3  2023 Results Summary

Results from 2023 indicate that all RA bay segments met chlorophyll-a thresholds accepted by the FDEP to maintain FDEP Reasonable Assurance for Tampa Bay and to comply with the EPA TMDL (Figure 3.1) and estuarine numeric nutrient criteria for Tampa Bay (EPA Amended Approval Letter Jun. 28, 2013). During the previous RA period (2017-2021), Old Tampa Bay exceeded the chlorophyll-a threshold for four of the five years. While the chlorophyll-a threshold was met in Old Tampa Bay for the 2022 and 2023 annual assessment periods, water quality conditions in this bay segment remain a priority concern for the Consortium. Chlorophyll-a concentrations are typically elevated in a poorly flushed region that has produced summertime blooms of Pyrodinium bahamense since 2009 (Figure 3.2; Note that individual station exceedences are not considered in this RA compliance assessment). This observation is reflected in the majority of summertime months with chlorophyll-a concentrations higher than long-term median values in Old Tampa Bay, although this was not observed in 2022 or 2023 (Figure 3.3). To address these water quality problems, the Consortium formed an Old Tampa Bay Working Group in early 2020 to prioritize additional investigations and future management actions that may alleviate the conditions fostering these summertime blooms. Additionally, the TBEP received funding from a NOAA Restore Actionable Science grant in 2021 to develop a research management plan for identifying potential actions to improve water quality conditions in Old Tampa Bay (Lopez et al. 2023). An assimilative capacity study for Old Tampa Bay will also be pursued in 2024 to evaluate the existing management paradigm and assess the potential need to adopt alternative indicators and/or load allocations to address recurring water quality issues in that bay segment.

The TBEP, in partnership with the Southwest Florida Water Management District, has previously developed an integrated ecosystem model to evaluate the net environmental benefits that may result from implementing various management actions in Old Tampa Bay including: reducing point sources, nonpoint sources, and causeway obstructions in Old Tampa Bay (Sherwood et al. 2015). Management actions that proximate and respond to current Old Tampa Bay conditions will be further evaluated using this model. Furthermore, the TBEP funded research conducted by the Florida Fish and Wildlife Research Institute to improve understanding of the cell physiology and behavior of Pyrodinium bahamense and evaluate the potential for using shellfish to mitigate these algal blooms in Old Tampa Bay. A water quality dashboard (https://shiny.tbep.org/wq-dash) continues to be available to further synthesize available data, assess additional water quality metrics (phytoplankton counts), and inform Consortium participants and other resource managers on the status of water quality in Tampa Bay. The dashboard allows for proactive response to anomalous water quality conditions on a month-to-month basis by the community. Potential modifications to existing modeling tools and the proposal of additional models will be explored under the Old Tampa Bay assimilative capacity assessment study in 2024.

Seagrasses were relatively stable in much of Lower to Middle Tampa Bay; however, additional declines to the ephemeral seagrass beds in upper Tampa Bay were observed between 2020 and 2022. Aerial photographs taken in December 2021 - January 2022 indicated that baywide seagrass coverage decreased by 4,160 acres, marking the third consecutive biennial reporting period with seagrass declines. Seagrass acreage showed the greatest decreases in Old Tampa Bay (-4,041 acres from 2018 - 2020, -2,518 acres from 2020 - 2022) and Hillsborough Bay (-627 acres from 2018 - 2020, -428 acres from 2020 - 2022). Notably, the coverage estimate for Old Tampa Bay was 4,183 acres in 2022, the lowest estimate ever recorded for that bay segment. The three major southwest Florida estuaries experienced reductions in estimated seagrass coverage between 2020 and 2022, with the most pronounced losses occurring in Tampa Bay. Additional research and discussion is being pursued by the Southwest Florida Seagrass Working Group to better understand the underlying mechanisms influencing these observations. The next SWFWMD seagrass coverage estimate will be developed from aerial photographs acquired over the winter 2023-24 period. Despite the documented baywide decline in seagrass coverage shown by the SWFWMD data, the previous two years of annual transect surveys conducted by TBEP and its partners have shown a slight increase in total frequency occurrence from 2021 to 2023 (shown in the seagrass transect dashboard). Although lower stormwater nutrient loads from lower than average summer rainfall may have contributed to this increase, the TBEP is cautiously optimistic that these increases will continue in future years. Finally, the role of long-term temperature increases and salinity reductions related to climate change and the potential relationships with seagrass declines since 2016 are being explored. The results of this work will likely be published in early 2024.

