System Dynamic Analysis of Water Quality of Agricultural Area
|關鍵字:||系統動態;農業;深水灌溉;灌溉水質;溼地;System dynamic;Agricultural;Deep-water irrigation;Quality of irrigation water;Wetland|
而灌排分離加下水道系統，即廢汙水不進入灌溉圳路，美濃農田回歸水最終流到旗山溪，發現水質改善，甚至在一月BOD濃度可以從原本約2.4 mg/L降至約1.5 mg/L；至於湖內鄉因為灌溉水質非常差，其改善成效不彰，僅重金屬鉛濃度因為灌排分離有稍稍改善。
The effect of quality of irrigation water on the overall quality of surface water bodies has raised significant concerns in Taiwan. In this study, quantity and quality of water bodies of Meilon and Hunai Townships was simulated with the system dynamic simulation software, Vensim□, to investigate the interaction between polluted irrigation water and other water bodies and farm land. The water bodies analyzed included the return flow, streams, and groundwater. Four scenarios were selected for simulation in order to evaluate possible schemes to reduce the pollution loading in the return flow and, thus, the streams. These scenarios are: “deep-impounding irrigation”, “irrigation and discharge separation”, “farm fallow”, and “crop rotation”. Under the “deep-water irrigation” scenario groundwater discharge in Meilon and Hunai increased 5 million tons and 1 million tons over the 100 months period simulated, respectively. In the “irrigation and discharge separation” scenario, return flow does not flow into irrigation channel and, thus, into farm lands again. Under this scenario, BOD concentration decreased from 2.4 mg/L to 1.5 mg/L decreases to 1.5mg/L even in January. Because of irrigation water in Hunai was heavily contaminated, the strategy to separate irrigation and discharge water did not show significant improvement. Nevertheless, the concentration of lead in the water bodies and the soil decreased. On the other hand, since the quantity of irrigation water treated by the temporary wetland converted from farmland had been so small, water quality in the water bodies was hardly noticed. Finally, when the crop rotation scheme was used as a way to conserve water, plants were used to uptake heavy metal from the soil of the farm land. As a result, the accumulation rate of heavy metal in the soil was reduced. For example, the total monthly accumulation of heavy metals in the soil of Hunai was reduced approximately 0.0025 mg/kg. The results of this study demonstrate that system dynamic analysis is capable of modeling various scenarios with complex management schemes. It was found that the “deep-impounding irrigation” and “separation of irrigation and discharge” are strategies that can significantly increase groundwater recharge and improve discharge water quality, respectively.
|Appears in Collections:||Thesis|