Wetlands
DOI 10.1007/s13157-013-0451-8
HYDROLOGIC RESTORATION
The Influence of Hydrologic Restoration
on Groundwater-Surface Water Interactions in a Karst
Wetland, the Everglades (FL, USA)
Pamela L. Sullivan & René M. Price &
Jessica L. Schedlbauer & Amartya Saha &
Evelyn E. Gaiser
Received: 28 December 2012 / Accepted: 20 June 2013
# Society of Wetland Scientists 2013
Abstract Efforts to rehydrate and restore surface water flow
in karst wetlands can have unintended consequences, as these
highly conductive and heterogeneous aquifers create a close
connection between groundwater and surface water. Recently,
hydrologic restoration efforts in the karstic Taylor Slough
portion of the Everglades has changed from point source
delivery of canal water (direct restoration), to the use of a series
of surface water recharge retention basins (diffuse restoration).
To determine the influence of restoration on groundwatersurface water interactions in the Taylor Slough headwaters, a
water budget was constructed for 1997–2011 using 70 hydro-
Electronic supplementary material The online version of this article
(doi:10.1007/s13157-013-0451-8) contains supplementary material,
which is available to authorized users.
P. L. Sullivan (*)
Earth and Environmental Systems Institute,
Pennsylvania State University, University Park, PA 16802, USA
e-mail: [email protected]
P. L. Sullivan : R. M. Price : A. Saha : E. E. Gaiser
Southeast Environmental Research Center,
Florida International University, Miami, FL 33199, USA
P. L. Sullivan : A. Saha : E. E. Gaiser
Department of Biology, Florida International University, Miami,
FL 33199, USA
R. M. Price
Department of Earth and the Environment,
Florida International University, Miami, FL 33199, USA
J. L. Schedlbauer
Department of Biology, West Chester University,
West Chester, PA 19383, USA
meteorological stations. With diffuse restoration, groundwater
seepage from the Everglades toward the urban boundary increased, while the downstream delivery of surface water to the
main portion of the slough declined. The combined influence
of diffuse restoration and climate led to increased intra-annual
variability in the volume of groundwater and surface water in
storage but supported a more seasonally hydrated wetland
compared to the earlier direct tactics. The data further indicated
that hydrologic engineering in karst wetland landscapes enhances groundwater-surface water interactions, even those
designed for restoration purposes.
Keywords Ecohydrology . Water budget . Climate variability .
Priestley-Taylor method . Evapotranspiration
Introduction
Near-surface karst regions occupy approximately 20 % of icefree terrestrial land on Earth and supply roughly 20–25 % of
the world’s population with groundwater (Ford and Williams
2007). Ecologically, karst regions are important as they also
support many wetlands around the world, especially in Europe
and North America (Gondwe 2010). Over the last 200 years,
mounting human pressure, such as agricultural and suburban
expansion, has led to a substantial loss in wetland cover
globally (≈50 %; Zedler and Kercher 2005), while many
remaining wetlands have undergone some degree of degradation. In karst wetlands, the influence of these human modifications can be amplified (Ford and Williams 2007), as small
water level changes in highly transmissive aquifers can yield
significant shifts in groundwater flow (Bonacci et al. 2009).
Wetlands
As wetlands are estimated to provide approximately 40 % of
the world’s ecosystem services (Zedler and Kercher 2005), the
challenge facing scientists and managers now is how to balance the increasing human demand for water (Oki and Kanae
2006) while maintaining and restoring wetlands, especially in
karst regions.
As the site of one of the most extensive karst wetland restoration efforts to date, the Everglades, USA, provides a unique
environment to study the influence of human modification and
demand on wetland ecohydrology. Spanning almost the entire
southern portion of the Florida peninsula (Fig. 1), the Everglades
is primarily underlain by the Biscayne Aquifer (≈ 66 % of the
Everglades), which supplies drinking water to a population of
over 5 million. The construction of canals, dikes and levees
starting around the turn of the 20th century led to the compartmentalization of the majority of the wetland and the reduction in
surface water flow. Along the northern and eastern boundaries of
the Everglades water levels have been significantly lowered to
provide flood protected agricultural and suburban lands, while
water levels in interior portions have been significantly increased
to conserve water (Light and Dineen 1994). These changes in the
hydraulic gradient across the Everglades have altered both regional and local groundwater flow patterns and enhanced
groundwater-surface water interactions (particularly near canals;
Harvey et al. 2004; Harvey and McCormick 2009). In parts of
the Everglades, ecosystem level changes have been concurrent
with increased nutrient and mineral loading associated with canal
water inputs, but may also be attributed to the quantifiable
change in the discharge of high nutrient groundwater to the
oligotrophic surface water.
The headwaters of Taylor Slough is just one area along the
Everglades eastern boundary where the appearance of cattail
(Typha domingensis; Surratt et al. 2012) and the reduction in
periphyton biomass (Gaiser et al. 2013) have occurred.
