Remote sensing gives USACE an edge in detecting HABs

The rapid bloom of tiny freshwater microorganisms, called cyanobacteria, sometimes releases toxins that are harmful to aquatic life and can contaminate drinking water. These harmful algal blooms (HABs) pose a significant threat to public health and safety, ecosystems, freshwater resources and recreation. They also cause about $82 million in economic losses to the seafood, restaurant and tourism industries each year.

HABs pose significant challenges for U.S. Army Corps of Engineers (USACE) districts, which are responsible for maintaining hundreds of inland waterbodies that cover vast geographic areas. More than 20 districts are actively engaged in HAB response, and all face the challenge of monitoring such a large area and detecting these harmful events early enough to successfully treat them.

Current federal policy identifies harmful algal blooms as one of the most complex and economically damaging aquatic issues threatening the nation’s ecosystems. However, USACE water quality managers now have a suite of effective tools for better detecting and monitoring HABs.

“There’s a critical information gap surrounding small, inland waterbodies that’s yet to be fully addressed and is an ongoing area of current and future work. We are aware that our federal partners, such as the National Oceanic and Atmospheric Administration and others, are interested in similar approaches and we continually engage them to see where collaboration and future research opportunities exist.”

A collaborative R&D effort between USACE and other federal, state and academic partners has developed methods to use remotely sensed satellite imagery to provide an early warning about the possible presence of harmful algal blooms.

“Geographic Information System (GIS) tools backed by foundational remote sensing research help with early HAB detection, allowing districts to better focus limited resources,” said Molly Reif, a research geographer in the U.S. Army Engineer Research and Development Center’s (ERDC) Environmental Laboratory. “More specifically, GIS software tools developed using remotely sensed data assist with decision support, providing timely estimation of potential HAB conditions across multiple waterbodies.”

Remote sensing refers to the ability to gain information about a target without coming into physical contact with it, as opposed to taking field measurements. In this case, it involves airborne and spaceborne satellites that carry sophisticated cameras. Filters on these cameras can sense specific parts of the electromagnetic spectrum not visible to the human eye, providing data that can be used to detect HABs.

Research has focused on detecting three water quality indicators of HABs: chlorophyll-a, a measure of the amount of algae growing in a waterbody; phycocyanin, a proxy for cyanobacterial or blue-green algal biomass; and turbidity, a measure of water clarity.

USACE has spent more than a decade conducting research and development to better understand and help advance the role of remote sensing in inland water quality monitoring. The work has been a collaborative effort between ERDC, the University of Cincinnati, the U.S. Environmental Protection Agency’s Office of Research and Development, the USACE Great Lakes & Ohio River Division, the USACE Louisville and Huntington Districts, the Joint Airborne Lidar Bathymetry Technical Center of Expertise, and the Kentucky Division of Water.

“I’ve watched this technology evolve over the years into something very practical and useful to water quality managers in the field,” said Erich Emery, a water quality specialist at the USACE Great Lakes & Ohio River Division and chair of the Water Quality Committee under the Hydrology, Hydraulics & Coastal Community of Practice. “HABs are such a dire challenge for USACE water quality managers and the nation, and these tools give us the detection edge we need to stay ahead of the challenge.”

First researchers had to evaluate the ability of satellite sensors and algorithms to characterize water quality parameters. Then they had to develop software tools for estimating the three primary water quality indicators.

“During initial beta testing of the software tools, we engaged interested USACE district endusers who helped provide very useful feedback,” Reif said. “That feedback has turned out to be an ongoing dialogue.”

The GIS software tools have been rolled out over the last three to four years, with the most recent ESRI-based tools delivered in October and November 2021, building on research that began in 2012.

“The tools assist water quality managers by serving as a proactive warning system to better monitor and manage potential HAB outbreaks,” Reif said. “They also reduce costs and labor through optimizing field-based sampling across space and time. And they facilitate interagency coordination through communication of HAB potential to managers, leadership, partners and the public.”

The software tools developed by ERDC researchers have varying capabilities to meet a wide range of early detection and monitoring needs and end-user skill sets. They include the ability to create abundance maps of HAB indicators, as well as a web application that rapidly screens for potential HAB conditions in five easy steps.

“All of the tools have gone through or are currently undergoing updates, so in that sense they are living, evolving solutions that we can improve upon ― whether to address technical glitches or enable enhanced software solutions,” Reif said.

Reif anticipates that this field will continue to evolve.

“There’s a critical information gap surrounding small, inland waterbodies that’s yet to be fully addressed and is an ongoing area of current and future work,” she said. “We are aware that our federal partners, such as the National Oceanic and Atmospheric Administration and others, are interested in similar approaches and we continually engage them to see where collaboration and future research opportunities exist.”

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