Ditch-Plugging - Restore America's Estuaries

Legacies of ditching and ditch-plugging in New
England salt marshes: long-term effects on
hydrology, elevation, and soil characteristics
Robert Vincent 1 , David Burdick 1 , Michele Dionne 2
1
University of New Hampshire Jackson Estuarine Lab
2
Wells National Estuarine Research Reserve

I. Introduction
Contents
• Self-maintenance
• Ditching and Ditch-plugging
• Study Sites
II.
Effects of hydrology on created and natural
habitats
• Study Design
• Results: hydrology, elevation, soils, vegetation
III. Synthesis
• Implications for self-maintenance

Salt Marshes
Introduction
• Highly productive
transition zones between
marine and terrestrial
habitats
• Develop over thousands
of years
• Dynamic processes
o Hydrology
o Sedimentation
o Vegetation
o Surface elevation
• Influences habitat selfmaintenance

Salt Marsh Self-Maintenance
• Requires tidal ebb and flow
• Above ground vegetation
traps sediments
transported on tidal flows
• Below ground vegetation
contributes organic matter
to sediments
• Marsh accretion must keep
pace with sea level or selfmaintenance
breaks down
leading to habitat loss
(Morris et al. 2002)

Ditching (Ancestors legacy)
Ditching and Ditch-plugging
• Civilian Conservation Corps 1930s
• >90% of New England marshes ditched
(Kennish 2001)
• Management Objective
o Mosquito control
• Reduce surface water and breeding
habitat
Ditch-Plugging (Our legacy)
• More recent activity (1990s)
o
Plug seaward end of ditches creating pool
• Management Objective
o Increase surface water
o Mosquito control
• Larvivorous fish habitat
o Wading bird and waterfowl habitat

Ditching and Ditch-Plugging
• Ditching and ditch-plugging are forms of target
management
– Mosquitoes, fish, birds
• What are the ecological effects of ditching and
ditch-plugging?

Salt Marsh Water Features
• Natural Controls
o Natural Creek
o Natural Pool
• Created Habitats
o Altered Hydrology
o Created Ditch
o Ditch-plug Pool

Study Sites
• Three Gulf of Maine
back barrier marshes
o Sprague River Marsh
Phippsburg, Maine
o Chauncey Creek
Marsh Kittery, Maine
o Parker River Marsh
Newburyport, Massachusetts
Sprague River Marsh
Chauncey Creek Marsh
Parker River Marsh

Study Design
• Localized response of habitats to
altered hydrologic regimes
• Four habitats per marsh
o
o
o
o
Natural Creek
Natural Pool
Created Ditch
Ditch-plug Pool
• Four replicates per habitat at each
marsh
o
o
Three sections per marsh for representation
throughout marsh
Randomly selected using aerial photo and
numbered grid overlay
• Eight 20-meter transects per
habitat at each marsh
o
o
o
Two transects per replicate
Sampled 0, 2, 7, 15, 20 meters each transect
10 plots averaged per replicate

Results: Physical Characteristics
Habitat
Water
Level
(cm)
Marsh Surface
Elevation
NAVD88 (cm)
Pore-water
Salinity
(ppt)
Soil Redox
Potential Eh
(mv)
Soil
Strength
(Kg/cm 2 )
Bulk
Density
(mg/cm 3 )
Carbon
Storage
(mg/cm 3 )
Organic
Content (%)
Created Ditch -2.52 c 110 b 26.1 b 7 a 4.51 b 605.01 b 34.2 a 18 a
Natural Creek -4.01 c 105 bc 26.2 b 52 a 4.21 bc 761.76 a 34.1 a 14 b
Ditch Plug 5.51 a 102 c 30.9 a -165 b 3.57 c 550.79 b 28.7 b 17 ab
Natural Pool -0.49 b 121 a 26.9 b 31 a 5.87 a 575.11 b 37.4 a 21 a
Levels not connected by the same letter are significantly different based on Tukey-Kramer post hoc tests for each variable (p< 0.05)
• Ditch-plug significantly different from natural pool except for bulk density
and percent organic content
• Created ditch similar to natural creek except for bulk density and percent
organic content

Results: Hydrology
• Percent of time water was in rooting zone (0 to -10 cm):
o Higher in pools than channels
o Higher in created ditch than natural creek
o Differences can influence plant growth, decomposition, and self-maintenance
70
60
50
40
Created Ditch
Natural Creek
Ditch Plug
Natural Pool
Water level (cm)
30
20
10
0
-10
-20
-30
0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96
Percent of time

Results: Marsh Elevations
• Elevations higher for natural pool than all other habitats
• Elevations lower for ditch-plug than all other habitats
o Promotes surface water retention
• Appears to be subsidence over time in created habitats
o Implications for self-maintenance
Marsh surface elevation NAVD88 (cm)
120
110
100
90
80
70
60
Created Ditch
Ditch-plug
Natural Creek
Natural Pool
0 2 7 15 20
Distance from edge of water feature (m)

