NSW streams and coastal waterways have evolved in a landscape characterised by a regime of relatively low-intensity, mosaic fires which may periodically modify the delivery of sediments, carbon types and nutrients during runoff events.
The scale and intensity of the 2019–20 fires are unprecedented, giving rise to concerns about potential changes to hydrology and pollutant generation from fire grounds and the downstream effects on receiving waters that are outside the expected natural variation. Loss of vegetation near waterways, soil erosion, falling ash and changes to the water flows can all have an impact.
One of the biggest concerns for water quality after a fire is heavy rain. After a fire, it is likely that there will be increased water runoff which can lead to erosion and flooding. The runoff carries soil, leaves, ash and other burnt organic debris with it into waterways, and this has an immediate effect on water quality.
It may be many months or even up to a year before we can fully understand the impacts on water quality. Burnt leaves and branches that wash into waterways break down over time, using up oxygen from the water column which supports fish, oysters and other aquatic species.
To help measure these changes, we've added more monitoring indicators to the statewide water quality monitoring program to further understand the effects on water quality and ecological health. Where it is safe to do so, our scientists are surveying areas to collect samples and assess the impact.
As of 6 February 2020, we are monitoring 7 catchments that are at very high risk for water quality impacts. These catchments are:
- Wonboyn River
- Khappinghat Creek
- Tuross River
- Conjola Lake
- Durras Lake
- Termeil Lake
- Meroo Lake.
Following the heavy rainfall event that happened New South Wales between 8 and 12 February 2020, our scientists together with NSW EPA, Department of Planning, Industry and Environment's South East Regional Water Floodplains and Coastal Team, NSW Department of Primary Industries Marine Parks officers and local government conducted monitoring to assess water quality effects across 18 waterways along the NSW south coast. These waterways were selected as bushfire affected catchments that have been affected by recent flooding.
Water quality was monitored in the field for salinity, temperature, dissolved oxygen and turbidity. Water samples were also collected for further analysis at our environmental forensics laboratory. These samples are being tested for nutrients, total suspended solids, trace metals and organic pollutants. The data from this monitoring is available on SEED.
An interim dataset of water quality following the heavy rainfall in these 18 south coast waterways is available on SEED. As more data becomes available, and following a comprehensive laboratory analysis, this dataset will be updated.
This monitoring is helping provide vital information to determine how the combination of a bushfire-affected landscape and heavy rainfall, effects the community and environmental values of estuaries. These values include recreational use, visual amenity, health of aquatic ecosystems, fishing activities and aquaculture.
We are working with local councils and other water management authorities to assist the recovery of these catchments, and providing advice, expertise and information on management strategies. Our existing statewide water quality monitoring program as part of the NSW Marine Estate Management Strategy will continue to assist in tracking the condition of waterways and the effects of bushfire and other pressures on water quality across New South Wales.
More information about what our scientists are doing to address water quality concerns can be found in our Water Quality science in response to the NSW Bushfire Emergency fact sheet.