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Historical Changes in Water Quality, Temperature Regimes, and Cyanobacteria Densities of 20 Midwestern USA Reservoirs
Citation:
Smucker, N., J. Beaulieu, C. Nietch, J. Young, M. Higgs, AND W. Barnett. Historical Changes in Water Quality, Temperature Regimes, and Cyanobacteria Densities of 20 Midwestern USA Reservoirs. 2017 Society for Freshwater Science Annual Meeting, Raleigh, NC, June 04 - 08, 2017.
Impact/Purpose:
Cyanobacteria harmful algal blooms (HABs) have been increasingly observed in reservoirs and can threaten water quality, human health, economic activity, and ecosystems. This work characterized changes in the occurrence and severity of cyanobacterial blooms since 1988 in 20 reservoirs located in Indiana, Kentucky, and Ohio. The goal of this research is to understand what factors have led to increased occurrences in most of these reservoirs, which will inform future management efforts and decisions affecting watersheds, aquatic ecosystems, and responses to HABs.
Description:
Water quality and cyanobacteria densities from 1989-2015 were compiled for 20 Midwestern USA reservoirs. Maximum summer cyanobacteria densities increased over the last 7-15 years of the record, with greatest increases typically observed in reservoirs with low watershed forest cover. In 2015, greater summer maximum cell densities were associated with decreased watershed forest cover, and 17 reservoirs had densities posing high probabilities of human health risks (>100 million cells/liter). Summer months had little increase in surface water temperature over the 26-year record, but May temperatures increased, particularly in reservoirs with low surface area to volume ratios (1–2 degrees Celsius/decade). In one reservoir (analysis of others in progress), mean dissolved oxygen in May decreased in the hypolimnion (5.4 to 2.9 mg/L) and increased in the epilimnion (8.3 to 10.8 mg/L) since 1989. Earlier seasonal warming of reservoirs likely contribute to changes in stratification regimes and may interact with increasing nutrients to affect cyanobacteria blooms. Ongoing analyses seek to link environmental change and reservoir characteristics with cyanobacteria abundances and to inform future management of algal blooms.
