Landscape Analysis of Gramminoid Habitats to Water Quality and Hydrology in Arthur
R. Marshall Loxahatchee National Wildlife Refuge.
Wiley M. Kitchens
USGS/Florida Cooperative Fish and Wildlife Research Unit, Gainesville, FL
The northernmost remnant of the intact Everglades habitat is located in the 57,235 ha
(200 square mile area) of the Loxahatchee National Wildlife Refuge. Historically, this
system was comprised of a spatially complex mosaic of wet prairies, saw grass stands,
tree islands, alligator holes, and sloughs. However, upon completion of the extensive
Army Corps of Engineers’ Central and South Florida Project, the refuge began to
experience large scale habitat conversions associated with altered hydroperiods and
agriculturally derived pollution (i.e., contaminants and nutrients). This area has been
subject to a rigidly imposed regime of water deliveries and severely degraded water
quality as a result of the conversion of its primary watershed to agricultural land uses.
A multi-year interdisciplinary study (1986-91) was conducted to resolve the issues of
hydrological alterations and nutrient loading impacts on this important piece of the
Everglades system. As a result of altered hydrologic regimes and excessive nutrient
loading, the vegetative habitats of the refuge have responded by conversion to massive
monospecific stands of cattails in areas influenced by runoff waters. There has been a
tendency to drown habitats in the south of the refuge and desiccate those of the north.
This study defined gradients of nutrient addition effects and hydroperiods resulting from
the management of water on the refuge. The study employed a community-level
investigation of vegetative associations in response to the environmental gradients with a
spatial characterization of the environmental variables in the GIS. We developed a
spatial hydrological simulation model, a vegetative cover database from classified
satellite imagery, a spatial coverage of water column/substrate nutrient concentrations,
and landscape topography, all geo-spatially articulated in a GIS. Simultaneous studies of
wading bird and forage fish distributions in response to habitat conditions were
conducted to examine the influence of hydroperiod and water quality on wading birds
and their prey base.
In order to spatially portray the various water depths and hydroperiods imposed on the
wetlands and examine vegetative responses, a spatially articulate hydrological model was
adapted from an existing model and applied very successfully to the area. The model
incorporated approximately five hundred 1 km cells and was verified with field data. This
capability provided a means hind-casting into the past and recreating the hydroperiod
regimes for the past 16 yrs. Patterns of habitat use were influenced strongly by seasonal
variation in water levels and decapod and fish assemblage structure varied among
habitats. The bottom line results of the study were that there were indeed impacts and
vegetative change resulting from hydrological alterations, but the principal agent
responsible for the conversion of approximately 8000 acres to cattail was principally
phosphorus in the substrates proximal to agricultural inflows.
This work was an innovative approach for its time, employing a hierarchical approach
spanning landscape level to community ecology level techniques with GIS technology.
The study was however conducted approximately 15 years ago and needs to be upgraded
with better imaging, modeling techniques, and community analysis techniques.
Kitchens, Wiley, Florida Cooperative Fish and Wildlife Research Unit, Bldg. 810,
University of Florida, Gainesville, FL 326211- Phone: 352-836-0536, Fax: 352-8460841, kitchensw@wec.ufl.edu, Ecology
This is for oral presentation in the Loxahatchee research session.