Fire and Water

We have seen short-term impacts of bushfires, but what are the possible long-term impacts for marine environments?

The bushfire season of 2019–20 was ferocious and unprecedented in scale, intensity and longevity. It engulfed all states and territories, especially in the south-east where some fires burned to the shorelines of estuaries and beaches. The immediate social and physical impacts on fire-affected communities were stark and terrible. The economic costs, in terms of insurance claims and lost income to tourism and businesses, will run to billions. However, the long-term impact on marine and coastal environments is far more difficult to predict and may take months or years to manifest.

THE AMCS REPORT

DAMAGE TO RIPARIAN LANDSCAPE

The 2019–20 bushfires devastated coastal habitats in many locations, including thousands of square kilometres of riparian vegetation that protected catchments and waterways by reducing water temperatures and restricting sediment loads. Once stripped of this vital cover, the landscape is exposed to elements that cause erosion and siltation. 

SEDIMENT SLUGS

Ash and debris can form ‘sediment slugs’ that clog fish gills and impair the breathing of filter feeders like mussels, sponges and corals. Assisted by flooding rains, sediment can be swept downstream through estuaries into open waters, impacting marine ecosystems, like seagrass and kelp beds, which provide refuge and nursery habitats for commercially and recreationally important species.

Heavy rains along the east coast during January and February 2020 generated flash flooding and land slips in fire-affected areas. Large amounts of ash and debris washed into the Tambo River, Victoria, killing eels and depleting fish stocks in the Gippsland Lakes. Siltation and turbidity also caused large-scale fish deaths in catchments upstream of Moruya, at Tilba Lake, on the Clarence River, NSW, and along a 70km stretch of the Macleay River upstream from Kempsey.

WATER POLLUTION

Bushfire ash contains nutrients such as carbon, nitrogen and phosphorous, which can promote harmful algal blooms that consume oxygen and suffocate fish and aquatic invertebrates. It also contains metals, including copper, mercury and zinc, and synthetic and manufactured materials. In areas where houses have been destroyed, the ash could contain asbestos and other carcinogens. These toxic contaminants can kill marine life and work their way up the food chain. 

SMOKE HAZE AND AIR POLLUTION

An air quality index (AQI) reading of 200 or higher is considered hazardous. On 15 November 2019, Port Macquarie had the world’s highest AQI at 1739. By mid-January, smoke from the Australian bushfires had circumnavigated the globe, turning New Zealand glaciers brown with ash, thereby encouraging heat absorption and increasing glacial melt, with implications for the rate of sea level rise.

When airborne ash and other debris settles on coastal and nearshore waters, the obstruction of sunlight impedes photosynthesis in marine organisms, including coral reefs, mangroves and seagrasses, and the absorption of oxygen in the water, causing fish to suffocate. 

IMPACT ON COMMERCIAL FISHERIES AND AQUACULTURE

The most immediate and dramatic impact of the 2019–20 bushfires on south coast fisheries was the destruction of the Mallacoota Abalone Cooperative buildings and processing facilities, the main employer in the town. Bushfires also forced the closure of oyster farms in ten New South Wales estuaries, including the Shoalhaven and Clyde Rivers, Tuross Lake and Narooma, due to high readings of algae and contaminants considered a threat to human health. Road closures kept buyers away and prevented farmers from getting their product to market during what is usually their busiest sales period. 

Coastal lakes, estuaries and lagoons support mangrove forests, shellfish reefs and seagrass meadows that are habitats and spawning grounds for economically important species of fish, prawns, mussels and oysters. It is estimated that more than 75 per cent of commercial fish catch in Australia, and in some regions up to 90 per cent of all recreational angling catch, spend part of their life within estuaries and inshore wetlands. Their reliance on clean water and tidal flow make them particularly vulnerable, with pollutants, ash and debris reducing fish populations, eliminating some species and altering overall species composition. 

IMPACT ON TOURISM AND RECREATIONAL FISHING

East Gippsland and the NSW South Coast are summer holiday playgrounds for many Australians, including boaters and anglers who patronise tackle shops, petrol stations, charter fishing operators and camping grounds. But this summer’s bushfires forced mass evacuations and holiday cancellations, causing estimated losses to local businesses and regional tourism ranging between hundreds of millions to more than $4 billion. The impacts forecast for commercial fish stocks will also affect recreational fishers that catch the same species. 

CONCLUSION

The catastrophic bushfires were fuelled by record-breaking heat and prolonged drought directly linked to global warming, such is the unanimous opinion of hundreds of scientists, climate experts and emergency services veterans. Sir David Attenborough says it is “palpable nonsense” to suggest otherwise.

Unabated, these conditions will continue, and Australia will experience longer, more intense fire seasons in future, placing an even greater burden on estuarine and marine habitats that are already under considerable stress from development, pollution, overfishing and climate change. The report advocates that Australian governments at all levels work together to address global warming by cutting carbon emissions to net zero as quickly as possible, to mitigate the impact of bushfires and restore the health of our coastal waterways. 

For more information and a full copy of the report visit marineconservation.org.au.