New research determines dredging effects on seawater quality
WAMSI Dredging Science Node researchers have, for the first time, quantified dredging effects on seawater quality conditions, which is critical to realistic testing in the laboratory.
The literature review along with the examination of some large environmental monitoring datasets from recent dredging projects provided by Chevron Australia, Woodside Energy and Rio Tinto Iron Ore, have been published in PLOS ONE.
Lead author of the paper: Temporal Patterns in Seawater Quality from Dredging in Tropical Environments, Dr Ross Jones from the Australian Institute of Marine Science (AIMS), said bringing the current knowledge together means previous laboratory testing can be appraised on the relevance of the pressure fields used, and that future testing, including the next phase of WAMSI’s dredging science program, now has a peer reviewed reference.
“The reviews of existing monitoring datasets from industry have allowed us to more accurately quantify how dredging affects seawater quality conditions temporally and spatially,” Dr Jones said. “This information is critical to test realistic exposure scenarios.”
The research found that dredging effectively alters the overall probability distributions of fine temporal scale turbidity and light changes, increasing the frequency of extreme values and dampening the probability distribution.
“When averaged across the entire baseline and dredging phases separately for the three Pilbara dredging projects, turbidity values increased by 2–3 fold but when examined by the IDF analysis across baseline and dredging periods, dredging increased the intensity (magnitude) of turbidity peaks by over an order of magnitude, generated peaks that lasted five times longer than the baseline period, and may cause peaks to occur up to three times more frequently,” Dr Jones said.
The second prominent and characteristic feature of the seawater quality conditions during the dredging programs were the low light, or ‘daytime twilight’ periods. Such conditions are well known to be associated with wind and wave events.
“One of the objectives of this analysis was to provide a temporal analysis of seawater quality to allow the design of more realistic experiments examining the effects of sediments on tropical marine organisms (corals, seagrasses, sponges ascidians etc),” Dr Jones said. “The analysis has provided a matrix of empirical data of seawater quality (turbidity and light levels) which effectively captures the entire range of likely seawater quality conditions associated with dredging in a reefal environment.”
“Collectively this information could contribute to the development of seawater quality thresholds for dredging projects and ultimately improve the ability to predict and manage the impact of future projects,” Dr Jones said.
R. Jones, R. Fisher, C. Stark, P. Ridd (October 2015) Temporal Patterns in Seawater Quality from Dredging in Tropical Environments PLOS DOI: 10.1371/journal.pone.0137112
The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.