Stormwater runoff has resulted in heavy metal contamination throughout much of
the Port Jackson estuary, Sydney, Australia. Metal partitioning was
investigated in the benthic estuarine sediments of Iron Cove, an off-channel
embayment of Port Jackson. Contamination was greatest near the stormwater
canal, where sediments were anoxic and contained high concentrations of
sulfide in the porewater. Away from the canal a layer of non-cohesive,
sub-oxic surficial sediment containing high dissolved iron was found
overlaying a more cohesive substratum. At all sites, porewater Cd, Cu, Ni, Pb
and Zn were <2.5 g L–1, and negligible metal
release was observed upon sediment resuspension. According to water quality
guidelines, the ecological risk posed by dissolved metals from the Iron Cove
sediments is low. Estimated fluxes of Cd, Cu, Ni, Pb and Zn from the sediments
were calculated to be <0.2 mol m–2
day–1. The rapid oxidation then hydrolysis of
iron(II) in porewaters caused a drop in pH and the formation of iron hydroxide
precipitate. These processes may affect dissolved metal concentrations; hence,
oxidation of samples must be avoided during sampling and extraction
procedures. Sediment-bound zinc was the metal most easily mobilized.
Stormwater modelling indicated an average annual discharge from Sydney estuary catchment of 215,300 mL and loadings of 0.8, 0.5, 1.7, 3.2, 1.1, 3.6 and 17.7 tonnes for As, Cd, Cr, Cu, Ni, Pb and Zn, respectively. Priority for remediation should be given to creeks with high-metal loads in the upper and central estuary, as well as discharging to the western shores of Middle Harbour. Managerial strategies need to target dissolved and particulate metal phases to ensure effective remediation. The proportion of metals discharged under low- (<5 mm rainfall/day), medium- (>5 to <50 mm/day) and high-flow conditions (>50 mm/day) was approximately 10%, 60% and 30% of total loading, respectively. Under high-flow conditions the estuary becomes stratified and most metals are exported to the sea, whereas metals discharged during low-flow may be remediated by infiltration. Effective remediation will depend on the extent to which 'first-flush' metals associated with medium-flow conditions can be remediated.
Understanding the rate of extraction from bores (or wells) can be essential in estimating groundwater discharge at a regional scale and understanding pressures on sustainable use. The challenges in doing so include the impracticality of directly measuring extractions from all, or even a large proportion of, operating bores using flow meters, especially in rural and remote areas. This challenge may be addressed by metering a representative sample of bores and generalising results to develop estimation methods; however, even achieving this presents considerable obstacles. While the benefits of metering a subset of bores to progress groundwater science and management are recognised, the obstacles to implementing metering and guidance on overcoming them are not well documented. In the Surat Basin, Australia, most groundwater bores are used for stock watering and domestic purposes, with less than 0.1% metered. As part of a research program to understand regional groundwater extraction in this area, a voluntary bore metering program has been undertaken. In this paper the challenges that arose when recruiting participants, installing and maintaining flow metering equipment, and interpreting and using data collected are described. Lessons learnt during implementation of the program that can guide other voluntary metering of rural groundwater extractions are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.