Fig. 1 The headwaters of Taylor Slough (outlined in black) are located
along the eastern boundary of Everglades National Park (ENP) in an
area known as the Rocky Glades
These changes suggest nutrient enrichment is taking place
as a result of point source canal water restoration techniques
(referred to as direct hydrologic restoration efforts) used to
rehydrate and restore flow to the wetland. In an effort to
reduce the ecological ramifications associated with direct
hydrologic restoration efforts, a more diffuse water delivery
method was enacted for the first time along the Taylor
Slough headwaters Everglades-Urban boundary at the end
of 1999 (Fig. 2). The goal of the diffuse hydrologic restoration efforts was to use a series of water and nutrient retention
basins (S332BN, B, C and D) in conjunction with associated
pump stations to create a hydrologic divide between the
Everglades National Park (ENP) and the adjacent canal
system (SFNRC 2005; Fig. 3), thereby rehydrating the headwaters and supporting downstream freshwater delivery to
Taylor Slough while reducing nutrient loading. Since operation, the four retention basins have typically acted as closed
surface water systems (Hydrogeologic, Inc. 2010); however
their influence on the discharge of groundwater to the surface
water or the recharge of surface water to the groundwater (R;
groundwater-surface water interactions) and the overall
ecohydrology of the headwaters have yet to be determined.
Fig. 2 Hydro-meteorological stations (various symbols) used to determine the influence of direct and diffuse hydrologic restoration efforts on
the Taylor Slough headwaters water budget (1997–2011). The L-31 N
and C-111 canals form the Everglades-Urban boundary
Wetlands
Rocky
Glades
= water level
Retention
Basin
Pump
Urban
R (?)
SWrecharge
Biscayne
Aquifer
GWdischarge
SWrecharge
GWflow
(?)
Miami Limestone
GWSeep
Canal
Fort Thompson Formation
Fig. 3 A schematic of the diffuse restoration techniques employed
between 2000-present along the eastern boundary of Everglades National Park (ENP). Water budget calculations in the paper were used to
determine if diffuse restoration efforts resulted in the westward groundwater flow (GWflow) and significantly influenced groundwater-surface
water interaction (R=SWrecharge−GWdischarge) in the Rocky Glades or
the Taylor Slough headwaters. Arrows indicate potential flow directions
while inverted triangles indicate potential water levels
The goal of this paper was to determine the influence of
diffuse hydrologic restoration on R in the Taylor Slough
headwaters. To achieve this goal we used a water budget
approach to estimate annual and monthly R from 1997 to
2011, assessed the spatial influence of diffuse hydrologic
restoration efforts on the Taylor Slough headwaters, and then
reviewed current literature to gain a better understanding of
the ecohydrologic influence of this restoration technique on
the area. Finally, future success of diffuse restoration tactics
in the Taylor Slough headwaters was evaluated in terms of
the hydrologic implications of predicted climate change.
Water Management and Study Area
Taylor Slough is the second largest waterway within
Everglades National Park (ENP; Fig. 1) and plays an important role in delivering fresh water to downstream estuaries.
The construction of canals along its eastern boundary, starting
in the 1950’s with the L-31 N canal, has resulted in a substantial reduction in fresh water inputs from Taylor Slough to
Florida Bay, shunting water toward the Atlantic. Numerous
ecohydrologic changes have been observed over this period
such as hypersaline conditions in Florida Bay (Van Lent et al.
1993), saltwater encroachment on the freshwater marsh (Ross
et al. 2000) and a decline in vertebrate populations (Jorenz
2013). At the headwaters of Taylor Slough, wetland drainage
by the eastern canals (L-31 W, L-31 N and C-111; Fig. 2) has
led to an increase in fire frequency, desiccation of peat in some
areas (McVoy et al. 2011), introduction of non-native fish and
vegetation (Kline et al. 2013; Rehage et al. 2013) and loss of
habitat for the endangered Cape Sable Seaside Sparrow and
the American Alligator (Davis et al. 2005). In 1980 direct
hydrologic restoration efforts to reestablish the historic fresh
water inputs from the Taylor Slough headwaters southward
were enacted. Up through 1999, water management plans
authorized the inputs of canal water from L-31 N into L31 W through the S-174 spillway where it eventually
discharged through the S332 pump into the wetland. The
current diffuse hydrologic restoration efforts were then put into
operation along the Everglades-Urban boundary between 2000
and 2002 (Fig. 2).
Like most of the Everglades, this area is underlain by the
Biscayne Aquifer, an extremely transmissive (≈100,000 m2 d−1)
aquifer that consists of four limestone facies; bryozoan, oolitic,
coralline and coquina (Genereux and Guardiario 1998; Genereux
and Slater 1999). The Biscayne Aquifer is ≈13.6 m thick in the
study area with the upper third consisting of the Miami
Limestone Formation and remaining aquifer represented by the
Fort Thompson Formation (Genereux and Guardiario 1998). The
canals (L-31 N, C-111 and L-31 W) running along the eastern
boundary of ENP cut through approximately 5.7 m of the upper
portion of the aquifer, completely bisecting the Miami Limestone
and upper portions of the Fort Thompson Formation (Genereux
and Guardiario 1998).
The headwaters of Taylor Slough occupy most of the Rocky
Glades (Fig. 1), an oolitic limestone outcrop that helps to separate
the southwestward surface water flow of Shark River Slough
from Taylor Slough (Armentano et al. 2006; Price and Swart
2006). Exposed pinnacle rock and solution holes generate the
small topographic differences (60 cm) found in the area
(Genereux and Guardiario 1998; Davis et al. 2005). The shallow
soils (≈15 cm thick; Armentano et al. 2006; Schedlbauer et al.
