基于能值分析的我国小水电生态影响研究

如何系统定量地评价小水电开发过程所引起的景观变化、河流局部断流等生态影响,是平息争议、进行合理规划与开发小水电前提之一。运用能值分析方法,以贵州省赤水市观音岩水电站为例,将小水电建设、运行的资源投入,以及河道中水流的时空改变所导致生态服务功能的损失纳入核算体系,对其生态影响进行综合定量评估。从2010年的实际结果来看,由于河流断流,导致水坝下游生态系统服务功能的能值损失为2.77×1018sej,占到了系统建设运行总投入的44.84%,其中重点保护鱼种在影响河段的生境破坏是最大的能值损失。若不考虑下游生态系统服务功能损失,系统的环境负载率为1.92,可持续性指标为1.22;而考虑下游生态影响之后,系统环境负载率增大至4.26,可持续性指标减小为0.34。研究表明,小水电的开发必须遵循适度开发、规划优先,保障河流最基本的生态需水底线,是协调小水电开发和河流健康矛盾、追求小水电持续发展的刚性要求。

Emergy evaluation for ecological impacts of small hydropower in China

In China, most of the small hydropower (short for SHP) plants are currently seeking for benefits in power generation and economic revenue with little consideration of environmental flows for ecosystems, causing great impacts on river ecosystem services in the downstream of the dams. Negative ecological impacts of small hydropower have drawn increasing attention from the public. This paper used emergy analysis, one of the ecological energetic accounting methods, to evaluate the overall ecological impacts of construction and operation of small hydropower and took Guanyinyan hydropower plant in Chishui City, northwest of Guizhou Province as an example. Having capabilities in accounting multiple forms of energy and materials both from environmental and economic points of view on a common energy basis, the method of emergy analysis was widely used for supporting the evaluation of agricultural, wetlands and urban systems and was proved to be a useful tool for evaluating the overall performance of a mixed ecological and economic systems. The related indices and ratios based on emergy flows such as emergy yield ratio (EYR), environmental loading ratio (ELR) and emergy sustainability index (ESI) can be used for characterizing resource consumptions, environmental impacts and overall system sustainability. Through incorporating losses of the downstream ecosystem services into the operation cost of the power production system, the results showed that the studied system was supported by a total emergy of 6.18×10¹⁸sej in 2010 to produce 2.26×10¹³J of electricity, of which the downstream ecosystem service losses was the largest among multiple marginal costs, accounting for 44.84% of total ecological economic cost. The losses of ecosystem service mainly included those due to biodiversity losses (especially rare species losses) and climate regulation losses, with 2.77×10¹⁸ and 4.63×10¹³ sej/a respectively. Without considering the ecosystem service losses, the ELR of the studied system was 1.92 and the ESI was 1.22. However, when considering ecosystem service losses, the ELR of the studied system increased to 4.26, which was much larger than those of large hydropower generation projects in Mekong River or those in Korea, showing an increased pressure on local environment. And the value of ESI decreased to 0.34, which was much lower than 1, indicating that the studied power production system was not sustainable. Furthermore, the results suggested that the degradation of river ecosystem in the downstream of the dam during operation period greatly reduced the sustainability of the system. Thus, for a small hydropower, occupying environmental flows of the downstream and the development pattern at the expense of the ecosystem approach would be unsustainable. Sufficient environmental flows would be essential to the river ecosystem in the downstream, especially for maintaining the aquatic biodiversity. Environmental-friendly and social harmonious development of water resources would be necessary to achieve sustainable development for small hydropower. Relevant authorities should strengthen the planning and management of water resources development to ensure the sustainability of small hydropower and the health of river ecosystem. In addition, this paper reflected that emergy analysis, as a measure of the environmental support and the work to keep ecosystem sustainability, is an effective tool that is capable of providing an integrative assessment, and then provide a basic for the sustainable development of small hydropower.