King County’s urban rivers are showing signs of improving health. Just ask the insects.



Diane Yeh, King County’s assistant environmental director, used hand tools Tuesday morning to stir up the muddy sediment on the bed of Thornton Creek and release writhing earthworms and pea-sized freshwater clams into nets.

The city’s flow begins at the Shoreline, weaving through neighborhoods where the stench of sewage has drawn attention in the past and Northgate, once buried beneath a mall parking lot but later spilling into Lake Washington. ing.

Despite habitat degradation over the past century and a half, a recent study led by King County environmental scientists suggests that streams like this one are more resilient than once thought. .

For the past 20 years, researchers have used nets and bottles to collect river bugs from more than 100 sites across dozens of watersheds in King County. The creatures are sensitive to changes in watersheds, such as rising water temperatures, increased pollutants, and sediment associated with forests cleared for apartments and fields paved for parking lots, leading scientists to It can tell you a lot about health.

Remarkably, some of King County’s streams are recovering. Of the 120 research sites monitored by the county, about a quarter are now in better health than they were at the start of the study, while about 3% are in worse health.

Across the county, researchers observed an overall improvement in the biological condition of streams and the type and abundance of stream insects. They found this improvement in 16 of the 38 watersheds, but only one, Deep Creek, showed a decline.

Coal Creek, Issaquah Creek, Little Bear Creek, Lower Cedar River, and Lower Green River are among the watersheds that have seen improved biological conditions over the past 20 years.

“The reason we didn’t necessarily believe our results initially is because if you look at the size of the basins, many of these basins had increased development over the course of our study,” Kate said.・Mr. McNeil stated. He co-authored a recent report on these trends and is the county’s environmental scientist.

County Executive Dow Constantine and Seattle Mayor Bruce Harrell celebrated the results Tuesday at a small news conference in Thornton Creek.

“The development that’s happened in the last 20 years has been less harmful and less impactful than the old-style development,” Constantine said as cars passed by nearby 95th Street. “I think it has to do with regulations, building codes and new technologies to be more respectful of the natural environment.”

For thousands of years, Coast Salish people have managed the coniferous forests, freshwater roads, and vast estuary nurseries for young salmon that surround what is now King County. With the arrival of white settlers in the mid-1800s, an intensive mining process began. Forests were flattened for timber, floodplains were diked and drained for agriculture, rivers were rerouted and dried up, and industrial waste was poured into waterways.

By the 1920s, very little lowland forest remained. By the 1950s, the county’s waterways were filled with sewage sludge, toxic substances, and other unregulated pollutants. In the 1960s, river protection began to be slowly rolled out.

Dating back to the past few decades, new regulations have mandated the treatment of stormwater runoff and restricted development in urban growth areas. The Coast Salish Nation is leading investment in projects that restore farmland and hotels to wetland estuaries, reforestation along riverbanks, restore the river’s natural flow, restore spawning habitat, and support local and state governments. The government is also participating.

From 2001 to 2019, impermeable cover, i.e., paved or impervious surfaces, increased from 0 to 12.7% across the study basins. King County’s population jumped from 1.76 million to 2.25 million from 2002 to 2021.

The scientists expected that growth would reduce the biological conditions of the rivers they studied.

Not by insects, but by the Benthic Index of Biological Integrity (B-IBI), which in scientific terms is a measure of a river’s health based on the type and abundance of different benthic invertebrates.

“The best way to get a comprehensive picture of how rivers are doing and what they should be doing is from a living perspective,” McNeil says.

It’s expensive and difficult to chemically quantify all the problems happening in urban watersheds, but longtime University of Washington professor Jim Carr suggests scientists can ask living things questions instead. McNeil said he led the development of the index. It aims to figure out whether the creatures that are supposed to be there, the creatures that we know are supposed to be there, are there. So how are they doing?

Insects are also important to fish. Young salmon rely on insects to fatten up before traveling to seawater and eventually returning to spawn.

If the insect community indicates that the river is unhealthy, then the fish probably aren’t doing well there either.

But fish have their own set of requirements, so scientists can’t accurately say that if the river the bugs are showing is a high-quality river, there will be fish there too. Only fish can tell if toxic levels of certain chemicals are present, lack of vegetation along rivers contributing to unsustainable temperatures or insufficient trees in river habitat .

Investigating bugs can tell you about the state of the river, but it cannot explain why it is the way it is. So scientists began digging into how other environmental conditions changed during this time, which could help explain those trends and provide future test questions.

They expected that as temperatures rose, more insects would become resistant and fewer insects would be sensitive to rising temperatures, but the data did not reveal such a pattern. Some insects, such as caddisflies and stoneflies, that are sensitive to environmental stressors such as heat, sediment and pollutants, are not as abundant as they once were in many watersheds, but are increasing in some watersheds in the county.

Meanwhile, more resistant insects, such as flatworms and fly larvae, have declined, suggesting conditions in the river are improving.

Climate change may have some influence on these trends, but it is probably not the main factor.

The positive trends scientists are seeing aren’t just occurring in one type of site. It’s not just happening in cities and suburbs. It’s happening in forested suburbs, urban basins. Beth Sosik, the county’s water quality planner and co-author of a recent report on trends, said all boats are rising at the same level.

Another county report compared watersheds with similar levels of development and found that the more recently developed watersheds had higher bug scores, suggesting new regulations could help protect and improve river conditions. This suggests that there is a possibility that

Mr Sosik said a reduction in the impact of fine sediments, water pollution and improved river flows could be driving this trend. But not all streams are doing well. Urban development and climate change continue to threaten some sensitive bugs and the overall health of the river.

Although scientists have not yet pinpointed the factors contributing to these improvements, the study suggests that urban rivers should not be abandoned and may be more resilient than previously thought. Some people say

“A cynical person might look at these trends and say, ‘Well, we’ll just wait for the flow to get better,’” Sosik said. “My conclusion from this report is that this set of safeguarding regulations and practices that we have put in place over the last 20 years is making a difference and we need to keep it that way. is.”

“This also tells us that we can move the needle, so we should do more,” Sosik continued. “Urban rivers can recover more than we thought.”

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