Evaluating Wetland Restoration Success Using Aquatic Macroinvertebrate Assemblages in the Sacramento Valley, California

Patterns of Assemblage Structure Indicate a Broader Conservation Potential of Focal Amphibians for Pond Management

Small freshwater ponds host diverse and vulnerable biotic assemblages but relatively few conspicuous, specially protected taxa. In Europe, the amphibians Triturus cristatus and Pelobates fuscus are among a few species whose populations have been successfully restored using pond restoration and management activities at the landscape scale. In this study, we explored whether the ponds constructed for those two target species have wider conservation significance, particularly for other species of conservation concern. We recorded the occurrence of amphibians and selected aquatic macro-invertebrates (dragonflies; damselflies; diving beetles; water scavenger beetles) in 66 ponds specially constructed for amphibians (up to 8 years post construction) and, for comparison, in 100 man-made ponds (created by local people for cattle or garden watering, peat excavation, etc.) and 65 natural ponds in Estonia. We analysed nestedness of the species assemblages and its dependence on the environment, and described the co-occurrence patterns between the target amphibians and other aquatic species. The assemblages in all ponds were significantly nested, but the environmental determinants of nestedness and co-occurrence of particular species differed among pond types. Constructed ponds were most species-rich irrespective of the presence of the target species; however, T. cristatus was frequent in those ponds and rare elsewhere, and it showed nested patterns in every type of pond. We thus conclude that pond construction for the protected amphibians can serve broader habitat conservation aims in the short term. However, the heterogeneity and inconsistent presence of species of conservation concern observed in other types of ponds implies that long-term perspectives on pond management require more explicit consideration of different habitat and biodiversity values. We also highlight nestedness analysis as a tool that can be used for the practical task of selecting focal species for habitat conservation.

Changes in benthic nutrient sources within a wetland after hydrologic reconnection

Removing dams and levees to restore hydrologic connectivity and enhance ecosystem services such as nutrient removal has been an increasingly common management practice. In the present study, the authors assessed geochemical and biological changes following engineered levee breaches that reconnected eutrophic Upper Klamath Lake and Agency Lake, Oregon, USA, to an adjacent, historic wetland that had been under agricultural use for the last seven decades. Over the three-year study, the reconnected wetland served as a benthic source for both macronutrients (dissolved organic carbon [DOC], soluble reactive phosphorus [SRP], and ammonia) and micronutrients (dissolved iron and manganese). The magnitude of those benthic sources was similar to or greater than that of allochthonous sources. The highest DOC benthic flux to the water column occurred immediately after rewetting occurred. It then decreased during the present study to levels more similar to the adjacent lake. Dissolved ammonia fluxes, initially negative after the levee breaches, became consistently positive through the remainder of the study. Nitrate fluxes, also initially negative, became negligible two years after the levee breaches. In contrast to previous laboratory studies, SRP fluxes remained positive, as did fluxes of dissolved iron and manganese. Our results indicate that the timescales of chemical changes following hydrologic reconnection of wetlands are solute-specific and in some cases extend for multiple years beyond the reconnection event. During the present study, colonization of the reconnected wetlands by aquatic benthic invertebrates gradually generated assemblages similar to those in a nearby wetland refuge and provided further evidence of the multiyear transition of this area to permanent aquatic habitat. Such timescales should be considered when developing water-quality management strategies to achieve wetland-restoration goals.