Study On Water And Nutrient Kinetic Balance Model Of Landscape Water Bodies

Most landscape water bodies artificially constructed or naturally preserved as scenic spots and recreational areas are closed aquatic ecosystems where water either remains nearly static or flows at relatively low velocities. The areas of most landscape water bodies are usually small with relatively small water reserve capacities and thus low self-purification abilities to resist pollutions. The impact of aquatic animals or plants and in particular human activities on water environment can lead to increases in contents of suspended solid, turbidity, organic pollutants and microorganisms. Increased contents in N, P, and other nutrients under high temperature conditions can accelerate the growth rate of algae while the abnormal algae reproduction may consequently destroy the ecological balance of water ecosystems. Eutrophication is a process of deterioration of the structure and function of aquatic ecosysterns. Water pollution is the initiator which leads directly to a series of environmental problems including deterioration of water quality, degradation of ecological function, and destruction of ecosystem balance.The present study was carried out to investigate the cause, status and the effect of eutrophication phenomena observed in landscape water bodies with low levels of water mobility and self-purification ability. Attentions were in particular paid to secondary pollutions due to lack of adequate water pollution control measures and management strategies. With the introduction of the laws of thermodynamics, using Yanghu Wetland Park as the study base, the present research were focused on four important issues, water input and output quantities; nutrient balance; landscape value; and water quality maintenance and management. The main results are summarized as follows:(1) Analytical data showed that the water quality in Yanghu Wetland Park was slightly improved along the water flow path, indicating that the water ecosystem possessed a certain level of self-purification capacity though its pollutant removal ability was relatively weak. In order to maintain the water quality at high standards, the integrated functions of the aquatic ecosystems in YangHu Wetland Park should be improved with main purpose to enhance its natural purification ability.(2) A kinetic water balance model was established using the data obtained from Yanghu Wetland Park by taking into consideration the water sources, water conservation capacity of the park, water replenishment and discharge methods, water losses due to various causes. The calculated results indicated that in order to maintain the water quantity baseline in the wetland park, the water quantity input to YangHu Wetland Park in its water recycling process should be more than 40,000 t/d.(3) In accordance with the kinetic water balance model, a kinetic nutrient equilibrium model was further set up to determine the input-output rates of nitrogen and phosphorus in the aquatic ecosystem of Yanghu Wetland Park. The discharged effluent from the wetland treatment system was identified to be the major source of these two nutrient pollutants that, though being inputted daily in low quantities, had potential impact on water quality, landscape value and ecosystem safety of the park. Ecological technologies should be applied in the park to reduce nitrogen and phosphorus contents and raise the water quality from Grade IA of the Discharge Standards for Pollutants for Municipal Wastewater Treatment (GB 18918-2002) after the wetland treatment to above Grade III permitted by Surface Water Environment Quality Standard (GB3838-2002). Regulated harvests of aquatic plants and animals should be operated to remove the nutrient pollutants from the water ecosystems of the park.(4) The total amounts of nitrogen and phosphorus inputted into the wetland park due to the discharge of the effluent from the wetland treatment system were calculated using the monitoring data from the Pingtang Wastewater Treatment and Landscape Water Regeneration Plant. Based on the estimated N and P uptake rates and utilization efficiencies of different aquatic plants and animals by taking into accounts their adaptabilities to seasonal changes, an integrated multiple species model using selected aquatic plants and animals was proposed for maintaining the landscape water quality at expected levels.(5) Based on analysis of cause and effect of eutrophication and mechanisms of related amending methods, comparisons were made among various biological and ecological technologies currently applied for pollution control and water environment management including microbial, plant and animal remediation, constructed wetlands and floating islands, etc. It was recommended that for establishment of a completed food-chain with high nutrient cycling efficiencies in the wetland park, it is necessary to enrich wetland plant species with seasonal characteristics; use immobilized and effective microorganisms to increase BOD removal rates; build up land-water eco-interception belts to avoid pollution from run-off and daily park activities and to regulate the cultivation and harvest of plants and animals. Relevant suggestions were also given for improvement of the daily water quality maintenance and management in Yanghu Wetland Park.