Macro-Tidal Salt Marsh Ecosystem Response to Culvert Expansion

The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic conditions pre-restoration and the initial 2 years post-restoration at a partially restricted macro-tidal salt marsh site. Replacement of the culvert increased tidal flow by 88%. This was instrumental in altering the geomorphology of the site, facilitating the creation of new salt marsh pannes, expansion of existing pannes in the mid and high marsh zones, and expansion of the tidal creek network by incorporating relict agricultural ditches. In addition, the increase in area flooded resulted in a significant increase in nekton use, fulfilling the mandate of a federal habitat compensation program to increase and improve the overall availability and accessibility of fish habitat. The restoration of a more natural hydrological regime also resulted in the die-off of freshwater and terrestrial vegetation along the upland edge of the marsh. Two years post-restoration, Salicornia europea (glasswort) and Atriplex glabriuscula (marsh orache), were observed growing in these die-back areas. Similar changes in the vegetation community structure were not observed at the reference site; however, the latter did contain higher species richness. This study represents the first comprehensive, quantitative analysis of ecological response to culvert replacement in a hypertidal ecosystem. These data will contribute to the development of long-term data sets of pre- and post-restoration, and reference marsh conditions to determine if a marsh is proceeding as expected, and to help with models that are aimed at predicting the response of marshes to tidal restoration at the upper end of the tidal spectrum.