Report Date - May 15th to May 21st, 2023

Prepared By: Andrew Kamerosky and Rachel Scime

For the week of May 15th, 2023, to May 21st, 2023, all basins in the IRL experienced an increase in estimated median ChlA. The largest increase over the week was observed in the C-BRL with a 13.84 µg/L increase, while the N-BRL had the highest median ChlA at the end of the week at 21.59 µg/L. The C-NIRL had an increase of 12.59 µg/L, with the highest ChlA concentrations around the NASA Causeway. Then the N-CIRL had an increase of 11.14 µg/L. The smallest increase was in the N-NIRL with only an increase of 0.69 µg/L, with both the N-NIRL and SML having the lowest median ChlA at the end of the week at 6.83 and 7.64 µg/L respectively. 

There were 2 usable Sentinel-2 scenes and 5 Sentinel-3 scenes during this period. 

Table 1 - Sentinel 3 estimated ChlA percent change for the week of May 15, 2023, to May 21, 2023, by IRL Basin.

The availability and usability of satellite imagery is contingent upon both the satellite being overhead and low cloud cover. The orbits of the Sentinel satellites will on occasion cover a portion versus all of the Indian River Lagoon. Likewise, cloud cover can also result in only portions of the Indian River Lagoon (IRL) being visible. Table 2 below lists the availability of Sentinel imagery and its usability for Harmful Algal Bloom (HAB) analysis.

Table 2 - Sentinel 2 and 3 imagery availability for May 15th-May 21st, 2023

N - Imagery Not Available

Y - C - Imagery Available, Cannot Use Due to Cloud Cover

Y - P - Imagery Available, Only Partial Imagery of IRL

Y - G - Imagery Available, No Issues Over the IRL

20 May 2023 - Sentinel 2B

There were 2 scenes from Sentinel 2 that were usable for the detection of bloom activity from May 15th, 2023, to May 21st, 2023. The following analysis focuses on the partial scenes from May 15th and May 20th. During both of these days data from the N-NIRL, SML, and C-NIRL were not available. Due to excessive cloud cover over the C-BRL, N-CIRL, and S-NIRL on May 20th ChlA estimates were only calculated from cloud free areas and may not represent the entire basin. (Figure 1, Figure 2)

Figure 1 - Sentinel 2 estimated Chlorophyll A (ChlA) Levels in Micrograms/Liter (µg/L) for May 15th, 2023, over sections of the Mosquito Lagoon (ML), Indian River Lagoon (IRL), and Banana River (BR). The box plot represents the range of estimated ChlA values for each Basin, with the boxes showing the second quartile, median, and third quartile, and the whiskers representing the first and fourth quartiles.

Figure 2 - Sentinel 2 estimated Chlorophyll A (ChlA) Levels in Micrograms/Liter (µg/L) for May 20th, 2023, over sections of the Mosquito Lagoon (ML), Indian River Lagoon (IRL), and Banana River (BR). The box plot represents the range of estimated ChlA values for each Basin, with the boxes showing the second quartile, median, and third quartile, and the whiskers representing the first and fourth quartiles.

18 May 2023 - Sentinel 3B

21 May 2023 - Sentinel 3B

There were 5 scenes from Sentinel 3 that were usable for detection of bloom activity from May 15th, 2023, to May 21st, 2023. The following analysis focuses on scenes from May 18th and May 21st. Due to excessive cloud cover over the N-BRL May 21st ChlA estimates were only calculated from cloud free areas and may not represent the entire basin. (Figure 3, Figure 4).

Figure 3 - Sentinel 3 estimated Chlorophyll A (ChlA) Levels in Micrograms/Liter (µg/L) for May 18th, 2023, over sections of the Mosquito Lagoon (ML), Indian River Lagoon (IRL), and Banana River (BR). The box plot represents the range of estimated ChlA values for each Basin, with the boxes showing the second quartile, median, and third quartile, and the whiskers representing the first and fourth quartiles.

Figure 4 - Sentinel 3 estimated Chlorophyll A (ChlA) Levels in Micrograms/Liter (µg/L) for May 21st, 2023, over sections of the Mosquito Lagoon (ML), Indian River Lagoon (IRL), and Banana River (BR). The box plot represents the range of estimated ChlA values for each Basin, with the boxes showing the second quartile, median, and third quartile, and the whiskers representing the first and fourth quartiles.

SJRWMD IRL Continuous Monitoring Stations

The St. John River Water Management District (SJRWMD) Continuous Monitoring (CM) stations measured Chlorophyll Reflective Fluorescence Units (RFU), 3 of 5 stations experienced a decrease. (Figure 5, Table 3)

Current and historical data are added to the SJRWMD’s database continuously; subsequent visits may reflect such additions or revisions. SJRWMD provides no warranty as to the accuracy, reliability, or completeness of these data.

Figure 5 - St Johns River Water Management District (SJRWMD) Indian River Lagoon Continuous Monitoring Station Relative Chlorophyll A (ChlA) readings from May 15th-May 21st, 2023, as described in Table 3.

Below are the estimated ChlA levels measured by SJRWMD continuous monitoring stations and Sentinel 3 within a radius of 0.75 miles (1.2 km) of the SJRWMD continuous monitoring stations for May 15th, 2023, to May 21st, 2023. The Continuous Monitoring Station data is reported hourly by SJRWMD and this report provides the 95th percentile of RFU for a given day. Data for IRLML02 for May 15th 7:00-8:00, May 16th 1:00-4:00, and May 16th 10:00- May 21st 23:00 were not available. 

Table 3 - St Johns River Water Management District (SJRWMD) Indian River Lagoon Continuous Monitoring Station Average Relative Chlorophyll A (ChlA) 95th percentile levels for the week of May 15, 2023.

Methods

HAB’s observed by this project are defined as over 80 Micrograms/Liter (µg/L) Chlorophyll A (ChlA) (as estimated by a calibrated Normalized Difference Chlorophyll Index (NDCI)) and persistent across the week in review. The algorithms that transform the NDCI index value to estimated ChlA concentrations were developed using a second-order polynomial equation. The Sentinel 2 (S2) equation has a Root Square (R2) of 0.81 with a Root Mean Square Error (RMSE) of 14.14 ug/L of ChlA. The Sentinel 3 (S3) equation has an R2 of 0.92 and an RMSE of 9.92 ug/L ChlA. The RMSE is a measure of the accuracy of a model in estimating values, ChlA in this instance, where a lower value is indicative of higher accuracy. It does not identify if the model consistently over or underestimates the modeled values. The equations are below:

• S2 Estimated ChlA = 297.36(NDCI)2 + 313.98(NDCI) + 36.152

• S3 Estimated ChlA = 437.07(NDCI)2 + 348.98(NDCI) + 33.928

   Figure 6. SJRWMD Continuous Monitoring stations and IRL Basins used for S2 and S3 analysis. 

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