Abstract
Land reclamation projects and the installation of drainage infrastructure has impacted coastal wetlands worldwide. By altering water levels and inundation extent, these activities have changed the viable ecosystems onsite and resulted in the proliferation of freshwater species. As more than 50% of tidal wetlands have been degraded globally over the last 100 years, the importance of this issue is increasingly being recognised and tidal wetland restoration projects are underway worldwide. However, there are currently limited sites where large-scale reintroduction of tidal flushing has been implemented with the explicit aim to foster the growth of a threatened ecosystem. In this study, the tidal restoration of an internationally recognised Ramsar listed wetland in eastern Australia is described to highlight how coastal saltmarsh can be targeted by mimicking inundation depths and hydroperiod across the 410-ha site. Coastal saltmarsh is particularly important to this site as it is part of the east Australasian flyway for migratory birds and the minimum saltmarsh extent, as listed within the Ramsar’s limits of acceptable change, have been breached. To recreate coastal saltmarsh habitat onsite, water level and hydroperiod criteria were established based on similar vegetation patterns within the adjacent estuary. A calibrated 2D hydrodynamic model of the site was then used to test how the preferred inundation criteria could be applied to the largest possible restored wetland area. Once optimised, a synthetic tidal signal was implemented onsite via automated hydraulic controls. The onsite vegetation response over an 8-year period was assessed to highlight the ecosystem response to controlled tidal inundation and denoted substantial saltmarsh expansion during the period. The techniques applied onsite have successfully met the restoration targets and can be applied at similar sites worldwide, offsetting sea level rise impacts to natural inundation hydroperiod.
Highlights
Over the past century large-scale reclamation of tidal wetlands, including mud flats, mangrove, and saltmarsh ecological communities, have been undertaken worldwide [1, 2]
Initial modelling simulations indicated that unrestricted tidal flushing across the site would impact neighbouring properties and result in hydrologic conditions that are favourable to mangroves, not coastal saltmarsh
Theoretical inundation statistics likely to occur across the restoration site were calculated based on the muted tidal signal (Fig 8). These statistics indicated that whilst inundation depths were not predicted to exceed 0.3 m, as observed in the estuary wide vegetation survey, the duration of inundation was expected to increase. This was due to the muted tidal signal that produced an extended period of inundation at the maximum acceptable cut off elevation of +0.4 m Australian Height Datum (AHD), whilst the downstream natural tidal signal rises above the cut off elevation
Summary
Over the past century large-scale reclamation of tidal wetlands, including mud flats, mangrove, and saltmarsh ecological communities, have been undertaken worldwide [1, 2]. The ecosystem loss from landscape reclamation has significantly impacted habitat for aquatic and terrestrial fauna, including internationally protected migratory wader birds [10, 11]. In recognition of these issues, estuarine restoration projects have gained significant momentum worldwide [12,13,14,15]. Large-scale tidal restoration projects have been successfully undertaken globally, including the USA [19, 20], China [21,22,23], Korea [24], Europe [25], and Australia [26,27,28]
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