Altered Hydroperiod and Saltwater Intrusion in the Bald Cypress Swamps of the Loxahatchee River...

Altered Hydroperiod and Saltwater Intrusion in the Bald Cypress Swamps of the Loxahatchee River“Not So Deep”

20th Saltwater Intrusion Meeting – Naples, FL – June 23-27, 2008

David A. Kaplan1, Rafael Muñoz-Carpena1, Yuncong Li2, Yongshan Wan3, Marion Hedgepeth3, and Dick Roberts4

1Agricultural and Biological Engineering, University of Florida2Soil and Water Science, University of Florida, Tropical Research and Education Center

3 South Florida Water Management District, Coastal Ecosystems Division4 Florida Department of Environmental Protection, Division of Recreation and Parks

Photo by Paul Lane

Introduction - Loxahatchee River

• 240 square mile (~620 km2) watershed

• Public lands = conserved ecosystems

Ecologically diverse

• National “Wild and Scenic River” (NPS)

• Minimum Flows and Levels

“…the last free-flowing river in southeast Florida…”

Source: SFWMD 2005 Atlantic Ocean

C14

Source: Loxahatchee River District

Introduction - Hydrology

• Construction of the C-18 canal (1958) and minor canals that direct water away from the historic watershed

– Reduces freshwater flow in the NW Fork severely

• Lowering of the regional groundwater table

• Permanent opening of the Jupiter Inlet (1947)

Introduction - Floodplain Vegetation

Introduction - Minimum Flows and Levels

• Florida requires Water Management Districts to minimum flows and levels (MFLs) (Chapter 40E-8 of the FAC) – protects water resource functions: flood control, water quality, water

supply and storage, fish and wildlife protection, navigation, and recreation

• MFLs linked to valued ecosystem components (VEC) – Intended to prevent “significant harm”– Lox VEC’s: FW floodplain swamp, downstream estuarine resources

• Loxahatchee River MFL adopted in April 2003– Intensive modeling effort, but only in river channel– Flow in NW Fork may not fall below 35 cfs for > 20

consecutive days within any calendar year – Required the development and implementation of a

Recovery Plan

Introduction - Bald Cypress

• Bald cypress (Taxodium distichum) life cycle requirements:

• Require moist soil, but will NOT germinate under water

• Low germination rates, short viability

• Germination reduced by increasing salinity

• Seeds from brackish sources more tolerant

Source: hiltonpond.org

Seeds Seedlings

• Growth and survival dependent on hydroperiod and salinity

• Tolerates shallow flooding, but causes stress

• Moderately salt tolerant (2 ppt) (Li et al. 2006)

• Impacts of combined flooding and high salinity greater than either alone

Source: Dr. Yuncong Li, UF, TREC Copyright Raymond Gehman, 2005

Mature Trees

• Highly flood tolerant• Salinity tolerance less

well-established

Objectives

• Characterize soil moisture and soil porewater salinity dynamics in the floodplain of the Loxahatchee River over several wet and dry seasons

Copyright Clyde Butcher, 1989

• Establish functional relationships between river stage and soil moisture and porewater salinity to better predict the effects of proposed restoration scenarios on the root zone of bald cypress

• Two established vegetation transects chosen for monitoring soil moisture and salinity

Materials and Methods

– Transect 7: Transitional riverine/ upper tidal swamp with mix of freshwater swamp species (bald cypress, red maple, cabbage palm) transitioning to red mangrove ~30 m from river

– Transect 1: “Unimpacted” riverine swamp dominated by mature bald cypress

Materials and Methods

• 24 combined dielectric probes (Stevens Hydra Probe) installed– Determines soil moisture and conductivity by

measuring soil dielectric properties

= K 0 (1)

K = r - i i (2)

– εr (m3

m-3 ) εi

a (S/m)

– Soil-specific calibrations by Mortl (2006) for a

w (S/m) based on

– Soil moisture, porewater electrical conductivity, and temperature measured every 30 minutes

Results – Transect 1


Distance along Transect 1 (m)

Soil Map UnitSoil description by

depth (cm)Vegetation

25Winder fine

sand

0-90: fine sand cabbage palm, slash pine, bald

cypress transition

90-120: sandy clay loam

65 Fluvent

0-30: clay

bald cypress, cabbage palm,

red maple, water hickory

30-50: sandy clay

50-80: fine sand

80-120: loamy sand

Soil Horizon (Transect)

Field - ρb

(g/cm3)† Ks (cm/hr) † θr θs %C

Fine sand (Tr. 1)1.36 ± 0.18

(1.06 - 1.55)37.04 ±7.70

(29.26 - 48.42)0.04 0.40

0.45(0.1-0.48)

Fluvent (Tr. 1)0.69 ± 0.38

(0.30 - 1.22)84.33 ± 83.52 (0.81 - 166.17)

0.20 0.9011.0

(1.0-15.0)

Source: Mortl (2006)

Station T1-60

Station T1-50

Station T1-30 Station T1-1

Soil Moisture – Transect 1

T1-60 T1-50

T1-30 T1-1

T1-60 T1-50

T1-30 T1-1


e A

1 exp x b

c

Source: www.hydram.epfl.ch

•Conceptual Model – Sigmoidal Curve

e r

s r

River Stage - e Relationship

River Stage (m, NGVD29)

T1-60 T1-50

T1-30 T1-1

River Stage - e Relationship (T-1)



e (

m3/m

3)

- surface

- middle

- deep

Probe Depth e

(-)

