Download Impact of Mosquito Ditching

10/26/2016
Why are salt marshes important?
Salt marsh ecosystem services
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Carbon sequestration
Denitrification
Wildlife habitat
Shoreline protection
Water quality maintenance
Paul Broadmeadow
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Dominant New England salt marsh plant species
Spartina patens (salt marsh hay)
Gobotany.com
Spartina alterniflora (salt marsh cordgrass)
Seagrant.umaine.edu
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Pool /Panne
nhdfl.org
Salicornia sp.
Common name: Glasswort
zottoli.wordpress.com
Human impacts on salt marshes
 Nutrient loading
 Tidal restrictions
 Sea level rise/climate change
 Mosquito ditching
 Filling for development
 Mowing/Cutting
www.nps.gov
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Ditching: History

Humans have been ditching marshes since colonial
times to increase the productivity of salt marsh hay
for cattle grazing (Ranwell 1967)

During the 1930’s 90% of the Atlantic coastal
marshes were ditched to drain surface water for
mosquito control and to increase the workforce
during the great depression (Clarke et al. 1984)
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Ditching in Rhode Island
Winnapaug Pond
Matunuck Soil Series
0-30cm Oe (Peat)
30+ 2Cg (Sand deposits)
Narrow River
Pawcatuck Soil Series
0-116cm Oe (Peat)
116+ 2Cg (Sand deposits)
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2012 Study
 Purpose: Determine the impact of ditching on
salt marsh vegetation patterns in Narrow River,
RI.
 Hypothesis #1: Mosquito ditches alter the salinity
regimes within fringe salt marshes which
determine vegetation composition
 Hypothesis #2 : Ditches increases the extent of
pannes and pools because ditching alters the
topography of the marsh
Study Site

Narrow River
Rhode Island
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Methods

Delineated marsh
units using RI soil
survey
MU
Mk
ChD
CdB
WgB
QoC
Mk
Ws
ChD
Mk
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Methods

Delineated ditches
Methods: Vegetation Composition
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Methods
Methods: Vegetation Composition
Sampled along 30m transects.
Recorded vegetation composition
 Determined salinity of each sample
using saturated paste method
 Determined extent of
vegetation zones

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Methods Extent of Pools



Collected field data via kayak to document extent
of pannes and pools
Delineated pannes and pools within marsh units:
total of 1500 polygons
Determined
relationship
between % pool
area and density
of ditches
Results

Ditches
 Total length = 5830.192 meters
 Mean length = 30.4 meters

Marsh units
 Total area = 982950.0902 meters2
 Mean area = 32765 meters2

Pools/pannes
 Total area = 120643 meters 2 (8%)
 Mean area = 82.68884 meters2
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Percent Species Composition
120
% Species composition
100
80
Alterniflora
60
Patens
frutescens
Salicornia
Bare Soil
40
20
0
0
5
10
15
20
25
30
35
Distance from ditch (m)
Narrow River: Surface Horizon EC25(1:5)
6
5
EC25(1:5)
4
3
Mean
2
1
0
0
1
5
15
30
Distance From Ditch (m)
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Ditch Density vs. % Pool Area
50
45
% Pools/Pannes (m2/m2)
40
35
30
25
20
15
10
5
0
0.000
0.000
0.006 0.016 0.007 0.002 0.102 0.016
Total length of ditches/marsh area (m/m2)
0.007
New Hypothesis

Extent of pools has increased because
of sea level rise

Methods: Delineated extent of pools
using 1952 aerial photography and
compared total area of pools with results
from 2011
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Results

1952
 Total pool area = 119670.2 m2
 Mean pool area = 383.5583 m2

2011
 Total pool area = 120643 m2
 Mean pool area = 82.68884 m2

% Change = +972.833 m2
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