Frequently Asked Questions: Preserving Lake Munson's Water Quality
What is the 2022 Lake Munson Action Plan?
The Action Plan for Lake Munson, approved by the Leon County Board of County Commissioners (Board) on October 11, 2022, and modified on March 21, 2023, provides short- and long-term strategies to address the challenges experienced during the Summer of 2022, including algal blooms, depressed oxygen levels, and invasive exotic vegetation. The Plan better articulates ongoing and long-term infrastructure projects to benefit the basin, which includes an immediate and temporary drawdown of the Lake water level, enhanced water quality monitoring with more frequent testing, and aerial topographic surveys of the Lake bottom to measure elevations of compacted sediment. Long-term strategies and best management practices (BMPs) include a new vegetation management program for treating invasive exotic plants to supplement the State’s program, using hydrogen peroxide to treat algal blooms, implementing routine periodic drawdowns every 5-10 years in consultation with FWC to reduce the need to mechanically remove organic-rich sediment, and ongoing engagement and continued water quality monitoring over the next two years to evaluate the Lake’s response to the drawdown. Regular status updates to the Board every six months are also part of the Plan.
Why was the 2022 Lake Munson Action Plan developed?
The Action Plan for Lake Munson was developed in response to the Lake's ongoing environmental challenges, including elevated nutrients, algal blooms, rapid growth of invasive exotic aquatic plants, low game fish productivity, and depressed oxygen levels. The Plan aims to mitigate these problems and enhance the Lake's water quality through a series of immediate and long-term strategies.
What has previously been done to improve the water quality of Lake Munson?
Since the 1990s, Leon County, the City of Tallahassee, and the Blueprint Intergovernmental Agency have dedicated hundreds of millions of dollars and completed numerous projects in the Lake Munson basin to improve the water quality flowing into Lake Munson by providing water quality treatment, reducing sediment transport, and collecting trash. The primary goal of the Leon County Lake Munson Restoration Project is to improve the water quality in Lake Munson. The project included the construction of the Lake Henrietta stormwater facility, improvements to Munson Slough with the creation of living shorelines and reduction erosion, removal of trash and the sediment delta from Lake Munson, and restoration of the wetlands around Lake Henrietta and Lake Munson. Routine drawdowns of the Lake have been conducted approximately every ten years to allow the nutrient-rich sediment to dry out and form a cap, reducing the nutrients leaving the sediment.
Has the water quality changed at Lake Munson?
The water quality in Lake Munson has improved over the past several decades as a result of the significant investment in improvements within the Lake Munson basin by Leon County, the City of Tallahassee, and Blueprint Intergovernmental Agency.
The water quality in Munson Slough (above the Lake) has improved so much that the nutrient concentrations are better than the target levels required by the State. Based on available information, this is the first time in the data history of Munson Slough, which dates to 1971 (one year prior to the enactment of the Clean Water Act), that nutrient-based water quality standards have been met. Since the early 1970s, nitrogen and phosphorus have reduced by more than 95%.
The water quality in Lake Munson has also experienced measurable improvements. Within the Lake, the nitrogen concentrations have been consistently below the State limit since 2017, and the phosphorus concentrations have steadily improved (24% reduction since 2013) such that it is approaching the State standard.
Learn more about Lake Munson’s water quality by visiting the Leon County Water Quality Journal.
What about the sediment?
Decades of development upstream of Lake Munson have resulted in a nutrient-rich sediment layer covering the bottom of Lake Munson. Since 2019, two studies have been completed, evaluating the sediment in Lake Munson. During this evaluation, contaminants were identified in the sediment. These relic contaminants are tightly attached to the sediment particles and were likely transported to the Lake from somewhere upstream prior to current regulations or during development decades ago. The studies also found that once the sediment particles settle to the bottom of the Lake, the contaminants remain stuck to the sediment and are not released into the water. The Action Plan included a one-time contaminant testing, which supports this determination that the sediment on the bottom does not release toxins and is stable.
The two studies on the sediment in Lake Munson are also used to guide the evaluation and analyses of lake management strategies and potential future restoration projects. As a result of these studies, in-lake sediment removal is not a viable mitigation option to reduce nutrient levels in Lake Munson at this time. Based on science today, dredging is not recommended because it will result in more harm than good by resuspending sediment and contaminants, degrading habitat, removing natural seed sources that give way for invasive exotic vegetation, and potentially creating a sinkhole by opening underlying karst features. The Action Plan utilizes drawdowns to improve water quality, manage aquatic vegetation, and compact sediment. Drawdowns are a proven, natural mitigation method that mimics the natural drying and refilling cycle of a lake and are the recommended strategy for low-risk (to ecological and human health) sites, such as Lake Munson. However, as more technologies and information become available, additional strategies may become viable options in the future.
The Action Plan includes aerial topographic surveys of the lake bottom during the drawdown to measure how much the sediment compacts, which provides information to evaluate the effectiveness of the drawdown. The Plan also includes routine periodic drawdowns every 5-10 years, in consultation with the Florida Fish and Wildlife Conservation Commission, to continue the compaction of the sediment and reduce the need to mechanically remove the organic-rich sediment. And finally, the Action Plan includes the exploration of new and innovative technologies, coordinated with FDEP and FWC. Any opportunities will be presented to the Leon County Science Advisory Committee and State agency partners, with new solutions brought to the Board of County Commissioners.
