Year

2020

Degree Name

Honours degree of Bachelor of Science

Department

School of Earth, Atmospheric and Life Sciences

Advisor(s)

Jeffrey Kelleway

Abstract

Coastal wetlands are highly productive ecosystems with an exceptional capacity for sequestering organic matter in the accumulating substrate. Recent studies have focused on intertidal saltmarsh and mangrove communities with limited research extending to the supratidal wetland forests, especially in temperature regions. The overall aim to fill the knowledge gap present in current literature by addressing two aims. The aims of this study is to (1) determine the processes driving the development and persistence of supratidal wetland forests in Corner Inlet, Victoria, Australia; and (2) reconstruct the historic vegetation shifts that have occurred in the embayment over the Holocene. A combination of stratigraphic analyses and photogrammetry were used to achieve these aim. Cores were collected to quantify the accumulation and preservation of organic matter across the intertidal-supratidal wetland gradient. Results from stratigraphic logs, bulk density and loss-on-ignition analyses, grain size, and high-resolution core logging (ITRAX) were compiled to determine the contribution and preservation capacity of organic matter in Melaleuca paperbark swamps (MPS) and to produce a paleo-reconstruction of the site. Along the study gradient, an increase in organic matter contribution was observed within the surface organic horizon shifting from the mangrove (5-10% organic matter) through to the MPS communities (up to 66% organic matter). The organic-rich soils of MPS noticeably declined at a greater rate in the more terrestrial substrate further from the seaward edge. This revealed a limitation in the preservation capacity of MPS with depth, with MPS having a greater effectiveness in organic preservation in more marine influenced settings. A time series analysis of historic aerial imagery, and paleo-reconstruction of sedimentary cores were used to reconstruct the historic vegetation shifts across the intertidal-supratidal wetland complex. Seaward migration of the wetland communities was identified during the paleo-reconstruction. Overtime, the infilling estuary revealed marine sands and seagrass meadows shift progressively to mangrove, saltmarsh, herbaceous wetlands and finally MPS. However, recent decadal shifts in the wetland community have inverted to a landward retreat. These results suggest that anthropogenic impacts on the Earth’s climate have increased the rate of sea-level rise to a point which exceeds the rate of vertical accretion. The landward retreat of MPS and related rise in sea-level may result in the belowground disruption of preserved organic matter. This may lead to alterations in the global carbon cycle with large proportion of organic matter sequestered in these forests to be remineralised into CO2, having further implications on anthropogenic climate change.

FoR codes (2008)

040607 Surface Processes

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.