2010) are mainly marls. These soils are generated by highly
calcareous periphyton mats (a collection of algae, bacteria and
fungi) characteristic of Rocky Glades (Gottlieb et al. 2006) along
with limestone bedrock weathering. While small tree islands are
scattered across the Rocky Glades, they only make up <3 % of
the area (Ruiz et al. 2013). The rest of the landscape is sparsely
vegetated (leaf area index of 1.7; Schedlbauer et al. 2010) and
dominated by sawgrass (Cladium jamaicense), muhly grass
(Muhlenbergi capillaris) and spikerush (Eleocharis cellulosa
Torr,) that reaches a canopy height of ≈73 cm (Armentano
et al. 2006; Schedlbauer et al. 2010).
The climate of southeast Florida is classified as tropical
(Beck et al. 2006) and monsoonal (Kottek et al. 2006). The
long-term average annual rainfall is approximately 138–
145 cm, with the majority typically falling between May
and November (wet season; Duever et al. 1994; Saha et al.
2011). During the wet season, rainfall inputs are marked by a
characteristic bimodal pattern, with peaks in June and
August–September (Duever et al. 1994). The potential ET
is normally greater than precipitation between December and
April (dry season; German 2000), but is also elevated compared to precipitation in May–July (Saha et al. 2011). The
mean, monthly temperatures in this area range from 15 to
32 °C, with an annual average of 25 °C (German and Sumner
2002; Price et al. 2008).
Wetlands
Methods
Taylor Slough Headwater Delineation, Hydrologic Stations
and Spatial Analysis
High accuracy elevation data points (± 15 cm) from the
Everglades and its eastern boundary (USGS; http://sofia.usgs.
gov/exchange/desmond/desmondelev.html) were combined and
used to develop a 400×400 m Digital Elevation Model (DEM)
by the ordinary kriging interpolation method (ArcGIS 10.0). The
elevation from the DEM was used to delineate the northern and
western boundary of the Taylor Slough headwaters, while the L31 N and C-111 canals defined the eastern boundary and the
Ingraham Highway delineated the southern boundary (Fig. 2).
Historically, during the wet season, water from Shark River
Slough was thought to flow into the Taylor Slough headwaters,
but geochemical indicators signify groundwater and surface
water are not exchanged between these two major water bodies
(Price and Swart 2006)
Daily data from a total of 49 surface water stages, 19
groundwater wells, 12 precipitation gauges, 4 pump station, 3
flow sites and 2 weather stations were used to develop a water
budget and define hydrologic trends in the Taylor Slough
headwaters from 1997 to 2011. A total of 62 % of these
hydrologic stations were monitored for the entire length of the
study. All of the hydrologic data were obtained from three
sources; the South Florida Water Management District
(SFWMD; http://my.sfwmd.gov/dbhydroplsql/), the United
States Geologic Survey (USGS; http://waterdata.usgs.gov/),
and ENP (DataforEVER; [email protected]). Water
level data reported in the National Geodetic Vertical Datum of
1929 (NGVD 29) were converted to North American Vertical
Datum of 1988 (NAVD 88) using VERTCON 2.0 developed
by the National Geodetic Survey (http://www.ngs.noaa.gov/
cgi-bin/VERTCON/vert_ con.prl). All water level data had an
accuracy of 1.8 cm.
Daily groundwater and surface water levels were used to
derive daily potentiometric surface water level surfaces, using
the ordinary kriging method (400×400 m; ArcGIS 10.0). Daily
water depth (d) was solved across the headwaters as the difference between the surface water level surface and the DEM.
Depths less than or equal to 0 m indicated the water table had
dropped below the ground surface, which is common in the
Taylor Slough headwaters during the dry season (Kotun and
Renshaw 2013).
Water Budget
A water budget of the Taylor Slough headwaters was derived
using the principle of mass conservation;
ΔS ¼ P þ SW in −ET −SW out −GW seep R Err
ð1Þ
where the change in storage (ΔS) is the sum of all inputs and
outputs to the watershed, including their associated error (Err).
Precipitation (P) and surface water inputs (SWin) were the two
known inputs to the budget, while evapotranspiration (ET),
surface water outputs (SWout) and groundwater seepage
(GWseep) out of the eastern and southern boundary of the
watershed comprised the quantifiable outputs to the system.
Groundwater-surface water interactions (R) were then estimated as the residual of all water budget components. Each input
and output, except SWin, SWout and R, was derived spatially
(ArcGIS 10.0) at a 400×400 m resolution. All values were
calculated as volumes, normalized to the area of the Taylor
Slough headwaters (192 km2) and reported as a depth (cm).
Precipitation (P)
Monthly P at each rain gauge station was calculated by summing the daily P values (Fig. 2). The monthly P in the Taylor
Slough headwaters was area-weighted using the Thiessen
polygon method, and then multiplied by the area of each
polygon to determine the monthly volume. A measurement
error of 10 % was assumed for P as the measurement error of
tipping bucket rain gauges has been found to range from 6 to
10 % depending on rain rate (Ciach 2003). To compare long
term mean and current rainfall patterns, annual rainfall values
from 1951 to 2011 were averaged from the Royal Palm Ranger
Station, located just south of the Taylor Slough headwaters, to
determine the 60-year mean rainfall.
Evapotranspiration (ET)
As the Rocky Glades are sparsely vegetated, daily evapotranspiration (ET) was determined using the Priestley-Taylor method
(Priestley and Taylor 1972; Table 1):
ETλρw ¼ α
Δ
ðRn −GÞ
Δþγ
ð2Þ
where λ is the latent heat of vaporization (MJ kg−1), ρw
represents the density of water (kg m−3), Δ signifies the slope
of the saturation vapor pressure temperature curve, γ is the
psychrometric constant (MJ kg−1), Rn denotes net radiation
(W m−2), G is soil heat flux (W m−2) and α represents the
Priestley-Taylor alpha value (unitless).
