Vegetative Habitats of Water Conservation Area-3A: Hydrologic Impacts of IOP
Wiley M. Kitchens
USGS/Florida Cooperative Fish and Wildlife Research Unit, Gainesville, FL
Paul Wetzel and Erik Powers
University of Florida, Gainesville, FL
A vegetation monitoring study has been initiated in Water Conservation Area-3A
(WCA-3A) to document impacts of a new hydrologic regulation schedule
implemented 1 July 2002 under the Interim Operation Plan for the Protection of
the Cape Sable Seaside Sparrow, Everglades Park – Alternative 7R (IOP-Alt.7R).
This study was implemented to address the concern that IOP-Alt.7R could
adversely affect the endangered snail kite (Rostrhamus sociabilis) and their
habitat in WCA-3A, the largest and most consistently utilized of designated
critical habitats. Much of the area is already currently seriously degraded.
Various studies have documented the conversion of wet prairies (preferred
foraging habitat) to aquatic sloughs in that area along with losses of interspersed
herbaceous and woody species essential for nesting habitat. The concern is
carrying capacity (habitat quality) will be further impaired from elevated water
depths and increased hydroperiods indicated by hydrological predictions.
The principal objective is to separate plant community responses due to typical
seasonal and year-to-year variances from effects due to new and /or predicted
hydrologic regimes. The vegetative community structure of these sites is an
expression of both recent past and current hydrological conditions. It is critically
important to determine how the species associations within these communities
respond differentially to changes in hydrology through time and over space.
Given the immense area of WCA 3A, this study focuses on areas represented by 2
Indicator Regions (IR’s 14 and 17). The areas include major gauging stations (GS
63, 64, and 65) and traditional foraging and nesting regions used by kites.
A multi-tiered approach was required to determine community change through
time and space while differentiating seasonal responses from projected hydrologic
changes.
1) Spatial Patterns and Change Detection at the Broad Vegetation Class Level(example, sawgrass strands, tree islands, cattail patches, and wet prairie/slough).
Aerial or satellite imagery will be used to remotely sense spatial distributions,
extent, and patterning of broad major vegetation classes. Change detection will
conducted on at least 3 sets of imagery, 4-5 years pre-project, at project onset, and
3-4 years post-project.
2) Development of “modeled-topographic” database and hydrologic
characterization of Indicator Regions. Stage information generated by SFWMM
model for the units comprising each Indicator Region is gridded 2 mi. on a side.
Stage duration curves generated from this data are determined from estimated
ground surface elevations generalized from a weighted mean over the 4 sq. mi.
area of each grid. This level of detail is far too generalized for assessment
impacts to habitat suitability of wetland vegetation for subtle changes in
hydroperiods and inundation depth regimes. To resolve this issue, we have
located 10 sample complexes (1 kilometer on a side) within each of the indicator
regions (14 and 17) (Fig. 1) using a stratified random approach (peat depths,
general elevation, and snail kite nest density). Water levels will be continuously
monitored in each complex. Each complex is subdivided into a grid 100-m on a
side. Replicate ground surface elevations will be measured (survey-grade GPS) in
each major plant community types (as per vegetation maps as per above) near the
intersection points in the grid. Elevations will be surfaced for each of the plant
types separately in each grid by confining kreiging routines for the elevations for
that plant type only within polygons labeled for that type. This is repeated for
each plant type and each cell. Polygons are re-composited and merged in a GIS
providing a topographic database driven by plant community types. Stage data
for the sample complex will be relativised to elevation data specific to each plant
community type creating stage duration curves for each vegetation type in the
individual cells. Long term and predicted hydroperiod and depth duration data for
each vegetation type in each cell will be generated by statistical regression with
the nearest permanent gauging station.
3) Establishment of permanent transects plots across elevation gradient in each
Indicator Region. Permanent monitoring plots (combinations of quadrats and
transects) have been established in the sample complexes across the local
elevation gradient in each complex. Regularly placed multiple or replicate
quadrats arrayed as continuous belts along a transect perpendicular to the
elevation gradient within each sample complex. Each site is sampled seasonally (3
times/yr) for species numbers, stem counts and biomass (both living and standing
dead). Water depths are monitored continuously within each sample complex for
determinations of hydroperiods and depth duration curves. Each complex
consists of three belt transect complexes, 5 plots of the principal habitat types
(sawgrass, wet prairie, sloughs), and 5 permanent tree island/shrub heads plots
sites typical of kite nest habitat. Multivariate techniques (NMS and multivariate
regression tree, and structural equation models) will be used to resolve
relationships between plant community structure and hydrology. Structural
equation modeling (SEM) will define statistical correlations among species and
associated hydrologic and other environmental parameters and provide
probabilistic measures for environmental mechanisms involved in plant
community succession.
Figure 1. Image of WCA-3A indicating IR and sample complex locations.
Kitchens, Wiley, Florida Cooperative Fish and Wildlife Research Unit, Bldg. 810,
University of Florida, Gainesville, FL 326211- Phone: 352-836-0536, Fax: 352846-0841, kitchensw@wec.ufl.edu, Ecology
This is for oral presentation in the ecology sessions.