Title:

Short-term restoration dynamics of living shorelines in the Great Bay system of New Hampshire

Salt marsh living shorelines (LSs) have been shown to improve the resiliency of coastal shorelines and restore salt marsh ecosystems. One popular type of LS is the restoration of fringe salt marsh habitat with the inclusion of a riprap sill at the low marsh edge. Studies have shown vegetation and faunal use of LSs can recover to reference levels within five years, however little data exists for LSs in a northern New England context. We monitored the short-term restoration trajectory of three LSs in New Hampshire by plot sampling vegetation and pore water chemistry and minnow trapping nekton in a BACI design. The Restoration Performance Index (RPI) quantified the restoration performance of the LSs by converting abiotic and biotic metrics into an objective score from 0 - 1. LSs recovered quickly to a RPI score of 0.54 within four years and followed a logistic restoration trajectory, plateauing at 0.52 ¬+ 0.04. The unweighted vegetation RPI score followed a similar logistic trajectory with rapid recovery and plateau at 0.67 + 0.06. Soil redox potential of the low marsh became slightly anerobic after three years (-41.7 + 10.9 mV). Mummichog densities and adult lengths were statistically similar between LSs and local references, suggesting LS projects may serve as meaningful salt marsh habitat within a few years. The abiotic and biotic factors recovered at different timeframes, with vegetation and nekton recovering to near reference conditions within four years. Soil and pore water chemistry may require decadal time frames to recover. The Cutts Cove LS experienced intense stressors such as erosion behind the riprap sill and geese herbivory which hindered restoration performance. The stagnation of recovery of vegetation and impacts from stressors may requiring continuing maintenance such as multiple planting events. The LSs in the Great Bay Estuary provide meaningful salt marsh habitat and shoreline resilience and should be viewed as another tool for coastal restoration.

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