Steve Monismith tracks water in the San Francisco Estuary

Monismith said that diverting so much water for human use alters the physics of the San Francisco Estuary. His research shows that the distribution of salt in the water changes, which affects the current – and the life cycles of local fish.

Steve Monismith: This network of islands and marshes – what do we want it to be, as a natural functioning system, and what’s realistic given the fact that there are 38 million people living in California using water that comes from there?

Steve Monismith of Stanford University is an expert on fluid mechanics, or the way water moves in the environment. He studies the San Francisco Estuary, a mix of salt and fresh water where two of California’s rivers meet near one of America’s most populous cities, and flow into San Francisco Bay.

Steve Monismith: So what affects that flow are two things. The big driver is the natural variability of precipitation, and the second thing is diversion of that water for use in agriculture, for us to drink.

Monismith said that diverting so much water for human use alters the physics of the San Francisco Estuary. His research shows that the distribution of salt in the water changes, which affects the current – and the life cycles of local fish.

Steve Monismith: Most estuaries are nurseries for fish that people care about. So protecting those estuaries is a way of also protecting coastal fisheries.

He added that California residents might not be aware of the direct impact they have on these local waters and fish.

Steve Monismith: The water that we put onto our lawns is water that’s not going into the estuary to support the ecosystem. So the things we do as individuals have a larger effect on these systems.

Monismith also noted that estuaries are rich in biodiversity.

Steve Monismith: Estuaries have lots of different kinds of organisms living in them, and I think that it’s important to protect regions of high biodiversity because, for example, there may be some organism that produces some chemical that can be used to cure pancreatic cancer.

Managing the flow of fresh water into estuaries is important, Monismith says, for keeping them healthy.

Steve Monismith: We know that changing flow affects these estuarian systems and so we should be thinking about for ourselves, how does our own use of water affects what’s happened?

In northern California, water flowing to the San Francisco Bay area is used by farmers, businesses, and homeowners. How much fresh water is siphoned off before it reaches the ocean, Monismith says, affects the Bay ecosystem.

Steve Monismith: In the local sense, for example, we talk a lot about this diversion of water from the delta by agriculture, yet the people who live here in Palo Alto, where I live, we get water that’s also diverted … so the water that we put onto our lawns in Palo Alto is water that’s not going into the estuary to support the ecosystem. So thinking about that personal connection, of the fact that the things we do as individuals have a larger effect on these systems.

While abundant fresh water is vital for homeowners and for industry, Monismith cautions that we must consider the environmental costs of our water use.

Steve Monismith: Be careful about water use. The other thing is, on a larger scale, we have to also have politicians who are willing to own up to making hard choices, telling people that if we really want to consume this water, you can’t expect a system like the Bay delta to function in a pristine fashion – you can’t promise both, that there are some trade-offs to be made.

Beth Lebwohl