Sheetflow Effects and Canal Backfilling on Sediment Source and Transport in Everglades Freshwater Wetlands: Analysis of Molecular Organic Biomarkers

Peter Regier1, Ding He1, Colin Saunders2, Carlos Coronado-Molina2, Blanca Jara1 and Rudolf Jaffé1

(1) Southeastern Environmental Research Center, Florida International University, Miami, FL, United States(2) South Florida Water Management District, West Palm Beach, FL, United States

Historic freshwater sheetflow in the Florida Everglades distributed sediment to form a ridge-and-slough landscape. Drainage of wetlands along with reduction and obstruction of flow has degraded topography. The Decompartmentalization Physical Model is a landscape-scale test project to assess options for re-establishing sheetflow and re-engineering barriers to flow in order to restore natural freshwater delivery levels to the Everglades. To validate proof of concept that increased flow will rebuild ridge-slough microtopography, biomarker proxies were established for ridge and slough organic matter sources and monitored in flocculent particulate organic matter (floc) before, during and after high-flow conditions. In addition, sediments were collected from partial and complete canal backfill sites with sediment traps. Four molecular organic biomarkers were evaluated: the aquatic proxy (Paq), C20 highly-branched isoprenoids (C20 HBI), kaurenes and botyrococcenes. Biomarkers were able to successfully differentiate ridge and slough organic matter sources with Paq and C20 HBI being most effective. Additional years of data are needed to assess the interactive effects of partial and complete canal backfilling and sheetflow on organic matter dynamics.

Abstract

AcknowledgementsThis work was funded by the South Florida Water Management District (SFWMD) DPM project. We gratefully acknowledge the DPM Team (Dr. Sue Newman, Dr. Fred Sklar, Eric Cline, Eric Tate-Boldt, Chris Hansen, Fabiola Santamaria, Michelle Blaha) for their assistance with field-work, insightful discussion of results and allowing the use of DPM data for this presentation. RJ and BH acknowledge additional support through the George Barley Chair and McNair Fellowship respectively.

Hypotheses1. Increased sheetflow will preferentially mobilize slough organic matter2. Sediment trapped in backfilled sites will differ from open canal traps

Discussion1. Biomarkers, particularly Paq, successfully differentiated ridge and slough organic matter

inputs in the DPM test plot.2. Slough material was mobilized by increased sheetflow, supporting Hypothesis 1.3. Sediment traps collected primarily slough-derived materials during low flow.4. High flow sediment trap inputs were less “slough-like”. Possible explanations include

• Disconnect in entrainment of slough-derived floc and ridge-derived fine POM• Seasonal nutrient inputs from producers of HBI and Botyrococcenes (algae)• Containment structure inputs scraped off and mobilized by increased flow

5. More data are required to fully understand the interactions of backfilling and sheetflow in order to test Hypothesis 2.

SummaryOur preliminary data indicates that under increased flow conditions, flocculent matter from sloughs is preferentially mobilized. This suggests that increasing sheetflow velocity in degraded ridge and slough wetlands is a viable restoration tool. Results from sediment traps are inconclusive regarding effectiveness of canal backfilling. Two additional years of data will be collected in 2014-2015 and 2015-2016, including two periods of increased flow. More advanced statistical analysis of the collected data is suggested before extensive interpretation of results.

Solvent Extraction

Column Chromatography

GC/MS

Freeze-dry floc and sediment

Paq

Differentiate between ridges and sloughs

Kaurenes

Indicative of ridges

HBI

Indicative of sloughs

Botyrococcenes

Indicative of sloughs

Methods

0.0

0.2

0.4

0.6

0.8

1.0

Paq

Z4-1 Paq

0

100

200

300

C20

HB

I (µ

g/gd

w)

Z4-1 C20 HBI

0.0

0.2

0.4

0.6

0.8

1.0

Paq

Z10-2 Paq

0

50

100

150

200

C20

HB

I (µ

g/gd

w)

Z10-2 C20 HBI

0.0

0.2

0.4

0.6

0.8

1.0

Paq

Z5-3 Paq

0

50

100

150

200

250

300

C2

0H

BI

(µg/

gdw

)

Z5-3 C20 HBI

Before High Flow High Flow After High Flow *Significant Difference: Before, High+After,p≤0.05

*

*

*

0.0

0.2

0.4

0.6

0.8

1.0

Paq

Ridge-Slough Transect - Paq

0

100

200

300

HB

I (µ

g/g

dry

wei

ght)

C20 HBI

10/2012 (LOW flow) 01/2013 (LOW flow) 10/2013 (LOW flow) 01/2014 (HIGH flow)

0

5

10

15

20

Ridge Ridge-Edge Slough-Edge Slough

Kau

ren

e(µ

g/g

dry

wei

ght)

Kaurenes

0

1

2

3

Ridge Ridge-Edge Slough-Edge Slough

Bo

tryo

cocc

en

es

(µg

/g d

ry w

eigh

t)

Botryococcenes

Results – Ridge/Slough

Fig. 2• Paq – can distinguish ridge and slough organic matter• HBI – can distinguish ridge and slough organic matter• Kaurenes – indicates ridge material, absent in sloughs• Botyrococcenes – strongly variable with season, present in very

low concentrations

Fig. 3• Significant increase in slough-like material for Paq and

HBI during and after increased flow• Increase consistent along flowpath

Fig. 2: Ridge to Slough transect Fig. 3: Test-plot spatial transect

CB1

CB2

0

0.2

0.4

0.6

0.8

1

Low High After Low High After Low High After

Ridge Slough Sediment

Paq

Fig. 4: Average Paq – All Samples

0.0

0.2

0.4

0.6

0.8

1.0

Paq

Fig. 5: Sediment Traps - Paq

CC1

CC2

CB1

CB2

CB3

High FlowBefore High Flow After High Flow

Results – Canal

Fig. 5• Decrease in Paq during high flow• Backfill sections appear to respond

differently to high flow conditions • Experimental site data is not

significantly different from controls

Fig. 4• Ridge Paq increased during and after

high flow• Slough Paq increased during and

after high flow• Sediment Paq decreased during high

flow

Fig. 1: Study Site

Georgia

Florida

Gulf of Mexico

Miami

Degraded topography

Natural topography

Control sites

Canal sediment traps

Flocculent matter sites

FlowpathZ5-3

Z4-1

Z10-2

CB3

CC1

CC2

CB2

CB1

Fig 1.: Map of sampling sites. The experiment plot is located between two levees bisecting Water Conservation Area 3, a peatland with historic ridge and slough topography. Control sites are located outside of the flowpath of sheetflow. Canal sediment traps are located in experimental canal backfill sections of the L67-C canal. Flocculent matter sites are located along the flowpath where flocculent mats were collected.

Fig. 2: Floc was sampled along a spatial transect from ridge to slough during low and high flow conditions.

Fig. 3: Floc was sampled spatially along the sheetflow path from the culverts (source of flow) to the canal backfill sections.

Fig. 4: Combination of ridge floc, slough floc and canal sediment samples separated into before, during and after high-flow treatment.

Fig. 5: Sediment trap results for canal backfill sites before, during and after high flow. CC1 and CC2 are control sites located outside of the main sheetflow channel (see Fig. 1). CB1 is open canal, CB2 is partially backfilled and CB3 is completely backfilled. Averages for each flow period are shown as dashed bars.

Analytical Methods Molecular Organic Biomarkers

a a d

b b,c

c d b,c

p≤0.05