Atlas of Bank Restoration Sites of the St. Lawrence River - Description of Themes
- Improving access to flooded plains for fishes
- Dismantling of embankments
- Stabilization of eroding banks
- Recuperation of diked spartina marshes
- Setting up sills on drainage canals drying out spartina marshes
- Creation of openings within emergent freshwater marshes too densely colonized
- Restoration of existing man-made ponds for waterfowl
- Eelgrass plantation
- Planting in rip-rap shores
- Planting in disturbed dunes
- Planting of trees and shrubs in anthropic green spaces
- Planting of trees and shrubs in agricultural lands
- Controlling of invasive plant species in wetlands
Improving access to flooded plains for fishes (installation of culverts, reshaping of banks, removal of sediments within some watercourses…)
Artificial barriers such as roads, sediments, badly designed culverts on some watercourses can significantly modify the hydrology of a marsh, ultimately transforming radically the original aquatic vegetation, to the benefit, for example, of more xeric vegetation. Slowed water drainage, a common result of the presence of these various elements, is likely, moreover, to lead to the eutrophication of the environment found behind. These artificial barriers, as well as the steep banks of some watercourses, can also cut off access to flooded plains normally used as feeding or spawning sites by fish. Likewise, those flooded plains can, occasionally, become veritable traps for aquatic fauna that venture into diked areas during spring floods or large equinoctial tides.
Dismantling of embankments
The St. Lawrence River has experienced many transformations since the beginning of the 20th century. One of the indirect consequences of urbanization is the growing popularity of recreational development and outdoor activities, which involve the unrestrained appropriation of banks by marinas and quays of all kinds. Industrialization also left its mark on the banks of the St. Lawrence. Factories were built on the outskirts of urban areas. Many were established along the St. Lawrence to take advantage of access to a waterway and the presence of a water body to dispose of their wastes.
The opening of the seaway had many direct and indirect consequences for all aspects of life in the river. It led to the disappearance of coastal shipping by boats with shallow drafts. The small village quays that served schooners were thus abandoned (Robitaille et al. 1988). Other port facilities were established in large centres or were enlarged in order to accommodate more ships. Some of them subsequently had to be abandoned due to insufficient patronage, high maintenance costs or a deterioration of their infrastructure that required astronomical repair costs.
The use and maintenance of the shipping channel has, over the years, required many buoys and booms. Breakwaters or seawalls were built to concentrate the flow in the navigable part of the river. Some of these structures have since been abandoned, as have many multipurpose embankments that are now disused. All those structures, while encroaching shorelines, reduced available habitats for wildlife.
Stabilization of eroding banks
Filling, draining and encroaching on the banks of the St. Lawrence River and estuary led to the loss of some 5000 ha of habitat from 1950 to 1980 (Le Groupe Dryade 1981). Even though habitat destruction attributable to these human activities is not as significant as it was in the 1990s, the loss of habitats seems to be continuing at a disturbing rate, mainly due to shoreline erosion, a phenomenon whose scale has been heretofore underestimated.
As part of the work conducted for the St. Lawrence Vision 2000 program, nearly 400 km of eroded shoreline was inventoried in the section between Cornwall and Montmagny alone, that is 25% of the shoreline in the section studied. The erosion is so severe in certain places that the bank is eroding more than 3 m or 4 m per year (Dauphin and Lehoux 2004). Some 1000 ha of islands are estimated to have been lost in this way over the past 35 years. Erosion has been the most pronounced in the section between Montreal and Lake Saint-Pierre, where 270 km of eroding shoreline has been inventoried (Argus Environmental Consultants Inc. 1996a). The more considerable erosion noted in this section can largely be explained by the fact that this section is very narrow, often less than 3 km wide and dotted in certain places with many channels. The narrowness of the area thus accentuates the impact of the wake produced by commercial ships and recreational boat.
Work done further downstream reveals that this phenomenon is also present in the bulrush and cordgrass marshes in the estuary, as well as along many tributaries. Some studies have reported that the small scarp eroded 1.6 to 4.6 m per year in the high marsh at Rivière-du-Loup between 1967 and 1995 (Dionne 1986; Argus Environmental Consultants Inc. 1996b). Annual erosion rates of 0.25 to 1.5 m have been recorded for the Cap Tourmente marsh over the nearly 25-year period between 1964 and 1990 (Lehoux et al. 1997).
