Relationship between alligator holes and EDEN hydrologic data in Everglades National Park, Florida
Zhongwei Liu, Ph.D.1 *
Frank J. Mazzotti, Ph.D.1
Laura A. Brandt, Ph.D.2
Stephanie S. Romañach, Ph.D.3
Danielle E. Ogurcak 4
Aaron L. Higer1
1. Ft. Lauderdale Research & Education Center, University of Florida2. U.S. Fish and Wildlife Service3. U.S. Geological Survey4. Florida International University
* [email protected] annual conferenceLas Vegas, NV, 3/2009
2
OutlineOutline Introduction
– Alligator hole– EDEN
Methodology – Data– Methods
Results– Hole morphometry– Hole morphometry and EDEN data– Hole drought
Conclusions
3
IntroductionIntroduction American Alligator
– Top predator, keystone species, ecosystem engineer in Florida Everglades
Alligator Hole– Small but persistent ponds excavated
and maintained by alligators– Dry-season refugia– Nest, colonization, and foraging sites
sawgrass marsh
sloughalligator holes
tree islandswet
prairiewet prairie
4
Alligator Alligator hole by hole by
habitat typehabitat type
Tree island hole in Taylor Slough
Sawgrass hole in Shark Slough
Wet Prairie hole in Southern Marl Prairie
5
Everglades Depth Everglades Depth Estimation Network Estimation Network
(EDEN)(EDEN) Integrated network of real-
time water level monitoring, ground elevation modeling, and water-surface modeling
EDEN Water-Surface Model– Developed by Pearlstine et
al. (2007) with spatial interpolation of water level data from 240 gage stations in ArcGIS
– Validated by Liu et al. (2009, in press, Ecohydrology)
– 2000 – present– Resolution: 400 m
6
Alligator hole dataAlligator hole data 62 holes (1/2006 – 8/2007) Accessed by helicopter/airboat or on foot Transect length (major and minor axes),
water and sediment depths at every 1-meter interval
Hole diameter, area, marsh water depth, basin depth, circularity index (Miller,1953)
Water and sediment profile of NW1 in NW ENP (E-W transect)
An alligator hole in NW ENP (NW1)
NW1
-260.0
-210.0
-160.0
-110.0
-60.0
-10.0
40.0
90.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37
Sampling interval (m)
Elev
atio
n (c
m)
Water level Ground Bedrock
Cattails marshWillowhead Open water
Hole water depth
Sediment depth
Marsh water depth
7
EDEN hydrologic dataEDEN hydrologic data Water level
– Direct EDEN model output (2000-2007)
Water depth– depth = water level – DEM (EDEN water depth)– depth = water level – estimated site ground elevation– estimated site ground elevation = water level – measured
water depth
Hydroperiod – Hydroperiod: the number of days per year an area is covered
by water (hole water depth >0).– Average hydroperiod: 8 years (2000-2007)
Drought– Hole bottom drought (hole water depth ≤ 0)– Hole top drought (0 < hole water depth ≤ basin depth)
8
MethodsMethods GIS analysis
Nonparametric statistical methods–Spearman’s rank correlation–Wilcoxon signed rank test for paired
data –Kruskall-Wallis ANOVA
9
Results: I. Hole Results: I. Hole morphometrymorphometry
Habitat Parameter All holes Sawgrass Tree Island Wet Prairie Sample size 62 41 12 9 Diameter (m) 8.0 4.0 8.0 3.8 8.4 4.2 7.5 4.9 Surface area (m2) 59.5 60.4 58.2 57.9 63.4 56.3 59.9 81.7 Circularity index 0.9 0.1 0.9 0.1 0.9 0.2 1.0 0 Basin depth (cm) 74.9 27.0 78.3 24.5 77.6 30.1 55.8 28.5 Sediment depth (cm) 152.3 50.7 148.7 49.0 156.9 54.6 163.9 58.1 Hole water depth (cm) 88.9 28.3 92.8 26.0 81.7 37.3 80.9 24.1 Marsh water depth (cm) 14.0 16.5 14.5 15.1 4.1 14.3 25.1 19.3
Note: Data shown are means ± s.d.
10
Morphologic variations by habitat and location–Average marsh water depths
varied with habitat type (Kruskall-Wallis, H = 12.44,
2 d.f., P = 0.002).–Average hole water depths
varied with hole location (Kruskall-Wallis, H = 14.52,
4 d.f., P = 0.006).
