BAY DELTA SCIENCE CONFERENCE: Dark Carbon and a Return to Abundance: How Detrital Floodplain Food Webs Can Help Recover Endangered Fish

In the pre-development Central Valley, winter-spring flooding once created a vast mosaic of productive wetland habitats that teemed with fish and wildlife. A major driver of this wildlife abundance was terrestrial carbon made available to aquatic food webs when floodplains were inundated.

Nineteenth and twentieth-century investments in drainage and a network of dams, canals, and levees transformed the Central Valley’s fertile floodplains into one of the world’s most productive agricultural regions. This system of water infrastructure also sped water off the landscape and cut off over 95% of the Central Valley’s floodplains from river channels. As a consequence, aquatic ecosystems no longer recruit the carbon (stored solar energy) needed to sustain robust food webs build abundant fish and wildlife populations. Put simply, levees starve aquatic ecosystems. Recovery of endangered fish populations will likely be impossible without first recovering some of the landscape-scale ecological processes which once supported historic abundances of native species.

At the 2018 Bay Delta Science Conference, Dr. Jacob Katz, Senior Scientist with CalTrout, gave this presentation focusing on how multi-species, multi-benefit floodplain management can help cultivate ecological solutions on working agricultural landscapes that will increase diversity, resilience and abundance of native aquatic species.

Dr. Katz began by saying he would be talking about flow – not just the flow of water across the landscape, but how the flow of water is intimately correlated and related to the flow of energy from the sun that comes across and through the landscape into the aquatic environment. Before human development, the Central Valley was a vast and dynamic mosaic of different kinds of habitat types; it was a big wet bowl or a bathtub; it was really defined by not any one of those habitats but by a tendency to stay wet by flood. He noted that the very names of the counties were the names of the flood basins before they became political jurisdictions.

The Sacramento Valley and the San Joaquin Valley were millions of acres of wetlands, of wet land, and then we drained it,” he said. “In the time really before we really knew how rivers worked, before we understood what fish need, way before anyone was thinking about fish food, we fundamentally altered the way the water flows across that landscape.”

It was done in a pretty simple way: building levees by piling dirt by the river; however, building levees fundamentally alter the landscape by divorcing the land from the water and pushing that water off as quickly as possible. Levees create a massive engineered exodus of the water off the landscape, which does have the benefit of flood protection and being able to control the agricultural landscape to make it one of the most productive and one of the most profitable on earth.

This is not necessarily a bad thing, but it happened in the time when we knew little about function,” he said. “We knew little about how rivers actually work. It’s ubiquitous; it’s not just levees, think about the landscape – a school play yard, a Safeway parking lot, an urban stream, your backyard, a farm field, every bypass – they all engineered to drain as quickly as possible. Humanity appears to abhor a puddle. Don’t let it slow down, can’t let that happen, get it off. We’re anti-beavers.”

Dr. Katz acknowledged that we’re not going back; the cities and farmlands will never be waving fields of tules 100,000 acres or more in extent.

We have one of the most altered and most highly managed landscapes on earth right here in the valley, and without it, we would not be right here,” he said. “But that alteration of flow pattern has had some unintended consequences. Well over three-quarters of fish in the state are in a pretty steep trajectory towards places we don’t want them to go. And why? Because they no longer recognize they systems they evolved in and that they are adapted to. They no longer recognize those patterns of flow across the landscape. And it’s our job to allow them to recognize them again and to allow them to thrive and flourish means allowing fish and other native critters to use their tools and their keys to unlock those watersheds which they evolved in and to which they are adapted.”

This is especially true of all four runs of Central Valley chinook, which are specifically adapted to the flow patterns that are specific to the Central Valley, and when those fish have a chance to spread out with floodwaters, there are really dramatic results, Dr. Katz said.

When the river stage is high enough, it flows over Fremont Weir and spills into the Yolo Bypass, and that habitat compared to the adjacent Sacramento River has very different results for fish. The fish on the left of the photo (lower, left) spent three weeks on the floodplain; the fish in the middle spent three weeks in the Toe Drain which is canal in the Yolo Bypass, and the fish on the right spent three weeks on the floodplain. “The growth is pretty extreme,” he said. “It’s very clear; the food is on the floodplain. Incredible growth – 700% growth in three weeks.”

The food energy is not in the Sacramento River; there’s a bit more food energy in the canal, and on the floodplain, there is an amazing density of protein, of solar energy embodied as fish food, Dr. Katz said.

All energy starts in the sun. That’s what these floodplains are – they are solar collectors, and they do it all year round,” Dr. Katz said. “In summer, those terrestrial floodplains and those agricultural fields are gathering sunlight, and taking hydrogen and carbon and putting it together and turning it into sugar. … In winter, the same thing is happening. Algae floating near the surface of the water is capturing that winter sunlight. If you spread it out, suddenly you have exponentially greater area to capture that energy and to get the energy into the water so fish can use it.”

