Matthew Regan
SUSSMAN INTERNSHIP FINAL REPORT
“Restoring the plant diversity of freshwater wetlands of the Upper St.
Lawrence River”
Introduction
Hydrology is one of the most important factors affecting the ecology of coastal
wetlands of the Great Lakes-St. Lawrence Basin. The seasonal and yearly fluctuation of
water levels results in the diversity and zonation of plant communities in wetlands. High
water levels flood many trees and shrubs that have encroached into lowland areas since
the last period of high water levels. Low water levels that allow herbaceous species to
germinate from buried seed banks. Wet meadows composed of Carex spp. develop in
shallower waters compared to marshes composed of Typha spp. The plant species
composition of wetlands is the result of the interaction between a diverse seed bank and
fluctuating water levels.
The St. Lawrence River experienced much anthropogenic disturbance in the 20th
century. Its hydrology was altered to allow for navigation, hydroelectric energy, and the
management of shoreline development. These activities were made possible by the
construction of the Robert Moses Robert H. Saunders Power Dam in Cornwall, ON and
Massena, NY in 1958. Since its creation, the dam has reduced the variability of water
levels. These stabilized water levels have resulted in the expansion of invasive Typha
spp. in wet meadows.
This research is part of a larger collaborative restoration project between Ducks
Unlimited, SUNY-ESF, US Fish and Wildlife Service, Natural Resource Conservation
Service, New York Department of Environmental Conservation and private landowners.
The restoration project aims to restore the diversity of coastal marshes of the Upper St.
Lawrence River and its tributaries. This collaboration developed a strategy to improve
habitat connectivity, restore natural water level fluctuations and restore native vegetation.
Restoration methods included water level manipulation from fish ladders, mechanical
removal of Typha spp., channel excavation, pothole excavation and habitat mound
creation. Four wetland sites were chosen for restoration treatments and four reference
wetlands were left unaffected by restoration to serve as reference sites (Figure 1). A
monitoring program was developed to evaluate the effects of the restoration project.
Summary of proposed research
I proposed to evaluate different methods of wetland restoration by monitoring the
plant community. My objectives were to compare water-level manipulation and the use
of dredge spoils for restoring a wetland’s plant community. Data collected would be used
to help understand the vegetation dynamics of a wetland after re-introducing high water
levels and the early colonization from an exposed seed bank.
Summary of work completed
The vegetation was surveyed at four reference sites (French Creek Reference,
Swan Bay, Plum Tree and Deferno) and four treatment sites (French Creek Treatment 1,
Pt. Vivian, Delaney, and Carpenter’s Branch). The two treatments were fish ladders to
manipulate water levels (Carpenter’s Branch and Delaney) and channel excavations to
restore habitat connectivity (French Creek Treatment 1 and Pt. Vivian). We established
three transects per site; ranging from 35 to 275 meters, and seven permanent plots per
transect on an elevation gradient (75.80; 75.34; 75.04; 74.89; 74.73; 74.58; 74.28 m
IGLD 1985) using a Trimble 5800. PVC pipes were installed at each transect point,
flagged and recorded with a GPS.
A 1 m2 PVC quadrat was used to survey vegetation at each sampling point. We
identified plants by species and recorded their percent coverage by ocular estimate within
the 1 m2 quadrat. Additionally, for Typha spp. we recorded the number of live and dead
stems, flowers, maximum height and visually estimated the percent coverage of live
stems and fallen leaf litter. Observations on the water depth and soil moisture were
recorded. All vegetation plots were surveyed once from July through August 2012.
A total of 168 1 m2 plots were surveyed on the elevation transects. An additional
85 1 m2 plots were randomly selected on the spoil piles at Pt. Vivian, French Creek
Treatment 1 and French Creek Treatment 2. Both habitat mounds that were part of the
original restoration design plan and smaller spoil piles leftover from the channel
excavation were surveyed to capture the vegetation response from seeded and non-seeded
dredge spoils.
