New research aims to solve the harmful algal blooms plaguing North Carolina’s largestnatural lake

By: Ciara Daly

Introduction

For this blog post, I had the pleasure of interviewing Mary Kate Rinderdale, a PhD candidate at the University of North Carolina Chapel Hill’s Institute of Marine Science (UNC IMS) in Morehead City. Rinderdale’s research is within the Dr. Nathan Hall lab studying cyanobacterial blooms and is advancing what we know about the largest natural lake in North Carolina, Lake Mattamuskeet. 

Rinderdale began her research journey at University of Ohio, where she was inspired by a water quality class; in her remaining time as an undergraduate, she completed a summer research experience for undergraduates studying cyanobacterial blooms in Lake Erie, where she met Dr. Hans Pearl from UNC IMS. As a PhD student at UNC, she has continued water quality work through her thesis project, which focuses on toxins produced by cyanobacteria in Lake Mattamuskeet.

The Lake Mattamuskeet Crisis

Spanning 40,000 acres, Lake Mattamuskeet is the largest natural lake in North Carolina. The lake functions as a crucial feeding and roosting ground for migrating waterfowl. The lake is managed as part of the Mattamuskeet Wildlife Refuge by US Fish and Wildlife, and not only a key habitat for aquatic species, but also serves as a recreational area for many people on the NC coast.²

Water quality in Lake Mattamuskeet has declined since the 1980s. The Lake has experienced die-offs of submerged aquatic vegetation coupled with harmful algal blooms (HABs) that overtake the ecosystem.³ Rinderdale explains that “harmful algal blooms are these big amounts of any type of phytoplankton that grow really quickly, can take over an ecosystem, and cause a lot of harm”.¹ Some of these negative ecological consequences produced from HABs include increased water turbidity, meaning plants on the lake floor can’t get the sunlight they need to survive, as well as toxins and oxygen dead zones that cause fish kills.

Studying cyanobacterial blooms 

Rinderdale describes why she chose cyanobacteria as the focus of her project because of their toxin production: “In particular, cyanobacterial algal blooms also produce a lot of toxins. These little prokaryotes (simple cells) when the conditions are right in a lake, they just grow rapidly and become dense to the point that it discolors the water. I am studying why that is happening in this lake, which is the largest natural lake in NC”.¹

Cyanobacteria are the smallest class of phytoplankton - meaning organisms that live in the water column and perform photosynthesis using sunlight to make their own energy. Phytoplankton serve as the basis of the marine food web. However, in the process of metabolization, cyanobacteria can produce harmful toxins that impact the surrounding aquatic ecosystems.

There are three primary components to this project. The first is toxin production, which involves assessing which kinds of toxins those cyanobacteria produce. This is coupled with nutrient acquisition, and analyzing the different acquisition routes of nitrogen, which is a critical element for primary producers. Finally, Rinderdale is overarchingly looking to see if there are potential commercial products such as algaecides that can be used to mitigate those blooms and their harmful consequences on the lake ecosystem.

Nutrients

Rinderdale points out that “one unique aspect of cyanobacteria compared to other phytoplankton is that they can fix atmospheric nitrogen to meet their own nitrogen demands in a process”.¹ In Lake Mattamsukeet, two dominant cyanobacteria species are nitrogen fixers; through using acetylene reduction assays (ARAS), she has been able to measure how much nitrogen would be fixed by cyanobacteria.

Cyanobacteria may proliferate in the lake because of their unique ability to fix their own nitrogen - meaning they are resilient to periods of otherwise low nutrient availability of nitrogen that other phytoplankton would be vulnerable to. Identifying if this is the case could be critical to determining how to proceed with conservation decisions that attempt to reduce nutrient influx to the lake to prevent blooms.

Toxins

To analyze toxin production, Rinderdale has been culturing cyanobacteria from the lake and running assays to detect toxin levels in the lab. In particular, she is focusing on a target species from the Raphidiopsis genus which is a known toxin producer in other similar lake systems. Preliminary results of these assays suggest the presence of cylindrospermopsin toxin-producing Raphidiopsis, which hasn’t previously been isolated and genetically confirmed yet in Lake Mattamuskeet. This type of cyanobacteria evolved in the tropics and has expanded to the United States; researchers suspect they may be transmitted by bird species from lakes on continent to continent.⁴

Mitigation and future directions

The mitigation aspect of this research has centered around testing a hydrogen peroxide-based algaecide in small microcosm experiments to test its efficacy and monitor any potential side effects, like killing non-harmful phytoplankton. These microcosm experiments could pave the way for future permitting to deploy the algaecide in Lake Mattamuskeet and prevent future algal blooms.

Conclusion

Rinderdale emphasizes that collaboration has been crucial every step of the way for her research. Through working with other researchers, she has been able to merge her advisor Dr. Nathan Hall and her own expertise in monitoring and assessing phytoplankton from an ecological niche standpoint with newer molecular technologies to provide more data on these communities. In the next stage of her project, Rinderdale is working with Professor Scott Gifford, who specializes in microbial genetics within the Earth and Marine Sciences department at UNC, to sequence the genome of cyanobacteria from the lake. In addition, she will soon be analyzing a metagenome from the lake. This is a pivotal step in understanding the overall phytoplankton composition and community structure in the ecosystem; Rinderdale describes a key aspect of this new methodology as “really getting the depth of sequencing the genomes tells us who is actually there and what they might be doing.”¹ Preliminary results suggest a lot of the target species, Raphidiopsis, is present in the population - making earlier findings regarding toxin production even more relevant.  Another collaborative effort has been with the Schnetzer lab at North Carolina State University’s Center for Marine Sciences and Technology; Astrid Schnetzer taught Rinderdale how to perform ELISA assays to assess toxins and served as a resource throughout the project.

Rinderdale’s favorite part of her project are the field days out on the boat at Lake Mattamuskeet taking water samples; she describes it as a beautiful environment to study and experience. When asked about her unique experience completing her PhD at the Institute of Marine Science in Morehead City, she says that “being at the beach with my friends and getting paid to study something that I am really interested in has been fantastic, I wouldn’t choose anywhere else for the world.”¹

References

1.     Interview with Mary Kate Rinderdale, PhD candidate, 2/13/2026

2.     Mattamuskeet National Wildlife Refuge. FWS.gov. https://www.fws.gov/refuge/mattamuskeet/about-us.

3.     Moorman, M. C.; Augspurger, T.; Stanton, J. D.; Smith, A. Where’s the Grass? Disappearing Submerged Aquatic Vegetation and Declining Water Quality in Lake Mattamuskeet. Journal of Fish and Wildlife Management 2017, 8 (2), 401–417. https://doi.org/10.3996/082016-jfwm-068.

4.     Laboratory, N. G. L. E. R. NOAA National Center for Research on Aquatic Invasive Species (NCRAIS). nas.er.usgs.gov. https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?Species_ID=2651.