Chitosan, a natural compound, is added to concentrations of local sediments and commercial clays to control harmful algal blooms. We are studying the impacts of this mitigation technique on natural populations of invertebrates, fishes, and submerged aquatic vegetation in Chesapeake Bay. Also, we are determining how much chitosan causes sufficient aggregation, sinking, and settling of local populations of the toxic cyanobacterium Microcystis aeruginosa.
Why We Care
Dense accumulations of some cyanobacterium Microcystis aeruginosa blooms in Chesapeake Bay accompany toxin levels (microcystin-LR) that exceed World Health Organization standards. These elevated toxin levels lead to beach closures, warnings prohibiting some recreational activities in the Chesapeake Bay watershed, and domestic animal mortalities. Nutrient enrichment of the coastal zone leads to conditions promoting harmful algal blooms and cyanobacteria, formally known as blue-green algae.
What We Are Doing
Clay or other particles combine with and aggregate cyanobacterium cells through the aid of the commercial flocculent chitosan. Chitosan is a complex carbohydrate, similar to chitin in insect and crustacean exoskeletons. The resulting heavy aggregates outweigh the buoyancy of the algal cells, causing the aggregated algal cells to sink to the bottom. As the aggregates sink through the water column, they continue to pick up more algal cells in a process called “sweep floc,” thus removing large amounts of the bloom and toxins within the cells. Once on the bottom, the algae and clay aggregates decay, mineralize, and the nutrients are released into the environment where they fuel submerged aquatic vegetation seed germination and growth.
There are four phases to this project: (1) laboratory experiments, (2) field mesocosm studies, (3) open water mitigation, and (4) operational and technology transfer.
- Laboratory experiments employ lab cultures and field-collected colonies of toxic and non-toxic M. aeruginosa populations to determine amounts of sediments, commercial clays, and chitosan most effective at removing M. aeruginosa populations from suspension. Using submerged aquatic vegetation (SAV) added to the sediment and floc mixture we determine germination and growth of seeds. Since clays can impact filter feeding rates in benthic suspension feeders, we assess macrofauna impacts through growth of cultured juvenile clams (Rangia cuneata). In addition, we estimate potential Chesapeake Bay fish responses to the sediment mixture as well as to Microcystsis aggregates.
- Field mesocosom studies (intermediate-size field enclosures) test the impacts of clay and chitosan together on the cyanobacterium blooms using mesocosm “limnocorrals;” one-meter-square, water column–long cylinders open at both ends, supported at the surface with floats and secured into the bottom sediment.
- In open water we deploy limnocorrals for one month in tidal fresh M. aeruginosa–rich areas for natural sediment or clay/chitosan applications. This compares natural SAV and benthic macrofauna mitigation responses to non-treated populations, including assessments of toxin concentration in exposed plants and animals; fish collected from bloom and non-bloom sites will be sacrificed for toxin analyses.
- We collaborate actively with the Maryland Department of Natural Resources (MD DNR). The results of this study may lead to an operational program within the state. Operational transfer to MD DNR will depend on our ability to prove that mitigated blooms pose little threat to natural populations of invertebrates and fishes and promote seed germination and subsequent growth of native submerged aquatic plants.
This project is led by the University of Maryland’s Center for Marine Biotechnology.
Benefits of Our Work
Our goal is to develop clay mitigation techniques that can be used by Chesapeake Bay’s coastal managers. This would expand the state’s role from monitoring and regulation to mitigation of recurrent blooms.
Next Steps
- We will assess stakeholders’ understanding of blooms and look for opportunities to develop community mitigation efforts through public workshops.
- We will document potential mitigation techniques for routine adoption by the State of Maryland.
- We will produce a manual detailing suppliers and procedures required to routinely and inexpensively mitigate recurrent Chesapeake coastal zone Microcystis blooms. The manual will include: (1) a list of required permits and recommended monitoring strategies, and (2) outreach and education activities to inform and allay local citizen and environmental group concerns about mitigation techniques.