Results: Habitat Indicators – Flooding and Eh Stress
• Canonical 1
14
o
Hydrology and edaphic stress
• Ditch-plug
13
Water Level
KgF/cm2
LOI
Carbon Storage
o
o
Distinctly different from all others
Higher Water levels
12
NP
o
o
o
o
Higher Salinity
Lower redox potential
Lower organic content
Lower sediment strength
Canonical2
11
10
DP
Salinity
CD
% organic
NC
Redox
• Canonical 2
o Sediment bulk properties
• Natural Pool
o Higher sediment strength
o Higher carbon storage
• Natural Creek
o Higher bulk density
o Higher redox potential
• Created ditch habitat
o Intermediate
9
Bulk Density
8
-11 -10 -9 -8 -7 -6 -5 -4 -3 -2
Canonical1
Ditch-plug Core Natural Pool Core

Results: Vegetation
100
90
80
B
A
AB
70
• Patterns of percent cover
and biomass across habitats
were similar, showing ditchplug
significantly lower than
all other habitats
• Only a few plants can
survive in ditch-plug habitat,
as indicated by all measures
of diversity
o
Richness, Shannon Hʹ, exp(Hʹ), and
Pielou’s J
Cover (%)
Biomass (g/0.0625m 2 )
Parameter Value
60
50
40
30
20
10
0
60
50
40
30
20
10
0
5.00
4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
C
Created Ditch Natural Creek Ditch Plug Natural Pool
A
B
B
C
Created Ditch Natural Creek Ditch Plug Natural Pool
A A
Created Ditch
A
Natural Creek
Ditch Plug
Natural Pool
A A A
B
B
A A A
A A A
B
B
0.00
Richness Shannon H' exp(H') Pielou's J

Results: Habitat Indicators - Vegetation
• Canonical 1
• High edaphic stress
o
Ditch-plug
• Distinctly different
• Canonical 2
• Algal mat, sulfur bacteria,
unvegetated, Salicornea spp.
• Pore-water drainage disturbance
o Natural Creek
• Better drained sediments
• Tall-from S. alterniflora
o Natural Pool
• Poorly drained sediments
• Short-form S. alterniflora
o Created Ditch
• Drainage intermediate between
natural creek and natural pool
• Forb species
Canonical2
7
6
5
4
3
SP
2
1
0
-1
-2
SSA
NP
CD
SU PU
NC
AP
JG
TSA
GM
TM
Algae Mat
DS
LN
Sulfur Bacteria
SE
PM
-3
-6 -4 -2 0 2 4 6 8
Canonical1
DP
Unvegetated
Ditch-plug pool

Self-Maintenance: Natural Creek
• Marsh elevations and tidal flow
promote flushing and sediment
delivery
• Sloping banks with tall S.
alterniflora promote sediment
trapping and accretion
• Higher mineral content facilitates
drainage alleviating edaphic
stress
• High vegetation productivity and
sedimentation have allowed
marsh accretion to keep pace
with sea level
• These conditions support the
self-maintenance process

Self-Maintenance – Created Ditch
• Habitat initially drained by ditches has
subsided over time reducing the depth
to water table and creating wetter
conditions than in natural creek habitat
• Elevations and hydrologic regime
supports vegetation growth but water
retention in the rooting zone alters
community composition (forbs),
sediment trapping, and soil organic
content
• Self-maintenance has been functioning
for the past 70 years, but questions
remain:
o Will accretion keep pace with sea
level rise?
o Will further subsidence occur and
limit self-maintenance?
• Impacts from ditching may be greater in
more extensively ditched marshes with
overlapping hydrologic regimes

Self-Maintenance: Natural Pool
• Moderate drainage supports
vegetation growth and reduces
decomposition
• High carbon content promotes
sediment strength and habitat
stability, providing a carbon sink
in the high marsh
• These carbon inputs combined
with moderate sedimentation
promote marsh accretion that
maintains consistently high
surface elevations
• The self-maintenance process
seems to be functioning well in
natural pool habitat

Self-Maintenance: Ditch-plug Pools
• Poor drainage results in surface
and pore-water retention that
promotes edaphic stress and
vegetation die back
• Low organic and mineral inputs,
low sediment strength, and
collapse of the root zone has led
to habitat instability and marsh
subsidence with lower elevations
• This hydrologic restriction leads
to a decoupling of the selfmaintenance
process with a
transition from vegetated to
open water habitat, and the
potential for additional loss of
salt marsh habitat with continued
sea level rise

Acknowledgements
• University of New Hampshire Jackson Estuarine Lab
• University of New Hampshire Marine Program
• Wells National Estuarine Research Reserve
• New Hampshire Coastal Program
• NOAA Restoration Center
• NOAA National Estuarine Research Reserve, Graduate Research
Fellowship Program
• US Fish & Wildlife Service Special Use Permits for Work at
Chauncey Creek and Parker River marshes
• The Nature Conservancy and Bates College for permission to work
at Sprague River Marsh

Questions?