Wetlands role in run-off mitigation

Wetlands could be described simplistically as ‘nature’s kidney’ filtering out pollutants. However, they provide many important ecosystem services. Depending on location, soil type, surface and ground water movement, a wetland may serve different environmental functions to different degrees, such as flood water retention, ground water exchange, and nutrient and sediment filtering. All wetlands, whether natural, restored, or manmade, serve as viable habitat for native wildlife, important carbon storage, and as water containment.

Wetlands mitigate nutrient run off through several complex paths: physical, chemical, or biological, and depend on the form of the pollutant (particulate, dissolved, organic, etc.) and the compartment of the wetland processing it (water, biota, soil).

The main inorganic nutrients entering wetlands are nitrogen and phosphorus from agriculture. Uptake of both these nutrients’ inorganic forms by wetland plants for growth serves as temporary storage in the spring and summer, which is mostly released again in the fall and winter as dead vegetation.

Audubon Corkscrew Swamp Sanctuary, an inland freshwater wetland with plants capable of taking up and sequestering excess nutrients

More long-term nitrogen removal primarily relies on microbes on solid submerged surfaces all over the wetland. The main transformations are ammonification (organic N to ammonia), nitrification (ammonia to nitrate/nitrite), and denitrification where nitrate is converted to nitrogen gas, which is then released into the air (volatilization) where it makes up 85% of the atmosphere. This process is the dominant, sustainable removal process in wetlands that undergo heavy nitrate loads. This is a temperature dependent process, meaning the rate of nutrient sequestration is seasonal.
Phosphorus typically enters wetlands as particulates that undergo sedimentation (deposited into sediment) via the slowing of water flow through the wetlands as they travel over submerged and emergent vegetation, allowing heavier particulates to fall to the bottom. Phosphorus also enters as
dissolved phosphate (PO₄) that accumulates in the soil as well; though there is a threshold for P levels in wetland soil.

Historically, Lake Okeechobee would fill and flow into the Everglades and eventually drain into the Gulf of Mexico to the southwest and Florida Bay to the south.

Florida had lost 46% of its original wetland acreage by the 1990s, and even today gutted legislature threatens these vital ecosystems. When inland wetlands are lost, runoff from storms flow straight into a watershed with all the excess sediment and nutrients that has been collected being deposited into streams, estuarine and coastal ecosystems, which can encourage algal blooms. This phenomenon can block light to aquatic plants and create hypoxic conditions as algae die and decompose, meaning there is not enough dissolved oxygen to support other organisms. Eutrophication (excessive nutrients) plays a role in red tides or harmful algal blooms (HAB), which can produce harmful toxins that kill off ocean life.

The continued existence of Florida’s beaches and coast as functional ecosystems and our own communities rely on the protection and maintenance of inland wetlands.

We all can play a part to help preserve our vitally important wetlands for all the species that rely on them, ourselves included. Maintaining a healthy septic system and reducing water use by using reclaimed water for landscaping are steps that can be taken on the individual level. You can also encourage your HOA to maintain native vegetation, allowing for nutrient filtration around water retention areas and support initiatives to reduce wetland loss associated with continued development in our region as a larger community invested in Florida’s future.

-Sam, Conservation Intern