If nothing is done in the coming years to try to put a stop to this problem, or at least to reduce its extent, we can expect, for example, the disappearance of the Îles de la Paix, and eventually of the 240 ha of marsh that encircles them, within 20 years; the disappearance of Îles Bellegarde, Îles aux Boeufs and Îles aux Prunes in the Verchères archipelago, respectively within 10, 25 and 30 years, and of those on the Îlots Lacroix and Île Chipeau in the Contrecoeur archipelago, within 10 to 15 years. In the following years, we can also expect a notable reduction in the dozens of hectares of marshes whose existence depends on these islands and the disappearance of the cordgrass marshes within a few decades.
Researchers who have worked on the St. Lawrence River identify several possible causes of shoreline erosion in its freshwater section, such as: boat wakes, waves generated by wind, ice, currents, frost, grazing and surface drainage (Department of Public Works 1968; Ouellet and Baird 1978; D’Agnolo 1978; Panasuk 1987; Dauphin and Lehoux 2004). Erosion can be further intensified by particularly high water levels, steep banks, exposure to dominant winds, a lack of riparian vegetation nearby or on the bank and a loose substratum. Clearly, the importance of each of these factors in the erosion process will vary from one place to another, and they can often act in synergy, thus making it more difficult to assess precisely the role of each factor in the process of shoreline erosion. Nevertheless, in the freshwater section of the St. Lawrence, waves generated by wind and the passage of ships are among the main factors, particularly when prevailing water levels are high.
Recuperation of diked spartina marshes
Cordgrass marshes have, over the centuries, been highly coveted by farmers. By the beginning of colonization, owners of land bordering these marshes already had the right to cut and dry the Prairie Cordgrass growing on their banks. In 1860, the École d’agriculture de Sainte-Anne-de-la-Pocatière erected the region’s first aboiteau. This aboiteau, comprising dikes with valves combined with a network of drainage canals, covered some 500 m in length and made it possible to dry out the cordgrass marsh by preventing the daily intrusion of salt water. From the following decades until the beginning of the 1980s, this practice intensified to the point where 35% of cordgrass marshes in the St. Lawrence, the equivalent of some 1500 ha, were diked for agricultural purposes. The most dramatic losses were noted in the Kamouraska and La Pocatière areas. The loss of cordgrass marshes due to agriculture explains in part the fact that Saltmeadow Cordgrass occupies no more than a few hundred hectares in Quebec today.
Cordgrass marshes are home to more than 80 bird species, including at least four with a precarious status: the Yellow Rail, the Short-eared Owl, the Least Bittern and the Nelson’s Sharp-tailed Sparrow. These marshes are the preferred habitat of the American Black Duck during nesting season. During the summer, it is not rare to see females with their ducklings feeding on seeds and invertebrates in the salt pools of the Saltmeadow Cordgrass zone. From time to time, 12 mammalian species take advantage of these environments. An attentive, patient visitor might spot a deer or a moose. Chance encounters are also possible with a raccoon, a fox or a coyote in search of seasonal food such as eggs, ducklings or small mammals. As far as fish are concerned, almost 20 species visit the intertidal zone, a dozen of which frequent the intertidal marsh (Dutil and Fortin 1983). The cordgrass marsh is a veritable food factory. An estimated three or four tonnes of organic matter per hectare is exported annually by the action of the tides, to the benefit of estuarine communities. In certain parts of the United States, an estimated 75% of commercially harvested or sport fish species depend, at one time or another, on the intertidal marsh.
Diking cordgrass marshes for agricultural purposes (cases of diked marshes that are not yet converted to agriculture) has numerous impacts, including:
- the creation of a physical barrier that limits exchanges with the ambient environment through the action of the tides and decreases exports of the organic matter that contributes to the estuary’s food chain;
- the gradual transformation of the wetland into a dryer environment and the disappearance of typical marsh plants;
- the disappearance of small pools;
- the disappearance of feeding sites for many bird species;
- the disappearance of nesting sites for the American Black Duck;
- the disappearance of spawning sites for Gasterosteidae and feeding sites for many other species;
- the disappearance of nesting sites for at least two species of special concern: the Yellow Rail and the Short-eared Owl;
- a decreased regional capacity of marshes to purify water;
- a local decrease in biodiversity
Dozens of hectares of diked marshes (not converted to agriculture) whose original functions have been disturbed, are still found along the coastal region between Kamouraska and L’Isle-Verte (Argus Environmental Consultants Inc. 1998). Creation of openings in dikes, for example, can allow to recover some cordgrass marshes.