FIGURE 1. Site descriptions
Site Name
Location
Geomorphology
Treatment
French Creek
Treatment
Clayton, NY
Drowned RiverMouth
Excavations and dredge
spoils
French Creek
Reference
Clayton, NY
Drowned RiverMouth
None
Clayton, NY
Fish Ladder
Fish ladder
Carpenter’s Branch
Deferno Branch
Clayton, NY
Pt. Vivian
Alexandria Bay,
NY
Alexandria Bay,
NY
Drowned RiverMouth
Drowned RiverMouth
Protected
Embayment
Protected
Embayment
Grindstone Island,
Protected
Swan Bay
Delaney
None
Excavations and dredge
spoils
None
Plum Tree
NY
Embayment
Grindstone Island,
NY
Protected
Embayment
None
PRELIMINARY RESULTS AND DISCUSSION
Species richness was recorded for each site and it was found that total species
richness was higher in the treatment sites when compared to the reference sites. The site
with the highest species richness was Pt. Vivian. It is hypothesized that Pt. Vivian’s high
species richness could be due to the effect of nutrient loading from the surrounding
landscape. Pt. Vivian is in close proximity to residences with large lawns that may
provide nutrient inputs that stimulate plant growth, especially from the exposed seed
bank. The mean species richness per site was highest in the excavation sites when
compared to the water-manipulation sites and control sites. This initial difference could
be due to the recruitment of species from the dredge spoils. The high water levels at the
water-manipulation sites might be more effective at reducing the presence of Typha spp.
than increasing species richnes.
Differences in mean species per plot were analyzed. There was a statistically
significant difference in species richness when comparing Carpeneter’s Branch to
Deferno Branch (p=0.00177, α = 0.05), and when comparing Delaney to Plum Tree
(p<0.001, α = 0.05). These results reveal differences in species richness are dependent on
scale. Dredge spoils contribute more to overall species richness on a larger landscape
scale than water level manipulations. Water level manipulations contribute more to
species richness at a smaller scale.
Analysis of variance (ANOVA) was used to analyze if there were differences in
species richness per plot. There was a significant difference in species richness per plot
compared among all sites (p<0.001, α = 0.05) in a 8 x 7 factorial using site and elevation
as factors. There was a significant difference in species richness per plot between restored
and reference sites (p<0.0001, α = 0.05) found in a 2 x7 factorial ANOVA using
restoration and elevation as factor. These ANOVA tests indicated that variability in
species richness per plot can be explained by differences between the all of the sites
regardless if they were grouped by treatment and reference sites or not.
Preliminary linear models looked at the effect of Typha spp. on species richness.
It was found there was a stronger direct relationship between the number of Typha live
stems and species richness in restored sites compared to reference sites. It was also found
there was a stronger direct relationship between Typha spp. coverage and species richness
in restored sites compared to reference sites. Restoration allowed more species to
germinate where there was more Typha spp. This relationship could be due to increased
competition for resources made available by restoration. The high water levels of the
water-manipulation sites may increase competition at higher elevations that weren’t
flooded.
FUTURE WORK
A second field season will be planned for spring and summer of 2013. Pt. Vivian
will have more excavations completed and a fish ladder installed to manipulate water
levels. The same protocol for the vegetation survey will be used. Soil samples will be
collected at all of the sites to analyze differences in pH, soil moisture, N, P and organic
matter. Soil samples will also be collected from the dredge spoils to be used for a
seedbank germination experiment comparing the species diversity of the dredge spoils
with the surrounding area.
ACKNOWLEDGEMENTS
I am thankful for my major advisor Dr. Donald Leopold for his input and
guidance for my research. I would also like to thank Dr. John Farrell, who is the principal
investigator for this project and a member of my steering committee. I am extremely
grateful for Sarah Fleming of Ducks Unlimited for agreeing to be the sponsor for my host
organization. I am also deeply thankful for the Edna Bailey Sussman Foundation and
their generosity, which made my fieldwork possible.