基于多目标线性规划的甲积峪小流域生态系统服务权衡优化

黄土高原是我国水土流失最严重的地区之一,区域生态系统服务退化。小流域是水土流失的主要发生地,在提升水土保持服务时如何权衡各类生态系统服务,是当前生态系统服务管理的重要内容。选取黄土高原典型小流域——甲积峪,以2012年为基准年,2022年为规划目标年,基于统计年鉴和调查数据,采用市场价值法、影子价格法、影子工程法、替代成本法和机会成本法对各土地利用类型的生态系统服务价值进行估算;采用多目标线性规划方法,将生态系统服务分为供给服务、水土保持服务与其他服务,以三者价值作为权衡子目标,生态系统服务总价值作为总目标构造目标函数,依据土地面积、粮油保障和各土地利用类型对坡度的适宜性,利用35个变量构造了17个约束方程,通过调整甲积峪土地利用类型实现小流域生态系统服务的权衡优化。结果表明,甲积峪生态系统服务价值主要受占地比例较大且生态系统服务价值较低的坡耕地和荒草地制约。权衡优化后,坡耕地和荒草地主要调整为生态系统服务价值较高的乔木林和梯田,土地利用结构得到明显改善。生态系统服务总价值增幅为9.23%,供给服务、水土保持服务与其他服务价值增幅分别为6.24%、9.81%和17.35%。三者增加量分别占生态系统服务总价值增加量的25.96%、54.42%和19.62%。与仅以供给服务、水土保持服务、其他服务或总服务价值为目标函数的优化结果相比,3个子目标的优化结果更加协调,且三大效益均明显增加。空间分布上,不同生态功能区的各生态系统服务价值增长率存在明显差异,上游其他服务价值增长率最高,中游水土保持服务价值增长率最高,下游供给服务和总服务价值增长率最高,与甲积峪上中下游生态功能区定位一致。充分考虑了土地利用适宜性,在保证供给服务的前提下,突出了水土保持服务并优化了其他服务,各综合治理效益评价指标均得到提高,符合黄土高原小流域的实际情况。

Multi-objective linear programming-based trade-off and optimization of the ecosystem services in Jiajiyu small watershed in the Loess Plateau, China

The Loess Plateau is one of the most serious soil-erosion areas with ecosystem service degradation in China. Small watersheds are the main place of soil erosion; therefore, it is important to evaluate various ecosystem services when promoting their water and soil conservation. This paper took Jiajiyu, a typical small watershed in the Loess Plateau, as the study area using 2012 as the base year and 2022 as the target year. Based on the Statistical Yearbook and investigation data, the ecosystem service values of different land-use types were evaluated by the methods of market value, shadow price, shadow project, alternative cost, and opportunity cost. The ecosystem services were evaluated and optimized based on the adjustment of land-use structure by multi-objective linear programming through adjusting land-use types. The supply service, water and soil conservation service, and other services values were taken as the trade-off sub-objectives and the total ecosystem service value as final objective, with 17 constraint equations developed by 35 decision variables. The constraint equations included the land-area control, grain and oil security, and suitability of land-use types on the slope. The results showed that the ecosystem service values of slope farmlands and waste grasslands were much lower than most of other land-use types, and both of them took a relatively higher proportion of small watershed area, which restricted the ecosystem service values of Jiajiyu. The land-use structure was obviously improved by the trade-off and optimization of ecosystem services, with most of the slope farmlands and waste grasslands adjusted to arbor forest or terrace, both of which have much higher ecosystem service values. The total ecosystem service value increased by 9.23%, and the value of supply service, water and soil conservation service, and other services also increased by 6.24%, 9.81%, and 17.35%, respectively. Increases in the three sub-objects of ecosystem service values were dominated by the total increase in ecosystem service values by 25.96%, 54.42%, and 19.62%, respectively. Compared with the optimization results, which only took supply service, water and soil conservation service, other services or total ecosystem service values as the objective function, the optimization results of the three objective sub-functions were more coordinated, and all three benefits increased significantly. Significant differences were observed in the growth rates of ecosystem service values in different reaches, with the highest growth rates observed in the other service values of upper reaches, water and soil conservation service values of middle reaches, and supply service and total service values of lower reaches, which were confomed to the ecological orientation of upper, middle, and lower reaches of Jiajiyu, respectively. In this paper, the suitability of land use was fully considered. Under the guarantee of supply service, the water and soil conservation service was highlighted, other ecosystem services were optimized, and the evaluation indices of comprehensive management were improved at the same time. Our results were consistent with the actual conditions of the small watershed in the Loess Plateau.