Setting up sills on drainage canals drying out spartina marshes
Diking for agricultural purposes in the maritime estuary during the last century had significant repercussions on cordgrass marshes on the periphery of aboiteaux (structures comprising a dike to prevent the intrusion of salt water in agricultural land reclaimed straight from cordgrass marshes, drainage canals and a structure for evacuating drainage water). In fact, in order for aboiteaux to efficiently drain agricultural land, farmers must extend drainage canals beyond the aboiteaux themselves, as far as remaining cordgrass marsh located in front of the aboiteau (and as far as neighbouring marshes). This practice lowers the water table over a distance of about 10 m on each side of the drainage canals (Bélair 1990) and changes the natural plant cover of the marsh, in certain places allowing only a few vascular species, such as Glasswort and Canada Sand-spurrey, to establish. The result is a decrease in local biodiversity.
Another adverse effect of drainage canals is the drying out of hundreds of nearby small pools and the consequent disappearance of Sea-grass and the many invertebrates associated with it. The drying out of these small water bodies also leads to a significant decrease in the preferred feeding sites of certain shorebirds, such as the Short-billed Dowitcher, the Red Knot, the Common Snipe, the Greater and Lesser Yellowlegs, (Sperry 1940; Bourn and Cottam 1950; Martin et al. 1951) and certain species of aquatic birds, such as the American Black Duck, the Great Blue Heron and the Black-crowned Night Heron, as well as important brood-rearing sites for the American Black Duck (Reed and Moisan 1971; Savard 1974). An examination of the ponds at low tide also reveals their importance for fish of the stickleback (Gasterosteidae) family, which spawn in those located in the Saltmeadow Cordgrass zone, in particular (Dutil and Fortin 1983).
Since aboiteaux spread over nearly 40 km of the maritime estuary’s south shore, between La Pocatière and L’Isle-Verte, and more than 40 drainage canals cross a large part of the remaining marsh (Argus Environmental Consultants Inc. 1998), agriculture can clearly have substantial impacts on the cordgrass marshes of this region.
Creation of openings within emergent freshwater marshes too densely colonized
Data on water levels in the St. Lawrence River during the last 80 years indicate cyclical changes in mean seasonal water levels that vary more or less in relation to the present level. Certain periods were marked by very low water levels, such as 1957 to 1966, while others were affected by very high levels, such as 1972 to 1981. Whether it is due to climate change or a change in the methods of flow regulation at the mouth of the Great Lakes, it nevertheless seems clear that we are inevitably headed for a drop in water levels in the fluvial section of the St. Lawrence. Major water-level fluctuations in the St. Lawrence have substantial impacts on both the fluvial and estuarine ecosystems. A period of high water levels over several years can rapidly deteriorate the riparian vegetation, particularly trees, and significantly erode banks, as has occurred on the Îles de la Paix and in the Rivière-du-Loup marsh.Furthermore, high water levels encourage the growth of submerged grass beds, to the detriment of emergent marshes. These grass beds are less favoured by waterfowl for brood-rearing. What’s more, biomass production in this type of environment is one third that of emergent marshes, some 100 000 metric tonnes compared to 300 000 metric tonnes. Lower biomass production means lower nutrient input to the aquatic habitats of the river and estuary, with all the repercussions this has on the various components of the food chain. Conversely, low levels encourage the development of emergent rather than submerged vegetation. The maintenance of low water levels for several years, however, can encourage the development of shallow marshes colonized by very dense emergent vegetation, which is unsuitable for birds and fish. For example, creation of openings within these marshes would improve their quality as brood-rearing sites for ducks.
Restoration of existing man-made ponds for waterfowl
The presence of water bodies in a habitat, whether it be on an island, a mainland, or even within a marsh, is an asset that can increase local biodiversity. Even in the case of the saltwater or brackish water environments of the maritime estuary, such ponds often allow the development of abundant aquatic vegetation vital to wildlife. This vegetation thus provides support for invertebrates, shelter for escaping predators, feeding sites, and even reproduction sites for some bird and fish species. These ponds are even more attractive when they provide promontories where birds can roost safely. Many places along the St. Lawrence River, like the embankments at Cacouna, the Cordgrass marshes at Rivière-du-Loup or ponds such as those within Cacouna’s harbour, would benefit either from the creation of ponds or the setting up of roosting structures for birds.
