Rebecca G. Harvey, William F. Loftus, Jennifer S. Rehage, and Frank J. Mazzotti
Introduction
Canals and levees are the foundation of south Florida's water-management system. However, degradation of Everglades ecosystems has resulted directly from these structures and their effects of drainage and impoundment. The purpose of this fact sheet is to summarize the science on ecological and hydrological impacts of Everglades canals and levees.
Native peoples in south Florida built small, shallow canals to connect villages to coastal trade routes. By comparison, the modern canal system covers hundreds of linear miles with wider and deeper cuts. Canals and levees were created to drain and reclaim the wetlands for urban and agricultural use, to store and provide water to developed areas, and to provide flood control. They have met those objectives but, in the process, have transformed the landscape and ecology of south Florida.
How do canals and levees affect Everglades hydrology?
Canals draw water from the surrounding wetlands. In combination with reduced water deliveries, this results in completely dry land during the dry season, diminished aquatic habitat during the wet season, soil loss, and flattening of the peat surface. Canals also alter surface water chemistry by directly exposing surface water to the bedrock.
Levee construction replaced relatively even water depths and flows with a "stair-step" system of impoundments, simultaneously making upstream portions too dry and downstream ones too wet, leading to widespread vegetation and soil changes.
How do canals and levees affect Everglades landscape and habitats?
Wetland Fragmentation
Hydrological barriers have led to loss of sheet flow and degradation of the distinct directional pattern of ridge and slough vegetation. The mosaic landscape has been replaced in many areas by large uniform stands of sawgrass, which offer fewer foraging areas and refuges for wildlife. Canals, levees, and roads also function as barriers to gene flow of aquatic fauna and to movement of fire across the landscape.
Nonnative Species
Canals facilitate establishment of nonnative fishes by offering permanent thermal and drought refuges. During the record cold event of January 2010, canal water temperatures remained above the lethal limits of nonnative fishes, which range from 6 to 15°C (43–59°F) (below). Canals also serve as pathways for nonnative species to invade interior wetlands, increasing the potential for impacts that may alter ecosystem structure and function.
Canals provide deep-water, nutrient-enriched habitats for expansion of nonnative pest plants such as water lettuce, hydrilla, and water hyacinth. These plants can modify water chemistry, deplete oxygen levels, shade out native species, decrease water flow, and interfere with navigation and flood control. Levees also provide disturbed upland habitat for noxious terrestrial pest plants, and corridors into the wetlands for insects such as fire ants.
Refuges and Sinks
Canals provide habitat for dense populations of alligators, but these populations are dominated by adults. Nesting success in canals is negligible. Alligators that rely on canals may no longer construct and maintain alligator holes, which provide critical dry-season habitat for wetland fishes, amphibians, and wading birds.
The sport fishery in Everglades canals is "subsidized" by prey from the wetlands that are forced into canals in the dry season. Canals may act as sinks for forage species, which suffer heavy losses from native and nonnative predatory fishes. Without canals, prey fishes would remain on the marsh, available to wading birds. The effect of the loss of this forage base to wading birds requires study.
How do canals and levees affect Everglades water quality?
Phosphorus delivery into wetlands via canals has led to replacement of periphyton/Utricularia mats with filamentous algal species that thrive in enriched waters, and the shift from a sawgrass-dominated vegetation community to one dominated by cattails. The most pronounced expansion of cattails is in WCA-2A, which receives water directly from the Everglades Agricultural Area. Cattails limit light penetration, decrease oxygen availability, and alter invertebrate and fish communities. Canals also transport chemical pesticides (e.g., endosulfan, atrazine) and sulfur (a mediator in methylation of mercury) into the Everglades.
Publication #WEC309
Release Date:August 31, 2017
Reviewed At:May 23, 2023
Related Experts
Harvey, Rebecca G
University of Florida
Mazzotti, Frank
Specialist/SSA/RSA
University of Florida
Related Units
Ft Lauderdale REC
Wildlife Ecology and Conservation
Related Topics
Everglades Agricultural Area Wildlife
- Critical Issue: Natural Resources and Environment
About this Publication
This document is WEC309, one of a series of theDepartment of Wildlife Ecology and Conservation, UF/IFAS Extension. Original publication date February 2011. Visit the EDIS website athttps://edis.ifas.ufl.edufor the currently supported version of this publication.
About the Authors
Rebecca G. Harvey, environmental education coordinator, UF/IFAS Fort Lauderdale Research and Education Center; William J. Loftus, Aquatic Research & Communication, LLC; Jennifer S. Rehage, assistant professor, Earth & Environment Department, Southeast Environmental Research Center, Florida International University; and Frank J. Mazzotti, professor,Department of Wildlife Ecology and Conservation; UF/IFAS FLREC; UF/IFAS Extension, Gainesville, FL 32611.
