Restoration efforts have succeeded in restoring waterfowl populations in the Yolo Bypass; can the same happen now for fish? Plus the latest research on methylmercury and wetlands restoration.
When the floodwaters flow into the Yolo Bypass in the late winter and early spring in some years, dramatic changes occur. Salmon, splittail, and other native fish species come onto the floodplain to feed on invertebrates. Vast numbers of waterfowl arrive almost instantly to feed on the fish, invertebrates, and agricultural residue. When the Yolo Bypass is fully inundated, the wetted area of the Delta is approximately doubled.
In the bypass, wetland managers and conservationists in the Yolo Bypass work to ensure that habitat is available, even when the floodwaters don’t come. About one-third of the Yolo Bypass is a mosaic of managed wetlands, ponds, and other associated habitats that support a wide variety of aquatic, avian and terrestrial wildlife.
Over 280 terrestrial species are known to use the habitats in the bypass, many of them special status species, 
including fairy shrimp, the giant garter snake, the northwestern pond turtle, snow plover, great blue heron, and the bald eagle.
As an important stop on the Pacific Flyway, the Yolo Bypass Wildlife Area has been recognized by the National Audubon Society as a Globally Important Bird Area, supporting significant numbers of waterfowl, including northern pintail, least sandpiper, and American white pelican. Recent research has shown that the flooded fields of the bypass are highly productive habitats for California’s native aquatic species, including salmon, steelhead, sturgeon and splittail.
In this segment of coverage from the symposium, Meeting Nature Halfway on a Floodplain: The Yolo Bypass as a Reconciled Ecosystem, Greg Yarris from the Central Valley Joint Venture discussed his organization’s efforts to restore waterfowl populations in the Yolo Bypass and the Central Valley, and Ted Sommer from the Department of Water Resources presented some of the research being done on the benefits of floodplains for native species. Extensive wetland restoration brings with it concerns for methylmercury; Stephen McCord from McCord Environmental shared the latest research on ways to control methylmercury discharges and wetlands.
(This is the second of three part coverage from the Yolo Bypass Symposium. For part 1, go here: Yolo Bypass Symposium, Part 1: A flood of plans and possibilities)
GREG YARRIS: The Yolo Bypass, waterfowl, and the Pacific Flyway
In 1988, the Central Valley Joint Venture was established as a regional partnership focused on the achieving the objectives for waterfowl and wetlands conservation as envisioned by the North American Waterfowl Management Plan. In the joint venture’s first regional plan released in 1990, the Yolo Basin was identified as a high priority due to its lack of protected land; however today, the CVJV considers the Yolo Basin a bird conservation success story, having met its population objectives for waterfowl, due in large part to the success of the Yolo Basin Foundation in establishing the Yolo Basin Wildlife Area in 1997.
Greg Yarris from the Central Valley Joint Venture discussed the success of the Yolo Bypass, and how the bypass has contributed to the rebounding waterfowl populations in the Central Valley.
The Central Valley is an important stop for waterfowl, with five to six million birds visiting annually, Mr. Yarris said. “For the Pacific Flyway, we’re definitely the most important wintering area with California supporting about 60% of the Pacific Flyway population and 20% of the continental waterfowl; 50% of the pintail in the continental US will winter in the Central Valley,” he said. “It’s pretty amazing sight.”
In the days before California was developed, there were a lot of seasonal wetlands and floodplains, but as the rivers were channelized, dams built and wetlands reclaimed for farming, most of these historic wetlands were lost, he said. “Today, with only five percent of the original wetlands remaining in California, it is critical that the remaining acres be managed in a way that optimizes value for waterbirds,” he said.
The Central Valley Joint Venture’s habitat objectives were to provide at least half of the needed energy requirements from natural wetlands with the remaining food supply provided by agricultural crops. Using a bioenergetic model that considers the different foraging values of the different habitat types and the population objectives, the CVJV calculated that 11,558 acres of natural wetlands were needed. Through the establishment of the Yolo Wildlife Area, lands managed by the Fish and Wildlife Service, and other easements, the goal of providing half the acreage from natural wetlands has been achieved, Mr. Yarris said.
The other important provider of food for waterfowl in the Yolo Bypass is agriculture, which provides the other half of the energy requirements from 3000 acres of flooded rice and 8000 acres of corn, he said. Rice is grown, harvested, and flooded to provide food for thousands of waterfowl, and corn fields are harvested to provide forage for geese and cranes.
