If you restore aquatic habitat in the Sacramento-San Joaquin Delta, will the fish come back?
That’s the basic question behind a major restoration project planned at Prospect Island, a 1,600-acre (650-hectare) tract of levee-protected farmland near Rio Vista that is now owned by the state.
The California Department of Water Resources and Department of Fish and Wildlife plan to breach the levees to restore tidal flow to the island, and reshape the terrain to create the kind of shallow habitat that could attract Chinook salmon and delta smelt. The agencies recently released a draft environmental impact report on their project.
The Delta, the largest estuary on the West Coast of the Americas, provides freshwater to 25 million Californians and some 3 million acres (1.2 million hectares) of farmland. The estuary was once a mixture of vast floodplains, wetlands, and open-water habitats, rich in fish and other wildlife that enjoyed more than 1 million acres of unique inland tidal habitat.
Most of this was converted to farmland more than a century ago by construction of levees and urban development. This created about 70 islands with some of the world’s richest farmland. But it eliminated the shallow flooding by tides and snowmelt that fish need to feed and breed.
Water extraction by state and federal export systems sucked away a lot of the freshwater that remained and reversed its flow, further jeopardizing habitat for salmon and smelt, which are federally protected endangered species. The additional influence of California’s ongoing drought has pushed these fish to the brink of extinction, resulting in further limits on water extraction.
Prospect Island is one piece of an 8,000-acre (3,250-hectare) restoration requirement imposed eight years ago under the federal Endangered Species Act. To understand what’s at stake, Water Deeply spoke with Jon Rosenfield, a conservation biologist at the Bay Institute whose post-doctoral research was on the ecology of Delta fishes.
Water Deeply: What’s special about the location of Prospect Island?
Jon Rosenfield: Prospect Island is located sort of near the bottom of the Yolo Bypass and in the vicinity of Cache Slough. That’s a pretty interesting area ecologically in the Delta because the Yolo Bypass, when it floods at the right time of year, serves as really good habitat for juvenile salmon.
There are at least two different reasons for that. When water spreads out on the floodplain, it’s like a big solar collector and the water’s not very deep, and it warms up. As a result of both of those things, it produces a lot of food, and the salmon get the food as they’re migrating downstream to get to the sea. That allows them to fatten up and grow better, and makes them more fit to survive in the ocean. That floodplain then drains down into this Cache Slough area and it’s carrying a lot of fish and it’s carrying food with it as well.
So the idea for Prospect Island is, let’s continue to build in what’s good about this area and make more shallow-water habitat. It’s being proposed as beneficial to migrating salmon and to delta smelt.
Water Deeply: Are there other potential benefits?
Rosenfield: Yes, tidal marshes are certainly good habitat for things other than these endangered fish. There’s no question waterfowl and shorebirds will enjoy this area.
Another thing they hinted at is the idea of restoring a wetland that has a lot of plants growing on it, and then the land surface is rising over time as the plants die on it, and it also becomes a carbon sequestration project. That’s what the Delta used to be: this giant carbon pool of peat islands and peat bogs.
Water Deeply: How feasible is this idea of a restoration site producing fish food?
Rosenfield: There are a lot of problems with that assumption. We don’t really know that it’s even theoretically going to happen. Even hypothetically, it might work exactly the other way. Along with that carbon sequestration idea is the fact that plants grow and die there, and organisms move in and die there. And those organisms consume food. So is it a source of food or a sink? That needs to be studied.
This idea that you can build marshes and export food is speculative at best. In order for it to work the way they describe you’ve got to restore, like, tens of thousands of acres of tidal marsh habitat. And the rules of the [Endangered Species Act] biological opinion are only intended to prevent extinction. They’re only intended to undo the damage created by the water projects.
Water Deeply: What other problems do you see with this idea?
Rosenfield: Another problem is, well, we have these invasive clams. What’s going to keep the clams from occupying this habitat? The freshwater invasive clam Corbicula could invade this site and suck all the food out. So, how do you know that you’re not just making more food for clams?
The next problem is, how do we keep the invasive plants out? Invasive plants like egeria, they create habitat for predators. They also scrub the water column of sediment. And sediment – turbidity in the water – is something delta smelt and salmon and all these other native fish rely on as cover from the predators.
A third problem: If predators are the problem, how do you keep the predators out of this habitat? How do we make a site that will grow food, allow the fish we want to come on the property and eat that food, without also just recreating the same dynamics that were causing the problem in the first place?
Water Deeply: So despite all of this, do you think the project is worth undertaking?
Rosenfield: I don’t want to create the impression you just can’t do this, it’s not ever going to work. But it’s not a matter of we’ll just knock down a levee and the water rushes on to the land and all the problems are solved. We really need to design these sites to hit a sweet spot between food production and export and the kind of environment that supports the native species and not the non-native species. That assumes there is a sweet spot. There may not be.
Water Deeply: Does this location present any unique risks?
Rosenfield: One thing to say about this site is that it is in this area that is currently the last stronghold of delta smelt. Given that we don’t necessarily know how this will work, and we also don’t know a ton about how delta smelt will react to it even if it will work as designed, there’s a question about whether we should be monkeying around in the last place that this fish lives. It’s like we’re doing this construction project around mom’s china cabinet.
From my point of view, it’s worth it to do these kinds of projects to see if we can benefit native fish species. But I’m a little uncomfortable with earth-moving projects and changing the hydrodynamics as well. This project goes in and modifies Cache Slough with the intent of making things better. Given that we don’t know a ton about delta smelt and we don’t know a ton about what will happen with this project, that’s a risky proposition.
Water Deeply: With all that in mind, where do you think is the best place to spend limited habitat restoration dollars?
Rosenfield: I would focus on Suisun Marsh. There’s this whole south side of Suisun Marsh where there could be more work done on restoration. There, this notion of food export actually begins to make a little more sense.
If we’re going to be able to export food from a tidal event, you want the food to be very close to the fish you want to feed. That area is right close to where the [smelt] adults are. It’s an area that’s less affected by the invasive predatory fish – most of the invasive bass species don’t live in salt water. Also there’s cooler water there because it has this oceanic water flow and a wind influence. It’s also more turbid there and the fish like turbid water. Suisun Marsh makes a heck of a lot of sense.
The state says a lot of stuff about how they’re going to do tens of thousands of acres of habitat projects and eliminate the bureaucracy. My reaction to that is: Well, how are you doing on that with your 1,600-acre project that was assigned eight years ago?
It’s coming on the end of 2016 now and we’re just about to produce the draft EIR [environmental impact report] for one project, and I think it’s the first project to satisfy this 8,000-acre requirement. We need a bunch of projects that are of this size where we can try our ideas and then study the heck out of them to see if they work. If this is going to be successful, we need to figure that out quickly and build a lot more that work. We gotta get on it.