Study area

We selected the states of Florida and Ohio as our study areas for three primary reasons (Fig. 1):

To examine cyanoHAB magnitudes in lakes that are known to have cyanoHAB related water quality issues. These two states also have a significant number of lakes that are resolvable in MERIS/OLCI data. Many lakes in the Coastal Plains ecoregion, which includes Florida, are known to have cyanoHAB issues, with 34% of lakes known to be hypereutrophic by the NLA in 2007³⁰. The 2007 NLA also reported that 43% of lakes in Florida had microcystin present³¹. Similarly, cyanoHABs are a common water quality issue in the Temperate Plains ecoregion, which includes western Ohio, where 45% lakes are considered hypereutrophic³⁰. Approximately 32% of lakes in Ohio had microcystin present in 2007³¹.

To consider results from lakes located in different geographic and climatic regimes. The climate in Florida is subtropical, with hot, humid, high precipitation summers and mild, dry winters. In contrast, Ohio has a temperate climate with cold winters, hot and humid summers, and year-round moderate precipitation³².

To assess the impacts of differences in data coverage in each location. MERIS full resolution (FR) data collection frequency prior to 2008 was inconsistent. The temporal frequency of MERIS FR data over Ohio is higher than that over Florida during this time period. The consideration of two states with different temporal data coverage will illustrate the effect of reduced data frequency on the bloom magnitude metrics.

Map of the study region showing the location of lakes in (A) Florida and (B) Ohio. In total, 135 lakes in Florida and 21 lakes in Ohio, were resolvable with the full resolution MERIS data and are used in this study. Land and lakes are shown in gray and blue colors respectively.

Figure 2 shows the steps of the data analysis and workflow carried out in this study. Individual components of the data and methods are presented below.

Schematic diagram of data processing and workflow for calculating bloom magnitude and area-normalized magnitude. Output stages in the workflow are shaded gray.