Document Type

Thesis

Publication details

Green, J 2009, 'Ecology of a saltmarsh restoration site', PhD thesis, Southern Cross University, Lismore, NSW.

Copyright J Green 2009

Abstract

This study measured saltmarsh restoration success after soil profile reconstruction in degraded saltmarsh surrounding Sponsors Lagoon, Fingal Peninsula on the north coast of New South Wales, Australia. Comparative sites at Brunswick Heads and Bulimba Creek located within 200km of Sponsors Lagoon were included in some aspects of this study. An experimental design to measure ecological restoration success was incorporated into the on-ground works planning at Sponsors Lagoon. Saltmarsh restoration sites (planted and non-planted) were compared with nearby disturbed (control) and reference sites. The study investigated abiotic and biotic factors to help in the understanding of progress towards saltmarsh restoration success.

Variables measured included environmental variables (soil moisture %, pH, and electrical conductivity (EC), Total Organic Carbon (TOC) and Total Nitrogen (TN)), soil algal abundance (chlorophyll a), diatom abundances, and flora and fauna colonisation. Time frames for the study of the different variables varied over a three year period. The measurements of chlorophyll a showed that the restoration sites were progressing towards, but were not equivalent to, the reference state in two years after restoration (2006), despite the fast growth rates of soil algae. Analyses of across-site variables and chlorophyll a over time showed that solar radiation, rainfall and tidal inundation were influential to microalgal growth.

Diatom species have site preferences related to elevation, tidal inundation and salinity. There was evidence of different species patterns at various microtopographic levels related to micro site features such as bare soil or grass cover. Soil variables, such as TOC, soil moisture content, pH, and EC affect the distribution of diatom species on a saltmarsh restoration site but seasonal and climatic influences, particularly rainfall and solar radiation, affect overall diatom abundances.

The dominant vegetation species in the restoration site were Saltwater Couch (Sporobolus virginicus), Suaeda (Suaeda australis), Sarcocornia (Sarcocornia quinqueflora subsp. quinqueflora and Sea Rush (Juncus kraussii subsp. australiensis). Changes in the vegetation cover in three years after soil reconstruction work (2007) showed that the dominant Saltwater Couch established only from vegetative growth arising from remnant vegetation but there was strong seedling regeneration of Suaeda and Sarcocornia. It was concluded that planting is important where the resilience of the individual species is lower and natural regeneration potential is limited.

Some fauna species require structural habitat features to facilitate colonisation. The saltmarsh gastropod, Ophicardelus spp. prefers the cover of taller vegetation such as taller Sporobolus virginicus or Juncus kraussii. These plant species provide a substrate for escape from higher tides. Phallomedusa solida was commonly on mud substrates and was more evenly distributed across the saltmarsh than Ophicardelus spp.

Total densities of gastropods were low in the first year after restoration works (2004 - 2005), with the highest recovery of total gastropod numbers in the last year of the study (2006 - 2007). In the final sample period, autumn 2007, the MDS ordination of sites based on the total densities of the three gastropod types, Ophicardelus spp, Phallomedusa solida and Littoraria scabra, demonstrated which sites were most similar in snail numbers to the reference sites. No restoration site became statistically similar to a reference site in terms of gastropod abundance during the study time.

Timescales for the measurement of variables should be relevant to the organisms under study. Monthly measurements of chlorophyll a and the soil microbial community were relevant in this study, but seasonal studies may be more useful where resources are limited. At least twice yearly sampling for vegetation and fauna was necessary to account for seasonal variability. A ratio for using various abiotic and biotic factors to assess the success of restoration, in relation to a reference state, over various timescales has been developed in this thesis.

The more recent recognition of impending effects of climate change emphasises the need for restoration of saltmarsh to include planning for migration zones to counter the potential loss of saltmarsh area and allow for the long-term viability of a restoration project. Because of the very specific habitat needs of saltmarsh communities in terms of tidal inundation and elevation, these communities are also threatened by other anthropogenic activities including land reclamation, dredging, pollution and recreational activities. A deeper understanding of fauna habitat requirements and restoration methods is required to assist in the protection and enhancement of saltmarsh communities. This study has provided important information that will help ensure that future saltmarsh restoration projects are successful and financial commitments by government and stakeholders provide scientifically sound conservation management outcomes.