Fremier Alexander K, Girvetz Evan H, Greco Steven E, Larsen Eric W
School of the Environment, Washington State University, Pullman, Washington, United States of America.
International Center for Tropical Agriculture, Nairobi, Kenya; School of Environmental and Forest Sciences, University of Washington, Seattle, Washington, United States of America.
PLoS One. 2014 Jun 25;9(6):e99736. doi: 10.1371/journal.pone.0099736. eCollection 2014.
Environmental legislation in the US (i.e. NEPA) requires defining baseline conditions on current rather than historical ecosystem conditions. For ecosystems with long histories of multiple environmental impacts, this baseline method can subsequently lead to a significantly altered environment; this has been termed a 'sliding baseline'. In river systems, cumulative effects caused by flow regulation, channel revetment and riparian vegetation removal significantly impact floodplain ecosystems by altering channel dynamics and precluding subsequent ecosystem processes, such as primary succession. To quantify these impacts on floodplain development processes, we used a model of river channel meander migration to illustrate the degree to which flow regulation and riprap impact migration rates, independently and synergistically, on the Sacramento River in California, USA. From pre-dam conditions, the cumulative effect of flow regulation alone on channel migration is a reduction by 38%, and 42-44% with four proposed water diversion project scenarios. In terms of depositional area, the proposed water project would reduce channel migration 51-71 ha in 130 years without current riprap in place, and 17-25 ha with riprap. Our results illustrate the utility of a modeling approach for quantifying cumulative impacts. Model-based quantification of environmental impacts allow scientists to separate cumulative and synergistic effects to analytically define mitigation measures. Additionally, by selecting an ecosystem process that is affected by multiple impacts, it is possible to consider process-based mitigation scenarios, such as the removal of riprap, to allow meander migration and create new floodplains and allow for riparian vegetation recruitment.
美国的环境法规（即《国家环境政策法案》）要求界定当前而非历史生态系统状况的基线条件。对于有着多种环境影响悠久历史的生态系统而言，这种基线方法随后可能导致环境发生显著改变；这被称为“滑动基线”。在河流系统中，流量调节、河道护岸和河岸植被清除所造成的累积影响，通过改变河道动态并排除后续生态系统过程（如原生演替），对洪泛区生态系统产生重大影响。为了量化这些对洪泛区发育过程的影响，我们使用了一个河道蜿蜒迁移模型，以说明流量调节和抛石护坡对美国加利福尼亚州萨克拉门托河迁移速率的独立及协同影响程度。从建坝前的状况来看，仅流量调节对河道迁移的累积影响是减少38%，而在四种拟议的调水工程方案下则减少42 - 44%。就沉积面积而言，在没有现有抛石护坡的情况下，拟议的水利工程将在130年内使河道迁移减少51 - 71公顷，有抛石护坡时则减少17 - 25公顷。我们的结果说明了建模方法在量化累积影响方面的效用。基于模型对环境影响进行量化，能让科学家区分累积影响和协同影响，从而分析性地界定缓解措施。此外，通过选择一个受多种影响的生态系统过程，有可能考虑基于过程的缓解方案，如拆除抛石护坡，以允许蜿蜒迁移、创建新的洪泛区并促进河岸植被恢复。
