Trajectories in soil surface elevation during tidal restoration of heterogeneous coastal wetlands

Abstract

Coastal wetland restoration projects are increasing as the ecological importance of these ecosystems becomes more apparent. With sea-level rise, coastal agricultural land that was drained and closed off from the tide decades ago is becoming available for restoration of coastal ecosystems. Conversion back to coastal wetlands usually involves reconnecting tidal flows through the modification or removal of tidal gates. Knowledge of the links between differing levels of hydrological connectivity over landscapes, vegetation growth and soil surface elevation increments is limited but important for understanding changes in ecosystem functions with restoration. Using Rod-Surface Elevation Tables (RSETs), marker horizons, sediment pins and pressure loggers, we assessed how these factors combined to create different habitats within the Yandina Creek Wetland at the Sunshine Coast, Queensland, Australia. Over time, adaptive management strategies aimed at limiting tidal ingress onto adjacent land have led to high variation in tidal connectivity across the landscape. Monitoring hydrology, vegetation and soil surface elevation over four years found that duration of inundation and salinity were factors driving the establishment of mangroves, open water areas for birds and fish, and supratidal forests. Surface elevation and surface accretion within the restoration site were similar to that observed in adjacent reference sites, but were not correlated with the %time inundated, but instead by seasonal differences in rainfall. This research will assist future coastal restoration projects in similar drained landscapes.