At the February meeting of the Delta Stewardship Council, Delta Lead Scientist Laurel Larsen discussed a new report on the benefits of floodplain habitats for fish production and updated the Council on the Delta Science Program’s activities.
Report spotlight: Farm to Fish: Lessons from a Multi-Year Study on Agricultural Floodplain Habitat
The report, Farm to Fish: Lessons from a Multi-Year Study on Agricultural Floodplain Habitat, led by Dr. Ted Sommer of the Department of Water Resources and coauthored by Louise Conrad and Lynn Takata with the Delta Science Program, discusses lessons learned from six years of managed floodplain experiments in the Yolo Bypass. The project is a collaboration among the UC Davis Center for Watershed Sciences, Department of Water Resources, Cal Trout, and the landowners themselves who really wanted their land to achieve the most benefit for a broad suite of purposes: farming, birds, and fish.
The article, which appears in the San Francisco Estuary and Watershed Science Journal, examines multi-benefit or nature-based solutions for ecosystem management, such as what is called for in Governor Newsom’s Water Resilience Portfolio. The project has been termed the Nigiri project (after the salmon and rice sushi roll) because the focus is the co-management of floodplains for fish and rice cultivation.
One of the study’s focal areas was the Yolo Bypass, which was initially constructed to route floodwaters away from Sacramento. As a flood bypass, the land has remained relatively undeveloped and is one of the last remaining active floodplain areas, albeit in a highly managed sense, within the Central Valley. In fact, more than 95% of natural floodplain wetlands in the region have been eliminated. Considering that those wetlands represent rearing habitat for juvenile salmon, the widespread elimination of floodplain access is considered a significant stressor on salmon populations.
The Nigiri project examined whether positive benefits could be realized for juvenile Chinook salmon by extending the natural flood pulse through the retention of water on fields, first in the Yolo Bypass and then ultimately in other locations throughout the Central Valley, including Sutter Bypass and Dos Rios Project in the San Joaquin River floodplain area.
“To be clear, the intervention that was examined here was manipulating drainage from the fields such that they retained naturally occurring floodwaters longer, so this is a fairly small intervention with potentially large impacts,” said Dr. Larsen. “And the answer to the question of whether this intervention produced benefits for the Chinook salmon was yes, yes, yes. Not only was the prey of the salmon and zooplankton more abundant in the floodplain habitat than in the adjacent river, as you can see in the schematic diagram that Byron Riggins prepared, but salmon growth rates were also higher. Surprisingly and conveniently, there was not much difference in these positive results across fields with different substrate types such as salad fields, disced fields, or those that were farmed for rice.”
However, she noted that certain conditions did need to apply to achieve the results, as shown on the slide. “First, the floodplain habitat needed to maintain a hydrologic connection to the river and maintain flows. The salmon were found behaviorally to be attracted to inflow locations, possibly because of the food they contain, but they also needed outflow connections in order to escape predation on the floodplain,” Dr. Larsen continued. “Second, these positive results did not hold for very dry years when the salmon essentially got cooked by the warmer floodwaters on the floodplain, ‘baked salmon instead of Nigiri,’ and suffered much higher rates of predation due to the much more limited and concentrated habitat for wading birds. Third, the conditions required for extended flood pulses were rather rare. During two wet years, the whole system was flooded, making it impossible to contain floodwaters within the study fields. But during the dry years, the Yolo Bypass didn’t flood at all. Only during moderate flood pulses was this type of intervention possible.”
The authors of the study acknowledged that the plans underway to notch the Fremont Weir will likely facilitate the achievement of these moderate flood pulses on a more frequent basis. However, the more frequent weather whiplash events that alternate between wet and dry extremes projected for the future will make those conditions rarer.
“This study was important, not just because it illustrates a successful set of examples of multi-benefit solutions of the type that might go into a water resilience portfolio, but it also directly addressed addresses one of the priority actions identified in the current Science Action Agenda, which is to investigate the most cost-effective methods to improve species habitat on working lands,” she said.
“But that success is conditional. It’s a little like winning free sushi in a raffle and then seeing the statement terms and conditions apply. This study underscores both the opportunity to identify additional lands in the Delta that could be managed in this win-win way, but also the need to prioritize these management decisions based on projections of changing flows and water temperatures. Both this need and opportunity argue for a landscape-scale perspective in planning for resilience; it also argues for a nimble system for water management that is responsive to thresholds or triggers in flow and temperature.”
NOAA, Cal Trout, and the Department of Fish and Wildlife, and others are planning a symposium on managed floodplains for the fall; Dr. Louise Conrad and Lynn Takata, coauthors on the paper, are involved with the planning committee. The symposium will identify what else we need to know to create a management paradigm that leverages these habitats most effectively. Prior to the symposium, the Delta Science Program will be producing fact sheets summarizing the latest science.
Activities of the Delta Science Program
Adaptive Management Forum
The Adaptive Management Forum, hosted virtually on February 3-5, was an opportunity for the Delta community to share knowledge and promote collaboration around adaptive management of the Bay-Delta system. The forum featured morning sessions with plenary talks and presentations by invited speakers, followed by Question and Answer panels and breakout discussions. There were three sets of workshops that were held during the afternoon sessions.
In addition to the workshop on the Delta landscape scenario planning tool, there was also a workshop on permitting adaptive management and adaptive management planning 101, which provided additional opportunities for the participants to interact, network, and learn about specific tools and practices. Over 250 people attended the forum, and each workshop itself had 35 to 70 participants.
Videos of the presentations are now posted on the Council’s website under the events drop-down, and a proceedings report will be forthcoming shortly.
“I’d also like to say that the ideas shared at this forum are already starting to influence the dialogue about adaptive management in the Bay-Delta,” said Dr. Larsen. “The Delta Landscapes Scenario Tool had a great reception and generated a lot of excitement at the workshop. And reports on other adaptive management projects within the Bay-Delta also did the same. So critically, these ideas are going to help shape the way the Delta Science Program will continue to work to fulfill the part of its mission-related to promoting science-based adaptive management with Delta agencies.”
Steelhead workshop on monitoring steelhead populations in the San Joaquin basin
The workshop on monitoring steelhead populations in the San Joaquin basin was held February 17 through 19 online. At the workshop, participants reviewed the management challenges and monitoring framework for steelhead and explored analytical approaches to measuring the impact of management actions on San Joaquin basin steelhead. This workshop supported the biological opinion on the long-term operation of the Central Valley Project and State Water Project, which aims to develop a plan to monitor steelhead populations within the San Joaquin Basin and on the San Joaquin River downstream of the confluence with the Stanislaus River; this includes steelhead and rainbow trout on non-project San Joaquin tributaries as well. A more detailed report on the workshop is forthcoming.
Bay-Delta Science Conference
The biennial Bay-Delta Science Conference will be held April 6 through 9. Registration is free. Click here to register.
Delta science proposal solicitation
The recent science proposal solicitation, offered jointly by the Delta Science Program, the Bureau of Reclamation, and California Sea Grant, will fund projects of 12 to 31 months duration that advance the 2017 to 2021 Science Action Agenda. The total amount of funding expected to be awarded is $9 million.
They received 99 proposals by the February 12 deadline, double the number received in previous years. The proposals are in the process of being reviewed by an expert review panel. Awarded contracts will have a start date as early as July 1 of 2021. A more detailed report on the projects that are awarded funding will come later this year.
