out frequently and its scale is continuing becoming larger, as it's known, nitrogen is the main limit factor of the eutrophication in estuaries and coastal seas. Besides the large amount of nutrient brought by rivers from the continent, the content of nutrient in the sewage discharged by the sewage outfalls which are constructed along the coastal area can't be neglected. With the development of cities, increase of the population and the rising of the living standard of people, the annual production of the garbage are increasing at a speed of 5% to 10%. Garbage fill and deposit is the popular and main way to deal with the garbage. But a kind of waste liquid named as garbage leachate will be produced during this process and also after the garbage is filled and deposited. The garbage leachate will pollute the surface water, groundwater and soil significantly if it can't be treated properly.Constructing garbage landfill near coastal area is very prevalent due to its great economic profit, but the garbage leachate let off from the landfill has a significant influence on the coastal water quality and the substantial cycling between different environmental medium. As the main sink of N, P and heavy metals in the estuary ecosystem, intertidal sediment play an important role in the eutrophication control and nutrient cycling process in the estuary. Various kinds of pollutants including N, P, and heavy metal et al. in the garbage leachate accumulate in the sediment, in which the intertidal sediment will decontaminate the nutrient through different physical, chemical and biological processes, while the heavy metals will accumulate in the sediment gradually, and will release to the environment under some specific conditions, leading to the secondary pollution. So it has important realistic and scientific meanings to study the environment effect on the tideland caused by the discharged sewage and calculate the decontamination capability of the tidal sediment to the polluted sea waters through the computation of the nutrient interface exchange fluxes of the tideland near the sewage outfalls.Choosing the tideland near the leachate outfalls in the developed Yangtze estuary, the influence of the leachate outfalls on the tidal environment and the decontamination mechanism of the tideland to the garbage leachate have been studied in this dissertation. This research will not only enrich and develop thebiogeochemistry theories in the estuary and coastal zone, but also provide reliable scientific basis for the environment protection, the eutrophication control and management of the Yangtze estuary as well as other estuary in our country. Through a large amount of field sampling and observation, experimental simulation and analysis, we get several main conclusions as follows:1. Due to the influence of the discharged leachate along the coastal zone the nutrient content in water and sediment of LG are higher than that in CM, and these tidelands have become a high deposition area of pollutants in Yangtze estuary. The partial pollution generally decreases with the distance to the sewage outfall, except that in low-tideland the pollution has a rising trend.2. The concentrations of the heavy metals in the sediment of LG which are influenced by leachate are higher than the environmental background values, and also higher than CM. The heavy metal pollution is serious in LG. The content of heavy metals in superficial sediment of LG decreases with the distance to the sewage leachate outfall, except that in the area between high-tideland and mid-tideland, the heavy metal pollution in the sediment is very serious. The content of heavy metals in the core sediment of tideland near the sewage outfall changes with the depth regularly to some extent, which can reflect the discharge situation of the sewage in a short period and the heavy metal pollution levels in sediment. By primary analysis, it's found that the heavy metals and nutrient in the sed...