Robust optimal diversion of agricultural drainage water from tea plantations to paddy fields during rice growing seasons and non-rice growing seasons
Robust optimal diversion of agricultural drainage water from tea plantations to paddy fields during rice growing seasons and non-rice growing seasons
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DOI：
10.1007/s10333-015-0494-y
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发表时间：
2015
影响因子：
2.2
通讯作者：
Goden Mabaya;K. Unami;H. Yoshioka;Junichiro Takeuchi;M. Fujihara
中科院分区：
文献类型：
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作者：
Goden Mabaya;K. Unami;H. Yoshioka;Junichiro Takeuchi;M. Fujihara
在一个以水稻和茶叶作物为主的小型农业流域，研究了不同土地利用方式下水质的季节变化。在茶园和茶叶排水渠中观测到的NO3-N含量足够高，足以造成全年的下游水质污染。反之，在弃耕和活跃稻田，NO3-N的降幅显著，在水稻生长季节，活跃稻田的NO3-N降幅最大。因此，一个问题是，故意从茶园引水到稻田是否是减少下游水污染的有效策略。然而，稻田中NO3-N比例的降低既不明显，也不事先知道，这种不确定性可能会导致进一步的环境风险，如NO3-N淋失和温室N2O气体的产生。我们假设稻田和排水渠的NO3-N减少率被约束在一个不确定的椭球集合中。建立了一个投资组合优化问题，以确定从茶叶排水渠到水田的最优分水率。该问题通过在不确定条件下最小化还原的最小硝态氮，采用稳健优化方法进行数值求解。一个应用表明，稳健的方法分配不同的最优转移率，以对冲可能出现NO3-N还原过程故障的风险。总体来说，最糟糕的情况是，由于增加了对活跃稻田的排水分配，水稻生长季节的NO3-N降幅最大。稳健的优化方法有可能支持决策过程，以减少N3-N污染和对水资源的用水需求压力，以及水稻生产成本。
We investigated seasonal water quality changes on different land uses in a small agricultural watershed dominated with rice and tea crops. Observed NO3–N in tea plantations and tea drainage channels was sufficiently high enough to cause downstream water pollution throughout the year. On contrary, significant NO3–N reductions were observed in abandoned and active paddy fields, and were highest in active paddy fields during rice growing seasons. Accordingly, a question is posed whether deliberately diverting NO3–N contaminated drainage water from tea plantations to paddy fields would be effective a strategy for reducing downstream water pollution. NO3–N ratios reduced in paddy fields are however neither distinct nor known in advance, and this uncertainty could consequently lead to further environmental risks like NO3–N leaching and production of greenhouse N2O gas. We assume that NO3–N reduction rates of paddy fields and drainage canals are constrained in an ellipsoidal set of uncertainty. A portfolio optimisation problem is formulated to determine optimal rates of diversion from tea drainage channel into paddy fields. The problem is numerically solved in robust optimisation approach by maximising minimum NO3–N reduced under uncertainty. An application demonstrated that robust approach allocates different optimal rates of diversion to hedge the risk of possible malfunctioning of NO3–N reduction processes. Overall worst-case NO3–N reduction is highest in rice growing season, due to increased drainage water allocations to active paddy fields. The robust optimisation approach has potential to support decision-making processes for reducing NO3–N pollution and water demand pressure on water resources, and cost of rice production thereof.