Inter-relationships–Hole area and sediment
depth–Hole water depth and basin
depth
0
20
40
60
80
100
120
Shark Slough(n=20)
NW ENP(n=15)
RockyGlades(n=16)
SouthernMarl Prairie
(n=6)
Taylor Slough(n=5)
Location
Wat
er d
epth
(cm
)
Spearman’s rank correlationr = 0.41, P = 0.001
0
50
100
150
200
250
300
0 50 100 150 200 250 300
Area (sq. m)
Sedi
men
t dep
th (c
m)
Spearman’s rank correlationr = 0.76, P < 0.0001
20
40
60
80
100
120
140
160
20 50 80 110 140 170
Water depth (cm)
Bas
in d
epth
(cm
)
11
Results: II. Morphologic Results: II. Morphologic features and EDEN features and EDEN
hydrologic variableshydrologic variables Hole area/basin depth and EDEN water level
–EDEN water level: daily value, and seasonal average (2000-2007)
–Spearman’s rank correlation, all P > 0.05.
Marsh water depth and EDEN water depth–Wilcoxon’s signed rank test, W = -213.5, P = 0.14–However, differences ranged from -60 to 30 cm
(60% absolute differences >10 cm).
12
Var1 Var2 r P-value
Hydroperiod
Area 0.30 0.02
Basin depth 0.31 0.02
Hole water depth 0.01 0.92
Average hydroperiod(2000-2007)
Area 0.18 0.18
Basin depth 0.44 0.0003
Hole water depth 0.25 0.046 Note: r - Spearman’s rank correlation coefficient.
Hole morphology and hydroperiod
13
Hole bottomdrought
–2000 – 2007 –18 holes;
270 days (14 holes: < 16
days)
Results: III. Results: III. Hole droughtHole drought
N= 270 (days)
0%
5%
10%
15%
20%
25%
April May June July
Month
Perc
enta
ge F
requ
ency
NW ENPRocky GladesShark SloughSouthern Marl PrairieTaylor Slough
14
Hole top drought
–2000 -2007
–62 holes
15
Hole top Hole top droughtdrought
(2000-2007; 62 (2000-2007; 62 holes)holes)
16
Hole drought by habitatHole drought by habitatHole bottom drought
Sawgrass(N = 72)
0%
10%
20%
30%
40%
50%
60%
4 5 6 7
Month
Tree Island(N = 111)
0%
10%
20%
30%
40%
50%
60%
5 6 7
Month
Wet Prairie(N = 87)
0%10%20%30%40%50%60%70%
5 6 7
Month
Hole top droughtSawgrass
(N = 20,879)
0%
10%
20%
30%
1 2 3 4 5 6 7 8 9 10 11 12
Month
Tree Island(N = 10,077)
0%
10%
20%
30%
1 2 3 4 5 6 7 8 9 10 11 12
Month
Wet Prairie(N = 6,123)
0%
10%
20%
30%
1 2 3 4 5 6 7 8 9 10 11 12
Month
17
ConclusionsConclusions The hole areas were from 5 - 269 m2 (60 ± 60 m2). The hole
basin depths were from 30 - 148 cm (75 ± 27 cm). Most holes were circular in shape.
Hole area and basin depth were not correlated with EDEN water level, but basin depth was associated with short and long-term hydroperiod.
Hole bottom drought: southern marl prairie and Taylor Slough (May - July)
Hole top drought: Taylor Slough and Rocky Glades (March – May)
The findings would help identify ecologically and biologically important habitats/sites (particularly during dry seasons) to conduct long-term monitoring and study of alligators, fish, wading birds, and vegetation dynamics.
18
Future StudiesFuture Studies Field surveys within both dry and wet
seasons for a single alligator hole
Drought duration
Hole volume and biomass estimation
Comparison and linkage with alligator ecological model simulations
Examination of the relationships with rainfall and evapotranspiration (ET)
19
AcknowledgementsAcknowledgements This research was funded by U.S. Army Corps of
Engineers, University of Florida, and U.S. Geological Survey Priority Ecosystems Science.
Everglades National Park and South Florida Water Management District provided logistical support including airboats, helicopters, and vehicles.
We thank other members of the field-data collection team at University of Florida: Ryan Lynch, Jemeema Carrigan, Debbie Kramp, Mike Rochford, Wellington Guzman, Joy Vinci, Mark Peyton, Brian Bahder, Clayton McKee, Matt Brian, Chris Bugbee, and Michelle Casler.
Top Related