Groundwater storage effects from restoring, constructing or draining wetlands in temperate and boreal climates: a systematic review protocol
Wetlands in many parts of the world have been degraded, as use of the land for food production and forestry for human needs have taken precedence. Drainage of wetlands has led to deteriorated wetland conditions and lowered water tables. Across the world, there are several programs for wetland restoration and construction, primarily to reintroduce lost habitats for wildlife, and to obtain nutrient retention functions. In Sweden, recent dry and hot summers have reinforced interest in the hydrological functions that wetlands may have, in particular as potential support for water storage in the landscape and added groundwater storage during dry periods. However, the agreement on substantial effects on groundwater is limited, and there are several critical knowledge gaps, including the extent to which such effects extend outside the wetland itself, and how they vary with local conditions, such as topography, soil, and climate. Therefore, this review will address the groundwater storage effect of restoring, constructing or draining wetlands in the boreo-temperate region. Methods: We will conduct a systematic review of the evidence, drawing on both peer-reviewed and grey literature. Articles in English, Swedish, Norwegian, Danish, French, German and Polish will be retrieved from academic databases, Google Scholar, and websites of specialist organizations. We will screen literature in two stages, first at the title and abstract level and then in full text, the latter with blinded decisions by two independent reviewers for all articles. Articles will be included based on relevance criteria for a Swedish context: wetlands on previously glaciated soils in boreal and temperate climates. Data will be extracted from all included articles, including wetland type, intervention type, and hydrogeological setting. Studies will be subject to critical appraisal to evaluate their susceptibility to bias. Provided enough evidence of sufficient reliability, we will carry out meta-analyses of effect sizes in relation to various factors. The review will include a narrative synthesis in which we summarize the results of the review.