On February 11, 2016, the Florida Department of Environmental Protection (FDEP) held a meeting at the UF IFAS Seminole County Extension Service office to discuss the latest model runs that predict nutrient loading for Lake Jesup, FL.
The original nutrient loading rates for the Lake were predicted many years ago using a Bathtub model. That model is now considered outdated and known to have several shortcomings for its intended purpose. Principle of those was the inability to predict nutrient attenuation, or the amount of nutrient uptake or deposition occurring in the surface water as it travels from point A to point B. The model also didn’t account for some very large sources of nutrient loading including groundwater and in-lake re-suspension.
The new model is separated into two efforts. The first combines an updated watershed module using Hydrological Simulation Program – Fortran (HSPF). It accounts for the nutrients and water flowing from the surface into the lake. Separately from that, the Environmental Fluid Dynamics Code/Water Quality Analysis Simulation (EFDC/WASP) software is being used to predict the volume and loading from in-lake processes.
According to the FDEP’s contractor, the HSPF portion of the model is well on its way to being completed. It still isn’t perfect and has some built-in error, but this module is better at predicting flow and volume than the Bathtub version, and accounts for attenuation. During testing, the contractor was also able to tighten the sub-basin boundaries to better predict smaller lakes. And they discovered that the land use loading rates simulated by Harvey Harper needed to be modified because they were over-predicting the nutrients coming from eroded sediment.
The second module predicting in-lake processes is not as far along. The EFDC is able to predict the lake volume, but relies on a USGS staff gage to predict water elevation that isn’t as accurate and precise as it could be. The WASP module still needs works and won’t be ready for a few months.
The total model won’t be complete until the contractor can finish the technical work, and the stakeholders have had a chance to comment. Following that, the Total Maximum Daily Loads (TMDL) may need updating because the total loading to the lake will change. Regardless of whether a TMDL revision is required, the Basin Management Action Plan (BMAP) will need to be updated to reflect the new numbers and allocate them to the stakeholders.
The only target for having all this complete given by the FDEP is the third or fourth quarter of 2016. The main reason for this uncertainty is because logic dictates that the total loading to the lake will increase and therefore the required reduction will also increase. That will cause most stakeholders to be unhappy because their allocations will increase, and so the BMAP document may take a while to achieve final consensus.
The water and nutrients coming from the surface will be fairly easy to parse and assign based on basin boundaries, but the in-lake nutrients will be a fight. How do you assign decades of legacy loading to the lake when you can’t determine where it came from? Not to mention that all stakeholders will be required to reduce their total nitrogen load now too.
It should be interesting to see how it plays out.