Daily net radiation and air temperature (min, max and
average), used to derive the input parameters (Table 1) to
solve for daily ET, were obtained from SFWMD’s S331
station located 6 km northeast of the watershed (Fig. 2). As
the water table typically drops below the ground surface
during the dry season in the Taylor Slough headwaters, the
traditional constant α of 1.2 for well-watered ecosystems
(Priestley and Taylor 1972; Morton 1983) could not be used.
Instead the observed correlation between α and d, as well as
average daily air temperature (Tempave) and G, (Table 1;
Wetlands
Table 1 Variables for calculating evapotranspiration (ET) using the Priestley-Taylor method (Priestley and Taylor 1972)
Slope of saturation vapor pressure temperature curve (Δ; kPa °C)
es =Mean saturated vapor pressure (kPa)
Tave =Average daily temperature (°C)
4098es
Δ ¼ ð273:3þT
2
ave Þ
Mean saturated vapor pressure (es; kPa)
max
es ¼ emin þe
2
emin ¼ 0:6108exp
17:27T min
237:3þT min
17:27T max
emax ¼ 0:6108exp 237:3þT
max
emin =Saturated vapor pressure at the minimum
emax =and maximum daily temperature (kPa)
Tmin =Minimum daily temperature (°C)
Tmax =Maximum daily temperature (°C)
Latent heat of vaporization constant (λ; MJ kg−1)
λ=2.501–0.00263·Tave
Psychrometric constant (γ; kPa °C)
γ¼
cp P
−3
ελ ⋅10
¼ 0:0016282 Pλ
cp = Specific heat of moist air (1.0133 kJ kg−1 °C−1)
P = Atmospheric pressure (101.33 kPa)
ε = Ratio of molecular weight of water vapor to that for dry air (0.622)
Soil heat flux (G; W m−2)
G=2.6081Tave −59.149
Coefficient of advectivity (α)
α ¼ 0:3327d þ 0:9205 d ≤ 0
α ¼ 1:17d > 0
d = Water depth (m)
Schedlbauer et al. 2011) derived from continuous eddy covariance and micrometeorological measurements at the
TSPH1 tower from 2008 to 2009 (Fig. 2) were used to
estimate daily α and G in the Taylor Slough headwaters from
1997 to 2011. Monthly ET (m3) values used in the water
budget were calculated as the sum of all daily ET (m3) across
the Taylor Slough headwaters for a given month. Using
similar methods, Price et al. (2007) determined the average
error for evaporation estimates in the area was 9 %, which
was also applied to this study.
eastern and southern boundaries to avoid underestimating
GWseep-south. Daily Q was summed for all pixels along the
eastern and southern boundaries to determine the total daily
GWseep from the headwaters. Monthly GWseep (m3) was then
attained by summing daily GWseep, and it had an estimated
error of 8–10 %. Error was associated with the gradient
calculation and did not include the variability associated with
the potential range in hydrologic conductivity values.
Groundwater Seepage (GWseep)
From 1997 to 1999 the S174 spillway and the S332 pump
regulated direct surface water inputs to the Taylor Slough
headwaters. Between 2000 and 2002, the S332B, BN, C and
D pump stations provided additional surface water input, but by
2003 surface water inputs into the Taylor Slough headwaters
were predominately relegated to the S332B, BN, C and D pump
stations as the S174 and S332 stations were phased out. As the
retention basins were essentially isolated from the Taylor
Slough headwaters, the amount of surface water that could
contribute to the water budget through inflitration was estimated by taking the difference between the amounts of water
pumped into the retention basins and that lost through ET.
Outflow from the Rocky Glades occurred at the S175 culvert
(until 2000), Taylor Slough Bridge (TSB) and 23 culverts
underlying the Ingraham Highway (Fig. 2). Mean daily flow
values (m3 s−1) for all structures were obtained from the
SFWMD. Within ENP, flow monitored at the TSB and varying
Daily GWseep along the eastern (GWseep-East) and southern
boundaries (GWseep-South) of the Taylor Slough headwaters
were estimated using Darcy’s law. Along the eastern boundary, hydraulic gradient was solved as the difference between
the groundwater and canal surface water levels in the adjacent pixels divided by 400 m (distance between the centers of
the pixels). Pixels adjacent to the canal were selected in an
effort to also capture local changes in groundwater seepage.
