Evaluating cumulative ecosystem response to tidal wetlands restoration projects in the Columbia River estuary, USA

As restoration is undertaken on increasingly large scales, the existing body of knowledge and techniques to assess cumulative impacts associated with ecosystem degradation provides a source of methods for assessing positive cumulative effects. Methods resulting from the National Environmental Policy Act and other legislation may be applied for assessing restoration at landscape scales; beyond the presumption of additive effects, they acknowledge alternate modes of accumulation (e.g., synergistic effects from multiple pathways). The restoration of wetland salmon habitat in the 235-km tidal portion of the Columbia River, through multiple hydrological reconnection projects, provides a case study to evaluate net cumulative effects. We are developing a framework for evaluating effectiveness at the project and program levels, testing spatial and temporal patterns of cumulative effects with standardized monitoring data on physical and biological metrics collected by multiple constituencies. In 2004-07 field studies, baseline and post-restoration data were collected on restoration and reference sites representing brackish marsh and tidal freshwater swamp – habitat types that have sustained substantial areal losses and may play important roles for salmonids. Three kinds of restoration actions were implemented on the sites and evaluated: tide gate replacements, culvert replacements, and dike breaches. The meta-analysis will include data on vegetation/elevation relationships, water depth and temperature, organic matter and nutrient flux, fish species composition, salmonid prey availability, biological legacies, and channel evolution. With a recent call by the National Research Council for the U.S. Army Corps of Engineers to undertake basin-wide restoration, cumulative effects assessment methods may help to quantify ecosystem response.