By Jen Seiter-Moser, Ph.D., Mandy Michalsen, Ph.D., P.E., and Holly Kuzmitski
In 2014, a toxic harmful algal bloom (HAB) in Lake Erie cut off drinking water access for more than two days and caused an estimated $71 million in economic losses to Toledo, Ohio. A similar costly event occurred in Lake Okeechobee, Fla. Freshwater HABs and the nuisance species that cause them—cyanobacteria, or blue-green algae— represent a significant threat to the nation’s water resources and economy stability. Their growing frequency and severity impact reservoir operations, recreation, water supply, fish and wildlife, and health and safety.
From 2016 to 2018, a total of 18 states reported 421 HAB events. Consequently, Congress directed the U.S. Army Corps of Engineers (USACE) to implement a five-year technology demonstration program focused on tools for HAB detection, prevention, and management. The directive required that developed technologies be scalable to reduce HAB frequency and their effects on water resources. In response, the U.S. Army Engineer Research & Development Center (ERDC) is seizing an opportunity to harness the problem-solving power of its scientists and engineers to combat this burgeoning problem.
ERDC’s research strategy factors in all aspects of HAB events. By working with federal and state agencies, along with academic partners, ERDC is delivering scalable HAB solutions and investing in research projects and demonstrations that will provide early detection and forecasting. Teams are focusing on engineered solutions for algae neutralization or removal and re-evaluation of current reservoir operations as potential HAB prevention and management strategies. User-friendly detection tools are also being developed.
In the prevention arena, an ERDC-led team is investigating using federally registered algaecides to treat the problematic algae in the sediment, where it overwinters. Algaecides have been a very effective short-term treatment for HABs for many decades. However, they are not without inherent risks. With this project, ERDC is seeking to evaluate a preventative treatment strategy using algaecides to reduce the abundance of overwintering algal cells in sediment. This will reduce the algal cells and their likelihood of seeding bloom events during subsequent growing seasons.
A body of water with HABs can be seen as analogous to a garden with weeds that spread rampantly every year. Gardeners can ignore the problem and wait for those weeds to grow and take over the garden. However, if time is spent pulling weeds when they are sprouts, significantly less time and energy will be exerted later, and there will be a decrease in the risk of those weeds overtaking the garden.
In the same way, preventative treatment of algae seed beds in sediment has the potential to decrease the intensity of seasonal blooms. Over time, this could potentially diminish the bloom occurrences altogether and restore a body of water’s intended uses. This research could provide new information to help minimize these seasonal HAB impacts.
Another research team is leading advancements in HAB detection with specialized software tools that USACE district water operations managers can use to help monitor water quality indicators. The primary benefits of the software are more rapid detection and less costly methods to detect indicators of HABs. This technology is the result of 10 years of collaborative research that ERDC conducted with academic institutions and other government organizations. Federal agencies, such as the National Oceanic & Atmospheric Administration, are developing similar approaches and have focused on large bodies of water and coastal areas. However, ERDC recognized the need to address specific issues with smaller bodies of water, such as the inland lakes and reservoirs for which USACE is largely responsible.
The tools being developed make use of regularly collected and freely available satellite images that are detailed enough to show where HABs are likely occurring. Many satellites have sophisticated camera-like sensors that take images in which algae pigments can be identified. These pigments would be undetectable by the human eye.
This technology improves detection because field-based sampling may not show conditions across an entire lake and can be cost-, time-, and labor-intensive. In contrast, freely available satellite imagery can provide water operations managers with a full picture to be able to better monitor water quality conditions across an entire body of water using computer-based mapping software that rapidly utilizes geographic information systems and help prioritize where field sampling may be needed. This improved situational awareness leads to more proactive management and control of HABs.
The idea is to apply the cavitation strategically to lessen the impact of HABs in large bodies of water, such as lakes and reservoirs, where the blooms can be so vast it would be impractical to apply the technology to the entire area.
Overall, ERDC is leading 15 separate research efforts directed toward managing HABs when they occur. Among these is a project addressing the design, construction, and testing of a cavitation system for the rapid destruction of cyanobacteria. The study is focusing on using controlled hydrodynamic cavitation, which is the rapid pressurization/depressurization of a flowing liquid through a structure, such as a nozzle. Cavitation results in microbubbles. The collapse of the microbubbles then creates pressure changes that destroy the cyanobacteria. Additionally, the bubble collapse generates chemical reactions that form reactive oxygen species, including superoxides and hydroxyl radicals that destroy the toxins produced by the cyanobacteria. Within hours the reactive oxygen species react with organic material in the water and dissipate. As a result, the technology’s impact on other ecosystems is small.
The idea is to apply the cavitation strategically to lessen the impact of HABs in large bodies of water, such as lakes and reservoirs, where the blooms can be so vast it would be impractical to apply the technology to the entire area. The objective would be to manage the algae where it is likely to do the most harm.
ERDC has been investigating cavitation on and off for several years, starting in 2015, with smaller-scale studies. In laboratory tests, a 71 percent reduction in chlorophyll was seen after 30 hours of treatment, indicating that the technology is as effective as they imagined. Currently, the research team is developing plans to test the cavitation system with a powerful pump and a variety of nozzle sizes at the pilot scale at Lake Neatahwanta in upstate New York. The next step would be to develop design specifications and equations for the system.
Through its collaboration with federal, state, and university partners, ERDC is leading the way on engineered solutions to prevent, identify, and manage harmful algae. This work is on top of 24 additional research projects ERDC has underway that will result in the reduced occurrence, duration, and intensity of HAB events. Reducing the frequency and severity of HAB events will lessen ecological, economic, and public health impacts on our nation’s water resources. It will also minimize impacts to navigation, operations, and recreation missions while leading to improved guidance for water management and response plans nationwide.
Jen Seiter-Moser, Ph.D., is Technical Director, Civil Works Environmental Engineering and Sciences, Mandy Michalsen, Ph.D., P.E., is Strategic Initiatives Program Manager, and Holly Kuzmitski is Public Affairs Specialist, U.S. Army Engineer Research & Development Center. They can be contacted at email@example.com; mandy.m.michalsen@ usace.army.mil; and firstname.lastname@example.org.
[This article first published in the July-August 2021 issue of The Military Engineer.]