Since no canal exists at the southern extent of the headwaters, hydraulic gradient was calculated as the difference in
groundwater levels north and south of the Ingraham
Highway, and then divided by 400 m. The cross-sectional
area over which GWseep occurred at the pixel level was
constrained by the average canal depth (5.7 m) and the width
of a pixel (400 m). The same depth was used along the
Surface Water Inflows (SWin) and Outflows (SWout)
Wetlands
Table 2 Annual water budget parameters for the Taylor Slough headwaters from 1997 to 2011 normalized to the area of the watershed and reported
as depth (cm). Precipitation (P), and surface water (SWin) were inputs to the
water budget while surface water (SWout), evapotranspiration (ET), and
groundwater seepage (GWseep) were outputs. Change in storage (ΔS) and
groundwater-surface water interactions (R) fluctuated between positive and
negative depending on the year
Management
Years
P
SWin
SWout
ET
GWseep-East
GWseep-South
ΔS
R
Err
S332 in operation
1997
1998
1999
2000
175
133
162
143
47
57
82
106
−62
−49
−96
−61
−97
−106
−98
−116
−9
−11
−11
−11
−9
−8
−10
−11
17
−7
12
−15
−58
−5
−12
63
5
3
4
7
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Stdev
158
147
138
122
149
125
143
129
143
135
131
14
128
122
215
126
234
50
70
175
246
257
99
73
−49
−38
−58
−22
−61
−16
−9
−41
−46
−32
−18
23
−108
−120
−117
−107
−136
−105
−124
−124
−112
−114
−92
13
−9
−13
−16
−13
−14
−12
−11
−13
−16
−15
−8
2
−10
−12
−11
−8
−11
−10
−9
−11
−12
−11
−6
2
8
−8
9
−2
7
−14
−9
24
2
−20
17
12
19
39
67
34
57
35
25
43
58
76
−17
31
9
8
12
8
13
4
6
7
16
19
7
5
Installation of pumps & basins
S322B, C & D pumps and retention in operation
culverts was correlated to surface water stage and used to
calculate mean daily surface water flow (m3 s−1) out of Taylor
Slough with a rating curve developed by ENP (DataforEVER;
[email protected]). Mean daily inflow and outflow
(m3 s−1) was multiplied by the number of seconds in a day
(83,400 s) to determine the total daily flows (m3 d−1), and
summed to determine the monthly surface water inflows and
outflow for the Taylor Slough headwaters. Error associated with
flow was estimated at 7.5 % by the SFWMD (Imru and Want
2005).
Change in Storage (ΔS)
Monthly ΔS (m3), or volume of water in storage, was calculated as the difference between the surface water level surfaces on
the first and last day of each month; positive values represented
the loss in storage over the month. If d was less than or equal to
0 m, the monthly water level difference was multiplied by the
porosity. Ground penetrating radar and borehole images in the
Rocky Glades indicated the total porosity, within the first 2-m
of the aquifer, ranged between 0.40 and 0.50 (Cunningham
2004). The lower porosity (0.40) boundary was used to represent the effective porosity in calculating ΔS.
and negative values indicated groundwater recharged by the
surface water.
Data Analysis
Water budget parameters were averaged according to the three
distinct water management periods: I Direct Hydrologic
Restoration Efforts (S332 operation, 1997–1999), II Transition
(2000–2002), and III Diffuse Hydrologic Restoration Efforts
(operation of retention basins, 2003–2011). To determine the
influence of direct vs. diffuse hydrologic restoration on the
groundwater-surface water interactions and the Rocky Glades
water budget, yearly and monthly averaged inputs and outputs
were compared to pump discharge using regression analysis.
Linear regressions were also developed to evaluate significant
trends over time, while one-way analyses of variance
(ANOVAs), along with post-hoc Tukey tests (α=0.05), were
used to determine significant differences among the three time
periods.
Results
Climate
Groundwater-Surface Water Interactions (R)
R across the system was estimated as the residual of the water
budget variables and solved on the monthly time step. Positive
R values indicated groundwater discharged to the surface water
Annual precipitation (P) inputs ranged from 122 to 175 cm
between 1997 and 2011 (Table 2; Fig. 4). For 60 % of the study
time, P inputs were above the 60-year mean of 138 cm (Royal
Palm Station; EMS 1). Below-average annual P inputs occurred
Wetlands
Fig. 4 Annual amount (cm) of precipitation (black) compared to the
60-year mean precipitation (Royal Palm Station, dashed line) and
annual amount of evapotranspiration (gray)
between 2004 and 2011 when the retention basins were fully
operational. Regression analysis of annual inputs revealed a
relatively steady decline in P over the study period (R2 =0.33,
p=0.02). Annual ET losses represented 55–96 % of the annual
P inputs and ranged between 92 and 136 cm y−1 (Table 2;
Fig. 4), with the largest annual losses between 2002 and 2008.
Daily ET averaged 0.31 cm with values ranging between 0.10
and 0.60 cm d−1 over 96 % of the study period. A one-way
ANOVA indicated that annual ET losses were substantially
greater between 2000–2002 and 2003–2011 as compared to
1997–1999 (p=0.005; Fig. 4), most of which was accounted for
by a significant increase in wet season ET during this time
(p<0.001).
Groundwater and Surface Water Level
Annual surface water levels significantly declined (p≤0.05) at
36 % of the surface water stages over the study (1997–2011),
Fig. 5 The average (a) Annual
difference in water levels (cm)
between the diffuse (2003–2011)
and the direct restoration efforts
(1997–1999), as well as at the
height of the (b) Wet Season
(September) and (c) Dry Season
(March). Light colors represent
an increase in the water levels
under diffuse restoration as
compared to direct efforts
with the majority of the stations located along the northern and
western boundary of the Taylor Slough headwaters. Conversely,
a comparison of average annual water levels between periods of
direct (1997–1999) and diffuse restoration (2003–2011) suggested water level remained constant or slightly increased in
the vicinity of the retention basins (Fig. 5a). These spatial
changes in water levels across the basin may help to explain
the overall decline in surface water levels observed between 2003
and 2011 near the bridge (TSB) that connects the headwaters to
the main slough (Kotun and Renshaw 2013). Along the eastern
boundary of Taylor Slough, average monthly groundwater levels
substantially increased between July and November with the
onset of the diffuse restoration efforts (Fig. 6). At the height of
the wet season (September), diffuse restoration efforts were
concurrent with an increase in water levels (up 24 cm; Fig. 5b)
in the eastern and southern portion of the headwaters as compared to direct techniques. In the dry seasons, groundwater levels
along the Everglades eastern boundary remained relatively similar across all three periods, with the occasional exceptions of
February, March and May when groundwater levels under direct
restoration operations surpassed that of those under the diffuse
efforts (Fig. 6). Conversely, the difference in average water levels
between diffuse and direct restoration at the height of the dry
season (March), suggest a large decrease (up to 75 cm) along the
northern and western portions of the headwaters (Fig. 5c).