“With ag in the equation, we’re doing okay in the Yolo Basin, and all through the season, supply is always greater than the demand,” he said. “Without agriculture, you’d start to get into this situation where in January, food supplies would be running low and the birds would be getting stressed.”
In fact, flooded rice fields are an important source of food for waterfowl In the Central Valley, providing 60% of all food resources available to ducks and geese, and replacing the food now provided by rice fields with wetland-based foods would cost over $1.5 billion, Mr. Yarris noted.
Waterfowl managers have long since reconciled themselves to the fact that the wetlands of the Central Valley are an artificial system and it has been so for a long time, Mr. Yarris said. California’s wetlands are intensely managed with control structures that manipulate water levels and artificially simulate historic patterns, and the cost of owning and maintaining wetlands is high, with expenses that include water costs, levee repair, water control structures and pumps, vegetation control, mosquito abatement, and soon, likely fees for mercury discharges as well, he said.
Hunters are big contributors to waterfowl management, Mr. Yarris pointed out. Waterfowl hunting contributes significantly to maintaining the state’s wetland habitats through hunting license fees, state and federal duck stamps, and taxes on firearms and ammunition. In addition, many wetlands in the Central Valley are privately owned and managed duck clubs, so maintaining the tradition of waterfowl hunting is critical for maintaining this habitat, he said. “It’s very costly, so we’re basically relying on the people who have those private wetlands, the duck hunters themselves, to foot the bill every year to maintain those wetlands,” he said.
The Yolo Basin is a conservation success story; the wetland conservation partnership led by the Yolo Basin Foundation has been extraordinarily successful, he said. “Back in 1989, the Central Valley Joint Venture’s Plan listed the Yolo Basin as the top priority because virtually no wetlands were protected from other uses,” he said. “Today, the Yolo Basin is the only planning region where restoration objectives have been met. I congratulate everyone who’s been working in the Yolo Basin for having such an impact.”
TED SOMMER: Native fishes and managed floodplains: Mimicking natural processes
While the Yolo Bypass has become important habitat for a variety of bird species, recent experiments have shown that it can also be a valuable habitat for fish species as well, and could be an important factor in helping to recover salmon and other listed fish species. Ted Sommer from the Department of Water Resources Aquatic Ecology Section discussed some of the latest promising research for fish on the floodplain.
Ted Sommer has been studying the Yolo Bypass as far back as the 1990s when he and his colleague Randy Baxter began studying the Sacramento splittail, a large native minnow endemic to the Central Valley. They quickly found that the Yolo Bypass was important to the splittail as they are associated with shallow water habitat, not found in narrow rocky channels of the Delta. “The simple story is that the splittail is perhaps the most floodplain dependent species that we have in the region,” he said. “It moves out into the floodplain and spawns there, it rears there, and it does really well when we get at least three weeks of flooding.”
The Yolo Bypass is a major migration corridor for important species such as Chinook salmon, steelhead trout, and sturgeon; however, there is a problem with the fish moving up the corridor and getting stuck at the Fremont Weir. “It’s probably the major fish passage issue that we have in the lower valley here,” he said. “It’s certainly something that we need to reconcile.” He said DWR and Reclamation are currently working on an EIR/EIS to evaluate different alternatives.
The Yolo Bypass is also one of the major nursery areas for juvenile salmon and splittail, providing a large area of food-rich habitat; experiments with salmon have shown that they grow amazingly fast out on the floodplain. “The fish basically grow twice as fast if they can get out in the Yolo Bypass migration corridor, and the reason is bugs, bugs, bugs,” he said. “Bottom line, it’s a really juiced up food web that generates great growth rates.”
Studies of releases of coded wire-tagged fish found that when the fish have an opportunity to use the Yolo Bypass, they spend a month or more there. “If you get long duration flooding, you grow really big fish, and this is a big thing for salmon production in the valley,” said Dr. Sommer. “We produce a lot of pathetic little skinny fish coming out of the Sacramento River that don’t survive well to the ocean fishery, and if we can get these larger fish by providing rearing habitat, we’re definitely giving the ocean fishery a shot in the arm.”
One of the issues in the bypass is that the floodplain is heavily graded and is designed to move water as quickly as possible through the system. “The problem for fish in this is that fish get these great benefits from being allowed to stay out in the floodplain, but because of the way we designed the floodway, we’re forcing them off early and they are not getting the survival and growth benefits that they might need,” he said.
