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On behalf of the Tampa Bay Nitrogen Management Consortium, please find attached the {{< var maxyr >}} update on water quality and seagrass resources in the Tampa Bay estuary. This update has been developed in accordance with the compliance assessment adopted through [FDEP’s Tampa Bay Reasonable Assurance determination on December 22, 2010](https://drive.google.com/file/d/1wV3w8ack_fLNK3yS-xTR7LTmziNtZ8CN/view?usp=share_link), FDEP’s subsequent [approval](https://drive.google.com/file/d/1IIloBN5RoZPB6vgWzEjmMQyFjFL3fq0Y/view?usp=share_link) of the [2022 RA Update](https://drive.google.com/file/d/18HHMx4U6vHNrFyepEFuoTJ_sEKyTA_gu/view), and the [federally-recognized TMDL for Tampa Bay](https://drive.google.com/file/d/18_W1qKT2I0j9m0mLC7wWjndSNR-0iWEF/view?usp=share_link). The formal annual compliance assessment utilized by the Consortium is detailed in Section VIII.B of the [Final 2009 Reasonable Assurance Addendum: Allocation and Assessment Report](https://drive.google.com/file/d/10IjJAfcGFf007a5VdPXAUtUi4dx-cmsA/view).
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Chlorophyll-a concentrations for all four major bay segments were below FDEP-approved numeric nutrient criteria thresholds in {{< var maxyr >}}. Additionally, concentrations for the Remainder Lower Tampa Bay segment that includes Boca Ciega Bay South, Terra Ceia Bay, and Manatee River were also below the criteria. The approved chlorophyll-a thresholds were adopted as part of FDEP’s 2002 Reasonable Assurance determination for Tampa Bay, and, at that time, it was determined that Tampa Bay’s seagrass restoration goals could be achieved if annual, uncorrected chlorophyll-a concentrations remained below these thresholds. If a bay segment’s chlorophyll-a concentration remains above thresholds for 2 concurrent years, additional compliance assessment steps are required by the Consortium. This nutrient management strategy has been consistently used by the TBEP and Consortium in their Annual Decision Matrix and Assessment reports [@tbep0325].
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Seagrass coverage in Tampa Bay increased by 1,407 acres between 2022 and 2024. The Southwest Florida Water Management District's (SWFWMD) 2024 baywide seagrass coverage estimate is 31,544 acres, below the baywide target of 40,000 acres (@fig-seagrass). Gains were observed in all bay segments, except Old Tampa Bay where a loss was observed. Additional research, assimilative capacity assessments, and restoration initiatives are being conducted in response to this localized trend. The Consortium’s approved nutrient management strategy remains a necessary tool to adaptively manage and address nutrient loading to the Tampa Bay estuary. For all Tampa Bay segments, water quality remained supportive of seagrass resources in {{< var maxyr >}}, though continued seagrass losses in the Old Tampa Bay segment continue to be examined. Annual [seagrass transect surveys](https://shiny.tbep.org/seagrasstransect-dash) for Old Tampa Bay show a shift from rooted macroalgae (*Caulerpa prolifera*) to cyanobacteria and green drift algae, suggesting that nutrient loading continues to be a problem for this bay segment.
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Seagrass coverage in Tampa Bay increased by 1,407 acres between 2022 and 2024. The Southwest Florida Water Management District's (SWFWMD) 2024 baywide seagrass coverage estimate is 31,563 acres, below the baywide target of 40,000 acres (@fig-seagrass). Gains were observed in all bay segments, except Old Tampa Bay where a loss was observed. Additional research, assimilative capacity assessments, and restoration initiatives are being conducted in response to this localized trend. The Consortium’s approved nutrient management strategy remains a necessary tool to adaptively manage and address nutrient loading to the Tampa Bay estuary. For all Tampa Bay segments, water quality remained supportive of seagrass resources in {{< var maxyr >}}, though continued seagrass losses in the Old Tampa Bay segment continue to be examined. Annual [seagrass transect surveys](https://shiny.tbep.org/seagrasstransect-dash) for Old Tampa Bay show a slight increase in seagrass in recent years, although definitive changes in coverage cannot be assessed until the next update from the SWFWMD using aerial images obtained over the winter 2025-26 period.
