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Evaluation of cyanobacteria cell count detection derived from MERIS imagery across the eastern USA
Lunetta, R., B. Schaeffer, R. Stumpf, D. Keith, S. Jacobs, AND M. Murphy. Evaluation of cyanobacteria cell count detection derived from MERIS imagery across the eastern USA. REMOTE SENSING OF ENVIRONMENT. Elsevier Science Ltd, New York, NY, 157(0):24-34, (2015).
Cyanobacteria (Cyano) and their cyanotoxins (Cyano-t) are unregulated contaminants. However, Cyan-t are included in the US Environmental Protection Agency (USEPA) Safe Drinking Water Act’s “Contaminant Candidate List” (USEPA, 2013a). Cyano-t blooms occur worldwide and are associated with human respiratory irritation, taste and odor of potable water, and human illness as a result of ingestion or skin exposure during recreational activities. Pets, domestic animals, and wildlife are also affected by exposure to Cyano-t, with deaths reported annually (Backer, 2002). Cyano-t can be found in water bodies used for drinking, aquaculture, crop irrigation, and recreation (Stewart et al., 2006). It has been hypothesized that Cyano-t could even be transferred to crops designated for human consumption via spray irrigation (Hunter et al., 2010). Cyano harmful algal blooms (CyanoHABs) can be aesthetically unappealing, which is enhanced by their tendency to linger and concentrate along shorelines where they are encountered frequently by the public (Wynne et al., 2010). Increasing frequency, duration and magnitude of blooms within some systems has prompted management actions. Postulated causes of CyanoHABs include excessive nutrient loads, introduction of invasive species (Budd et al., 2001), and increasing temperatures from climate change and variability, where certain CyanoHABs favor warmer surface waters (Paerl and Huisman, 2008). Alterations in land-cover (e.g., urbanization) and changes in land-use practices, such as intensive agricultural practices and biofuels mandates (e.g., 2007 Energy Independence and Security Act) can result in watersheds experiencing additional sediment loading and nutrient delivery, which can influence Cyano growth (Lunetta et al., 2010; USEPA, 2011; Michalak et al., 2013).
Inland waters across the United States (US) are at potential risk for increased outbreaks of toxic cyanobacteria (Cyano) harmful algal bloom (HAB) events resulting from elevated water temperatures and extreme hydrologic events attributable to climate change and increased nutrient loadings associated with intensive agricultural practices. Current monitoring efforts are limited in scope due to resource limitations, analytical complexity, and data integration efforts. The goals of this study were to validate a new ocean color algorithm for satellite imagery that could potentially be used to monitor CyanoHAB events in near real-time to provide a compressive monitoring capability for freshwater lakes (>100 ha). The algorithm incorporated narrow spectral bands specific to the European Space Agency’s (ESA’s) MEdium Resolution Imaging Spectrometer (MERIS) instrument that were optimally oriented at phytoplankton pigment absorption features including phycocyanin at 620 nm. A validation of derived Cyano cell counts was performed using available in situ data assembled from existing monitoring programs across eight states in the eastern US over a 39-month period (2009–2012). Results indicated that MERIS provided robust estimates for Low (10,000–109,000 cells/mL) and Very High (>1,000,000 cells/mL) cell enumeration ranges (approximately 90% and 83%, respectively). However, the results for two intermediate ranges (110,000–299,000 and 300,000–1,000,000 cells/mL) were substandard, at approximately 28% and 40%, respectively. The confusion associated with intermediate Cyano cell count ranges was largely attributed to the lack of available Cyano taxonomic data for the in situ measurements that would have facilitated conversions between cell counts and cell volumes. The results of this study show that MERISderived products could be used to monitor the onset of CyanoHAB events and potentially provide an alarm capability for major outbreaks of concern in freshwater systems.