The Knaggs Ranch project is a project underway in the bypass which utilizes existing infrastructure to experiment with managed flood events to create fish habitat. They have been bringing in fish and looking at the performance of the fish and the food web, and they are also finding really good growth rates. “In fact, the growth rates in the Knaggs project have been some of the best that anyone has seen in the Central Valley,” he said. It’s common to see a millimeter of growth per day, better than other studies, he noted.
There are a number of potential changes that can be made, some of which are fairly difficult, but it’s worth the effort, said Dr. Sommer. “I can’t think of any other landscape that we have out in the Delta with a greater potential to make an impact on the resources of the estuary,” he said.
STEPHEN MC CORD, The Mercury Melee: Costs versus benefits of methylmercury controls in floodplains
Mercury comes from many sources, both natural and anthropogenic. A byproduct of coal combustion and volcanic eruptions, it can be transported by wind and rain. It can also be naturally occurring in soils and springs, particularly in California’s Coast Range. And in many areas of California, it is a legacy contaminant from gold rush mining, both nestled into the sediments that line the rivers, streams, and floodplains of the Central Valley. Even today, some abandoned mines are still leaching mercury into the environment.
Most of these sources provide mercury in a non-toxic inorganic form, but when the mercury reaches a wetted environment, such as a wetland, it settles to the bottom where bacteria in the sediments convert it to the more toxic, organic form called methylmercury. The rate of methylmercury production varies by habitat and is affected by water chemistry factors, such as oxygenation and carbon availability.
The methylation of mercury is a key step in the entrance of mercury into the food web, as methylmercury is a bioaccumulative pollutant which concentrates as it moves up the food chain, from algae to zooplankton to prey fish and the predators that eat them, such as trout and bass.
Methylmercury is especially a concern for restoration projects in the Yolo Bypass and the Delta as the creation of additional seasonal wetlands and the flooding of fields for wildlife can lead to conditions favorable for its production. In addition, a large portion of mercury and methylmercury in the Delta is thought to be originating in Cache Creek, a tributary to the Yolo Bypass. With up to 20,000 acres of flooded wetlands envisioned for the Yolo Bypass, this has heightened concerns about increased methylmercury and the associated public health and wildlife impacts.
In recent years, much research has been done to find successful management processes that can reduce or even eliminate discharges of methylmercury from wetlands. Stephen McCord with McCord Environmental next discussed some of the research being conducted in the Yolo Bypass.
Mr. McCord began by saying that water quality regulations present a conundrum that is much like a rock and a hard place: how to reduce methylmercury discharges without worsening conditions on site. “The hard place is a regulatory program that says “Thou shalt not do something: don’t pollute the waters of the US”, but the rock is the wetland habitat, the bypass under most situations, and even when it’s flooded, the regulatory conundrum is how to reduce the discharges coming off those lands without making it worse on the site with the habitat values and everything it already has,” he said.
Part of the problem is the regulations and what they are intended to solve, he said, presenting a slide showing average concentrations of methylmercury concentrations in the different subareas of the Delta. “The methylmercury problem is that it’s distilled down into exposure of methylmercury to the ecosystem and the aquatic ecosystem, and then the exposure to humans and wildlife that consume those fish,” he said. “The concentration is very low in the Central Delta and that’s great, but the highest concentration is in the Yolo Bypass.”
He explained that the chart pairs the concentration in the water to the concentration in the fish. “You can see that more in the water, you get more in the fish,” he said. “The Central Delta is at an acceptable sort of level, so the idea with the regulatory program is to reduce the concentrations to those levels. So to get from .27 nanograms per liter to .06 – that’s a huge decrease in loads coming off the landscape at 78%. So keep that number in mind. 4/5ths of the concentration of methylmercury has to get dropped from the Yolo Bypass.”
He then presented a pie chart of the sources of mercury. He noted that in the Yolo Bypass falls into different categories, depending on whether the land is flooded or if it is land draining into water. “The Yolo Bypass is both open water and wetlands, so it’s part of both of those pieces of the pie chart,” he said.
