Quantifying national and regional cyanobacterial occurrence in US lakes using satellite remote sensing
Citation:
Coffer, M., B. Schaeffer, J. Darling, E. Urquhart, AND W. Salls. Quantifying national and regional cyanobacterial occurrence in US lakes using satellite remote sensing. ECOLOGICAL INDICATORS. Elsevier Science Ltd, New York, NY, 111:105976, (2020). https://doi.org/10.1016/j.ecolind.2019.105976
Impact/Purpose:
This study provides a metric to quantify the percentage of lakes across CONUS and within nine climate regions experiencing cyanoHABs for each week from 2008-2011 and 2017. Using satellite data, we presented results for the percentage of lakes with a bloom, the percentage of lakes without a bloom, and the percentage of lakes with no valid data for each weekly composite. The CONUS bloom season followed a seasonal pattern that is well-supported in the literature. Cyanobacteria blooms increased gradually throughout the growing season before reaching a peak in late-summer or early-autumn and decreasing rapidly into winter months. The percentage of lakes not experiencing a bloom peaked earlier in the summer before declining, as more of these lakes began to experience blooms likely with increasing air and water temperature. Wintertime data was persistently limited due to snow and ice cover, particularly in the northern latitude regions. On a regional scale, results revealed an interesting cyanoHAB percentage pattern in the Southeast. Contrary to the pattern seen at the CONUS scale, in the Southeast region we found that the percentage of lakes experiencing a bloom peaked over the winter and reached its lowest values during the summer. A small case study on Lake Harris in Florida illustrated this phenomenon on a monthly timescale. Several possible explanations were addressed, including environmental conditions, anthropogenic impacts, and satellite artifacts. Further research is needed to fully understand this pattern. Results from this research can be used to monitor annual trends in the presence of cyanobacteria in inland lakes across CONUS. Once more data becomes available, comparisons can be made to understand how the presence and phenology of cyanobacteria events might be changing on an annual basis.
Description:
Cyanobacterial harmful algal blooms are the most common form of harmful algal blooms in freshwater systems throughout the world. However, in situ sampling of cyanobacteria in inland lakes is limited both spatially and temporally. Satellite data has proven to be an effective tool to monitor cyanobacteria in freshwater lakes across the United States. This study uses data from the European Space Agency Envisat MEdium Resolution Imaging Spectrometer and the Sentinel-3 Ocean and Land Color Instrument to provide a national overview of the percentage of lakes experiencing a cyanobacterial bloom on a weekly basis for 2008–2011, 2017, and 2018. A total of 2321 lakes across the contiguous United States were included in the analysis. We examined four different thresholds to define when a waterbody is classified as experiencing a bloom. Across these four thresholds, we explored variability in bloom percentage with changes in seasonality and lake size. As a validation of algorithm performance, we analyzed the agreement between satellite observations and previously established ecological patterns, although data availability in the wintertime limited these comparisons on a year-round basis. Changes in cyanobacterial bloom percentage at the national scale followed the well-known temporal pattern of freshwater blooms. The percentage of lakes experiencing a bloom increased throughout the year, reached a maximum in fall, and decreased through the winter. Wintertime data, particularly in northern regions, were consistently limited due to snow and ice cover. With the exception of the Southeast and South, regional patterns mimicked patterns found at the national scale. The Southeast and South exhibited an unexpected pattern as cyanobacterial bloom percentage reached a maximum in the winter rather than the summer. Lake Jesup in Florida was used as a case study to validate this observed pattern against field observations of chlorophyll a. Results from this research establish a baseline of annual occurrence of cyanobacterial blooms in inland lakes across the United States. In addition, methods presented in this study can be tailored to fit the specific requirements of an individual system or region.
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DOI: Quantifying national and regional cyanobacterial occurrence in US lakes using satellite remote sensing