Managed Surface Water Inputs, Surface Water Outputs
and Groundwater Seepage
Annual SWin into the Taylor Slough headwaters significantly
increased from 1997 to 2011 (p=0.05; Table 2). Monthly SWin
substantially increased between July and October following the
early implementation of the diffuse hydrologic restoration efforts
(Fig. 7a). However, SWout significantly decreased at the annual
level, with the most significant declines detected during dry
Wetlands
a
a
b
b
c
c
Fig. 7 Monthly averages and standard errors of (a) surface water
inputs, b groundwater seepage eastward and (c) surface water outputs
under Taylor Slough Bridge during direct hydrologic restoration (1997–
1999; open circle), transition period (2000–2002; gray triangle) and
diffuse hydrologic restoration (2003–2011; black square)
d
Fig. 6 The average monthly average groundwater level and standard
error at four wells along the eastern boundary of Everglades National
Park under: direct hydrologic restoration (1997–1999; open circle), the
transition period (2000–2002; gray triangle) and diffuse hydrologic
restoration (2003–2011; black square). These wells represent a north
to south transect (top to bottom): (a) G-3437, (b) Rutzke, (c) G-3622
and (d) FROG
season (Feb–Apr; p=0.03). When monthly values between the
three restoration periods were evaluated, SWout from the Taylor
Slough headwaters was also on average substantially lower in
May and September following 1999 (Fig. 7b).
From 1997 to 2011 the average annual GWseep-East was only
slightly elevated compared to GWseep-South (Table 2), but roughly
increased per annum over this time period, unlike GWseep-South.
Monthly changes in the amount of GWseep-East were observed
after 2000 (Fig. 7c), with a substantial increase in the average
GWseep-East between June and December after 2002. Overall the
total GWseep accounted for 9–16 % of the annual loss of water
from the Taylor Slough headwaters, while regression analysis
indicated these SWin explained a large portion of the variability
in annual GWseep (Fig. 8a). In addition, SWin was negatively
correlated to the combined downstream flow of GW and SW
between 2003 and 2011 (Fig. 8b, i.e., larger surface water inputs
yielded a larger southward flow), while between 1997 and 2002
there was more southward flow for the given surface water
inputs.
Change in Storage
On an annual time step the ΔS remained fairly stable with an
average of −1 cm and a range of ±22 cm between years
(Table 2). However, the monthly standard deviation in the ΔS
within years significantly increased over the study period
Wetlands
a
b
c
Fig. 8 Annual surface water inputs pumped in the Taylor Slough
headwaters had a significant relationship with (a) groundwater seepage,
the combined (b) southern output of surface water and groundwater, as
well as (c) groundwater-surface water interactions between 2003 and
2011 (diffuse restoration, black square). These relationships were also
significant (solid line) between 1997 and 2003 (direct restoration, open
circle; and the transition period, gray triangle) for (a) groundwater
seepage and (c) groundwater-surface water interactions
Fig. 9 The (a) standard deviation in the annual and (b) average seasonal change in storage across the Taylor Slough headwaters from 1997
to 2011
discharge between October and February from 2000 onward
(Fig. 10). Groundwater recharge, which predominantly occurred
between May and June, remained fairly consistent amongst all
three periods.
(Fig. 9a; n=12). Seasonal data analysis indicated substantial
shifts in the ΔS during the transition periods between the wet
and dry seasons were concurrent with the addition of the
retention basins. For example, an increase in the amount of
water lost during the dry-wet transition (May–Jul) was observed, while there was an increase in the input of water during
the wet-dry transition (Nov–Jan; Fig. 9b).
Groundwater-Surface Water Interactions
Annual water budget calculation indicated R increased with the
onset of the diffuse restoration efforts (Table 2; p=0.009). This
estimated increase groundwater discharge was concurrent with
the increased SWin into the retention basins (2000–2011;
Fig. 8c), while monthly values over the three periods of management also indicated a substantial increase in groundwater
Fig. 10 Average monthly groundwater-surface water interactions in
the Taylor Slough headwaters under direct hydrologic restoration
(1997–1999; open circle), the transition period (2000–2002; gray triangle) and diffuse hydrologic restoration (2003–2011; black square).
Positive values indicate groundwater discharged to the surface water,
while negative values indicate surface water recharged the groundwater
Wetlands
Discussion
Restoration in a Karstic Wetland
Results from this study support the growing body of research
that indicates human modifications have substantially increased groundwater-surface water interactions in the
Everglades (Nemeth and Solo-Gabriele 2003; Harvey et al.
