Estuary Health

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Lakes Entrance, Gippsland Lakes, Victoria.

Last week I participated in a presentation by fellows of the Academy of Technological Sciences and Engineering (ATSE) to the Productivity Commission’s inquiry on national water reform. Jan Dolan, one of the Commissioners, commented on the growing disconnect between science and policy in what is a contested space in public policy. She referred to several “big picture” themes as challenges to be addressed in water reform including population growth, climate change, indigenous water strategies, and how to manage for extremes in water scarcity and other impacts. I was given the opportunity to comment on estuaries.

My presentation touched on 3 points: one, the importance of healthy estuaries as places of economic production and social use being threatened by a range of pressures that will make them less sustainable; two, the complex eco-hydrological processes that operate for a diverse range of estuary types that require better understanding of dynamics and how those dynamics are influenced by variability in freshwater flows; and three, the need to develop standards for effective monitoring of critical indicators that inform communities and decision makers on need for action before certain tipping points are reached. These three points were expressed in the context of different governance arrangements around Australia related to estuary management.

Over many years I have come to enjoy many of our diverse estuary types. As a child I swam in oily parts of Sydney Harbour; as an undergraduate I enjoyed the quiet waters of Port Stephens with its then vibrant oyster industry and the apparent wildness of Myall Lakes; and after I returned to Australia in 1971 I spent months on the Ord estuary and Cambridge Gulf with Don Wright witnessing horrible fish kill associated with pesticide use on upstream cotton fields. It was a privilege in the following years to visit many of the coastal lakes and deltas of the southeast coast and learn more of their geology, entrance dynamics, ecology and geomorphic history with Peter Roy and others. In 2002 I led an inquiry into the need to improve tidal exchange in Lake Illawarra. All the time there was this sense of disquiet about their environmental health arising from adverse impacts of land use practices in river catchments and the training of estuary entrances to permanently alter tidal regimes.

Australia has examples that sadly reflect on activities that have left harmful legacies in some harbours and river mouths. The two that stand out are Sydney Harbour (Port Jackson) and the Derwent in Tasmania. In both cases past heavy industry has left a trail of pollutants that are to some extent now locked up in a more recent mud cover. However, continued industrial and urban development in catchments still constitutes a threat to public health which governments are endeavouring to mitigate. Fortunately in both places freshwater runoff and tidal flushing assists these efforts. Other challenges arise where freshwater flows are intercepted for agriculture and other purposes thus denying the estuary of those sources of water and nutrients on which healthy ecosystems depend. These impacts are compounded where the entrance to the sea is also altered.

Our recent paper on the River Murray mouth and its associated lakes and lagoons is one such case (Thom et al., in River Research and Applications, 2020). Overallocation for irrigation purposes has greatly reduced freshwater flow to the mouth. The estuary system is also divided by a system of barrages. What is noticeable is that wetland conditions and water chemistry of the waters are changing in ways that many see as irreversible and at odds with their status under the international Ramsar Convention. Much has been written about these matters. They were covered extensively in the South Australian Royal Commission on the Murray-Darling Basin Plan (2019), and the recently edited book published by the Royal Society of South Australia (2018) on the “Natural history of the Coorong, lower lakes, Murray mouth region.

Another example is in southwest Western Australia. I refer to the story of the Dawesville Cut. This is a channel cut through an aeolianite ridge to connect the Peel-Harvey Estuary and the Indian Ocean. Agricultural settlement in low-lying lands adjoining the estuary accompanied by vegetation clearing, drainage and excessive use of superphosphate allowed for the build-up of nutrients in river and estuary waters. The result was continued degradation of water quality permitting the growth of toxic macroalgae and massive blooms of blue-green algae. This was all well studied by a wonderful ecologist well known to many of us, Ernst Hodgkin. Efforts were made to address this eutrophication but, in the end, a dramatic and costly method of cutting a new channel to the sea was required (completed in 1994). Although this has also required sand bypassing works at the entrance, the result has been no further blue-green algal blooms assisted by remediation action in the catchment.

In 1960 I became familiar with the work of Eric Bird on the Gippsland Lakes. He had just completed his PhD and commented on the dieback of reed swamp vegetation which he attributed to the trained permanent opening to the sea at Lakes Entrance. Salinity changes in the lake system has been documented in subsequent years. This beautiful part of Australia is under threat. I receive regular reports from a concerned community on the impacts of different pressure on the ecological condition of lake waters and adjoining wetlands which are Ramsar listed. Ross Scott, a former General Manager of the Lake Wellington Rivers Authority, is a man on a mission. He is working tirelessly with colleagues to make the nation more aware of the progressive impacts of salt intrusion into the lakes.

 There is a sense of denial in the way this Victorian coastal area is being managed. Increasingly precious freshwater flows are being diverted for agriculture in the catchments; healthy estuaries need a supply of freshwater especially where entrance conditions are changed to allow marine waters to be exchanged more “efficiently”. And this is what has occurred at Gippsland Lakes. Boat access at Lakes Entrance over the last decade has been enhanced by deeper dredging. Ross and others have noted changes to tidal speed within the lake system and hence erosion of channel banks with adverse impact on ecological functions. A call for an independent audit of all these impacts which should involve the federal government because of its Ramsar obligations have so far been refused. At the moment power is vested in different commercial interests at either end of the estuary complex making it very hard for environmental concerns to receive attention. This is a very sad state of affairs and Ross and his team need all our support to help save the Gippsland Lakes from further degradation.

There are more stories to tell about changes to our estuaries and adjoining lowlands that adversely affect estuary health. As noted at the Productivity Commission hearing, they are areas under both increased population pressure and impacts of climate change as well as encountering extremes in freshwater flows. National water reform should recognise their environmental, social, and economic importance and not ignorantly sacrifice their intrinsic ecological and public amenity values to other interests. 

Bruce Thom

Words by Prof Bruce Thom. Please respect the author's thoughts and reference appropriately: (c) ACS, 2020, for correspondence about this blog post please email austcoastsoc@gmail.com

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