741
In our biological studies, the two restoration cells have been treated as two replicates, but differences between them are informative. The SE cell started with a
lower overall elevation than the NW cell, and so has been experiencing more sedimentation (Fig. 21.13). In the areas with the greatest amount of sediment deposition
in the SE cell (in its northwest section and its southeast tip), overall plant coverage
was still much less in 2015 than elsewhere in that cell or than throughout the NW
cell. Note that a significant difference in S. alterniflora density was not detected
between restoration cells in 2015 (Fig. 21.21), partly because a substantial portion
of the SE cell has nearly full plant cover and partly because of where our permanent
transects are located (which did not include the northwest section of that cell). In the
first 2 years, the northwest section of the SE cell was not accessible by walking,
except when frozen, because the mud was very soft and fluid. As the mud solidified,
S. alterniflora seedlings became established in this section in 2014 and 2015, and
small patches were observed in 2015 and 2016 that resembled the pattern of patches
seen in Fig. 21.22a (i.e., observed throughout the NW cell in 2013). The fact that
overall plant cover is less in the SE cell than in the NW cell is of concern, because
the SE cell is narrower (75–100 m wide) than the NW cell (125–200 m wide). It is
not clear whether a functioning salt marsh will develop in the SE cell before the old
dike degrades so much that it no longer offers protection from waves and sediment
resuspension (e.g., French et al. 2000). It may also be too narrow to provide sufficient accommodation space for the salt marsh to adjust to the local rate of relative
sea level rise. Simply put, healthy vegetation cover is crucial to a salt marsh, both in
terms of ecosystem services as well as in trapping sediment and baffling wave
energy, and the low amount of vegetation in sections of the SE cell reduces the
prospect of its successful restoration.
Another difference between the restoration cells is the almost complete disappearance of the large salt pool in the SE cell, starting in 2014, partly because of sedimentation but also because of the extra armoring of the new dike placed in that cell
in the autumn of 2013. The added rock and fill material placed adjacent to the new
dike locally displaced the marsh surface upward, causing the large salt pool to partially drain. Other than plant coverage and the recent disappearance of the large salt
pool, the various biological communities have had similar composition and dynamics in both cells, as represented by the clustering of points from each year in the
nMDS graphs (Figs. 21.20 and 21.24).
In summary, the biological community dynamics that we observed to date are
within the range reported for other salt marsh restoration projects in New England
and Maritime Canada (Burdick et al. 1997; Roman and Burdick 2012; Warren et al.
2002). Of the intentional restoration projects undertaken to date in the Bay of Fundy
(Bowron et al. 2012), those at Walton River (Neatt et al. 2013; van Proosdij et al.
2010) and Cogmagun River (Bowron et al. 2015), in Minas Basin, Nova Scotia, are
most similar to our project in that they involved breaching a dike and salt marsh
vegetation was essentially absent from the sites to be restored. Although both projects are located in a macrotidal environment, they differed from ours in being relatively recently diked (1989 and 1991, respectively) to create a freshwater
impoundment, and in being located 2–3 km upriver and so are protected from waves.
21 Returning the Tide to Dikelands in a Macrotidal and Ice-Influenced Environment…
In our biological studies, the two restoration cells have been treated as two replicates, but differences between them are informative. The SE cell started with a
lower overall elevation than the NW cell, and so has been experiencing more sedimentation (Fig. 21.13). In the areas with the greatest amount of sediment deposition
in the SE cell (in its northwest section and its southeast tip), overall plant coverage
was still much less in 2015 than elsewhere in that cell or than throughout the NW
cell. Note that a significant difference in S. alterniflora density was not detected
between restoration cells in 2015 (Fig. 21.21), partly because a substantial portion
of the SE cell has nearly full plant cover and partly because of where our permanent
transects are located (which did not include the northwest section of that cell). In the
first 2 years, the northwest section of the SE cell was not accessible by walking,
except when frozen, because the mud was very soft and fluid. As the mud solidified,
S. alterniflora seedlings became established in this section in 2014 and 2015, and
small patches were observed in 2015 and 2016 that resembled the pattern of patches
seen in Fig. 21.22a (i.e., observed throughout the NW cell in 2013). The fact that
overall plant cover is less in the SE cell than in the NW cell is of concern, because
the SE cell is narrower (75–100 m wide) than the NW cell (125–200 m wide). It is
not clear whether a functioning salt marsh will develop in the SE cell before the old
dike degrades so much that it no longer offers protection from waves and sediment
resuspension (e.g., French et al. 2000). It may also be too narrow to provide sufficient accommodation space for the salt marsh to adjust to the local rate of relative
sea level rise. Simply put, healthy vegetation cover is crucial to a salt marsh, both in
terms of ecosystem services as well as in trapping sediment and baffling wave
energy, and the low amount of vegetation in sections of the SE cell reduces the
prospect of its successful restoration.
Another difference between the restoration cells is the almost complete disappearance of the large salt pool in the SE cell, starting in 2014, partly because of sedimentation but also because of the extra armoring of the new dike placed in that cell
in the autumn of 2013. The added rock and fill material placed adjacent to the new
dike locally displaced the marsh surface upward, causing the large salt pool to partially drain. Other than plant coverage and the recent disappearance of the large salt
pool, the various biological communities have had similar composition and dynamics in both cells, as represented by the clustering of points from each year in the
nMDS graphs (Figs. 21.20 and 21.24).
In summary, the biological community dynamics that we observed to date are
within the range reported for other salt marsh restoration projects in New England
and Maritime Canada (Burdick et al. 1997; Roman and Burdick 2012; Warren et al.
2002). Of the intentional restoration projects undertaken to date in the Bay of Fundy
(Bowron et al. 2012), those at Walton River (Neatt et al. 2013; van Proosdij et al.
2010) and Cogmagun River (Bowron et al. 2015), in Minas Basin, Nova Scotia, are
most similar to our project in that they involved breaching a dike and salt marsh
vegetation was essentially absent from the sites to be restored. Although both projects are located in a macrotidal environment, they differed from ours in being relatively recently diked (1989 and 1991, respectively) to create a freshwater
impoundment, and in being located 2–3 km upriver and so are protected from waves.
21 Returning the Tide to Dikelands in a Macrotidal and Ice-Influenced Environment…