Report Date - May 22nd to May 28th, 2023

Prepared By: Andrew Kamerosky and Rachel Scime

For the week of May 22nd, 2023, to May 28th, 2023, all basins in the IRL experienced a decrease in estimated median ChlA. The largest decrease over the week was observed in the N-BRL with a 12.36 µg/L decrease, the remainder of the BRL also experienced notable decreases of 8.71 µg/L in the S-BRL and 5.74 µg/L in the C-BRL. The SML experienced the second largest decrease of 9.42 µg/L over the week. All sections of the NIRL experienced smaller decreases around 3.65 µg/L and the N-CIRL decreased by 5.69 µg/L over the week. Due to excessive cloud cover over the SML and NIRL ChlA estimates were only calculated from cloud free areas and may not represent the entire basin.

There were no usable Sentinel-2 scenes and 2 Sentinel-3 scenes during this period. 

Table 1 - Sentinel 3 estimated ChlA percent change for the week of May 22, 2023, to May 28, 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 22nd-May 28th, 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 no useable scenes from Sentinel 2 for the detection of bloom activity from May 22nd, 2023, to May 28th, 2023. The following analysis focuses on the previous week’s partial scenes from May 15th and May 20th. During both 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.

22 May 2023 - Sentinel 3B

27 May 2023 - Sentinel 3A

There were 2 scenes from Sentinel 3 that were usable for detection of bloom activity from May 22nd, 2023, to May 28th, 2023. The following analysis focuses on scenes from May 22nd and May 27th. Due to excessive cloud cover over the SML and NIRL 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 22nd, 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 27th, 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), 2 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 22nd-May 28th, 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 22nd, 2023, to May 28th, 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 from May 22nd 1:00 - May 23rd 11:00 and IRLTITUS from May 23rd 13:00-14:00 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 22, 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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