Detailed results for the 2022-2026 RA implementation period are provided in Tables 3.2, 3.3, 3.4, 3.5, and 3.6 for each bay segment. Notably, results for the Remainder Lower Tampa Bay segment (Boca Ciega Bay South, Terra Ceia Bay, Manatee River) are included for the first time in this annual assessment. As of the 2023 reporting period, NMC Actions 2-5 are not necessary based upon observed water quality conditions within Tampa Bay, though additional work is being pursued by the TBEP and TBNMC to understand the most recent trends in seagrass coverage and Old Tampa Bay’s current assimilative capacity. Individual annual reports of the bay’s conditions from 2023 can be found on the TBEP website, as specified in the following link (Beck, Burke, and Sherwood 2024) and the water quality dashboard. A summary of historic attainment of the regulatory chlorophyll-a thresholds for each of the bay segments is depicted in Figure 3.5.

Lastly, annual hydrologic conditions within two of the major bay segments in 2023 were below 1992-1994 levels (Table 3.1). Therefore, hydrologic adjustments for evaluating compliance with individual entity load allocations/permitting targets should be applied for the Middle Tampa Bay and Lower Tampa Bay segments (Janicki Environmental, Inc. 2012, 2016). The estimated hydrologic loads for each bay segment relative to observed 1992-1994 levels are indicated in the table below. The estimated compliance load adjustment factors (if applicable) are also specified. A tool to calculate the hydrologic estimates and adjustment factors by bay segment is available online through an interactive dashboard and automatically updated as provisional hydrologic estimates are approved by monitoring agencies (https://shiny.tbep.org/tbnmc_hydrologic_estimates/).

Table 3.1:

Hydrologic load estimates in 2023 relative to 1992-1994 levels and estimated compliance load adjustment factors for the major bay segments.

Bay Segment	1992 - 1994 Hydrology (95% Prediction Interval, million m3)	Hydrology Estimate (million m3)	Compliance Load Adjustment Factor
Old Tampa Bay	383 - 548	423.82
Hillsborough Bay	753-1110	886.53
Middle Tampa Bay	524-756	368.67	0.57
Lower Tampa Bay	312-402	274.49	0.76

Figure 3.1: Historic chlorophyll-a annual averages for the four major bay segments of Tampa Bay and those that include the Remainder Lower Tampa Bay segment (Boca Ciega Bay South, Terra Ceia Bay, Manatee River). Annual averages in 2023 were below the regulatory thresholds developed under the Tampa Nitrogen Management Consortium’s nutrient management strategy in all bay segments. Vertical grey bars indicate the portion of the 2022-2026 Reasonable Assurance compliance assessment period covered by the results.

Figure 3.2: Map depicting individual station chlorophyll-a exceedences in Tampa Bay relative to FDEP regulatory thresholds for chlorophyll-a in 2023. Note individual station exceedences do not indicate failed compliance at the bay segment scale.

Figure 3.3: 2023 monthly chlorophyll-a bay segment means (red dots) compared to monthly distributions from prior years (box plots and black dots). Prior years extend to 1975 for Old Tampa Bay, Hillsborough Bay, Middle Tampa Bay, and Lower Tampa Bay, 1991 for Boca Ciega Bay South, 1989 for Terra Ceia Bay, and 1990 for Manatee River. Note that Pinellas and Manatee County data are used for Boca Ciega Bay South, Terra Ceia Bay, and Manatee River and has less frequent sampling intervals than data from the Environmental Protection Commission of Hillsborough County used for the other bay segments. Boxes encompass the 25th and 75th percentiles, while whiskers bound the interquartile range. Dots beyond the whiskers represent outliers throughout the 1975-2022 sample period.

Figure 3.4: Historic seagrass coverage estimates for Tampa Bay. The target coverage of 38,000 acres was changed to 40,000 acres in 2020 to reflect programmatic goals in the 2020 Habitat Master Plan Update (TBEP #07-20). Data source: TBEP & SWFWMD.

