WAMSI 2 - KMRP Project 2.2.9: Historical Water Quality using sediment records

Brief description

The remote Kimberley coast of north-western Australia is one of the few marine environments domains on earth largely unaffected by human use. However, the region is undergoing increasing economic importance as a destination for tourism and significant coastal developments associated with oil and gas exploration. The objective of the project was to reconstruct a timeline of inferred water quality changes from the sediment record for a selected set of sites in the Kimberley, Western Australia.

The project made use of palaeoecological approaches to reconstruct a chronology of change over the last approximately 100 years using a series of biogeochemical proxies for phytoplankton composition and biomass, temperature and terrestrial influences. Where possible these were matched to historical land/water use, meteorological or hydrological observational records. The project examined sediment cores from three coastal locations, Koolama Bay (King George River), Cygnet Bay and Roebuck Bay. Each sampling location provided a contrast with which to evaluate changes over either a spatial or temporal gradient of human or natural influence.

Sediment cores (up to 1.5 m) were obtained from each of these locations in the expectation that they would provide a time series for about the last 100 years. A set of parameters was measured along the core length (every 1-2 cm) for some or all cores depending on the particular focus for the location: 210Pb and 137Cs; 15N isotope; 13C isotope; Carbon/Nitrogen ratio; Sedimentation rate and grain size; Total Organic Carbon (TOC) and Total Nitrogen (TN); Biosilicate; Biomarkers; TEX86; long chain n-alkanes (C27+C29+C31); Elemental carbon (or black carbon).

Rainfall data was obtained from the Australian Bureau of Meteorology website (www.bom.gov.au). Stream flow data was obtained from the Western Australian Department of Water website (www.water.wa.gov.au). Historical bushfire data was obtained from the Western Australian Department of Parks and Wildlife.
The metadata record only relates to data generated as part of the sediment analysis.

Lineage: Sediment cores taken at each site (Koolama Bay [King George River], Cygnet Bay and Roebuck Bay) were obtained using a polycarbonate sleeve 6 cm in diameter within a 1.5m long steel casing. At each site, three or four replicate sediment cores with a length of approximately 1.0 – 1.4 meters each were collected. The cores were then frozen on board the ship in a vertical position and were later thawed as they stood vertically and were then sectioned into sub-samples at 1 cm intervals, weighed and freeze dried before being reweighed and then stored in a freezer at -20oC before being analysed.

Parameters measured:
•\t210Pb and 137Cs isotopes – age of core, integrity of age structure in sediment;
•\t15N isotope – a proxy for nitrogen source – anthropogenic or natural;
•\t13C isotope – proxy for carbon source – land or marine derived carbon;
•\tCarbon/Nitrogen ratio – can also be used to infer whether primary carbon source is marine or terrestrial;
•\tSedimentation rate and grain size shows the variation of sedimentary environment (e.g. river input, sediment texture, other factors governing deposition and preservation);
•\tTotal Organic Carbon (TOC) and Total Nitrogen (TN) indicate levels of productivity and deposition of organic matter;
•\tBiosilicate indicates siliceous phytoplankton deposits (e.g. diatoms, silicoflagellates), enhanced productivity;
•\tBiomarkers – sterols can be used as proxies for dinoflagellates (dinosterol), diatoms (brassicasterol) haptophytes (alkenones); TEX86 index for sea temperature; and long chain n-alkanes (C27+C29+C31) for terrestrial influence.
•\tElemental carbon (or black carbon) – indicators of biomass burning (e.g. from bushfires) or hydrocarbon burning (fossil fuels).

For Full details, see KMRP 2.2.7 Final Report.

Rainfall data was obtained from the Australian Bureau of Meteorology website (www.bom.gov.au). Stream flow data was obtained from the Western Australian Department of Water website (www.water.wa.gov.au). Historical bushfire data was obtained from the Western Australian Department of Parks and Wildlife. \t