We’re starting to understand is that sunlight makes sugar, sugar makes bugs, and bugs make fish, but we’ve fundamentally altered the underlying landscape in such a way that we’ve severed this energy flow, he said. “There is a relationship between energy and mass, and in this case, what we’re talking about is that the energy that comes into a system comes to a very great extent from the act of spreading water out and slowing it down. When we’ve lost 95% of our floodplains and wetlands, why are we surprised when we end up with 5% of our fish biomass?

We’ve built this system and so there is the potential to build ourselves out of it and to understand the natural processes that build rivers and make fish, and integrate that back into the way we manage the system, said Dr. Katz. “Endangered species to a very great extent are not an inevitable consequence of human development; they are a direct consequence of a system built before we understood what fish need and how to manage the system and how to manage rivers.”

Dr. Katz said that it’s time for levees 2.0; 150 years is long enough to divorce the terrestrial landscape from the water. Where there once was a very shallow slope and a transitional zone between the land and the water, what is there is now a very precipitous zone between.

Let’s create puddles everywhere we can and not do this in an ad-hoc way,” he said. “Let’s understand that we’re doing it in the midst of a managed landscape, and then we can use the very same infrastructure that we now use to irrigate, to divert, to protect from flood, and to create puddles where it makes sense. That’s on the floodplains for sure. On the other side of the levees is possible; even though fish aren’t going to get there, the fish food can be made and sent back into the river. Let’s integrate the floodplain back into way that we manage our waters. Let’s stop squandering the incredible natural wealth that happens in that puddle.”

When the water is slowed and allowed to reside on the landscape, it allows the microbial action to break down the plant matter and turn it into bugs. That doesn’t happen immediately; it takes time, it takes weeks.

The same thing is true for the algal trophic, the light web and the dark web, they are both incredibly important but they both are directly dependent on this key spreading water out, slowing it down. So spread it, slow it, sink it, and grow it. And that’s a bagful of bugs.”

Dr. Katz said they are cultivating ecological solutions on agricultural lands using them as surrogate wetlands. He noted that this is the very place that the food was once made for tens of millions of waterfowl and for 2 million salmon coming back through the Golden Gate and back into the system. “We can, on these very same lands, grow people food in the summer, and food for the environment and habitat in winter,” he said.

But the scales of those processes are different, he noted. The Yolo Basin was 100,000 acres and it took a long time to drain which had the capacity for that natural productivity. That vast size and scale is not possible in these times; conservation opportunities happen in hundreds of acres, maybe 1000 acres, he said.

In those places, if we’re going to mimic the natural processes that once occurred there in order to restore the ecological function, we have to actively manage,” said Dr. Katz. “We have to understand that ubiquitous drainage is the altered state. What we have to do is learn to slow that water down, to spread it out, to actively manage it in such a way.”

Dr. Katz presented a map of the Sacramento Valley, noting that 95% of the historic floodplains in the Sacramento Valley has been drained and converted to other crops. In California, 550,000 acres of rice is farmed annually, and now, many of the rice fields are managed for migrating birds during winter months. “The management is key,” he said. “We’re mimicking natural flood patterns but we’re working within the constraints of scale and often what we’re working now is that field scale.”

But that’s not foreign to conservation,” Dr. Katz said. “The greatest success story when it comes to conservation, not just in the state but nationally, is the amazing story of waterfowl in the Central Valley. When I was young, in this valley, birds were at all-time low numbers and now they are at all-time highs. A big piece of that was an alteration in the agricultural landscape. We went from burning our rice fields to flooding them, and in so doing, we allowed the ducks and the geese that had flown over for generations and looked down at dry fields to recognize the wetlands of the Pacific Flyway, and we had this incredible comeback. Why is that? It’s access to that floodplain energy created this incredible visible biomass, biomass you can feel when the snow geese take off at Gray Lodge.”

Fish, however, are underwater and somewhat invisible, but the same tools that have recovered birds can be used to recover fish, he noted. “We need these wetlands, they are important for energy flow into the aquatic ecosystem. The primary tool for managing that energy flow is managing water and creating the residence time necessary to natural productivity go to work. That can happen on our winter flooded rice field or a corn field or a field full of weeds or riparian oxbow or a side channel or a perched floodplain, on the American River or the Yuba – it’s no single thing. We need a portfolio of ways of slowing water down, of creating off-channel habitats, and when you do, you get something that’s pretty dramatic.”

Fish have to eat, and we’ve built a system that doesn’t recognize that simple fact, Dr. Katz said. “Let’s make it better and we can do it together. So when you go back to your own classrooms and your own restoration projects, remember that the residence time – slowing it down – is absolutely key if we’re going to recover species and if we’re going to put energy back into the water to create these biomasses.”

It’s not just in water; the idea of integrating the working knowledge of the resource disciplines that we’re all engaged in into the way we manage is happening in other places, such rangeland fires. “Now we understand how hooved animals in grasslands co-evolved, we can do a much better job there,” he said. “This is a revolution that is happening across all of our disciplines, it’s happening in a myriad of ways and it really gives me great hope. The Central Valley can be a place where we have ample water for our cities, for our farms, and for fish, ducks, geese, and other critters.”


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