In a collaborative effort between CA Department of Water Resources, US Bureau of
Reclamation, CA Department of Fish and Wildlife, United States Geological Survey,
San Francisco State University, and UC Davis, this study will investigate the role of
augmented summer and fall flows in the Yolo Bypass and North Delta areas on lower
trophic food web dynamics and the benefits to listed fish species. Using both continuous
and discrete sampling approaches, this study will relate hydrologic patterns to
chlorophyll-a, nutrients and primary productivity, plankton densities and composition
(phytoplankton and zooplankton), contaminant concentrations, as well as water quality
parameters such as electrical conductivity, turbidity, temperature, and dissolved oxygen.
In addition, caged hatchery Delta Smelt will be monitored to determine the effects of the
managed flow action and increased food web productivity on fish survival, growth, and
Due to the food-limited nature of the San Francisco Estuary, it is critical to understand
mechanisms that result in successful food web productivity including phytoplankton
blooms. Food limitation is one of the primary hypothesized causes of the Pelagic
Organism Decline. In 2011 and 2012 there was evidence that a moderate Yolo Bypass
flow pulse during fall agricultural drainage periods was followed by phytoplankton
blooms in the lower Sacramento River. Managed flow actions in the following years
showed an increase in food web productivity could be repeated;however, results varied
across years and flow actions indicating more research is warranted to understand
correlations between flow and abiotic conditions, and the biological response of the food
web. The increases of summer/fall flows in North Delta, has been considered a
management strategy as part of complying with USFWS Delta Smelt Biological Opinion
Action 4. The augmentation of flows through the Yolo Bypass/North Delta is also
included as one of several Delta Smelt Resiliency Strategies by Natural Resources
• Determine if managed flow actions through the Yolo Bypass stimulate increased
primary productivity locally and downstream, and if it is repeatable.
• Characterize how nutrients, chlorophyll and plankton (composition and density) in
the Toe Drain, Cache Slough Complex, and lower Sacramento River change in
response to flow pulses.
• Determine if nutrient subsidies of the source water and downstream are limited
by abiotic and biotic factors.
• Characterize spatial differences and transport of pesticide contaminants in the
Yolo Bypass in response to the flow actions.
• Determine survival, growth and behavior of caged hatchery Delta Smelt before
and after the flow action in the Yolo Bypass.