Changes in waterway health linked to high rainfall

Michael Orr, Environmental Technician with the Department of Planning and Environment, doing water monitoring in the Karuah River.

AN interactive museum and family fun day was held on Saturday 10 December to celebrate MidCoast Council’s release of its annual Waterway and Catchment Report Card.

Water sampling is undertaken every summer across the MidCoast region’s six major catchments.

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The results improve our understanding of their overall health.

It also helps us understand patterns, trends and cycles of our waterways.

In 2022, estuaries were impacted by the large amounts of rain during the summer sampling period.

Of the sites sampled, nine maintained their grade from 2021.

Five locations dropped a grade and only three improved their grade.

“We’re continuing to see Report Card grades being influenced by the amount of runoff from the catchment.

“The wetter than average sampling period resulted in a decrease in water clarity and increased algal growth,” said Dr Rebecca Swanson from the Department of Planning and Environment.

“La Nina was in effect during the 2021-22 summer and the large amount of rain increased sediments and nutrients.
“However, the majority of our systems maintained their grade.

“This shows the resilience of the estuaries and their ability to cope with extreme conditions,” Dr Swanson said.

The Report Card results also help us measure the success of many water quality projects undertaken by Council, the community and delivery partners.

“These results are a reminder of the importance of setting strategic priorities for our waterways. Managing our waterways helps to protect their environmental, social, cultural and economic values for the future,” said Council’s Water Quality and Estuary Coordinator, Prue Tucker.

“We have been working with our community to develop a ten-year action program to protect the health of the Manning River.

The program takes a holistic approach.

It recognises that what happens upstream impacts the estuary.

“Its primary focus is addressing the impacts of land-use on water quality and ecosystem health,” said Mrs Tucker.
A similar program is now being developed for the MidCoast southern estuaries.

The Report Card is funded by MidCoast Council’s Environmental Rate and supported by the New South Wales Government through its Coast and Estuary Program and the Department of Planning and Environment.

Karuah River Estuary

The grade for the Karuah River Estuary dropped to fair this year driven by a significant increase in algal growth.

Large, localised algal blooms were recorded on most sampling occasions.

The Branch Estuary retained its good grade as it didn’t experience the same increase in algal growth as the main estuary. However, there was a decrease in water clarity due to frequent runoff.

Myall Lakes

The grade for Myall Lake remained in excellent condition this year.

Bombah Broadwater remained in good ecological condition despite a significant decrease in water clarity due to considerable runoff from the Myall River catchment.

The salinity of both systems was close to freshwater as a result of another very wet summer.

For the first time in over a decade of monitoring, the average salinity was higher in Myall Lake than the Broadwater.

This reflects the unique hydrology of Myall Lakes which have no major tributaries, only receiving runoff from the surrounding catchment.

Manning River Estuary

The Mid and Lower Manning River Estuaries have remained in good ecological condition, while the Upper Manning Estuary improved from fair to good.

There was a general decrease in water clarity across the entire system due to continuous inflow of sediments from the catchments.

Farquhar Inlet was open to the ocean all summer and while its grade remained good, there was a reduction in water clarity that was likely caused by resuspension of the sandy shoals due to wind and surf conditions.

The Dawson River Estuary saw a drop in grade from good to fair due to reduced water clarity and increased algal levels.

Similar results were observed in Browns Creek which also scored a fair grade in its first summer of monitoring.

Two new sites were added in tributaries of the lower estuary, one in the upper Lansdowne River Estuary and one in Ghinni Ghinni Creek.

The Lansdowne River Estuary scored an inaugural grade of fair due to issues with water clarity, while Ghinni Ghinni Creek was in good ecological condition with a comparatively clear water column.

Khappinghat Estuary

The Khappinghat Estuary improved from fair to good condition this year due to a decrease in algal growth.

Salinity levels in the estuary were very low reflecting another wet summer which resulted in water clarity remaining fair.

The estuary appears to be recovering from the impacts from the bushfires in 2019-20. Algal levels decreased possibly due to less nutrients in runoff the catchment due to regrowth of vegetation.

Wallis Lake

Wallis Lake and Charlotte Bay both dropped from excellent to good this year due to higher algal growth during the summer.

Pipers Creek, Mid Wallamba and Coolongolook Estuaries retained their good grades. Water clarity was good but frequent runoff events delivered nutrients to the estuaries which fueled algal growth.

Wallamba Cove’s grade improved from fair to good, despite frequent runoff over summer. Nutrient levels in runoff remain a problem driving algal growth in the estuary.

Seagrass depth range was reduced at all sites in Wallis Lake as runoff from frequent rainfall restricted the depth to which seagrass can grow.

To see the full results and find out more about the project visit www.midcoast.nsw.gov.au/reportcard

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