To picture a watershed, think of a leaf. From a single stem, moisture flows outward through a network of capillaries branching, with increasing complexity, into a filigree of tiny veins. Reverse the process – and magnify it – and you have an approximate picture of a watershed. Rainfall that does not seep into the hills runs down into the streams. Streams flow into the river, and the river flows into the bay. Along the way, water seeps through the streambeds into the aquifer beneath. The whole system feeds and is fed by a network of living species ranging from the tiniest mayfly all the way up the food chain to us. That is a watershed. What happens to one part affects all the others.
Physically defined, a watershed is an area that cups the rain and sends it down through a network of creeks and streams into a river and outward to the ocean or a bay. Sonoma County has two: the Russian River watershed, which drains into the Pacific Ocean, and the Sonoma Creek watershed, which drains into the San Pablo Bay. When ecologists talk about restoring or protecting even the smallest stream, they are talking about protecting the whole.
On a recent warm, October day, geomorphologist Lisa Micheli, PhD, Sonoma Ecology Center’s Restoration and Stewardship Program manager, joined Michael Bowers, a fisheries biologist with Southern Sonoma County Resource Conservation District and Gordon Becker, of the Center for Ecosystem Management and Restoration (CEMAR) in Oakland, to examine a Glen Ellen stream they have cited as an ideal candidate for a project that would restore the creek’s natural flow and its potential as a habitat for fish. The group’s hope is that with sufficient financial support, the property, now privately owned, can be purchased and set up as a little park, along the lines of an open space district, that would offer habitat for steelhead, a recreational opportunity for the community and a laboratory for environmental education, as well.
They want to be able to study the health of steelhead in this and other creeks. “There’s a whole native fish assemblage in these creeks,” said Bowers, “but for a number of reasons, because steelhead is an endangered species, people use it to measure the health of the stream. If the stream can support the entire steelhead life cycle, it’s a good measure of the health of the stream.”
Micheli explained why. “To the ecologist, salmonids, particularly steelhead, are considered ‘indicator species.’ By noting their condition, scientists can tell the health of the stream, from primary [species] all the way to the top of the food chain.” Becker agreed. “If the top of the food chain’s not making it, there’s something wrong with the bottom of the food chain.”
What can go wrong in a watershed?
From the Rancho de Sonoma resident who worries about arsenic levels in his well water to almost any child picked at random, the first thought that springs to mind when asked to name a water problem would likely be: pollution. Bowers said the streams in the Sonoma Creek watershed used to be called “Pacific streams,” but now, even though they have not geographically relocated, they’re called “urban streams.” Urbanization of streams creates reciprocal problems. Urban wastes pollute the streams, over-appropriating depletes them and building on floodplains crowds them, with flooding as a result.
But there are less visible problems, such as sedimentation, which occurs as a result of hillside erosion. “Sonoma Creek is listed as being polluted by excess fine sediment,” said Micheli. This is a problem because fish need gravel to lay their eggs in, and if you have too much sedimentation, the spawning medium gets covered up and their breeding is disrupted. “So they’re a pretty sensitive indicator of [too much sedimentation],” she said.
Proper stream temperature is another vital feature. In a healthy watershed, the forest canopy keeps streams shady and cool. “If we lose the canopy,” said Micheli, “the stream heats up and becomes inhospitable for the fish. The stream then becomes hospitable to algae blooms, which attract more non-native, warm-water tolerant fish.”
Unseen, largely unmeasured, but essential to human habitation, is groundwater. The river and streambeds form filtration systems for water flowing in, and the groundwater reciprocates, letting enough water seep up into the streambeds to maintain fish. Micheli pointed to areas in the dry streambed where water bubbled up through. “If you draw down the groundwater,” she said, “it reduces the amount of water available for the stream, as well.” The demand for groundwater is high. So how does the study of fish in a tiny stream help the whole, when part of the whole is as huge as agriculture?
“All of our agriculture is on groundwater,” she said. “All of it. That aquifer is our bank account of water for humanity. I think the point is: If our fish aren’t doing well, our bank account isn’t doing well. If they die out, they’re just telling us we have a credit problem!”
