Coastal Wetlands in Manitoba

Transcription

1 Herbert 1 Coastal Wetlands in Manitoba 1.0: Introduction: Among the largest in North America, the coastal wetlands of Lake Winnipeg are vast, covering an estimated 1404 km 2 (see Notes ). However, studies of these wetlands remain somewhat neglected, and as such the value of them to the overall quality of Lake Winnipeg is unknown by many, and at best underestimated by others. As a result of this lack of knowledge, a number of strains have been placed on the wetlands over the last one hundred years. Addressing these stressors is now of great importance, as the effects that degraded coastal wetlands are having on the overall integrity of Lake Winnipeg are quickly becoming noticeable. 2.0: History and Background: As a result of the enormous watershed that is the Lake Winnipeg basin, Manitoba contains an extremely large number of wetland areas. Coastal wetlands in particular provide a range of economic and environmental values, including hay production, spawning and breeding habitats for fish, staging and breeding habitats for waterfowl, shoreline stabilization, flood and drought protection, carbon sequestration, water purification, and groundwater replenishment. They also serve as important habitats for a range of species, and are of important cultural value to aboriginal peoples. Wetlands act to filter toxins and nutrients from water systems. This is an especially important factor in areas such as the Lake Winnipeg basin, where agriculture is very prevalent. Approximately 87-88% of nitrogen and phosphorous may be absorbed by the emergent vegetation in wetlands (MBEN 2009). This prevents widespread algal blooms, slows erosion, and prevents sediment from clogging waterways. The dominant type of wetlands around Lake Winnipeg are riverine, amounting to an area of approximately ha (see Notes ). Of these riverine coastal wetlands, the Netley-Libau marsh, located at the southern end of Lake Winnipeg, is the largest at approximately ha, making it arguably the largest coastal wetland in North America (see Notes). In particular, the northern areas of Netley-Libau have undergone drastic change over the last one hundred years due to a number of factors. Over the period of , significant changes in Netley-Libau marsh have taken place. The erosion of uplands separating adjoining water bodies has resulted in the amalgamation and expansion of many of the bays and ponds of the marsh. The loss of land to water expansion in wetlands leads to a decrease in emergent vegetation, and ultimately a decrease in overall biodiversity. Currently, 51% of the total marsh is open water, compared with Netley-Libau 35% in 1979 (Grosshans et al. 2004). While the dominant type of emergent vegetation in Netley-Libau is cottontail, other plant species such as hard and soft-

2 Herbert 2 stemmed bulrushes have declined ten-fold in abundance (ibid). However, plant communities in drier sites of the marsh have remained relatively unchanged. 3.0: Problems: The major problem in Netley-Libau marsh is the ever-growing open water surface and the loss of available uplands for emergent vegetation. This loss is likely the result of a number of stressors working in combination with each other. Among the major stressors on the marsh are increasing urbanization in areas surrounding it, agriculture in surrounding areas, exotic and invasive species, river dredging (or lack thereof), and most importantly, altered hydrology. Since the 1930 s and 40 s there have been few dry periods on both the marsh and Lake Winnipeg (see Notes ). As a result, there has been a slow but consistent loss of vegetation in the coastal wetland areas. Dry periods are an essential part of the life cycle of a wetland, as they provide upland areas that allow new emergent vegetation to establish and grow. In addition to the few dry periods over the last one hundred years, the current management of Lake Winnipeg water levels for hydroelectric power production keeps the water levels of Lake Winnipeg (and therefore the wetland areas surrounding it) artificially high. This further prevents low water levels from occurring on the wetlands, thereby contributing to further loss of vegetation via the erosion and submersion of upland areas. As a result, the erosion of upland areas has caused the joining of lakes with areas of the wetland to create a vast shallow lake. Also, high nutrient loads, combined with the arrival of invasive species such as the common carp contribute to enhanced algal growth and therefore the loss of submerged vegetation. This in turn results in the destabilization of bottom sediments and increased wind-wave action, furthering erosion. In their discussion, Goldsborough and Wrubleski identified four main factors as causes of death in Netley marsh. The first was the dredging of what is known as the Netley Cut in This was essentially a small channel cut into the upland ridge separating Netley-Libau marsh from the Red River that connected the two bodies of water. The original intent of the cut was to reduce flood damage caused by the Red River by using the adjacent wetlands as a large drainage area. However, it was soon evident that the cut was very prone to erosion, and it began to widen somewhat rapidly. Efforts were made to close the gap, but to no avail. Since then, the size of the channel has changed drastically, and it is now wider than the river itself. The river now flows into the Netley-Libau wetlands, bringing with it and depositing sediments, as well as eroding upland areas. As a result, it is harder for vegetation to survive and reproduce. The second factor identified by Goldsborough and Wrubleski is that there have been relatively few periods of low water over the last one hundred years, and especially since 1975, when Manitoba Hydro began artificially regulating Lake Winnipeg water levels for the purposes of power generation. Variable water levels are essential for the health and continued survival of any wetland. Periods of low water are needed for vegetation to establish itself and for other forms of disturbance such as fire to have their effect. This is not to say that raised water

