非點源污染補助方案之效益分析

Abstract

水庫集水區的污染控制一般採用最佳管理作業(Best Management Practice，BMP)來進行控制，然而由於實行BMP初期可能造成經濟負擔及農作物產量減少，導致農民實施意願低，補助方案是鼓勵農民實行BMP的一個有效經濟誘因手段之一，唯一個適當的補助方案，除了能鼓勵農民實施BMP外，更需考量控制非點源污染之效率及公平性，且不宜太複雜。本研究針對德基水庫集水區採用AGNPS模式模擬分析非點源污染負荷及不同BMP之效益，依所得結果及考量公平性指標、農民損失、農民總花費、補助比例、總磷污染負荷降低量、水庫淤積沈滓污染負荷降低量擬定補助全額損失、等成本補助比例、等總花費補助比例、等單位污染去除當量補助金額及等單位面積補助金額等五個補助方案，並建立混合整數規劃模式，用以分析比較不同方案之差異性、優劣點及成本、總磷、沈滓與公平性各目標間的折衷關係。結果顯示，補助全額損失方案的水質效益與公平性均接近最佳，等補助成本比例及等補助總損失比例方案之水質效益及公平性與補助全額損失方案均差異不大。

Non-point source pollution (NPSP) generated from the upstream watershed of a reservoir can be effectively controlled by Best Management Practices (BMPs). However, at the initial stage of implementing a BMP for a cropland may cause extra cost load and decreasing harvest. Therefore, the farmer may be reluctant to adopt the BMP. Subsidy is one of effective strategies to encourage the farmer to adopt a proper BMP. An appropriate subsidy policy, in addition to encourage the farmer to adopt a proper BMP, should be fair, effective in reducing NPSP, and not too complex. This study applied the Agricultural Non-point Source Pollution (AGNPS) model to simulate NPSP loading and BMP efficiencies. Four indexes for evaluating equity were established based on four subsidy rates of loss, BMP cost, total cost (loss+cost), and pollution reduction equivalence unit, respectively. Five subsidy policies of subsidy of loss (SL), uniform cost sharing rate (UCSR), uniform total cost sharing rate (UTCSR), fixed subsidy per pollution reduction equivalence unit (FSPREU), and fixed subsidy per unit area (FSUA), were proposed based on the equity indexes, loss, BMP cost, and BMP effectiveness in reducing NPSP. A mixed-integer programming model was developed for evaluating the effectiveness of each subsidy policy in terms of cost, phosphorus and sediment reduction, and equity. The watershed of the Derchi reservoir located in central Taiwan was the area studied. The proposed policies and model were applied to the watershed. The result shows that the SL policy has best water quality efficiency with a proper level of equity. When the budget is limited between 10 and 15 hundred millions, the pollution reduction rate achieves 70%. The UCSR and UTCSR policies perform slightly, but not significantly, worse than the SL policy. The UCSR policy with the budget limit of 15 hundred millions and cost sharing rate of 40% or 45% and the UTCSR policy with the budget limit between 15 and 20 hundred millions and cost sharing rate of 30% or 40% can also achieve 70% pollution reduction.