Contacts
- Frank Mazzotti
- Venetia Briggs-Gonzalez
FAQs
How do canals and levees affect Everglades hydrology? Canals draw water from the surrounding wetlands. In combination with reduced water deliveries, this results in completely dry land during the dry season, diminished aquatic habitat during the wet season, soil loss, and flattening of the peat surface.
What is a benefit of building canals and levees in the Florida Everglades? ›
Canals were constructed to drain and reclaim the wetlands and to convey water to southeastern Florida where it recharges into the aquifer to supply well fields for the urban population.
How do canals affect the environment? ›
Habitat destruction: Concrete canals can have a detrimental effect on the environment as they destroy the natural homes of plants and animals, ultimately causing a decline in biodiversity.
Are there canals in the Everglades? ›
Following another population boom after World War II, and the creation of the Central and Southern Florida Flood Control Project, the Everglades was divided into sections separated by canals and water control devices that delivered water to agricultural and newly developed urban areas.
Why was the flow of water through the Florida Everglades changed? ›
Since the 1800s, water diversions and flood-control projects have severed the flow of water between different parts of the Everglades, while large areas of its lands were converted to agricultural or residential areas.
How canals and levees affect the Everglades ecosystem circular? ›
How do canals and levees affect Everglades hydrology? Canals draw water from the surrounding wetlands. In combination with reduced water deliveries, this results in completely dry land during the dry season, diminished aquatic habitat during the wet season, soil loss, and flattening of the peat surface.
What is a levee advantages and disadvantages? ›
Floodwalls and Levees Advantages and Disadvantages
| Advantages | Disadvantages |
|---|
| Reduces flood risk to the structure and its contents | Requires interior drainage |
| Reduces the physical, financial, and emotional strains that accompany flood events | May affect local drainage, possible resulting in water problems for others |
10 more rowsIn combination with reduced water deliveries, this results in completely dry land during the dry season, diminished aquatic habitat during the wet season, soil loss, and flattening of the peat surface. Canals also alter surface water chemistry by directly exposing surface water to the bedrock.
What are the environmental impacts of levees? ›
Artificial levees prevent flooding. But they also create a new problem: levees squeeze the flow of the river. All the river's power is flowing through a smaller space. Water levels are higher and water flows faster.
What are the advantages and disadvantages of canal? ›
Perennial canals are fed by a perennial source of water, and provide water throughout the year. Canal irrigation has several advantages, such as providing a reliable source of water for agriculture, but it also has disadvantages, such as being expensive to construct and maintain.
Since 1900 much of the Everglades has been drained for agriculture and urban development, so that today only 50 percent of the origi- nal wetlands remain. Water levels and patterns of water flow are largely controlled by an extensive system of levees and canals.
How is development affecting the Everglades? ›
Originally the Greater Everglades ecosystem had a large diversity of habitats connected by wetlands and water bodies. Since the 1800s, humans have been altering the Everglades landscape. Water diversions and flood control structures restrict the flow of water across the sensitive landscape.
How does the Everglades water naturally clean itself? ›
Seagrass is one of the key secrets to filtering the pure water in the Everglades. Signs along the beginning of the Anhinga trail are all about educating visiting hikers about water: water habitats, phosphorus levels, and especially water purity.
What are 5 facts about the Everglades? ›
Everglades National Park is:
- Largest continuous stand of sawgrass prairie in North America.
- Predominant water recharge area for all of South Florida through the Biscayne aquifer.
- A World Heritage Site, a Biosphere Reserve, a Wetland of International Significance, and an Outstanding Florida Water.
The Everglades gets a lot of its water from rainfall (somewhere around 60 inches per year on average). When it starts raining over south Florida, it rains everywhere including on our largest lake, Lake Okeechobee. This is the start of the most indirect way for water to flow into the Everglades.
What is the primary cause of degradation to the Everglades? ›
Phosphorus in agricultural and stormwater runoff has degraded water quality in the Everglades since the 1960s. The natural plant and animal communities for which the Everglades are known developed under very low phosphorus conditions.
What are the benefits of building canals? ›
Canals are advantageous because they provide waterway short cuts from one region to another, allowing for more efficient and convenient transport of goods.
What are the benefits of the Florida Everglades? ›
For example, the Everglades ecosystem provides drinking water for one-third of Floridians and irrigation for much of the state's agriculture. The wetlands improve water quality by filtering out pollutants and absorbing excess nutrients, replenish aquifers, and reduce flooding.
What is the purpose of canals in Florida? ›
Canals in Florida serve many purposes: drainage, flood control, irrigation, navigation, and recreation. They also create waterfront home sites.
What are the advantages of raised levees? ›
Levees may be used to increase available land for habitation or divert a body of water so the fertile soil of a river or seabed may be used for agriculture. They prevent rivers from flooding cities in a storm surge.