The lowest zone of the bottom portion of cordgrass marshes, which is flooded by every tide, is composed of mud, Fucus and sometimes Eelgrass. The latter species was practically eradicated from its range in the early 1930s by, it seems, a parasitic mushroom. It has recovered relatively well and in the 1990s was occupying an estimated 6000 ha area covering the estuary, gulf and Gaspé Peninsula (Lemieux and Lalumière 1995). The largest Eelgrass beds are located on Isle-verte in the maritime estuary (almost 1000 ha), and in Cascapédia Bay, in the Baie des Chaleurs (more than 1600 ha). This species prefers zones with weak currents and is generally found in shallow depressions where water collects at low tide. Despite the relatively rapid recovery of the species throughout its range, it appears that some areas with all the conditions required for the development of Eelgrass beds remain entirely devoid of the species.
Given the high value of this habitat for wildlife, restoration projects aimed at introducing the species in locations where it has not gained a foothold, despite their strong potential, are thus important. In fact, Eelgrass beds are known to play a key role for both fish and birds. In this regard, they occupy a strategic position in the intertidal zone, the lowest part of the foreshore, which is exposed at low tide but continuously flooded at high tide. Furthermore, it is interesting to note that in work conducted in James Bay by Benoit et al. (1992), these grass beds were shown to be visited by several species of waterfowl in search of food or simply a roosting site, such as the Brant, the Canada Goose, the American Black Duck, the Northern Pintail, the Lesser Scaup, the Greater Scaup, the Common Goldeneye, the Common Merganser, the Ruddy Duck and the White-winged Scoter. The presence of many invertebrates in Eelgrass beds is probably the reason. Additional studies in the estuary and the Gulf of St. Lawrence, as well as in the maritimes on the relationship between fish and Eelgrass beds indicate that these grass beds also serve as spawning sites for Lumpfish. They furthermore provide cover for escape and/or feeding for the American Smelt, sticklebacks, plaice and sculpins. They could also serve as escape cover or feeding sites for hakes, the Atlantic Tomcod, the Atlantic Herring, and young Atlantic Cod (Jean Morisset, Fisheries and Oceans Canada, personal communication).
Planting in rip-rap shores
A study conducted by Argus Environmental Consultants Inc. (1996a) indicates that nearly 700 km of shoreline between Dundee and Montmagny, the equivalent of 45% of the shoreline in this section of the river, were covered by rip-rap in recent decades. More than 50% of these human-modified shores are listed in the fluvial section between Dundee and Boucherville alone. Covering the banks of water bodies with rocks is a common technique used to stabilize areas that are particularly exposed and vulnerable to erosive agents. While efficient, it renders the environment unsuitable for vegetation to be reintroduced naturally. The coarseness of the materials used, combined with the process of erosion, prevents the formation of a substrate favourable to plant colonization (Argus Environmental Consultants Inc. 1998). Plants are essential to the survival of numerous species of fish, birds, mammals, amphibians and reptiles, for which natural riparian environments are preferred habitats.
Planting in disturbed dunes
Several dune environments on the Îles de la Madeleine have deteriorated over the years. Even though the disturbed sites are not all known and mapped, it is known that several sites, totalling about 10 km of shoreline, have serious erosion problems. The main factor contributing to erosion, once the vegetation has been destroyed by human activities, is the wind, which, in time, gradually thins the dune system. Once displaced, in some cases the sand can progressively enter adjacent lagoon environments, which are very important habitats for plants and wildlife. Furthermore, lacking vegetation to stabilize them, coastal dunes progressively thin, no longer accumulating enough sand to buffer wave energy during storms. Their disappearance thus leads to the flooding of adjacent lowlands and the possible contamination of groundwater (fresh water) with salt water.
