The influence of habitat construction technique on the ecological characteristics of a restored brackish marsh
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The primary goal of most habitat restoration projects is to improve ecosystem functions as compensation for habitat loss or degradation, but the optimal engineering approach to achieve that outcome is not always known a priori. Restored coastal wetlands are frequently engineered to create mound and terrace formations at low marsh elevations, but there have been few opportunities to quantitatively compare the ecological characteristics of construction methods that differ in soil source and configuration. Our study took place in a restored (2008) brackish marsh (Texas, USA) that included mounded formations built from on-site soil, off-site dredge material, or a combination of soil sources. We used a two-year (2009-2010) dataset from a restoration monitoring program that included emergent plant, water, soil, aquatic plant, and aquatic faunal characteristics to address two questions: (1) Do construction methods combining different soil sources and dredging techniques confer unique ecological characteristics? (2) Is there an ecological benefit to incorporating heterogeneity in a restored site by employing multiple construction methods? Our analyses revealed that plant root biomass and soil nitrogen and phosphorus concentrations were two times higher in the reference area than in any of the restored areas. Among the restoration construction methods, ecosystem characteristics were similar to each other within two years of restoration. In general, ecosystem characteristics were affected more by temporal variation between years than by construction method. Differences between years were driven by water characteristics; unusually high tides in 2010 doubled salinity and decreased water chlorophyll a concentration and dissolved inorganic nitrogen by half. Although the restored areas did not achieve all reference characteristics during the early development of the site, the differences among engineering approaches were relatively subtle. Therefore, the recommendation for practice is to use the approach that is most cost-effective for a specific site. In our study area, the dredging methods yielded the largest area of emergent marsh per unit effort, but the on-site soil excavations created more aquatic habitat. When ecological integrity is defined as the provision of a wide range of biotic and abiotic conditions at a landscape scale, then the use of different engineering approaches at different sites within a region creates habitat heterogeneity, thus conferring regional-level ecological benefits. 2013 Elsevier B.V.
