NEW Publication: Impact of Water from Inland Sources on Florida's Coral Reef

December 5, 2025

Dr. Brian Walker

Impact of Water from Inland Sources on Florida's Coral Reef

This study used long-term data sets and machine learning to analyze the previously undefined linkages between watershed inputs and water quality on coral reefs in southeast Florida, including interactions with meteorological (rain and wind) patterns. The collaborative research team found that nutrient levels on the reef are highly impacted by rainfalls and canal outflows, with their machine learning models able to to predict up to ~70% of variation in water quality when using new data that the model had not seen before.

Breaking Down the Results 

The research suggests that total phosphorus and orthophosphate levels on the reefs are heavily influenced by rainfall over the preceding 24 hours, and over the prior 2 weeks for orthophosphate. They found that both canal outflows 3 days prior and longer-term outflow conditions (30 and 90 days prior) predicted nitrate and nitrite concentrations on the reefs. This suggests that terrestrial runoff may have both acute effects impacting the reefs immediately after water releases and chronic longer-term influences that may also reflect biogeochemical cycling of nutrients within the system. 

Excess nutrients can harm coral reefs by blockng light needed for photosynthesis, fueling algae growth, and directly causing stress to the coral organism themselves. High nutrient levels can also affect the health of the corals’ symbiotic algae, which in turn makes corals more vulnerable to heat stress and disease. In Florida, outbreaks of stony coral tissue loss disease (SCTLD), which has caused major coral die-offs, have been strongly linked to higher freshwater outflow from coastal canals, especially when combined with warmer temperatures and rainfall. This study supports previous research, and suggests that nutrient-rich runoff may be contributing to the spread and severity of SCTLD and other coral diseases.

How the Data Can be Used

While the linkage between terrestrial freshwater flow and offshore/reef water quality has long been hypothesized, this study provides evidence of the relationship using real-world data and advanced modeling. These findings provide a scientific basis for future management of land-based sources of coastal pollution, and may be applied to ongoing discussions about water quality criteria (i.e. state-level regulations) that are protective of coral reef ecosystems in the region. The research identifies conditions associated with low nutrients on the reefs that could be incorporated into management decisions about when to release water from the canals to tide to minimize water quality impacts to the nearshore reefs.

Learn more about this study's results and their implications for water quality and 

coral reef conservation in the video below!

Find out more about the impacts of water quality on Flordia's Coral Reef:

Defining water quality seascapes in the Kristen Jacobs Coral Aquatic Preserve, their relationship to hydrographic modeling connectivity

Walker, B., Williams, G., Hanert, E., Dobbelaere, T., Whitall, D., Maynard, J., & Aeby, G. (2025). Defining water quality seascapes in the KJCAP, their relationship to hydrographic modeling connectivity, the 2023 coral bleaching, and SCTLD. Final Report. https://www.nova-ncri.org/news/How-Inland-Waters-Shape-Coral-Reef-Health-in-Southeast-Florida. 

Hydrographic connections of inland water to diseased corals and water quality sites in SE FL

Dobbelaere, T., Hanert, E., Williams, G., Whitall, D., Aeby, G., Maynard, J., & Walker, B. (2024). Hydrographic connections of inland water to diseased corals and water quality sites in SE FL. Final Report. https://floridadep.gov/rcp/coral-protection-restoration/documents/hydrographic-connections-inland-water-diseased-corals

Antibiotic Resistance in Marine Microbial Communities Proximal to a Florida Sewage Outfall System

Griffin, D. W., Banks, K., Gregg, K., Shedler, S., & Walker, B. K. (2020). Antibiotic Resistance in Marine Microbial Communities Proximal to a Florida Sewage Outfall System. Antibiotics, 9(3), 118. https://www.mdpi.com/2079-6382/9/3/118