USGS Geological Research Activities with U.S. Fish and Wildlife Service

Priority Ecosystems

Science in support of the south Florida ecosystem restoration effort

The south Florida ecosystem, including the Everglades, has been greatly impacted by many disturbances that have resulted in a loss of wildlife habitat.  More than 35 percent of the original natural ecosystem has been converted to agricultural or urban use, much of the remaining wetlands are threatened by altered (unnatural) hydroperiods that result in too much water in wet years and drought and fires in dry years, and over 2,250 km of canals dissect what was once wetlands and discharge contaminated water into the ecosystem. Water quality is one of the biggest issues facing restoration of the Everglades.

USGS research on the south Florida ecosystem supplies resource-management agencies with information that will enable them to reestablish the water regime and to manage and maintain the components of the hydrologic system so that natural ecosystem functions can recover.

 

 

 

 

 

Biogeochemical studies in the Everglades

USGS scientists are working with the Loxahatchee National Wildlife Refuge (NWR), Water Conservation Area 3, and the Everglades National Park to understand sources of water contamination, ecosystem response to the contamination, and the likely effects of restoration efforts on water chemistry.  Contaminants of concern include nutrients, sulfur, and mercury (the three most important contaminants currently affecting this ecosystem) as well as anthropogenically produced organic substances (pesticides, herbicides, polycyclic aromatic and aliphatic hydrocarbons) and other metals.  USGS studies in the Loxahatchee NWR are aimed at addressing USFWS concerns about potential contamination from leakage along canals at the periphery of the refuge that could lead to build up of methyl mercury in the refuge.

Experiments are designed to help answer management questions, such as:

• What reductions in toxicity (mercury methylation and bioaccumulation) would be realized if atmospheric mercury emissions were reduced by 75%?
• What environmental factors control high methylmercury production in Stormwater Treatment Areas (STA's)?
• Over what time scales will improvements to the ecosystem occur if nutrient and sulfur loading are reduced by implementation of agricultural best management practices in the STA's?
• What are the toxic effects of sulfur contamination of the ecosystem? 

 

 

 

Tree islands of the Florida Everglades - A disappearing resource

Tree islands are important centers of biodiversity in the Everglades and have two to three times the plant and animal diversity of the surrounding wetlands. This high diversity results from greater elevation relative to the wetlands; seasonally dry conditions provide refugia and nesting sites for animals and allow establishment of various tree and shrub species. Since 1950, the number of tree islands in the Everglades has been halved, possibly because of changing water management practices. Restoration of these islands is an important component of the Comprehensive

Everglades Restoration Plan, which requires solid scientific evidence on requirements for tree-island formation and development in order to maximize chances for successful tree-island restoration. USGS research is designed to understand environmental requirements for tree-island formation and to assess the response of tree-island communities to hydrologic changes, particularly those of the 20th century. Efforts have focused on the Loxahatchee NWR, Water Conservation Areas 2A, 3A and 3B, and the Everglades National Park. These analyses form the basis for prediction of tree-island response to different restoration schemes.

Until recently, the timing and cause of tree-island formation were poorly understood, with estimates of initial tree-island development ranging from as early as thousands of years ago to as recently as the last few decades. To increase our knowledge about the origins of these features, sediment cores were collected on and around tree islands. These cores were dated using radioisotopic techniques, including carbon-14 dating, which provides reliable dates from ~40,000 to ~300 years ago, and lead-210 dating, which provides age models for the last century. The age models were paired with vegetational reconstruction based on pollen analysis from cores to identify the timing of tree-island formation and assess past tree-island response to hydrologic changes in the 20th century.

The northeastern Everglades, including Loxahatchee NWR, contain the thickest and oldest peats of the Everglades. Wetlands are dominated by waterlily sloughs, which require the deepest water and longest flooding intervals of Everglades wetland communities. Within this landscape, there are a number of elongate tree islands called strand islands, which now are characterized by homogeneous vegetation and dominance of hollies (Ilex). These islands formed on shallow sites in a deeper marsh.

USGS study of sediment cores from strand islands indicates that tree-island taxa (characterized by abundant ferns in pollen and spore assemblages) were well-established more than 1,100 years ago. Although holly and wax myrtle (Myrica) abundance began increasing early in the 20th century, the greatest changes have occurred since 1960, when holly abundance increased more than fourfold. This trend suggests that total enclosure of Loxahatchee NWR by water-management structures in 1961 had substantial impacts on the composition of vegetation on the strand islands.

The original distribution of tree islands was determined by local topographic highs where water depths were shallower than average, ultimately undergoing sufficient seasonal drying for trees and shrubs to become established. These features have been a distinctive component of the Everglades ecosystem for centuries, but altered water management practices of the past century have changed their vegetational composition and size to varying degrees. While tree islands in some parts of the Everglades have disappeared due to overly long hydroperiods and deep water, those in other regions have become larger due to reduced water supplies. Therefore, restoration plans designed to improve Everglades tree-island health should develop regionally based performance measures; these would incorporate differences in both hydrology (past, present, and future) and inherent differences in species composition based on latitude within the Everglades.