Five-Year Study of Algal Blooms in Lake Fayetteville Reveals Trends
For the last five years, scientists with the Arkansas Water Resources Center (AWRC) have monitored the cycles of nutrients, cyanobacteria and toxins in Lake Fayetteville, aiming to determine better ways to guide recreational users on the risk of harmful algal blooms.
These scientists, a part of the Arkansas Agricultural Experiment Station, have focused on cyanobacterial harmful algal blooms (HABs) in the 194-acre lake since 2018. Originally created in 1949 to supply the city’s water, the lake is now used for fishing, kayaking, and other recreational purposes.
Lake Fayetteville, a small watershed, is greatly influenced by human activity. As Fayetteville’s population grows, the watershed has shifted from agricultural to urban, allowing the AWRC to study a hypereutrophic system – very productive lake.
Hypereutrophic water contains high concentrations of nutrients such as phosphorus and nitrogen. Although necessary for plant growth, excess nutrients can lead to harmful blooms of cyanobacteria, some of which produce toxins like microcystin, which can be dangerous to humans, as well as pets and wildlife.
While warnings about HABs are often posted with signage, AWRC envisions a more comprehensive, data-driven approach to managing the lake’s occurrence of HABs and the likely presence of toxins like microcystin.
Instead of relying solely on expensive toxin analyses, AWRC proposes using simpler and more cost-effective measurements, such as water temperature and the fluorescence of phycocyanin, a pigment in cyanobacteria, and chlorophyll, a pigment in all algae. Raw fluorescence of chlorophyll and phycocyanin increase when more algae and cyanobacteria are in the water, but there is some balance between these two pigments. These indicators could serve as proxies for toxin levels and help assess recreational safety in near real-time.
Dr. Brian Haggard, director of the AWRC, and his team analyzed a subset of 2020 monitoring data from Lake Fayetteville.
The study, titled “Microcystin shows thresholds and hierarchical structure with physiochemical properties at Lake Fayetteville, Arkansas, May through September 2020,” revealed that microcystin levels peak during late spring, early summer, and fall, coinciding with the lake’s turnover cycles, where nutrient mixing promotes cyanobacterial growth.
These findings suggest that understanding the natural cycles of nutrient mixing and their effects on cyanobacterial blooms is critical to managing Lake Fayetteville’s water quality.
Since 2020, the data at Lake Fayetteville has proven to be a critical tool in monitoring developing cyanobacterial blooms. The toxin concentrations have shown some general trends, including, where these toxins might be in greater concentrations:
- water temperature needs to be greater than 77 F (25 C),
- raw fluorescence of phycocyanin need to be greater than ~4500,
- The ratio of phycocyanin to chlorophyll fluorescence needs to be between 0.5 and 2.
The rather simple measurements might provide an easier way to provide guidance about whether the risk of cyanobacterial blooms and potential toxins is high. For more about this topic, check out the study titled “Chlorophyll and Phycocyanin Raw Fluorescence May Inform Recreational Lake Managers on Cyanobacterial HABs and Toxins: Lake Fayetteville Case Study.”
AWRC’s ongoing research aims to equip city officials with the tools they need to monitor these blooms more effectively and to ensure that the lake remains safe for recreational use, even as the city continues to grow.
