By Dr. Steve Davis, Chief Science Officer for The Everglades Foundation
Excerpt from the Science Insider, Summer 2023 Volume 8
We often refer to the quantity, quality, timing, and distribution of water as important targets for Everglades restoration. Why is each of these elements important?
Fundamentally as a wetland, the Everglades ecosystem requires flooded or saturated soil conditions for wetland plants to proliferate over plants adapted for higher grounds. These wetland conditions also deliver a variety of benefits across the Everglades, such as recharging the aquifer, enhancing water quality, and sequestering carbon. However, in the Everglades' current unrestored state, wetland conditions do not always last throughout the year, damaging water quality, causing shortages in our water supply, and fueling losses of both habitat and peat soil.
An essential component of restoration is increasing the quantity of water delivered to the Everglades. The primary means of doing this is by reconnecting Lake Okeechobee to the Everglades through improved operations such as the Lake Okeechobee System Operating Manual and large storage reservoirs such as the Everglades Agricultural Area (EAA) Reservoir project. Increasing freshwater flow will also have downstream benefits in Florida Bay, reducing the frequency and severity of hypersalinity conditions that can lead to seagrass die-offs.
Water quality is a catchall term for a variety of water’s physical, chemical, and biological properties such as temperature, pH, and dissolved oxygen. In the Everglades, phosphorus levels are of utmost concern. Elevated mostly by agricultural pollution, excess phosphorus transforms Everglades marshes to cattails and contributes to foul-smelling, toxic algae blooms in rivers and lakes.
Another restoration target is keeping phosphorus levels low, below a critical threshold of 10 parts per billion (ppb). We can achieve this target by routing polluted water through stormwater treatment areas (STAs), which are large, engineered wetlands that remove phosphorus from water and sequester it in the soil. However, these stormwater treatment areas appear to have a limit in their ability to cut phosphorus levels, reducing inflow concentrations on the order of 80 to 85%. The ability of STAs to achieve 10 ppb regularly can be enhanced if farmers reduce phosphorus running off their fields. Sending more clean water south will keep Everglades wetlands and peat soils hydrated, making them less likely to oxidize and release phosphorus when exposed to the air.
The timing of water levels and flow is tied to our seasonal rainfall pattern in South Florida. On average, we get four to five feet of rainfall every year, with 75% of that falling in the wet season from mid-May to November. As a result, water levels rise across the Everglades in the wet season and decline throughout the dry season. In its current, overdrained state, the Everglades dries out too early in the dry season, leading to a lack of food (e.g., small fish) for nesting wading birds and alligators. As a result, wading birds abandon their nests, leading to massive chick mortality, while alligators suffer from reduced weight.
As a key target for Everglades restoration, restoring the timing of water entails large storage reservoirs, such as the EAA Reservoir, that store water during the wet season and release it during the dry season. STAs and conveyance features such as the Tamiami Trail bridges also allow for the delivery of that water to the Everglades throughout the dry season, while mimicking the natural decrease in water levels. Restoring the timing will improve foraging conditions for nesting wading birds and alligators, as well as conditions for a variety of species dependent on habitats like sawgrass ridges, sloughs, and tree islands.
The final piece to the restoration puzzle is distribution, which reflects the pattern and location of water deliveries. The historic Everglades was characterized by sheet flow—abroad, shallow, sheet of clean freshwater over 100 miles long and up to 50 miles wide slowly flowing from the southern rim of Lake Okeechobee to Florida Bay. However, canals and water control structures carved up the Everglades, reducing sheet flow. Furthermore, the water flowed in ways that no longer followed the topography of the remaining landscape; only 50% of the Everglades was spared from development. These changes damaged both habitats and species such as tree islands and the endangered Cape Sable Seaside Sparrow.
Restoring the distribution of water flows requires having more clean water to send south. Beyond that, projects that remove canals and levees in the Everglades, such as backfilling the Miami Canal north of Alligator Alley, will aid in restoring the natural sheet flow of water. At the southern end, projects along Tamiami Trail, along with improved operations, are redistributing flows into Everglades National Park. The target is to send 2/3 of the flows under the Tamiami Trail bridges and 1/3 through the S-12 structures further west (see map). This will be a vast improvement over past operations that diverted 90% of flows through the S-12 structures, flooding the Cape Sable seaside sparrow’s nesting habitat.
When complete, Everglades restoration will provide for the needs of 2,000 species of plants and animals that depend on this ecosystem. A restored Everglades means more clean water for South Florida, less toxic algae and damaging impacts to our estuaries, enhanced carbon sequestration across the system, and improved resilience to the impacts of sea level rise and climate change.