2004; Harvey and McCormick 2009). Hydrogeochemical investigations conducted prior to 2000 indicated surface water
predominantly recharged the groundwater in the Taylor Slough
region (Harvey et al. 2000; Price and Swart 2006). Water
budget estimates from this study indicated that diffuse hydrologic restoration efforts (S332B, BN, C, and D retention basins
and pump stations) from 2000-present, were associated with
groundwater discharge to the surface water in the Taylor
Slough headwaters representing a reversal in the chief direction
of groundwater-surface water interactions, compared to the
earlier investigations. The increased utilization of canal water
for supporting diffuse restoration efforts also resulted in an
increase in groundwater seepage eastward away from the basin
as compared to direct restoration, especially during the wet
season. While diffuse restoration supported elevated water
levels along the eastern boundary of the headwaters, these
efforts did not lead to an increase in the downstream delivery
of water to the main portion of Taylor Slough.
Our findings support the modeling efforts and field studies in
the northern Everglades (Water Conservation Area 2) that have
indicated groundwater-surface water interactions substantially
increase within 600–1000 m of levee-canal systems (Harvey
et al. 2004; Harvey and McCormick 2009). Enhanced groundwater discharge not only transfers more water but also contributes to additional loading of ions and nutrients to the surface
water, which in turn influence the overlying vegetation (Sah et al.
2013). These findings indicate that in a karstic wetland, with a
low topographic gradient and high transmissivity, any engineering structure that influences hydraulic gradients, even one that
was designed with an attempt towards restoration (i.e. the retention basis), would be expected to enhance groundwater-surface
water interactions in close proximity to the engineered structures.
Hydrologic Response of the Taylor Slough Headwaters
Precipitation and evapotranspiration have been identified as the
largest drivers in South Florida’s water budget. Therefore, the
observed decline in rainfall in the Taylor Slough headwaters
would be expected to lead to an increase in the surface water
recharge of groundwater as surface water levels declined
(Harvey et al. 2004). The elevated ratio of ET:P observed over
this study, especially between 2002 and 2008, should have
exacerbated the decline in surface water levels. Conversely,
groundwater and surface water levels along the eastern boundary of the Taylor Slough headwaters typically indicated water
level remained the same or slightly increased. As expected, the
comparison of water levels between direct and diffuse restoration indicated a significant decline in both annual and dry
season water levels along the northern and western boundary
of the headwaters (Fig. 5). These findings signify that surface
water inputs into the retention basins were influencing adjacent
surface water levels in the interior of the Taylor Slough
headwaters.
Diffuse restoration efforts used approximately 60 % more
canal water than direct restoration, but the diffuse efforts were
concurrent with a decline in surface water outputs to the main
portion of the slough (south of TSB; Fig. 2). This observed
decline is likely attributed to both reduced precipitation and a
decline in the amount of water entering the Taylor Slough
headwaters associated with the change in restoration efforts.
Under direct restoration efforts (1997–1999) ≈62 cm y−1 of canal
water entered into the wetland, while during diffuse restoration
(2000–2011) more canal water was pumped into the retention
basins, but resulted in only ≈42 cm y−1 entering the wetland by
way of groundwater discharge to the surface water.
On an annual scale, groundwater discharge along the eastern boundary supported a slightly wetter environment under a
mostly below average precipitation period, while along the
western and northern boundaries of the Taylor Slough headwaters conditions became drier. Intra-annually, the diffuse
hydrologic restoration efforts resulted in increased variability
in the change in storage. During the wet-dry transition the
diffuse restoration increased volume of water stored in the
Taylor Slough headwaters, which supported surface water
levels that were closer to values prior to the construction of
the eastern canals (1933–1937; Van Lent and Johnson 1993).
However, diffuse restoration efforts could not support the
elevated dry season water levels that persisted prior to the
mid-1930s. While it is unlikely that maximum water levels
will be restored, the diffuse restoration efforts may be restoring the historic annual difference between high and low water
levels (1933–1937: 1.08 m; 1965–1989: 0.85 m; Van Lent and
Johnson 1993), but at a lower mean annual water level.
Ecohydrologic Implication of Diffuse Restoration
Long-term monitoring of vegetation communities (Sah et al.
2013) as well as comparisons of surface water stages (Kotun
and Renshaw 2013) support the findings from this study
that the eastern portion of the Taylor Slough headwaters has
become seasonally wetter under the diffuse restoration efforts.
Our results further signal that organisms in this area must
respond to and tolerate severe flood and drought conditions
(Davis et al. 2005; Schedlbauer et al. 2011), as the water budget
indicated an increased variability in the intra-annual volume of
water in storage. Vegetation community (Sah et al. 2013) and
diatom (Gaiser et al. 2013) compositional shift near the retention basins have indicated that diffuse restoration efforts may
Wetlands
also be associated with nutrient loading, specifically phosphorus, to the wetland.
Water budget results from this study indicate that groundwater water discharge became a predominant source of water
to the Taylor Slough headwaters when diffuse restoration
tactics were enacted. The indicators of elevated nutrient concentrations in the headwaters may support our finding of
increased groundwater discharge, as earlier studies have
showed nutrient concentrations, such as total phosphorus, in
the canal water (≈ 8 μg L−1; Surratt et al. 2012) and the
underlying groundwater (≈ 11 μg L−1; Gaiser et al. 2010) were
similar but elevated compared to the oligotrophic wetland
surface water (≈ 5 μg L−1; Surratt et al. 2012). In addition,
water level analysis from this study suggests the current area
influenced by groundwater discharge likely spans the majority
of the eastern boundary, extending into the Taylor Slough
headwaters. These findings indicate that diffuse hydrologic
restoration efforts likely resulted in a larger portion of the
wetland influenced by nutrient loading as compared to the
direct point source delivery of canal water. Conversely, the
volume of potentially nutrient rich water entering the wetland
would have been spatially diluted compared to direct restoration efforts, which might in turn slow the ecologic response
time of the Taylor Slough headwaters to these diffuse tactics.