Dunes also serve as screens that protect against the sanding-up of road infrastructure, homes, marshes and peat bogs, and forests. In addition to their protective role, dune environments are of great ecological interest. Coastal lungs of a sort, dunes conceal a fascinating biological richness. They provide habitat for a great variety of animal species: insects, mammals and birds. The Red Fox, the largest mammal on the Îles de la Madeleine, burrows in the islands’ dunes. Dune environments are occasionally also home to certain rare plant species or plant species at risk, such as Broom Crowberry (Corema conradii [Torrey]) and Sand Heather (Hudsonia tomentosa) (Attention FragÎles 2004).
Planting of trees and shrubs in anthropic green spaces (parks, rest areas, cycle paths…)
Over the years, several factors have contributed to the disappearance of the riparian zone in high marsh areas, such as encroachment, residential, industrial, road or port construction, and agricultural or forestry activities. It is difficult to estimate the proportion of riparian environments lost due to human modification in recent decades. We do know, however, that nearly 50% of the shoreline between Cornwall and Montmagny has been modified by human activities, compared to 28% of the entire St. Lawrence shoreline (Argus Environmental Consultants Inc. 1996a; Picard et al. 1997). The 28% (1400 km) of shoreline that has been modified along the St. Lawrence has no doubt markedly decreased its biodiversity. Close to 20 tree associations and a dozen shrub associations have consequently been completely eliminated from the most heavily urbanized sections. Local populations of close to 60 bird species have decreased in abundance or completely disappeared from the most developed regions. Certain fish species, notably the Yellow Perch, which lays eggs in wide ribbons that it suspends from branches of submerged shrubs, may have suffered particularly hard from the systematic disappearance of this type of cover along shorelines. Some 20 species of mammals that depend to some extent on riparian habitats may, to some degree, have also been affected by shoreline modification. Riparian habitats lost in this way are generally gone forever. The best we can do is to focus our restoration projects on habitats that have suffered less damage, such as riparian parks, wayside rest areas and bike paths.
Planting of trees and shrubs in agricultural lands (windbreaks, plantation along dikes)
More than 40% of the surface area of islands inventoried in the freshwater section of the St. Lawrence River between Montreal and Lake Saint-Pierre, the equivalent of some 4000 ha distributed over 25 islands, is agricultural (Lehoux et al. 2003). The largest surface area of agricultural land (70%) is found mainly in the Lake Saint-Pierre archipelago. On the mainland, agriculture also occupies large surface. We estimate that 10% of the shorelines immediately adjacent to the St. Lawrence River are cultivated (Picard et al. 1997).
Within agricultural lands, riparian zones are often limited or non-existent, with all the attendant repercussions: loss of local biodiversity and increased erosion, turbidity and contamination of nearby watercourses. Ammonia nitrogen, pesticides and certain heavy metals can be acutely or chronically toxic to aquatic organisms. In addition to phosphorous from over-fertilization, soil loss can also alter habitats by plugging up spawning beds. The contamination of the aquatic environment with herbicides used on the cultivated land, notably on islands in the Montreal–Lake Saint-Pierre section, is definitely significant, considering that some 1000 ha of these lands are flooded every two years.
Within the St. Lawrence estuary, 35% of cordgrass marshes in the St. Lawrence, the equivalent of some 1500 ha, were diked for agricultural purposes. The most dramatic losses were noted in the Kamouraska and La Pocatière areas. The diking of cordgrass marshes has seriously decreased the local biodiversity.
Even if it impossible to recuperate most of the cordgrass marshes already impacted by agriculture, we can try to partly restore the biodiversity by, at least, vegetate dikes which nowadays surround these agricultural lands.
Controlling of invasive plant species in wetlands
Wetland composition is quite likely different from what it was 20 to 30 years ago. Reed-grass, Purple Loosestrife, Speckled Alder, and Narrow-leaved and Broad-leaved Cattail are invasive species that have displaced species that were more beneficial to wildlife. An aerial survey conducted between Montreal and the Saint-François River (in the lake St. Pierre area) in 1997, thus reveals the presence of Purple Loosestrife on more than 1000 ha and that of Reed-grass on close to 100 ha (Gratton 1998). It is difficult to determine the surface areas these species occupied at the beginning of the 1980s. A study conducted in the Cap Tourmente National Wildlife Area shows, however, that between 1978 and 1994, the surface area of Purple Loosestrife has nearly increased fivefold, which is a good indication of this plant’s aggressiveness and indicates that it can rapidly become a problem (Lehoux et al. 1997). We can try to control those species.