Drought threatens biodiversity of the river and laguna

By Camille Escovedo, Staff Writer, SoCoNews, August 4, 2021

creek santa rosa laguna

The drought is largely impacting surface water, lowering rivers and creeks, but the longer the drought lasts, the more groundwater depletes, according to Dr. Wendy Trowbridge of the Laguna de Santa Rosa Foundation. A shallow area of the laguna is pictured here on Saturday, July 31, 2021. (Photo Camille Escovedo)

The drought makes life hard  for humans and the Russian River’s biodiverse ecosystems. Life in and along the river persists under the pressures of human practices and a more extreme climate, according to local restoration experts.

On April 21, Gov. Gavin Newsom came to Lake Mendocino and proclaimed a state of emergency regarding the drought in Sonoma and Mendocino counties. The Sonoma County Board of Supervisors followed suit on April 27 to declare a drought emergency across all its cities and special districts.

According to Sonoma Water’s current water supply data, Lake Sonoma was about 50% of its water supply capacity on July 23, capable of holding 245,000 acre-feet of water, but storing approximately 123,000 acre-feet of water. Per the agency’s online update, that’s “the lowest storage for this date since the reservoir began operations.”

Lake Mendocino fares worse, reported by Sonoma Water to store 26,000 acre-feet of water in a 81,063 acre-feet target supply curve, only 32% of its water supply capacity.

The dry spell over the Russian River watershed is no less than historic in its second dry year in a row, following a dehydrated 2020 with lower reservoir capacities now than in the 2013-14 drought, according to Sonoma Water.

Drought strains life and biodiversity in the Russian River Watershed

Two local restoration experts spoke of the way drought and human practices together interrupt riparian ecosystems.

Birkin Newell, an aquatic biologist and Russian Riverkeeper’s education and restoration director, has found significant changes in riverbed plant communities and, of course, outlooks for the salmon.

In the short term, the drought threatens the endangered Coho salmon, in addition to chinook salmon and steelhead trout, with streams where they spawn, like Mill Creek, running dry.

“The creeks are not continuous anymore. There’s a lot of disconnected dry areas between isolated pools,” Newell said.

“And then, of course, the long-term effects of that in this drought is those fish will probably not survive and they probably won’t go out to sea and become adults and come back in a few years to spawn in that same stream,” he added.

Furthermore, less precipitation has meant longer wait times for the Russian River to rise and open the water channel up to the ocean in Jenner, allowing salmon to return to the streams of their birth, “and those little streams might not be connected to the main river because of the low water,” Newell said.

The potential for a big drop in numbers includes that two fires have also blazed in the spawning channels, warming waters and contributed stressful living conditions for the fish.

“That’s probably our biggest concern in the Russian River watershed, is the loss of salmon species because of this drought and fire combination. It’s really a doozy,” Newell said.

Invasive plants seize opportunity in drought to dominate in biodiverse ecosystem

Invasive, non-native plants outcompeting native plants during the drought also risk biodiversity in and along the river. Two such threats are mustard and ludwigia, a water primrose, according to Newell.

The water level is low enough that exposed gravel bars have been dry for long enough that weeds, like mustard, are pioneering them and where there once was a channel of water, he said. “This water primrose is really choking up the channels and causing big problems as well,” Newell said, as ludwigia can survive as the water level drops.

“I hate to throw vineyards under the bus here or blame them, but vineyards often use non-native plants like mustard in between the grape rows,” he said. The European mustard seeds enter the waterways and pioneer new habitats where the water has dried up.

Takeovers of invasive plants can disrupt symbiotic relationships and homogenized, unbalanced plant communities offer less attractive areas for shelter and food for various organisms. For example, a gravel bar dominated by mustard isn’t as suitable as a complex habitat with baby trees, different shrubs and ground cover plants.

“Biodiversity is super important for the health of the ecosystem because having more different kinds of species in an environment creates more opportunities for species above them in the food chain to find food,” Newell said.