Currently, the Taylor Slough headwater is characterized by
highly calcareous periphyton (Gottlieb et al. 2006) that is
adapted for oligotrophic conditions, and supports marl soil
formation. While periphyton is composed of collection of algae,
bacteria and fungi, the calcium carbonate coating on periphyton
in this region makes it substantially less edible/digestible by
most grazers compared to green algal mats (Geddes and Trexler
2003; Davis et al. 2005). The result of long-term nutrient
loading may drive changes in soil, vegetation and trophic
dynamics (Liston et al. 2008) in portions of the Taylor Slough
headwaters region as periphyton biomass, especially calcareous
mats, which have been shown to significantly decrease in
biomass with phosphorus loading (Gaiser et al. 2004, 2005).
While results from our study indicate the Taylor Slough headwaters is on a trajectory toward a wetter and more nutrient rich
environment, continued long-term monitoring is needed to
confirm this hypothesis and understand the ecological influence
of the increased spatial and temporal variability in hydrology
associated with diffuse restoration.
Influence of Climate Change on the Success of Diffuse
Restoration
This study revealed the effectiveness of the diffuse restoration
efforts on the Taylor Slough headwaters during a mainly below
average annual rainfall period (2004–2011); the influence of
these diffuse tactics may be substantially reduced during wetter
climatic periods. Since water levels east of Taylor Slough must
be maintained at a low level to avoid flood conditions (SFNRC
2005), greater inputs of precipitation would likely create a
larger hydraulic gradient between the Taylor Slough headwaters and the adjacent urban area as compared to 2003–2011
conditions. Results from this study indicated a large portion of
the water pumped into the retention basins was likely lost
through eastward seepage, especially during the wet season.
If water levels in the interior of the basin increase with wetter
conditions, the increased hydraulic gradient could lead to an
increase in eastward seepage, as well as a reduction in groundwater discharge and associated nutrient loading.
Future climate simulations predict annual precipitation inputs will on average decrease approximately 3.5–8.4 % in
South Florida over the next 100 years (Todd et al. 2012), while
the predicted increases air temperature (2–2.5 °C; Christensen
et al. 2007), solar radiation and vapor pressure deficit are
expected to increase evapotranspiration. Hydrologic and vegetative modeling efforts of the Everglades have indicated such
climatic change could result in shorter periods of surface water
inundation, which would influence plant communities by reducing the number of wetland communities while supporting
an increase in the percent cover of forested communities (Todd
et al. 2012). Results from this study suggest the influence of
climate change may be more variable across the Everglades
than expected. For example, in areas adjacent to restoration
structures, such as the four retentions basins in the Taylor
Slough headwaters, surface water levels changes associated
with reduced precipitation inputs may be mitigated by groundwater discharge into the Everglades. By supporting an elevated
water table, diffuse restoration efforts could counter any spatial
variability of ET across the Everglades, as the eddy covariance
data (Schedlbauer et al. 2011), indicated ET was significantly
reduced by the depth of the water table, once the water table
was below the ground surface. To better understand the ramifications of diffuse restoration efforts on the future ecological
patterns and process in the Taylor Slough headwaters, it is
critical that these restoration effort are included in future
Everglades ecosystem models.
Conclusion
Diffuse hydrologic restoration efforts resulted in a reversal of
groundwater-surface water interactions in the Taylor Slough
headwaters, with groundwater largely discharging to the surface
water at the annual time step from 2000 through present.
Despite the typically below average annual precipitation inputs
following 2003, the diffuse restoration efforts supported surface
and groundwater levels that either remained constant or slightly
increased along the eastern boundary of the headwaters and
surrounding the retention basins. Diffuse restoration also
resulted in the increase of eastward groundwater seepage from
the headwaters but did not support an increase in the downstream delivery of water to the main portion of Taylor Slough.
Wetlands
The combination of management and climate during this period
led to more variable temporal and spatial hydrologic conditions in the Taylor Slough headwaters. While restoration
efforts did help to rehydrate portions of the Taylor Slough
headwaters, our finding suggest engineered designs in karst
wetland landscapes results in enhancing groundwater-surface
water interactions, even when the engineering design was a
restoration effort.
Acknowledgments This publication was produced as part of a special
issue devoted to investigating the ecological response of over 20 years
of hydrologic restoration and active management in the Taylor Slough
drainage of Everglades National Park. Support for this research was
provided by the Department of the Interior’s National Park Service
through the Everglades Fellowship Program at Florida International
University. Support for this special issue was provided by: the Everglades National Park, the Southeast Environmental Research Center,
the Florida Coastal Everglades Long-Term Ecological Research program (National Science Foundation cooperative agreement #DBI0620409), the Everglades Foundation and the South Florida Water
Management District. A portion of R. Price effort was supported by
the NASA WaterSCAPES grant. This is SERC contribution no. 597.
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