Response of estuarine wetlands to reinstatement of tidal flows

Abstract

The importance of estuarine wetlands to ecosystem services such as primary productivity and flood attenuation, as well as their function as habitat for threatened species has prompted efforts to restore tidal flows to degraded wetlands. We tracked the response of estuarine vegetation to tidal-flow reinstatement over 12 years (1995–2007) in a wetland of the Hunter estuary, Australia. This site provides important habitat for migratory shorebird species, which favour shallow tidal pools and saltmarsh over mangrove forest. Increased tidal flows following culvert removal reduced shorebird roost habitat by 17% because of mangrove encroachment on saltmarsh and shallow tidal pools. Saltmarsh occurred in areas with a spring tidal range <0.3 m, hydroperiod <1.0 and elevation >0.4 above the Australian height datum (mAHD), whereas mangrove occupied areas with spring tidal range >0.3 m, hydroperiod <0.45 and elevation <0.4 mAHD. By using these parameters, it is possible to exclude mangrove from saltmarsh areas and to establish saltmarsh at lower elevations in the tidal frame than would occur under natural conditions, effectively expanding saltmarsh area. These measures can be useful where landward migration of estuarine communities is restricted by infrastructure; however, they should not be considered a substitute for conservation of remnant saltmarsh or establishment of landward buffer zones.

Rising tides, rising gates: The complex ecogeomorphic response of coastal wetlands to sea-level rise and human interventions

“…saltmarsh areas in the following years. This encroachment resulted in a reduction of shorebird habitat (Howe et al, 2010).…”

Modified sediments and subsurface hydrology in natural and recreated salt marshes and implications for delivery of ecosystem services

“…Yet, despite this evidence and the consequences for ecosystem service delivery, few studies have examined subsurface sediment structure and hydrology in recreated salt marshes, with most research focusing on measures of the hydroperiod/elevation, surface flows/water depths and proxies for subsurface hydrological functioning/sediment structure such as bulk density, moisture content and porosity (e.g. Howe et al , ; Beauchard et al , ).…”

Bund removal to re-establish tidal flow, remove aquatic weeds and restore coastal wetland services – North Queensland, Australia

“…For example, Smith et al , [65] describe how freshwater plants are being replaced by native salt marsh plants following the restoration of tidal flows to the Hatches Harbor salt marsh in Cape Cod, Massachusetts, USA. In Australia, tidal flows were reinstated into coastal wetlands in the Hunter estuary in New South Wales and this increased the area of salt marsh, largely through expansion into areas of pasture [27]. Conversely seawater intrusion into coastal wetlands such as the Gippsland lakes in Victoria [66] and the rivers in the Northern Territory [67] has also caused changes in wetland ecology, however, these are generally seen as undesirable, since in these cases they changed the wetlands from their natural freshwater state.…”

“…The widespread degradation of coastal wetlands has led to major shifts in species assemblages and declines in aquatic species productivity. In response, there has been increased effort to rehabilitate coastal wetlands by removing these artificial barriers [9, 10], and provide protection and restoration of coastal wetlands [11] to improve their ecosystem services including connectivity and functionality as productive fish habitat [12, 13] and also deliver opportunities for carbon sequestration and storage [14].…”

“…However, many of the wetlands along the north Queensland coast, and the services they provide, have been lost; for example, it has been estimated that between 60 and 90% of freshwater and saline wetlands have vanished in favour of rural and urban development [6, 25, 26]. Of the wetlands that remain, many are degraded via a combination of earth bunding, to exclude seawater and reclaim land for pasture [27–29], upstream agricultural use (grazing and sugar cane production) which leaches ecologically damaging nutrients and sediments [30, 31], and extensive aquatic invasive weed chokes [32, 33] which contributes to hypoxic conditions and fish kills [34, 35].…”