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Thank you again for your continued participation in the Consortium’s process. Please contact Ed Sherwood ([esherwood@tbep.org](mailto:esherwood@tbep.org)) with any questions about the Consortium’s Annual Compliance Assessment.
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Results from {{< var maxyr >}} 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 (@fig-thrplot) and estuarine numeric nutrient criteria for Tampa Bay ([EPA Amended Approval Letter Jun. 28, 2013](https://www.epa.gov/sites/default/files/2015-04/documents/florida-amended-determination.pdf)). Chlorophyll-a concentrations were elevated throughout the bay during late summer/fall months in {{< var maxyr >}} due to the influence of several tropical storms on the region (@fig-boxplot). Mixed-assemblage algae blooms were reported in Hillsborough Bay, Old Tampa Bay, and Middle Tampa Bay, while low concentrations of *Karenia brevis* continued to be observed in Lower Tampa Bay into the winter months. Although understanding and mitigating blooms of *Pyrodinium bahamense* in OTB continues to be a focus of research and management efforts, summer concentrations in Old Tampa Bay were lower compared to prior years and the chlorophyll-a criteria was met for the third consecutive year of the RA period. Preliminary recommendations from the assimilative capacity assessment for Old Tampa Bay 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 are underway [@tbep0924;@tbep0525].
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Results from {{< var maxyr >}} 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 (@fig-thrplot) and estuarine numeric nutrient criteria for Tampa Bay ([EPA Amended Approval Letter Jun. 28, 2013](https://www.epa.gov/sites/default/files/2015-04/documents/florida-amended-determination.pdf)). Chlorophyll-a concentrations were notably lower than the previous year for many bay segments likely because of lower rainfall and no tropical storm activity impacting the region in {{< var maxyr >}} (@fig-boxplot). Blooms of harmful algal species (e.g., *Karenia brevis*, *Pyrodinium bahamense*) were not observed in any of the bay segments. Although understanding and mitigating blooms of *Pyrodinium bahamense* in OTB continues to be a focus of research and management efforts, summer concentrations in Old Tampa Bay were lower compared to prior years and the chlorophyll-a criteria was met for the fourth consecutive year of the RA period. Recommendations from the assimilative capacity assessment for Old Tampa Bay to address recurring water quality issues in that bay segment were presented to the Tampa Bay Nitrogen Management Consortium (TBNMC) and Old Tampa Bay working group (OTBWG) in {{< var maxyr >}} [@tbep0924;@tbep0525;@tbep1725].
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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 [@tbep1015]. Management actions that proximate and respond to current Old Tampa Bay conditions will be further evaluated under the Old Tampa Bay assimilative capacity assessment project. 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](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. As part of the Old Tampa Bay assimilative capacity assessment, potential modifications to existing modeling tools and the application of additional models will be finalized in 2025.
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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 [@tbep1015]. Management actions that proximate and respond to current Old Tampa Bay conditions have been further evaluated under the Old Tampa Bay assimilative capacity assessment project. 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](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. As part of the Old Tampa Bay assimilative capacity assessment, additional empirical and mechanistic modeling tools were developed as alternative lines of evidence that supported the findings from previous work.
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Between 2022 and 2024, seagrasses throughout Tampa Bay increased by 1,407 acres. After several consecutive years of losses, aerial photographs taken in December 2023 - February 2024 indicate that Tampa Bay now harbors 31,544 acres of seagrass. Seagrass acreage showed the greatest increases in Hillsborough Bay (+756 acres), accounting for more than half of the increase observed baywide. Despite modest gains elsewhere, Old Tampa Bay lost an additional 326 acres of seagrass, the lowest estimate ever recorded for this bay segment. These trends are generally corroborated by annual transect surveys conducted by TBEP and its partners (shown in the [seagrass transect dashboard](https://shiny.tbep.org/seagrasstransect-dash)). Additional research and discussion is being pursued by the [Southwest Florida Seagrass Working Group](https://tbep.org/our-work/boards-committees/technical-advisory-committee/#seagrass) to better understand the underlying mechanisms influencing these observations. Analysis of the role of long-term temperature increases and salinity reductions related to climate change and the potential relationships with seagrass declines since 2016 was published in 2024 [@tbep1124]. The next SWFWMD seagrass coverage estimate will be developed from aerial photographs acquired over the winter 2025-26 period.
