Year

2015

Degree Name

Bachelor of Science (Honours)

ANZSRC / FoR Code

040607 Surface Processes, 040601 Geomorphology and Regolith and Landscape Evolution, 050301 Carbon Sequestration Science

Department

School of Earth & Environmental Sciences

Advisor(s)

Kerrylee Rogers

Abstract

Carbon sinks are recognised as an important environmental commodity, however are often assumed to be stable. Climate change, and in particular sea-level rise may alter the stability of coastal carbon sinks. Mangrove and saltmarsh are amongst the most efficient ecosystems at sequestering carbon; however the effect of sea-level rise on sediment accretion and carbon accumulation, and its subsequent effect on carbon sequestration and carbon retention remain unknown. This study uses a range of isotopic techniques, including

210Pb-dating techniques to determine a core sediment chronology, and stable carbon isotope analyse, to determine the effect of rapid sea-level rise on the sources of carbon in a coastal carbon sink. The study site, located at Chain Valley Bay, Lake Macquarie, underwent rapid submergence following the collapse of a long wall mine in the mid-1980s; and this submergence was used as a surrogate for exploring the effects of rapid sea-level rise on a coastal carbon sink. Temporal mapping of vegetation distribution highlighted the dieback of vegetation and subsequent recovery of vegetation following submergence; however areas in the lower intertidal zone remained permanently inundated. The permanently submerged wetland area had a higher accretion rate following submergence than the recovery area that is now vegetated with mangrove. The wetland has attempted to keep up with water level rise and as a result carbon sequestration increased in the submerged area from 300.0 g C m-2 yr-1 to 627.3 g C m-2 yr-1, and the mangrove area increased slightly from 56 g C m-2 yr-1 to 68 g C m-2 yr-1. Both zones had an increase in sediment mass, indicating a shift in sediment sources to more mineral based following inundation. Carbon isotope analyses reflected the changes in sediment sources in each zone. Isotopic values showed an obvious shift from marine sourced material to terrestrial material up the core and is indicated by the depletion of δ13C (values from -30‰ to -11.7‰). Sediment characteristics and carbon store indicate central mud basin sediments within lower cores due to the dominance of muds and silts and lower carbon store and fluvial delta sediments located middle core contained more recalcitrant carbon and larger grains sizes with significant gravel components. In the upper core there was a shift to high density of carbon. The amount of carbon is more in mangrove and mixed forest vegetation than saltmarsh. These results suggest that where hydrodynamic conditions are suitable and sediment supply is sufficient, coastal carbon sinks following sea-level rise will not become net carbon emitters but may increase their carbon storage capacity.

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