He then presented a chart plotting mercury concentrations in juvenile silversides against methylmercury concentrations in the water in the San Joaquin River near Vernalis, which is the downstream end of the San Joaquin River watershed where it enters the Delta. He noted that there’s not much happening until the spring flood pulse. “There is a big flood pulse, the floodplains get inundated, the water comes back, drains down the San Joaquin again, you get a huge spike in concentration in water, and sure enough you see that response in the little fish,” he said. “Presumably the big fish are eating the little fish and the birds and people are eating those and there’s your problem, so floodplains are a problem for methylmercury. Good everywhere else: good for flood control, good for wildlife habitat, but bad for mercury.”
He then presented a slide with two graphs showing salmon rearing data. The first graph compares the growth rates of the juvenile salmon in the Sacramento River versus the Yolo Bypass and depicts that the juvenile salmon grow better in the Yolo Bypass than in the Sacramento River. However, the second chart shows that the accumulation of methylmercury is low for fish in the Sacramento River and a lot higher for those in the Yolo Bypass.
“There is a parallel process where you have higher productivity of methylmercury and a higher exposure to those fish who are growing and eating so much faster,” he said. “The good news is that even though they are accumulating faster, they are generally gone before they get over threshold of concentration in those fish that’s considered too much, so that’s a good story there, but nonetheless, you see that it’s worse of a problem for methylmercury.”
Mr. McCord then presented results of some field scale work on four different fields in the Yolo Wildlife Area, noting that they are all in the same time frame because they are running parallel. The graphs show the individual loads in and out of the fields.
“They were different types of fields: some had wild rice, some had white rice, and some others weren’t managed for rice at all,” he said. “What you can see here is that in versus out, the concentration decreased generally for one field, but everywhere else you saw an increase. “So the field scale produced methyl mercury in the discharges; there’s more going out than coming in. Not good.”
He pointed out that there are very specific times. “Usually the fields would get flooded and the water’s fairly stagnant or maybe just a little bit of maintenance flow, so not much was really happening, but then they drain the water so they can harvest and then there is a huge spike, or even when they are reflooded, there are these big spikes,” he said. “That was a problem at the field scale, so when the same land gets flooded, the same people aren’t managing the water because now its flooded space, and then it drains and now you have another problem.”
He then presented a slide showing some modeling work of the ratio of methylmercury production to consumption. “One of the fascinating things about this model and an interesting story for everyone who works on the field scale is that they were finding the methylmercury didn’t seem to be leaving the field during the growing season, but what was happening was the net movement of water was down into the soil because it wasn’t getting picked up by the roots and transpired, so more water moving down and up through the plants then evaporating and leaving, so that’s where they saw the methyl mercury going. It was being fluxed down into the sediment.”
Mr. McCord then presented another slide of study results, noting that there were several fields studied in the Yolo Wildlife Area. “This is all of the data for the concentration of methyl mercury in the water in these fields and remember that the concentration had to be reduced to get to .06, and it was a 78% reduction to get to .06,” he said. He pointed out the dashed line representing that the water quality goal of .06. “That’s all the data, the hundreds of samples that they took and there wasn’t a single case of water coming in or water going out, dry season or wet season, or any type of field that was below that number, so there’s nothing being done on these fields right now that’s representative of how we could get there. That’s not a good story.”
But there are other stories here, Mr. McCord said. “One of the good ones is that permanent wetlands, highlighted in blue that didn’t get that flooding stage told a better story,” he said. “The concentrations in and out of those were lower, so one thing that’s happening these days is that there are some studies; people are installing permanent wetlands downstream of a seasonal one or rice field even, and seeing what if we discharge into that and then release it, we’d lose the methyl mercury or at least maybe down to those sort of levels, so that’s the idea.”
Prioritization of options for wetlands and irrigated agriculture
The Non Point Sources Workgroup identified a list of management practices that were ranked and prioritized based on range of criteria, such as the scientific certainty, cost, reduction potential and spatial applicability to the technical capacity to implement and the beneficial use impacts with the idea of identifying ‘potentially feasible’ practices for reduction of methylmercury, he said.
Mr. McCord then presented a long list of potential management practices, noting that the management actions are grouped into six different categories of land uses, and the color coding is the simple scoring that was used.
“It wasn’t complicated; it was just, is it positive or negative; is it going to be good or bad? That was all that we could do at this sort of scale with the number of things we were looking at,” he said. “The picture here isn’t the details; it’s the color coding, so you can look and see that there’s a lot of red over here in the criteria for beneficial uses, so we’d be making things worse if we did this on site, and the green being a benefit, and we found there were several management practices in that column that fit that criteria.”