Figure 3.5: Attainment of adopted chlorophyll-a thresholds (1975 - 2023) in the four major bay segments and Remainder Lower Tampa Bay segment (Boca Ciega Bay South, Terra Ceia Bay, Manatee River). Green (yes) indicates that average annual chlorophyll-a thresholds were met; red (no) indicates that threshold levels were not met. Grey line is the beginning of the current Reasonable Assurance implementation period.

Table 3.2:

Demonstration of reasonable assurance assessment steps for Old Tampa Bay. Green and red squares indicate outcomes of decision points outlined in the Consortium’s reasonable assurance assessment framework.

Bay Segment Reasonable Assurance Assessment Steps	DATA USED TO ASSESS ANNUAL REASONABLE ASSURANCE					OUTCOME
	Year 1 (2022)	Year 2 (2023)	Year 3 (2024)	Year 4 (2025)	Year 5 (2026)
NMC Action 1: Determine if observed chlorophyll-a exceeds FDEP threshold of 9.3 ug/L	No (7.1)	No (6.2)				All years below threshold so far, not necessary for NMC Actions 2-5
NMC Action 2: Determine if any observed chlorophyll-a exceedences occurred for 2 consecutive years	No	No				All years met threshold, not necessary for NMC Actions 3-5
NMC Action 3: Determine if observed hydrologically-normalized total load exceeds federally-recognized TMDL of 486 tons/year	N/A	N/A				Not necessary due to observed water quality and seagrass conditions in the bay segment
NMC Actions 4-5: Determine if any entity/source/facility specific exceedences of 5-yr average allocation occurred during implementation period						Not necessary when chlorophyll-a threshold met

Table 3.3:

Demonstration of reasonable assurance assessment steps for Hillsborough Bay. Green and red squares indicate outcomes of decision points outlined in the Consortium’s reasonable assurance assessment framework.

Bay Segment Reasonable Assurance Assessment Steps	DATA USED TO ASSESS ANNUAL REASONABLE ASSURANCE					OUTCOME
	Year 1 (2022)	Year 2 (2023)	Year 3 (2024)	Year 4 (2025)	Year 5 (2026)
NMC Action 1: Determine if observed chlorophyll-a exceeds FDEP threshold of 15 ug/L	No (8.9)	No (6.9)				All years below threshold so far, not necessary for NMC Actions 2-5
NMC Action 2: Determine if any observed chlorophyll-a exceedences occurred for 2 consecutive years	No	No				All years met threshold, not necessary for NMC Actions 3-5
NMC Action 3: Determine if observed hydrologically-normalized total load exceeds federally-recognized TMDL of 1451 tons/year	N/A	N/A				Not necessary due to observed water quality and seagrass conditions in the bay segment
NMC Actions 4-5: Determine if any entity/source/facility specific exceedences of 5-yr average allocation occurred during implementation period						Not necessary when chlorophyll-a threshold met

Table 3.4:

Demonstration of reasonable assurance assessment steps for Middle Tampa Bay. Green and red squares indicate outcomes of decision points outlined in the Consortium’s reasonable assurance assessment framework.

Bay Segment Reasonable Assurance Assessment Steps	DATA USED TO ASSESS ANNUAL REASONABLE ASSURANCE					OUTCOME
	Year 1 (2022)	Year 2 (2023)	Year 3 (2024)	Year 4 (2025)	Year 5 (2026)
NMC Action 1: Determine if observed chlorophyll-a exceeds FDEP threshold of 8.5 ug/L	No (5)	No (3.7)				All years below threshold so far, not necessary for NMC Actions 2-5
NMC Action 2: Determine if any observed chlorophyll-a exceedences occurred for 2 consecutive years	No	No				All years met threshold, not necessary for NMC Actions 3-5
NMC Action 3: Determine if observed hydrologically-normalized total load exceeds federally-recognized TMDL of 799 tons/year	N/A	N/A				Not necessary due to observed water quality and seagrass conditions in the bay segment
NMC Actions 4-5: Determine if any entity/source/facility specific exceedences of 5-yr average allocation occurred during implementation period						Not necessary when chlorophyll-a threshold met

Table 3.5:

Demonstration of reasonable assurance assessment steps for Lower Tampa Bay. Green and red squares indicate outcomes of decision points outlined in the Consortium’s reasonable assurance assessment framework.

