Citation:

Ignatius, A., Tom Purucker, B. Schaeffer, K. Wolfe, E. Urquhart, AND D. Smith. Satellite-derived cyanobacteria frequency and magnitude in headwaters & near-dam reservoir surface waters of the Southern U.S. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 822:153568, (2022). https://doi.org/10.1016/j.scitotenv.2022.153568

Impact/Purpose:

Cyanobacteria harmful algal blooms (cyanoHAB) are a costly water management issue and bloom recurrence is associated with negative impacts to human, animal, and environmental health, as well as the economy. The unique morphology of reservoirs also creates suitable conditions for excessive algae growth and associated cyanobacteria blooms by providing a shallow warm water environment with relatively high nutrient inputs, deposition, and nutrient storage. Evaluation of these cyanoHAB events revealed seasonal trends with the highest frequency occurring in mid-summer to fall. Within the southern U.S., spatial analysis of OLCI data for sixty large reservoirs revealed more frequent and higher magnitude cyanoHABs in the relatively shallow in-flow headwaters compared to near-dam surface waters. Of the sixty reservoirs studied, 98% had more frequent occurrence above the concentration of >100,000 cells/mL in headwaters compared to near-dam areas. Examination of reservoirs also identified extremely high concentration cyanobacteria events occurring in 70% of headwater locations while only 30% of near-dam locations exceeded the extremely high concentration threshold. These research results related to reservoir headwaters can be leveraged to characterize the trajectory, extent, and health impacts of HABs and incorporates large-scale surveillance datasets to map and characterize populations, assess health impacts, toxin distributions, and their frequencies.

Description:

Reservoirs are dominant features of the modern hydrologic landscape and provide vital services. However, the unique morphology of reservoirs can create suitable conditions for excessive algae growth and associated cyanobacteria blooms in shallow in-flow reservoir locations by providing warm water environments with relatively high nutrient inputs, deposition, and nutrient storage. Cyanobacteria harmful algal blooms (cyanoHAB) are costly water management issues and bloom recurrence is associated with economic costs and negative impacts to human, animal, and environmental health. As cyanoHAB occurrence varies substantially within different regions of a water body, understanding in-lake cyanoHAB spatial dynamics is essential to guide reservoir monitoring and mitigate potential public exposure to cyanotoxins. Cloud-based computational processing power and high temporal frequency of satellites enables advanced pixel-based spatial analysis of cyanoHAB frequency and quantitative assessment of reservoir headwater in-flows compared to near-dam surface waters of individual reservoirs. Additionally, extensive spatial coverage of satellite imagery allows for evaluation of spatial trends across many dozens of reservoir sites. Surface water cyanobacteria concentrations for sixty reservoirs in the southern U.S. were estimated using 300 m resolution European Space Agency (ESA) Ocean and Land Colour Instrument (OLCI) satellite sensor for a five year period (May 2016–April 2021). Of the reservoirs studied, spatial analysis of OLCI data revealed 98% had more frequent cyanoHAB occurrence above the concentration of >100,000 cells/mL in headwaters compared to near-dam surface waters (P < 0.001). Headwaters exhibited greater seasonal variability with more frequent and higher magnitude cyanoHABs occurring mid-summer to fall. Examination of reservoirs identified extremely high concentration cyanobacteria events (>1,000,000 cells/mL) occurring in 70% of headwater locations while only 30% of near-dam locations exceeded this threshold. Wilcoxon signed-rank tests of cyanoHAB magnitudes using paired-observations (dates with observations in both a reservoir's headwater and near-dam locations) confirmed significantly higher concentrations in headwater versus near-dam locations (p < 0.001).

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