DELTA LEAD SCIENTIST: Advances in mapping invasive aquatic vegetation

At the December meeting of the Delta Stewardship Council, Delta Lead Scientist Dr. Laurel Larsen discussed Council-funded research that will lead to improved management of invasive aquatic weeds.  She also gave an update on the activities of the Delta Science Program.

Article spotlight: Genus-Level Mapping of Invasive Floating Aquatic Vegetation Using Sentinel-2 Satellite Remote Sensing

For the final article spotlight of 2022, Dr. Larsen chose work funded by the Delta Stewardship Council’s 2018 funding solicitation that leverages advances in satellite technology and artificial intelligence to produce highly accurate maps of invasive weeds.

Invasive aquatic weeds in the Delta are a major problem; they are fast-growing and can choke waterways, they can harbor invasive predators of native fish species, they contribute to stagnant waters and warmer temperatures, and they are capable of wreaking ecological havoc that cascades through the system.  In addition, weeds are a problem for recreational fishing and boating communities and might be linked to harmful algal blooms.  For these reasons and others, limiting the spread of invasive aquatic weeds is a top management priority.

However, managing invasive aquatic weeds has many challenges.  Control is often through chemicals such as herbicides or mechanical removal, but chemicals are not effective in the Delta because tidal and river flows are very large, so they are quickly diluted and, therefore, less effective than when applied in lakes.

Invasive aquatic weeds grow and spread rapidly, so where they are and the extent to which they are growing is constantly changing.  Aquatic weeds have spread throughout the Delta, and the Department of Boating and Waterways and others typically spend around 10 to $20 million per year to control the spread of aquatic weeds, but with limited success due in part to technological and economic barriers.

Determining where to prioritize treatment requires up-to-date information about where the aquatic weeds are, particularly because they grow and spread so rapidly.  Until recently, the most useful mapping information came from aerial imagery acquired from airplanes; however, flights are expensive and only occur infrequently.

Satellites pass over the Delta more frequently, but until recently, satellite imagery did not have the resolution to create useful maps.   However, a new satellite called Sentinel 2 can provide images with much higher resolution than LANDSAT, its predecessor, and at a relatively high frequency of once every five days.

So in research funded by the Delta Stewardship Council, Christiana Ade led a team of researchers that developed a strategy to produce highly accurate maps of water hyacinth and water primrose distribution from the Sentinel 2 images.  Using artificial intelligence technology, the researchers first trained the computers to recognize water hyacinth and water primrose using data from field measurements mapped by folks on the ground.  Next, they tested the computer’s ability to classify different species by comparing the predicted classes of vegetation to the real data; and then compared the accuracy of the Sentinel 2-based maps against imagery collected from airplanes.

Amazingly, they found that their maps from Sentinel 2 had an overall accuracy of 90%, which is incredible,” said Dr. Larsen.  “For some years, the mapping of water hyacinth, in particular, was even more accurate than the state-of-the-art airborne imagery-based maps.  So the authors are now working to develop what’s known as an operational pipeline to generate these maps of invasive aquatic weeds almost immediately after the satellite images are available, which is once every five days.  Resource managers and agencies such as the Division of Boating and Waterways can then use the maps to prioritize where to apply the treatment.”

Dr. Larsen noted that this research is responsive to Action 3 of the 2022-2025 Science Action Agenda, which is to synthesize existing knowledge and conduct applied interdisciplinary research to evaluate the costs and benefits of different strategies for minimizing the introduction and spread of invasive species and to inform early detection and rapid response strategies.

Genus-Level Mapping of Invasive Floating Aquatic Vegetation Using Sentinel-2 Satellite Remote Sensing

