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Satellite-based monitoring of cyanobacteria blooms from 2002–2011 for 11 reservoirs with watersheds along an agricultural gradient
Citation:
Smucker, N., B. Schaeffer, J. Beaulieu, AND C. Nietch. Satellite-based monitoring of cyanobacteria blooms from 2002–2011 for 11 reservoirs with watersheds along an agricultural gradient. 2018 Society for Freshwater Science Annual Meeting, Detroit, MI, May 20 - 24, 2018.
Impact/Purpose:
Cyanobacteria harmful algal blooms (HABs) have been increasingly observed in reservoirs and can threaten water quality, human health, economic activity, and ecosystems. Satellite-based monitoring, such as the Envisat Medium Resolution Imaging Spectrometer used in our study, can be used to estimate cyanobacteria cell densities with high temporal frequencies. In this study, we used to MERIS data for 11 reservoirs in Indiana, Ohio, and Kentucky (1) to document changes in cyanobacteria cell densities from 2002-2011, (2) to compare these trends with those found using microscopy enumeration, (3) to characterize relationships with watershed land cover and field-based indicators of eutrophication (e.g., chlorophyll a, secchi depth, total phosphorus, and total organic nitrogen), and (4) to quantify the frequencies of bloom severities posing high probabilities of human health risks. Results can inform predictive models of blooms, the prioritization of waterbodies targeted for management, and actions affecting recreational and drinking water sources.
Description:
Imagery acquired by the Envisat Medium Resolution Imaging Spectrometer from 2002-2011 was used to estimate cyanobacteria cell densities for 11 reservoirs in Indiana, Ohio, and Kentucky, USA (surface areas 8–43 km2; 864 total images spanning May–September). This initial analysis is based on the means of all pixels (300 m resolution) for each reservoir on each observation date. Cyanobacteria cell densities significantly increased as watershed percent forested land cover decreased, and this relationship was strongest in June and July. Mean cyanobacteria cell densities were positively correlated with the means of chlorophyll a, total phosphorus, and total nitrogen, which were sampled intermittently during the timespan coinciding with satellite imagery. Based on the maximum mean cell density observed each year for each reservoir (n=110), 4.5% of observations had densities posing low risk, 35.5% had densities posing moderate risk, and 60% had densities posing high risk to human health. Additional work will examine temporal trends and make comparisons to field collected phytoplankton, but based on relationships with watershed land cover and field-based nutrient and chlorophyll measurements, these results highlight the potential usefulness of satellite derived estimates of cyanobacteria.