Bay Segment Reasonable Assurance Assessment Steps	DATA USED TO ASSESS ANNUAL REASONABLE ASSURANCE					OUTCOME
	Year 1 (2022)	Year 2 (2023)	Year 3 (2024)	Year 4 (2025)	Year 5 (2026)
NMC Action 1: Determine if observed chlorophyll-a exceeds FDEP threshold of 5.1 ug/L	No (3.6)	No (2.6)				All years below threshold so far, not necessary for NMC Actions 2-5
NMC Action 2: Determine if any observed chlorophyll-a exceedences occurred for 2 consecutive years	No	No				All years met threshold, not necessary for NMC Actions 3-5
NMC Action 3: Determine if observed hydrologically-normalized total load exceeds federally-recognized TMDL of 349 tons/year	N/A	N/A				Not necessary due to observed water quality and seagrass conditions in the bay segment
NMC Actions 4-5: Determine if any entity/source/facility specific exceedences of 5-yr average allocation occurred during implementation period						Not necessary when chlorophyll-a threshold met

Table 3.6:

Demonstration of reasonable assurance assessment steps for Remainder Lower Tampa Bay. Green and red squares indicate outcomes of decision points outlined in the Consortium’s reasonable assurance assessment framework.

Bay Segment Reasonable Assurance Assessment Steps	DATA USED TO ASSESS ANNUAL REASONABLE ASSURANCE					OUTCOME
	Year 1 (2022)	Year 2 (2023)	Year 3 (2024)	Year 4 (2025)	Year 5 (2026)
NMC Action 1: Determine if observed chlorophyll-a exceeds FDEP threshold of 5.1 ug/L	No (3.6)	No (2.6)				All years below threshold so far, not necessary for NMC Actions 2-5
NMC Action 2: Determine if any observed chlorophyll-a exceedences occurred for 2 consecutive years	No	No				All years met threshold, not necessary for NMC Actions 3-5
NMC Action 3: Determine if observed hydrologically-normalized total load exceeds federally-recognized TMDL of 349 tons/year	N/A	N/A				Not necessary due to observed water quality and seagrass conditions in the bay segment
NMC Actions 4-5: Determine if any entity/source/facility specific exceedences of 5-yr average allocation occurred during implementation period						Not necessary when chlorophyll-a threshold met

Beck, M. W., M. C. Burke, and E. T. Sherwood. 2024. “2023 Tampa Bay Water Quality Assessment.” 01-24. St. Petersburg, Florida: Tampa Bay Estuary Program. https://tbep-tech.github.io/wq-static/wq.pdf.

Janicki Environmental, Inc. 2012. “Development of a Screening Level Tool for Estimating Annual Hydrologic Loadings to Tampa Bay.” 05-12. St. Petersburg, Florida: Tampa Bay Estuary Program. https://drive.google.com/file/d/1C6Arwat9IxYs8jeTZpcmBB6WBTpeQ2nw/view?usp=drivesdk.

———. 2016. “Update on the Development of a Screening Level Tool for Estimating Annual Hydrologic Loadings to Tampa Bay.” 03-16. St. Petersburg, Florida: Tampa Bay Estuary Program. https://drive.google.com/file/d/11NT0NQ2WbPO6pVZaD7P7Z6qjcwO1jxHw/view?usp=drivesdk.

Lopez, C. B., S. G. Kaminski, S. Shankar, R. Pribble, E. T. Sherwood, M. C. Burke, and M. W. Beck. 2023. “Tampa Bay Restoration and Pyrodinium bahamense Bloom Dynamics: Filling Knowledge Gaps to Enhance Recovery, a Research and Application Plan.” 12-23. St. Petersburg, Florida: Tampa Bay Estuary Program. https://drive.google.com/file/d/140oBnV5R2BwOZ7cMuaY-4bu_ftL-YBVJ/view?usp=sharing.

Sherwood, E., H. Greening, L. Garcia, K. Kaufman, T. Janicki, R. Pribble, B. Cunningham, et al. 2015. “Development of an Integrated Ecosystem Model to Determine Effectiveness of Potential Watershed Management Projects on Improving Old Tampa Bay.” 10-15. St. Petersburg, Florida: Tampa Bay Estuary Program. https://drive.google.com/file/d/1BCviGfLykVX-p1tA3b0306deP3pKMagr/view?usp=drivesdk.