Authors: Christiana Ade, Shruti Khanna, Susan L. Ustin, and Erin L. Hestir

Invasive floating aquatic vegetation negatively impacts wetland ecosystems and mapping this vegetation through space and time can aid in designing and assessing effective control strategies. Current remote sensing methods for mapping floating aquatic vegetation at the genus level relies on airborne imaging spectroscopy, resulting in temporal gaps because routine hyperspectral satellite coverage is not yet available. Here we achieved genus level and species level discrimination between two invasive aquatic vegetation species using Sentinel 2 multispectral satellite data and machine-learning classifiers in summer and fall. The species of concern were water hyacinth (Eichornia crassipes) and water primrose (Ludwigia spp.). Our classifiers also identified submerged and emergent aquatic vegetation at the community level. Random forest models using Sentinel-2 data achieved an average overall accuracy of 90%, and class accuracies of 79–91% and 85–95% for water hyacinth and water primrose, respectively. To our knowledge, this is the first study that has mapped water primrose to the genus level using satellite remote sensing. Sentinel-2 derived maps compared well to those derived from airborne imaging spectroscopy and we also identified misclassifications that can be attributed to the coarser Sentinel-2 spectral and spatial resolutions. Our results demonstrate that the intra-annual temporal gaps between airborne imaging spectroscopy observations can be supplemented with Sentinel-2 satellite data and thus, rapidly growing/expanding vegetation can be tracked in real time. Such improvements have potential management benefits by improving the understanding of the phenology, spread, competitive advantages, and vulnerabilities of these aquatic plants.

Activities of the Delta Science Program

Delta resident survey

The inaugural Delta resident survey will launch in January of 2023.  The survey is being conducted by Dr. Jessica Rudnick and other researchers from California Sea Grant, Sacramento State University Institute for Social Research, UC Davis, UC Berkeley, and Oregon State University.  The survey will be mailed to about 60,000 households in the Delta; about a 1% response rate is expected.

The survey aims to reach a demographically and geographically representative sample of Delta residents.  The data collected will be used to establish a baseline of understanding for what Delta residents think about Delta issues, how they connect to the Delta as a unique place, and how residents are experiencing and adapting to climate changes.  Dr. Larsen noted that this survey aims to address a large gap in the current understanding of social and human behavioral aspects of the Delta.

Advancing Interdisciplinary Research Symposium

The Advancing Interdisciplinary Research Symposium, held in October, was attended by members of the Bay Delta Social Science Community of Practice and multiple collaborative science venues across the Bay-Delta that focus on biophysical and ecological components of the estuary.  The event was designed to facilitate coordination and integration across the social science disciplines and the natural science communities.  The symposium also provided context and training on why and how these interdisciplinary research approaches could help advance the state of relevant and usable science in the Delta.

Breakout sessions were held on the second day.  Social scientists and biophysical and ecological researchers brainstormed ideas for integrated research topics that could be submitted as proposals for future PSNs or other funding opportunities.  

The groups focused on four distinct areas:

  • Drought and salinity management, such as the ecological and engineering approaches available, the benefits and drawbacks of each, and how the state should prepare for longer-lasting and more frequent droughts.
  • Integrated social and ecological research opportunities for carbon sequestration, land subsidence, mitigation, and sustainable farming practices in the Delta.
  • Assessing shoreline vulnerability and flood protection in the Delta and adjacent communities.
  • Assessing ecological management approaches for their capability to address overlaying stressors such as drought, extreme heat waves, and invasive species and still preserve or restore essential ecological functions.

Groups continue to talk, and the Social Science Integration Team is planning next year’s activities and efforts to further conversations around those themes.  They are also working with the Delta Science Program and the National Center for Ecological Analysis and Synthesis (NCEAS) to identify a social science topic for training and further synthesis in 2023. 

Recordings of the symposium are available on the Council’s YouTube channel, and materials are available on the Bay Delta Social Science Community of Practice webpage.

Harmful algal blooms workshop

The Delta Science Program hosted a hybrid in-person and virtual Harmful Algal Blooms (HABs) workshop on November 8-9 to inform the development of a community monitoring strategy.  A report summarizing the workshop’s outcomes is being written.  The next steps are to develop a monitoring strategy the whole Delta science community can use to conduct monitoring in a way that adds to the collective understanding of harmful algal blooms by mid-2023.

Funding science solicitations

Dr. Larsen has been engaging with agencies that in the past were partners for competitive funding solicitations, as well as other agencies who fund competitive and non-competitive opportunities on their own, to explore ways to better coordinate science research funding opportunities.

A questionnaire has been developed to gather input from science funding entities on what efforts folks think would be worthwhile to foster greater coordination.  These efforts include holding regular meetings, creating a common pre-proposal process as a mechanism to generate greater alignment of proposals with management needs, and providing a way to direct scientists to the most appropriate funding opportunities.

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