River Stage (m, NGVD29)T1-60 T1-50

T1-30 T1-1


e A

1 exp x b

c

T1-60 T1-50

T1-30 T1-1

Sensor A b c NS

T1-60 (25 cm) 1 3.913 0.243 0.72

T1-60 (35 cm) 1 3.629 0.153 0.78

T1-60 (55 cm) 1 3.326 0.055 0.66

T1-50 (30 cm) 1 3.633 0.161 0.84

T1-50 (60 cm) 1 3.414 0.067 0.89

T1-50 (95 cm) 1 3.261 0.063 0.63

T1-30 (25 cm) 1 3.014 0.116 0.42

T1-30 (50 cm) 1 2.749 0.121 0.32

T1-30 (80 cm) 1 -- 0.000 1.00

T1-1 (25 cm) 1 3.125 0.086 0.60

T1-1 (50 cm) 1 2.759 0.120 0.42

T1-1 (72 cm) 1 -- 0.000 1.00

NS = Nash Sutcliffe Coefficient of Efficiency(1970)

elevation, distance


• Salinity dynamics likely not tied to river salinity

• Rainfall/ET driven

• Concentration of salts in the floodplain

Soil Porewater EC – Transect 1 D

EC

F


Distance along Transect 7 (m)

Soil map unitSoil description by depth (cm)

Vegetation

15Terra Ceia

Variant Muck0-40: muck

young bald cypress, poison

ivy

65Terra Ceia

Variant Muck

0-180: muck pond apple, pop ash, bald

cypress180: sand layer

145Terra Ceia

Variant Muck

0-130: muck red mangrove, cabbage palm, swamp fern, pond apple

130: sand layer

Soil Horizon (Transect)

Field - ρb

(g/cm3)† Ks (cm/hr) † θr θs %C

Muck (Tr. 7)0.25± 0.15

(0.14 - 0.54)3.05 ± 2.29 (0.23 - 7.18)

0.20 0.9020.0

(5-25)

Source: Mortl (2006)

Station T7-145

Station T7-90Station T7-25 Station T7-2

• High tide elevation greater than all probe elevations all but one day (6/10/06) All probes flooded twice daily


15-minute tide data from USGS station 265906080093500

River Salinity at River Mile 9.1 (T-7)

Data from USGS Station 265906080093500

2.0 ppt

11.8 ppt 16.1 ppt

River Salinity (T-7) — Stage (T-1) Relationship

Lainhart Dam stage data from SFWMD’s DBHYDRO browser

Porewater Salinity – Transect 7

T7-145 T7-90 T7-25 T7-2

River and Porewater EC Relationship (T-7)

T7-145 T7-90 T7-25 T7-2Percentage of Peak River EC Value

Reached in Porewater

Sensor 2005 2006 2007

T7-145 (20 cm) 4% 7% 12%

T7-145 (40 cm) 1% 5% 10%

T7-145 (67 cm) 0% 0% 3%

T7-90 (23 cm) 7% 11% 10%

T7-90 (40 cm) 7% 7% 13%

T7-90 (60 cm) 6% 6% 12%

T7-25 (23 cm) 6% 12% 23%

T7-25 (46 cm) 6% 10% 20%

T7-25 (66 cm) 6% 11% 18%

T7-2 (16 cm) 6% 9% 18%

T7-2 (32 cm) 5% 9% 15%

T7-2 (48 cm) 7% 4% 12%

Average 5% 8% 14%

River and Porewater Salinity Lag (T-7)

Time Lag (days):

Sensor 2005 2006 2007

T7-145 (20 cm)

22 50 51

T7-145 (40 cm)

41 64 52

T7-145 (67 cm)

--- --- 50

T7-145 (23 cm)

--- 22 31

T7-145 (46 cm)

--- 27 49

T7-145 (66 cm)

--- 60 49

T7-145 T7-90 T7-25 T7-2

Conclusions – Soil Moisture

• Variation in soil moisture is dominated by distance from river and topographical elevation of the floodplain and can be functionally tied to river stage at Transect 1.

management tool

• The floodplain at Transect 7 is inundated twice daily, though the effects of the daily tidal inundation on soil moisture can be seen over tidal cycle.

seed germination; microtopography

• Increases in porewater salinity in the floodplain are related to the magnitude and duration of river salinity.

• There is a time lag between river and porewater salinity peaks, which increases with elevation and distance from river.

• Groundwater flow towards the river is likely very important to maintaining low EC levels in the floodplain porewater

Next steps! GW data analysis, dynamic factor analysis, hydro-ecological modeling?

Conclusions – Porewater EC

Acknowledgements

• Funding for this project provided by the South Florida Water Management District

• Ph.D. Committee: Rafael Muñoz-Carpena, Gregory Kiker, Thomas Crisman, Yuncong Li, Yongshan Wan

• Previous work by Amanda Mortl (UF Masters Thesis)

• Thanks to the rest of the research team that collaborated in the field and laboratory efforts:

– Paul Lane and Lindsey Nolan (UF/ABE)– Guodong Liu, Qingren Wang, Newton Campbell, Tina Dispenza, and Harry Trafford

(UF TREC)– Marion Hedgepath, Yongshan Wan, Fawen Zheng (SFWMD), Dick Roberts and Jeff

Fisher (JDSP, FDEP), and Kevin Sullivan (NRCS) – Additional field assistance by Zuzanna Zajac, Stuart Muller, Jonathan Schroeder,

Daniel Preston, Karl VanDerlinden, Axel Ritter, Johanna Freeman, Roger Freeman.

• Special thanks to the SWIM Organizing Committee for providing travel funds!!!

Questions?

Photo by Paul Lane

Altered Hydroperiod and Saltwater Intrusion in the Bald Cypress Swamps of the Loxahatchee River...

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