Why not just dredge the Lake?
Dredging Lake Munson will cause more harm than good. Dredging is a highly complex, industrial process that will disturb and resuspend the sediment and contaminants, damage habitats, remove the natural seed source to give way to invasive exotic vegetation, and could potentially create a sinkhole by opening an underlying karst feature. Also, the muck/sediment layer on the bottom of the Lake provides a benefit to the ecosystem, providing organism habitat, a natural seed source, and immobilization of sediment and contaminants.
The dredging process removes all the sediment in the bottom of the Lake and there is no way to pick what is removed or save the beneficial parts of the sediment. Many of the organisms in the Lake (e.g., worms, midges, and microscopic algae eaters) will die when dredging removes the sediment and changes the habitat and environment they have adapted to. Fish will suffer from habitat impacts and loss of food sources.
Additionally, dredging removes all the natural seeds in the Lake, which could allow invasive plants to take over. Past experiences with dredging, like at Lake Jackson, have shown that invasive exotic plants thrive when the native seed bank is removed.
While dredging was recommended in the past, new information and understanding of these processes have changed over time. Based on present-day knowledge of the Lake, better information, today’s science, and current best management strategies and management practices, it is clear that the potential harm to the environment and human health far outweighs any potential benefits.
The evidence against dredging is also supported by recent studies, which show that any contaminants in the Lake's sediment are currently stable and not moving into the water. The Environmental Protection Agency also generally advises against dredging in areas with low to moderate risk. Therefore, County scientists and experts recommend continuing with drawdowns as the preferred method for preserving and improving Lake Munson's water quality.
Why are we doing a drawdown?
Drawdowns, or the deliberate lowering of a lake's water level, are a proven, natural mitigation method that mimics the natural drying and refilling cycle of a lake. They are the recommended lake management strategy for low-risk (to ecological and human health) sites, such as Lake Munson, and are used to improve water quality, manage aquatic vegetation, and compact sediment. Drawdowns are beneficial to the Lake by allowing the sediments to de-water, oxidize, and form a hardened crust over the Lake’s bottom. A drawdown would serve to “cap” the underlying sediment which would provide habitat for fish spawning and reduce nutrient recycling once the Lake is re-flooded.
Leon County is conducting a drawdown on Lake Munson as part of its Action Plan to address the recent challenges in the Lake during the summer of 2022 including algal blooms, a fish kill, and an abundance of invasive exotic aquatic vegetation. More information on the Lake Munson drawdown and the benefits can be found here.
Why was the drawdown extended?
The appropriate length of the drawdown is not determined by a specific timeline or set number of months, but rather driven by ecological targets and the evaluation of the drawdown results against these targets. The drawdown was planned to conclude in April or May 2023; however, a higher-than-anticipated rainfall over the winter led to discussions on the appropriate time to refill the Lake.
The Florida Fish and Wildlife Conservation Commission (FWC) recommended continuing the drawdown until summer 2024 to allow additional time for the Lake to dry and promote sediment capping to improve the water quality. FWC advised there would be additional benefits to the ecosystem and wildlife habitat. Without water in most of the Lake, terrestrial plants, which are plants that live on land, have filled in and are growing in the Lake. These plants provide an excellent benefit for wading birds as well as providing fish habitat when the Lake refills. Based on this recommendation, at the March 21, 2023 meeting, the Leon County Board of County Commissioners approved the modification to the Action Plan to extend the drawdown through the Spring of 2024.
If the County is conducting a drawdown, why is there water in some of the Lake?
During a lake drawdown, it's common for some water to remain in Lake Munson. This is due to several factors:
- Natural Water Sources: Lakes often have natural sources of water, such as springs, groundwater, or incoming streams and rivers. Even when the outflow of a lake is increased to lower the water level, these sources can continue to supply water. At Lake Munson, water is continually flowing in from Munson Slough to the north.
- Weather: During periods of higher rainfall, more water will be entering the lake than can leave the lake, and the lake will begin to refill. As the amount of water flowing into the lake decreases, the lake will slowly begin to drain again. During the drawdown at Lake Munson, the Lake has refilled on several occasions but has not reached the normal pool depth.
- Geography and Topography: The shape and depth of the lakebed can also influence how much water remains. Some areas of the lake may be deeper than others, and these deeper areas can still hold water even when the majority of the lake is drained. Some of the most noticeable areas in Lake Munson where this occurs are the north lobe (bunny ear) and the southwest portion (back foot).
- Environmental Considerations: In some cases, a certain amount of water may be intentionally left in the lake during a drawdown to protect aquatic life and native (good) aquatic vegetation. At Lake Munson, water is intentionally left in the areas that don’t naturally drain and not ditched or pumped because the water remaining in these areas provides an ecological benefit to the Lake.
In the case of Lake Munson, the drawdown is a temporary and controlled process designed to address specific environmental issues. It's not intended to completely drain the Lake, but rather to lower the water level to a point a majority of the Lake bottom is exposed and where the desired benefits can be achieved.