Integrating biogeomorphic feedbacks in the coastal zone to bolster coastal resiliency

<p>Living shorelines, defined in this study as narrow marsh fringes with adjacent sills, have been gaining traction as the preferred management strategy to mitigate shoreline erosion. These nature-based features provide the same ecosystem services as natural marshes while protecting coastlines. However, they also are threatened by the same environmental changes (sea-level rise, changing sediment supply) as natural marshes and may change characteristics of adjacent subtidal sediments. This study evaluates the role of plants in both the created marshes of living shorelines and, where present, beds of submersed aquatic vegetation (SAV) in the adjacent subtidal in the effectiveness, impacts, and resiliency of living shorelines over ~10 years in mesohaline Chesapeake Bay. At study sites, there is a net seaward movement of shorelines with living shoreline installation due to construction technique. This movement replaces shallow-water habitat immediately adjacent to the pre-existing shoreline; farther offshore, sedimentological changes vary among sites but do not appear to drive changes in the presence/absence of subtidal SAV. While current accretion rates in the created marshes are greater than local relative sea-level rise, there is evidence that accretion rates increase with marsh age, suggesting that living shorelines are most vulnerable in the first few years after installation. Because nutrient burial is maximized when SAV occur next to living shorelines, a management strategy that considers the subtidal and intertidal as integrated components of the coastal system is needed to optimize co-benefits of coastal protection.</p>

Fish Habitat: Essential Fish Habitat and Rehabilitation

<em>Abstract</em> .—In the Gulf of Maine region, projects to restore or create salt-marsh habitat to replace saltmarsh functions and values reduced or lost to tidal restriction are increasing. We assess fish utilization of marsh restoration and creation projects along the central Gulf of Maine coastline by addressing three questions: (1) how do fish assemblages in manipulated and reference marshes compare, (2) how do differences between manipulated and reference marshes change over time, and (3) how do fishes respond to different types of restoration? Fish utilization of restored and created marshes in New Hampshire and Maine (two created and four tidally restored marshes) is compared to adjacent reference marshes. The comparison of manipulated marshes with local reference marshes provides an internal standard for the monitoring of each restoration project, making it possible (1) to follow changes over time while accounting for natural variation and (2) to make valid comparisons about the magnitude and direction of changes between independent restoration projects. Our study provides the first density estimates for fish utilization of vegetated salt-marsh habitat in the Gulf of Maine. The highest fish densities from this study just overlap with the lowest fish densities reported from more southerly marshes. Overall, fish were distributed similarly among manipulated and reference marshes, and fish distribution did not change with time. Trends in the data suggest that fish utilize elevated marshes restored by dug channels to a lesser degree than impounded marshes restored by culverts. It appears that fish will readily visit restored and created marshes in assemblages similar to those found in reference marshes over the short term (one to five years post-restoration) but are subject to the influence of differences in tidal regime, access to marsh habitat, and vegetation density. In the large majority of cases, hydrologic restoration of tidally restricted marshes will improve a much larger area of fish habitat per unit cost than creation of new marsh and will not be subject to many of the constraints that limit the function of created marshes. The primary consideration in tidal restoration projects is not necessarily the cost of construction but the social, economic, and political issues that must be addressed. Often, tidally restricted marshes are in highly developed coastal areas where many individual property owners may perceive the increased tidal flow as a threat, even when flood hazard studies show that no such threat exists. In spite of this caution, thousands of hectares of coastal fish habitat can be improved through a concerted program to restore the hydrology of tidally restricted marshes in the Gulf of Maine.