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Lady Bird Lake

Despite zebra mussels, Austin’s waterways seeing a recovery trend

Monday, May 20, 2019 by Jessi Devenyns

The news is full of horror stories about zebra mussels invading intake pipes and sediment causing city water to be of questionable quality. Yet statistics show that, overall, the waterways of Austin are regaining their health.

According to Mateo Scoggins of the Watershed Protection Department, “We’re seeing an increase in overall health in these systems, which is remarkable.”

Scoggins, who presented the findings to the Environmental Commission at its May 15 meeting, said Watershed Protection measures the quality of the water through myriad variables in two monitoring programs: the Environmental Integrity Index, which monitors 125 creeks and streams, and the Austin Lakes Index, which monitors Walter E. Long Lake, Lake Austin and Lady Bird Lake.

In both indices, the health of the watersheds is monitored across regulatory environments but the results are compared between watersheds that were primarily developed before the 1986 Comprehensive Watershed Ordinance and those that were developed after. As Scoggins explained, that’s because “the pre-regulatory sites are always lower scoring.”

Although these sites are generally slower to recover than those developers built out under the auspices of Austin’s newer watershed ordinances, all of the watersheds have seen improvement in water quality over the last decade.

However, Scoggins warned not to take these indices at face value. Individual metrics that make up these trends tell unique stories. For instance, phosphorous levels in creeks have been dropping since 2010, while nitrate levels have been rising. “And that’s of concern, as you can imagine,” Scoggins told the commissioners.

Similarly, E. coli has seen positive trend growth. No single source can be attributed to the rise in the bacteria, but Scoggins suggested it likely has to do with increased human, animal and infrastructure contact with Austin’s waterways. He noted that this is particularly plausible since the most elevated concentrations are in the urban watersheds.

Nevertheless, “Austin is actually on longer-term ecological recovery,” he said. He attributed the damage to the boom in agriculture at turn of the century and heavy development in the 40s and 50s.

While things are on the up and up for now, commissioners noted that new invasive species like zebra mussels have the potential to change the ecology of the entire system. In addition, climate change poses a very real threat to historical ecological trends.

“I think it’s unlikely we’ll see these trends continue,” Scoggins noted. “The decisions that we are making right now will affect these trends over the next 10 or 20 years.” Likewise, he noted that there is a natural point at which improvements will level off as ecosystems reach homeostasis.

As scientists wait for new data, Austinites should take a moment to enjoy the rebalancing of the streams and lakes of the capital city. After all, no one knows what the future holds. “That’s the million-dollar question,” Scoggins said.

Photo by LoneStarMike from Wikimedia Commons, made available by a Creative Commons License.

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