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Between 2022 and 2024, seagrasses throughout Tampa Bay increased by 1,426 acres. After several consecutive years of losses, aerial photographs taken in December 2023 - February 2024 indicate that Tampa Bay now harbors 31,563 acres of seagrass. Seagrass acreage showed the greatest increases in Hillsborough Bay (+773 acres), accounting for more than half of the increase observed baywide. Despite modest gains elsewhere, Old Tampa Bay lost an additional 326 acres of seagrass, the lowest estimate ever recorded for this bay segment. These trends are generally corroborated by annual transect surveys conducted by TBEP and its partners (shown in the [seagrass transect dashboard](https://shiny.tbep.org/seagrasstransect-dash)), although slight gains in frequency occurrence in Old Tampa Bay suggest seagrasses may have increased in the last year. Additional research and discussion is being pursued by the [Southwest Florida Seagrass Working Group](https://tbep.org/our-work/boards-committees/technical-advisory-committee/#seagrass) to better understand the underlying mechanisms influencing these observations. Analysis of the role of long-term temperature increases and salinity reductions related to climate change and the potential relationships with seagrass declines since 2016 was published in 2024 [@tbep1124]. The next SWFWMD seagrass coverage estimate will be developed from aerial photographs acquired over the winter 2025-26 period.
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Detailed results for the 2022-2026 RA implementation period are provided in Tables [-@tbl-raotb], [-@tbl-rahb], [-@tbl-ramtb], [-@tbl-raltb], and [-@tbl-raraltb] for each bay segment. Results for the Remainder Lower Tampa Bay segment (Boca Ciega Bay South, Terra Ceia Bay, Manatee River) are also included in this annual assessment (reporting began with the 2023 annual assessment). As of the {{< var maxyr >}} 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 {{< var maxyr >}} can be found on the TBEP website, as specified in the following link [@tbep0325] and the [water quality dashboard](https://shiny.tbep.org/wq-dash). A summary of historic attainment of the regulatory chlorophyll-a thresholds for each of the bay segments is depicted in @fig-chlmat.
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Detailed results for the 2022-2026 RA implementation period are provided in Tables [-@tbl-raotb], [-@tbl-rahb], [-@tbl-ramtb], [-@tbl-raltb], and [-@tbl-raraltb] for each bay segment. Results for the Remainder Lower Tampa Bay segment (Boca Ciega Bay South, Terra Ceia Bay, Manatee River) are also included in this annual assessment (reporting began with the 2023 annual assessment). As of the {{< var maxyr >}} reporting period, NMC Actions 2-5 are not necessary based upon observed water quality conditions within Tampa Bay, though work is being continued by the TBEP and TBNMC to further understand drivers of seagrass change and Old Tampa Bay's current assimilative capacity. Individual annual reports of the bay’s conditions from {{< var maxyr >}} can be found on the TBEP website, as specified in the following link [@tbep0325] and the [water quality dashboard](https://shiny.tbep.org/wq-dash). A summary of historic attainment of the regulatory chlorophyll-a thresholds for each of the bay segments is depicted in @fig-chlmat.
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Lastly, annual hydrologic conditions among all the major bay segments in {{< var maxyr >}} were above 1992-1994 levels ([@tbl-hydrotab]). Therefore, hydrologic adjustments for evaluating compliance with individual entity load allocations/permitting targets should be applied for each major segment [@tbep0512;@tbep0316]. 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/>).
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Lastly, annual hydrologic conditions among all the major bay segments in {{< var maxyr >}} were below 1992-1994 levels for all segments except Old Tampa Bay ([@tbl-hydrotab]). Therefore, hydrologic adjustments for evaluating compliance with individual entity load allocations/permitting targets should be applied for each major segment except Old Tampa Bay[@tbep0512;@tbep0316]. 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/>).
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