Aquatic Vegetation Assessment Grant

Soon after starting graduate school, I began looking for research projects with an applied focus. Through my volunteer work with Putah Creek Council, I became acquainted with Putah Creek Streamkeeper Rich Marovich, who led me to a collaboration with the Solano County Water Agency (SCWA). The Agency is in charge of operating two dams and a 33 mile-long concrete-lined water distribution canal (the Putah South Canal) in the CA Central Valley, created as part of the Solano Project in the 1950s. Every summer, the canal gets choked with aquatic vegetation, which clogs screens and water intakes, necessitating costly annual clean-outs. Lake Solano and Putah Creek, water bodies upstream of the canal, were thought to be the source of this vegetation.

Putah Creek choked with aquatic plants

Putah Creek choked with aquatic plants. These plants produce a huge number of propagules, which make their way downstream and into the canal.

Aquatic plant propagules floating in Lake Solano. These stem fragments can grow into new plants.

Stem fragments (propagules) floating in Lake Solano.  Aquatic plants reproduce primarily asexually through stem fragmentation and dispersal.

To better inform management actions, SCWA sought greater understanding of the environmental and biological factors causing excessive growth of nuisance vegetation in and upstream of the canal. Because of my research interests in the drivers of aquatic plant communities, and my personal goals of using scientific methods to solve management challenges, a collaboration with SCWA was a perfect fit! In 2011, I began work as a principal investigator on a two-year project to 1) determine the current extent of aquatic weed infestations in the canal and in upstream water bodies (Lake Solano and Putah Creek), 2) identify environmental factors that may facilitate or hinder invasion and excessive growth of aquatic vegetation, and 3) develop management recommendations to reduce current and future infestations.

Pulling up vegetation from the Putah South Canal.

Aquatic plants and algae pulled out of the Putah South Canal.

PSC Map-plants

GIS map of plant (macrophyte) density in the Putah South Canal generated from my sampling data. Plants tend to be more abundant at the downstream end of check structures, presumably because of greater sediment accumulation.

Beginning in summer 2011, I conducted a survey of aquatic vegetation at over 200 points along the Putah South Canal. I also surveyed Lake Solano and Putah Creek upstream of the canal, and the Terminal Reservoir downstream of the canal, collecting data on aquatic plant species and abundance and environmental correlates such as light levels, soil nutrients, and water velocity. I used Boosted Regression Tree models, developed in collaboration with fellow graduate student David Harris, to determine the most influential environmental factors driving nuisance aquatic plant growth. The most important factors identified by the models were shading from riparian canopy cover, substrate texture, and water depth.

My study revealed that conditions in Lake Solano and Putah Creek upstream of the Putah South Canal were ideal for aquatic plant growth: shallow, open water with little shading provided ample light for photosynthesis, while flow regulation at the dams allowed fine, nutrient-rich sediments to accumulate that might otherwise be flushed out by high flows. The canal itself also had highly suitable conditions for plant growth. Sediment collects in the bottom of the canal over time, providing a substrate for incoming propagules to grow on, and light is plentiful in the open canal.

My recommendations to SCWA focused on addressing the underlying problem of sediment accumulation and light availability both in the canal and in the upstream water bodies. I discussed the potential pros and cons (to the agency, the environment, and other stakeholders) of a variety of management options, including the following:

  • planned high velocity “flushing flows” (dam releases) to remove sediments and vegetation
  • improved canal cleaning methods to leave less sediment and fewer propagules behind
  • restoration of upstream riparian areas to reduce erosion, a major source of the sediment that ends up the canal
  • introducing shade over the canal to reduce plant growth
  • converting the wide, open areas in Lake Solano (which are choked with aquatic plants) to a marsh or floodplain to reduce the production of aquatic vegetation
  • mechanical or chemical removal of plants in Putah Creek and Lake Solano (I advised against these options, as they would be short-term solutions that could cause collateral damage to the ecosystem, and potentially unintended consequences like algal blooms!)
  • biological control of vegetation in the canal with sterile triploid grass carp

Thinking through management options and discussing their feasibility with a government agency was a great experience. With SCWA’s lengthy experience in the practical aspects of running large-scale water operations, and my background in aquatic plant ecology, we were able to bring complementary knowledge to the table and learn from each other. This experience has further solidified my belief in the importance of collaboration for finding solutions to ecological and environmental problems.