• Rob Baker

Florida Bay Water Quality

I can't believe it has been over a year since my last post. Fishing has been ongoing, and I have had some success in recent months with both bass and seatrout. When they finally bite it kind of clears the memory of all of the skunked outings. When the COVID-19 Stay-At-Home restrictions are lifted I will head back out and continue the struggle.

The blogging plan is to post a bit more often and keep this thing going. Sometimes my topics will be about fishing and sometimes about environmental issues related to water and fisheries.

I am lucky in my professional life as a hydrogeologist and geophysicist to be able to work on projects that directly impact water quality in Florida. I have had a small role to play in multiple parts of the Comprehensive Everglades Restoration Projects (CERP) that include the Everglades Agricultural Area (EAA) storage reservoir, the Caloosahatchee Reservoir (C-43), the C-44 Reservoir and Stormwater Treatment Area (STA), the Caulkins Water Farm, and the C-139 Flow Equalization Storage Basin (FEB), among others. My role was bigger for a South Florida Water Management District (SFWMD) project to report, as co-author, on the groundwater salinity and hydrogeology of Water Conservation Area 2A (WCA-2A) located just south of Lake Okeechobee where the "River of Grass" starts.

WS-51 Title Page

In my own way I have tried to be part of a solution to water quality issues in south Florida particularly as ultimately related to the health of the fisheries, with anglers and fishing guides often taking a lead role as vocal advocates (Captains for Clean Water). In a small way I link my own novice-related inability to catch fish frequently with the generally poor health of Florida's coastal fisheries, although it might be too convenient of an excuse to cover me entirely. For this post I will describe a little of what is happening to improve the water quality in Florida Bay.

[Note that sometimes I am summarizing the work of others for technical content, but may not include a full reference. Contact me if you want more info about something.]

For millions of years prior to the early 20th century most of Florida south of Orlando drained into the Everglades, with much of that flow routed into and out of Lake Okeechobee (Lake O). Heavy rain events would often result in the flooding of low lying areas east, west and south of the Lake right up to the small ridges along the Atlantic coast where in recent human history the wealthy have lived. The map below shows a south Florida survey from 1859 (from USGS).

1859 Map of South Florida (from USGS SIR 2014-5025)

In the 1920's there were two very significant flood events that took the lives of thousands of south Floridians (mostly low income migrant workers) in the lowlands. In response, the US Army Corp of Engineers (USACE) began to build earthen berms and canals to control flooding in the areas around Lake O. By the 1950's the dikes, berms and canals looked a lot like they do today, for the benefit of flood control and agricultural land use.

Surface water that used to flow freely from Lake O into the Everglades was cut-off by the dams and canals and redirected. Freshwater redirected away from the Everglades remains a serious problem for the Glades themselves (in the form of peat collapse and saltwater intrusion), but has also notably decreased the freshwater supply to Florida Bay. Instead, most controlled discharges from Lake O go west into the Caloosahatchee River and east into the St. Lucie River. These discharges have gotten a lot of negative media attention in recent years because nutrient-fueled cyanobacteria in Lake O can be quite damaging to the downstream ecosystems.

Florida Bay is a series of shallow partially isolated pools where many fish spawn and adolescents grow to maturity. Although there is great resiliency in the natural system, the Florida Bay ecosystem suffers periodic hypersalinity events that cause large scale seagrass die-offs. Seagrasses are a cornerstone of healthy marine ecosystems.

In June 2019 I was invited to attend a workshop titled "The Groundwater Exchange Monitoring and Modeling (GEMM) Plan for Central Florida Bay."

There is strong evidence that by recharging the groundwater system along the southern mangroves of the Everglades with freshwater, the salinity levels in Florida Bay might not rise to extremes in periods of drought. Right now evaporation during the summer removes water faster than rainfall can replace it. The natural oscillations of salinity levels in the Bay are thereby elevated. The lows and mid-levels are ok, but the highs peak too high. The average values need to be reduced so the highs don't reach toxic levels.

Common with coastlines there is an underground inland movement of seawater driven by its higher density. The higher density salty groundwater eventually meets fresh groundwater and is redirected upward and back out to sea usually as gravity-driven seepage. The mixing that occurs at the freshwater interface is the key to delivering reduced salinity water back through the seepage part of the natural pump. On the freshwater side there needs to be enough volume to maintain head (gravitational) pressure on the cycling seawater to resist intrusion and to trigger seaward flow. Seepage of brackish-to-fresh groundwater back into Florida Bay, within the mangroves and below the Bay, appears to be the key to mitigating evaporation induced hypersalinity, or so scientists hope. Almost as damaging as hypersalinity would be too much freshwater delivered too quickly, especially if that water contained unmitigated nutrient levels and cyanobacteria. Marine biologists worry about fixing this problem too quickly and without the proper level of sensitivity. Recharging coastal groundwater with clean freshwater in effect allows the Bay to receive no more input than it needs, or so the early modeling seems to show.

If the salinity in Florida Bay can be stabilized, or held within a reasonable range of salinity, the net result is healthy seagrass communities supporting healthy fisheries. My fear is that groundwater seepage in the parts of the Bay that need it is inhibited by carbonate mud buildup occurring at a higher rate in those waterbodies. The mud is heavily burrowed by shrimp, but still inhibits seepage compared to areas where the mud is thin or absent. In a future post I hope to follow-up with more information about Florida Bay, particularly if I am able to win projects to perform some of the groundwater monitoring.

“A woman, who has never seen her husband fishing, doesn’t know what a patient man she married!” (unknown source)

#floridabay #waterquality #Everglades

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