Turbidity is a measurement of water clarity. Dirty water loaded with sediments and disturbed muck increases turbidity and decreases water clarity.
Historical recounts describe the clear “turquoise blue” water in the lagoon that one could see through to the bottom. The data demonstrate that turbidity significantly increased over the 20 years from 1996–2016.
Sediment enters the lagoon from canal discharges, stormwater pipes, and run-off. Muck on the bottom is easily stirred up by wind and wave action, muddying the waters until it settles again. Extensive algae blooms also increase turbidity.
Clear water is important for the lagoon’s sea grasses that must receive sunlight to photosynthesize and grow. Without seagrasses, fisheries decline, manatees starve, and primary production in the lagoon decreases.
Turbidity targets were established by the EPA, SJRWMD, and SFWMD. The EPA targets for turbidity were not specific for the IRL and required a good understanding of “natural conditions,” which isn’t available for the IRL, particularly for the different sublagoons.
After a comparison of the criteria from each source, it was decided that a combination of the established targets would be used in the Indian River Lagoon Ecological Health Assessment.
The SFWMD target is to be used for the SIRL and the SJRWMD targets for the BRL, CIRL, and NIRL. The use of the EPA targets was not chosen as the current background conditions for turbidity are unknown throughout the IRL. Similar to other parameters, SJRWMD had a target for the North and South subsections of the CIRL and these were used as-is by separating our sampling sites by subregion.
Additionally, it must be noted that to date no known target has been established for the ML. As a result, an in-house target was derived from the target of the closest sublagoon areas, BRL and NIRL, in which the annual median shall not exceed 4 NTU.
Turbidity had site-specific targets that used annual medians and results are reported in offsets from the established target summarized by year and for the period of record (POR). Once annual and POR medians were calculated per site, queries were created to calculate the number of records below the minimum targets provided in the table.
Outputs were exported to Microsoft Excel where pivot tables were used to summarize the data by averaging offsets of each sublagoon, or section of a sublagoon, for each year and the entire POR. The frequency distribution of the data, as shown in the figure guided the classes to be used for scoring.
To learn more about how scores were calculated, to see the targets for each region, and to read other sciencey stuff, check out the 2020 Health Assessment Methodology Report.