By Steve Davis, Ph.D.
The Everglades is recognized worldwide for its iconic wildlife like alligators, panthers, and wading birds. Many people also know the Everglades for its vast sawgrass marshes, sloughs filled with bladderwort and water lilies, and tree islands that form the high ground. Perhaps the most important aspect of the Everglades, though, is what lies beneath its surface—the soil.
This is not just a story about soil, though. It’s about the important interactions between water, plants, soil, and microbes that make the Everglades what it is—a massive peatland. Peatlands are wetlands that accumulate vast amounts of organic matter (old dead plants) in a soil that we call peat. You may be more familiar with muck—a colloquial term for peat.
Wetlands are landscapes that are flooded for extended periods or whose soils are saturated by fresh or salty water. As a result, the vegetation and soil conditions in wetlands are unique compared to drier, upland areas. It is these unique soil conditions that allow some wetlands to be rather effective at accumulating peat, which can lead to the building of new land and long-term sequestration of atmospheric carbon. In fact, Everglades peat soils store enormous amounts of carbon, which makes them a critical piece of the landscape in terms of climate change. How do they do this?
Generally speaking, drier areas have more oxygen in the soil. That allows microbes to “eat” (oroxidize) the organic matter produced by plants, breaking down dead roots, leaves, and stems rapidly. Deserts, with little moisture, are an extreme case, covered almost entirely in sand rather than organic matter. Compost piles are a good example, if you have one, you may turn it occasionally to aerate the compost. The more well-aerated your compost is, the faster the microbes will break it down.
But in wetland areas with persistent flooding like the Everglades, soil microbes consume oxygen faster than they receive it. Over time, this leads to a microbial community that can persist without oxygen. These specialized anaerobic microorganisms survive by consuming nitrate, sulfate, or even carbon dioxide. But there is a tradeoff since these microbes generally grow more slowly and oxidize organic matter less efficiently than their counterparts that use oxygen.
Most upland plants cannot survive under anaerobic conditions for long. If your property has ever flooded, you may have witnessed the dieback of your lawn and shrubs. In areas with extended periods of soil flooding or saturation, upland plants will usually be replaced by “wetland” plants that are better adapted to these conditions.
Under flooding, they continue to grow and shed leaves, roots and stems that become organic soil. In some cases, the organic matter piles up over time and the organic soil grows vertically - a characteristic that is unique to peatlands.
The Everglades peatland developed under wetland conditions for thousands of years-even through periods of drought, flood, and rising seas. As a result, the organic soils in some areas of the Everglades are more than 10 feet deep. Since these soils represent the accumulated remains of old plants, they not only contain carbon, but also nitrogen, phosphorus and other essential elements.
However, the water management system that drained the Everglades Agricultural Area and resulted in some areas being too dry for too long (e.g., marshes north of Alligator Alley or south of Tamiami Trail), has tipped the soil carbon balance in the wrong direction.
Drainage or excessive drying of these soils allows oxygen to move in, breaking down organic matter faster than it can be produced by plants, and releasing carbon dioxide to the atmosphere. In fact, several billion metric tons of carbon dioxide have been added to our atmosphere from this process in the Everglades. For instance, the Everglades Agricultural Area alone has lost 880 million metric tons of carbon dioxide over the last 120 years. Nitrogen and phosphorus also come out of the soil as water “pollutants.” A long-term consequence of this is that the land sinks. Some areas of the Everglades Agricultural Area have sunk more than nine feet over the past century due to drainage and the oxidation of organic matter from those ancient Everglades soils. If too dry, peat soils are also vulnerable to fire, resulting in an immediate release of carbon dioxide, nitrogen, and phosphorus.
The solution? Keep wetlands (especially peatlands) wet. Everglades restoration is our best strategy for protecting peat soils and the carbon and nutrients locked up in those soils. Preventing the release of additional carbon dioxide into the atmosphere is critical in fighting the growing problem of climate change. So, restoration will help protect the remaining Everglades habitats, and the health of our planet.