Denmark’s Wilson Inlet feeling the impact of climate change as revealed in new report

The Wilson Inlet is feeling the effects of climate change, with the opening of the sandbar at risk of becoming less frequent, according to a new environmental report.

Water Minister Dave Kelly last week released the Wilson Inlet Condition Report 2016-19, which provides an insight into the health and water quality of the inlet.

The report outlines the findings of the Department of Water and Environmental Regulation’s four-year monitoring program.

The health of estuaries can be affected by excessive nutrient inputs from catchment land uses and climate change impacts such as reduced river inflows, increased temperatures, ocean acidification and rising sea levels.

Denmark’s rainfall has declined by 20 per cent since 1940 and by 7 per cent since 2000, according to the report.

Between November 2018 and April 2019, there was no water flowing in from either the rivers or the ocean and high summer evaporation rates decreased water levels to the third lowest on record.

Reduced rainfall and decreased river flow have put environmental stress on the estuary system.

“Nutrient pollution and climate change are the biggest risks to the health of estuaries along the south coast of WA,” the report said.

“We have already observed dramatically reduced river flows which directly impact the sandbar opening.

“Continued lower river flows could make the annual sandbar openings less likely to occur.”

The Wilson Inlet sandbar is artificially opened in winter to reduce flooding of nearby low-lying land and in summer the sandbar closes naturally due to waves carrying sand back into the channel.

“We don’t know the consequences successive closed years could have for fish species which rely on marine recruitment, such as King George whiting, snapper or Australian herring,” the report said.

“Their populations may see a drastic decline if the sandbar remains closed for too many years in a row.

“Water and migratory bird populations could also be affected, as they rely on particular water levels at the time of breeding and feeding.”

Rising sea levels and an increase in storm surges — as a result of climate change — could make management of the sandbar opening more difficult in the future.

“Consequently, the sandbar may close earlier, leading to very low water levels during summer and autumn, making it even harder to reach a water level that would allow a successful opening in the next year,” the report said.

“The frequency of summer and autumn storm events is predicted to increase, these storms will deliver nutrient loads to the inlet when it is closed to the ocean and at times when temperatures are warmer, potentially triggering increased microalgal activity and macroalgal growth.

“Both would reduce the light available to seagrasses, causing a decrease in the extent of their meadows, which would have flow-on effects for water quality and the ecosystem.”

Despite the effects of climate change, the report indicated the inlet had shown resilience to nutrients entering from nearby agricultural and residential land.

“Although water quality is currently good, climate change together with the continuing supply of nutrients from the catchment are ongoing threats to the health of the inlet,” according to the report.

The Wilson Inlet is also known as Nullaki to the local Noongar people, meaning “narrow place of seagrass” which the report says could indicate that seagrass has been an integral part of the estuary for a long time.

There is only one seagrass species in the Inlet called Ruppia which grows in extended meadows in depths up to 2m covering about 43 per cent of the inlet.

Since 2007, there has been an 11 per cent decrease in the area covered by seagrass, mostly around the bay closest to the town site of Denmark and in the deeper areas in the east of the inlet.

Mr Kelly said the report gave them a better understanding of how to better manage the inlet.

“The partnership with the Wilson Inlet Catchment Committee allows us to implement on-the-ground actions to protect the ecosystem,” he said.

“The Wilson Inlet supports a wide range of economic and recreational activities and it is encouraging to see that nutrient levels have remained stable over the past 20 years with monitoring and management.”

Through the State Government’s Healthy Estuaries WA Program, the department will partner with the WICC, Department of Primary Industries and Regional Development, farmers and industry to help protect and improve the health of the estuary.

Warren-Blackwood MLA Jane Kelsbie commended the WICC on their efforts to protect the inlet.

“The Wilson Inlet, or Nullaki, is an important water source that supports grazing, viticulture, horticulture, dairies and forestry in our community,” she said.

“It also supports a number of tourism and recreational activities, enjoyed by visitors and locals alike.

“While there has been some environmental stress caused by reduced rainfall and rising sea levels due to climate change, it is pleasing to see that that the Wilson Inlet has shown good resilience to nutrients entering from agricultural and residential land.”