Cost-effectiveness of two small-scale salt marsh restoration designs

Two small-scale Black needlerush (Juncus roemerianus) marsh restoration designs were examined for cost-effectiveness by analyzing a suite of morphological and physiological metrics, along with vegetated area over time. The restoration was conducted by harvesting marsh sods from an adjacent natural marsh and planting in the restoration site. Both restoration designs are on suitable scales for private property owners to conduct, but differed in initially planted coverage area. One design was fully planted (100% coverage of planted marsh sods; termed full density design) and the other design was planted at half the density of the fully planted design (50% coverage of planted marsh sods; termed half density design). We found no consistent differences in the measured metrics between the two restoration designs and few differences between restored sites and reference natural marsh stands. These findings suggest the potential similar functionality across all treatments. The only metrics with consistent differences among treatments were increased leaf nutrient and chlorophyll content in the restored plots when compared to natural stands. These differences are potentially attributable to nutrient-rich runoff from an adjacent parking lot to the restoration site. Total vegetated coverage area for half density plots was similar to full density plots at 2.1 years after planting. Cost-effectiveness analysis of both designs across eight differing restoration scenarios (based on hiring or donation of cost categories) resulted in half density plots having higher or equal cost-effectiveness in seven of the eight scenarios. Half density plots were approximately twice as cost-effective in scenarios with donated pre-planting site construction. Based on the similar vegetated area between the two designs and lower cost and restoration effort, we suggest the half density design as a more cost-effective restoration strategy than the full density design and should be considered for small-scale Black needlerush restoration projects.