Field trials to determine the efficacy of aerators to mitigate hypoxia in inland waterways

Abstract

Following a series of fish deaths in the lower Darling River in the austral summer of 2018-19, several field trials were undertaken over two summers to determine the efficacy of various aerators to mitigate the effects of hypoxia to prevent fish deaths. The aerators evaluated included: low-powered, solar bubble-plume diffusers; high-flow, single-port Venturi systems; pontoon-mounted multi-port Venturi systems; and an ultra-fine bubble generator. The effectiveness of bubble diffusers appears related to their power, the number of units used and their running time. Pontoon-mounted multi-port Venturi aerators and high-flow, single-port Venturi aerators were much more successful in maintaining oxygen levels and may have prevented fish deaths in the Darling River in early 2019. However, the Venturi aerators were expensive to run, consuming hundreds to thousands of litres of diesel fuel per week. Trial of an ultra-fine oxygen bubble pump showed promise because it supersaturated the water with dissolved oxygen while not elevating total gas pressure to levels that would cause gas-bubble trauma in fish. Although aerators may play a role in emergency responses to hypoxic fish deaths, they have limitations regarding their area of influence (at best thousands of square metres) and their cost to deploy and operate.

Estuarine Hypoxia—Identifying High Risk Catchments Now and Under Future Climate Scenarios

“…For example, the removal of cuttings from slashed pastures has been suggested as an effective means of reducing the DOP of grazing lands (Eyre et al., 2006). Alternatively, mechanical oxygenation has been employed to mitigate blackwater impacts in the Swan and Canning rivers of Western Australia (Greenop et al., 2001), although this is generally regarded as an emergency response measure as it is substantially limited by the area that can be serviced and operational costs (Baldwin et al., 2022).…”

Mass fish kills catalyse improved water and fisheries management

“…Many of the technologies outlined in Boys et al (2022) require further field evaluation for efficacy, environmental risk and cost-effectiveness. Baldwin et al (2022) present field trial results, evaluating a range of aerator designs used during the 2018-19 fish kills. The performance and limitations of the different aerators are outlined, along with recommendations that can improve the way they are used in future events.…”

How fish kills affected traditional (Baakandji) and non-traditional communities on the Lower Darling–

“…In each case, a period of high temperatures and low-or noflow conditions led to thermal stratification of the weir pool above Weir 32 (NSW Department of Primary Industries 2019; Baldwin 2019; Baldwin et al 2021). During periods of thermal stratification, a warmer surface layer of water sits above a cooler, deeper layer (hypolimnion) in which dissolved oxygen can become depleted.…”

“…During periods of thermal stratification, a warmer surface layer of water sits above a cooler, deeper layer (hypolimnion) in which dissolved oxygen can become depleted. In the case of these fish kills, a mixing event resulting from a sudden weather change drove a decrease in temperature, resulting in the hypolimnic water mixing with the surface layer and causing hypoxia throughout the water column (Baldwin 2019;Baldwin et al 2021). After the first fish kill event, air temperatures in the region increased again, and remained high for ,2 weeks (resulting again in thermal stratification), before another cold weather change resulted in destratification of the weir pool.…”