It means organisms can move on to another species for food if one species declines in numbers or becomes diseased, according to the director. When annual weeds die off, there are fewer options left to eat.

“A stronger, more biodiverse habitat has a lot more options,” Newell said, across life that has adapted for it. “So, these native plant species are blooming throughout the year, they’re really adapted to drought and they are going to be more resilient through a two-year drought than we’re having now compared to more invasive species that are going to die off later this summer because there’s no water.”

Wetlands, though weakened, can act as protection in more extreme weather

Dr. Wendy Trowbridge is the director of restoration and conservation science programs at the Laguna de Santa Rosa Foundation. She sees how the drought and human practices like draining the wetlands can sabotage what the laguna can do to buffer impacts of extreme weather, intensifying under climate change.

The wetlands serve as a floodplain, absorbing more water in wet years so storage remains during dry years. When the river floods, the laguna stores water near Sebastopol, acting as flood protection for Guerneville downstream.

“I think the predictions for what’s going to happen is basically what has happened in the last couple of years,” Trowbridge said. “We’re going to have bigger floods and longer droughts. So, we’re basically going to have the same amount of precipitation, but it’s going to come all at once in a super wet year and then not for multiple years after that.”

Further, the Santa Rosa Plain is home to vernal pools that fill up in the winter and retain water in the clay soils underneath until spring, when they dry up slowly and wildflowers bloom around, Trowbridge said.

Housing extending into the plain has destroyed some vernal pools, she said, where in the spring an endangered tiger salamander reproduces and where three endangered flower species also grow.

Vernal pools recede into grasslands in the summer and fall until the rains return, depending on the rainfall from that same year. Trowbridge said they hardly filled with this year’s precipitation and that some endangered species monitored by the Laguna de Santa Rosa Foundation have disappeared in some places.

Trowbridge said she hopes the rain will come and some of their seeds will have survived in the soil, but they don’t know what next year holds for those species.

“The impacts this year are mostly in surface water. And so, the rivers are lower, all the creeks flowing out of the Mayacamas are drying up sooner than they would ordinarily,” she said. The drought’s effect on groundwater comes back to bite later.

While humans drill wells deeper and trees send their roots further underground, the lack of rain means less water absorbing into the ground and flowing down underground from the mountains to the laguna over years of time, she said.

If the two-year drought continues for five years, there will be less groundwater trickling down to fill up the laguna again.

Resilient wetlands challenged to purify water under current conditions

Wetlands are known to both improve water quality and act as natural sponges that provide flood protection. However, humans developing the area in the 1800s and 1900s drained much of the Laguna de Santa Rosa and established agriculture there and in the Santa Rosa Plain, according to the Restoration Vision for the Laguna de Santa Rosa of April 2020.

The San Francisco Estuary Institute partnered with the Laguna de Santa Rosa Foundation to create the document that also noted about 60% of the wetland habitat was lost to land and water changes, reducing the laguna’s capacity to foster native biodiversity.

“I feel like the wetlands, they’re sort of adapted to hanging on in situations like this, and so mostly we’ve been talking about water quantity, like how much water there is. But water quality is also a huge issue in the Laguna,” Trowbridge said of the wetland’s ability to purify water during the drought.

One issue is the debilitated wetlands cannot process the unusually high amount of excess nutrients, from treated wastewater, dairy farm runoff and other activity in the watershed.

Trowbridge said plants, algae and other life take up the nutrients that would be pollution and essentially become fish food, feeding in turn other animals around the food web.

Now that that system has become unbalanced, the overload of nutrients leads to algae and ludwigia overgrowth that take up oxygen from the water when they decompose, to the point fish don’t have enough dissolved oxygen to breathe and thus disrupt the food web, she said.

According to Newell, algae blooms even more in warm water, like shallow waters due to low flows under a drought. He said harmful algae has proliferated earlier than usual this summer, at the start of the season rather than the end of summer.

“One of the things that the Laguna Foundation is trying to do is restore the capacity of the wetlands to treat the water and remove all these excess nutrients,” Trowbridge said.

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