He said there’s a lot of overlap, and sometimes what causes a benefit in one place can cause an impact in another. “There’s always going to be that rock and a hard place; you do something good for mercury, it’s going to be bad on the landscape. Not always, but that’s what we saw.”
The list was then narrowed down to a subset of management practices that showed promise in that they didn’t have a lot of reds. “There were a lot more greens, particularly in the improvement in methylmercury, and so the message is that there are a lot more things that someone could do on their land to manage the water that might have a benefit for methyl mercury; many fewer for soil vegetation, and really just one for biochemistry, the idea there of adding some sort of coagulant and settling more stuff out, which the mercury would be absorbed to and then it wouldn’t discharge.”
He then presented a slide showing the subset of management practices divided into the six land use categories. “The key message here is that we identified biogeochemistry or this adding a coagulant as something worth evaluating,” he said. “There was some concern about adding some chemical or metal ion to natural waters and what would happen to that, but it had enough promise to say for these various land uses, we could study that some more.”
He said as for hydrology types of management practices, some needed to be evaluated more but others can start being applied in that they wouldn’t have negative consequences and probably would have some beneficial consequences. Studies are ongoing at Twitchell Island, the Cosumnes River preserve, the Yolo Bypass and Cache Creek, he noted. New mercury cycling models are currently being developed.
He then gave his conclusions and recommendations.
- It’s complicated – Organize appropriately & manage adaptively: “It is very complicated and wonderfully so, so you get organized and adaptively manage, and don’t let the uncertainty stop otherwise good things from happening.”
- It’s everywhere – Need many site- and source-specific solutions: “There are a lot of different things you could do; breaking it down by six land use categories, just for nonpoint sources was a big effort … there are different types and all kinds of complications, so you need a lot of different solutions.”
- It’s costly – Set priorities, be creative: “It’s costly and you’re not going to solve the problem in the near future, but we can set some priorities and be creative and start doing stuff.”
- Avoid a melee – Reconcile MeHg-centric discharge regulations with other management objectives: “Don’t’ let a regulatory driver force otherwise good things from being stopped. Recognize it and move forward.”
Mr. McCord said the long term approach of this work is going from the conceptual understanding to mechanistic-like models and then to site-specific studies to learn how water is moving around and where the methyl mercury is getting produced and bioaccumulated; then ultimately to move it up to scale. The nonpoint sources workgroup has also produced a land use analysis, a science synthesis, and information on management practices.
He concluded by saying that the long term interests include modeling, understanding the costs and benefits, climate change impacts, attainability, trading and reconciliation.
Mr. Mc Cord was asked what the evidence was that the mercury found in organisms either do harm to the fish or to the people who eat them at the levels found in the Yolo Bypass.
“That’s a good question for water quality regulations in general,” replied Mr. McCord. “It’s difficult to distinguish that for humans particularly. There have been some epidemiological scale studies that were done … to come up with the concentrations that are protective, you look at the dose response curve and you pick sort of the 99th percentile and then just for security, you divide that by ten, so we’re in that range, it’s the dividing by ten sort of range for humans.”
“There have been some studies by UC Davis folks on that for the wildlife,” he continued. “There have been studies locally that show bird egg success is lower and foraging success even for certain birds that are foraging in these habitats, so there are effects. The question would be, do you throw out the habitat value baby with the methylmercury water? Do you not have the habitat in that case? Now you have thousands of birds with mercury, but you didn’t have any birds before in some sort of habitat, so that’s definitely going to be the tradeoff. Same thing with the salmon. You flood the space and they grow a lot faster and they go out and they survive better, but maybe some of them didn’t survive because they had more methylmercury in them, but you wouldn’t want to stop that otherwise good from that.”
Coming up tomorrow …
Farms, flood, fish, and fowl: Putting the puzzle together (Part 3 of 3)
For more information …
- For more on the Central Valley Join Venture, visit centralvalleyjointventure.org.
- For more on fish and the Yolo Bypass: California’s Yolo Bypass: Evidence that flood control can be compatible with fisheries, wetlands, wildlife, and agriculture
- For more on the Knagg’s Ranch project: The Experimental Agricultural Floodplain Habitat Investigation at Knaggs Ranch on Yolo Bypass 2012-2013
- For more floodplain research by Ted Sommer and others, visit: DWR Aquatic Ecology Section
- For more on methylmercury research: Growing Science in Agricultural Wetlands
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