3 Herbert 3 levels are entirely bad for wetlands, simply that there needs to be a balance between high and low water levels in order for the wetland to remain healthy and functional. In order for the restoration of vegetation in Netley-Libau marsh, Goldsborough and Wrubleski recommend a decrease in water levels of approximately two feet for two years in order to allow for the re-establishment of emergent vegetation. Goldsborough and Wrubleski claim that this has been attempted and shown to be effective in similar studies done at Delta Marsh. The third factor identified was the cessation of river dredging in River dredging originally took place in order to facilitate the navigation of large ships into Lake Winnipeg, as the mouth of the Red River on Lake Winnipeg was relatively shallow, and impeded larger vessels from passage. As a result of the stoppage of dredging in 1999, the channels once again became shallower. However, when coupled with the Netley Cut, the reduced drainage of the river into Lake Winnipeg caused the Red River to back up, and actually increased the flows of water from the Red into Netley-Libau marsh, thus facilitating further erosion and sediment deposition. The final factor identified was the current efforts in Red River flood mitigation. Specifically, Goldsborough and Wrubleski identified the artificial cutting or breaking of ice on the river as a means of increasing drainage to reduce potential flood damage. However, the cutting of ice increases the volume of water that moves through the Netley Cut, further increasing the degradation of the marsh. 4.0: Solutions: In order to combat the further degradation of coastal wetlands surrounding Lake Winnipeg, there are a number of options to consider. First and foremost is that periodic lower water levels need to be created, either naturally or artificially to restore and maintain the natural cycles of the wetlands. The easiest way to accomplish this would be for Manitoba Hydro to reduce its artificial regulation of Lake Winnipeg water levels. However, this is easier said than done given the need for hydroelectric power generated by Manitoba Hydro, both domestically and internationally. Until better technology is developed in the way of long-term energy storage, other methods of creating low water levels need to be explored. One such approach could be to reattempt filling in Netley Cut. This would obviously be a very expensive endeavour, and may not be feasible economically. However, rather than addressing high water levels at the location where they are most visible, such as Netley-Libau marsh, flows into the Red River and its tributaries could be reduced at their sources. This would involve increased local water retention and treatment from agricultural and urban sources. If there were a greater retention of water on the landscape, then the need for the use of coastal wetlands as floodwater storage would be reduced. If less runoff goes directly into the river, but is instead gradually released over time, water levels in Netley-Libau may be reduced enough so that vegetation can re-emerge. A second step in reducing coastal wetland degradation lies in restricting forms of shoreline development that degrades coastal wetlands. Wetlands are

4 Herbert 4 often seen as cheap real estate on which to develop, as there is little preparation work that needs to be done prior to development, such as land clearing. Instead, higher economic value needs to be placed on wetlands so that development is not so quick to utilize them. This can be accomplished by the provision of funding incentives by the provincial government for farmers and developers to institute best management practices and/or set aside wetlands for preservation. Alongside these incentives, those involved in commercial fishing could also be offered similar incentives to harvest common carp over other native species, thereby reducing the impact of carp on the state of the coastal wetlands. In order to determine if any attempts at reducing the damage to coastal wetlands is effective, more research and mapping of coastal wetlands is of the utmost importance. Currently, there is very little information available, both historically as well as on the year-to-year changes in the coastal wetlands surrounding Lake Winnipeg. Yearly mapping, coupled with further investigation of the factors suspected to be contributing to vegetation decline must be undertaken in a greater capacity. There also needs to be increased future monitoring of water levels, quality, and vegetation. At the same time, archival research is recommended by Goldsborough and Wrubleski in order to compile past literature on Netley-Libau marsh to create a thorough bibliography on the subject. Lastly, public education and cooperation between urban and rural residents, as well as all levels of government is needed if any headway is to be made in addressing these problems. This is often the most difficult segment to gauge success in, as there are so many interests at stake. Ultimately, foresight and willingness to compromise are key criteria needed to ensure a favourable outcome. 5.0: Conclusion: The state of coastal wetlands surrounding Lake Winnipeg is at best still unknown. Although areas in the southern basin of the lake are fairly well known and increasingly well studied, the state of coastal wetlands in northern regions of the lake are for the most part unknown. While more attention to the coastal wetlands of the southern areas is definitely needed, it is of prime importance that coastal wetlands in the north are studied to the same degree as those in the south. Simply because there is a greater segment of the population in the south is not a justifiable reason to focus research and management resources disproportionately. Each coastal wetland is a segment of a dynamic system that fits into the larger Lake Winnipeg watershed. Solving the problems faced by the watershed will not come from solely attending to areas that we deem to be important, but rather from addressing the situation as a whole.

5 Herbert 5 Notes: 1. Some notes were gathered from a March 19 th, 2011 lecture by Drs. Dale Wrubleski and Gordon Goldsborough on coastal wetlands of Lake Winnipeg given at the University of Winnipeg as part of a conference discussing Lake Winnipeg water regulation. 2. Additional notes were gathered from a powerpoint presentation by Drs. Wrubleski and Goldsborough given in conjunction with their lecture. References/Works Cited Grosshans R. Wrubleski D. Goldsborough G Changes in the Emergent Plant Community of Netley-Libau Marsh between 1979 and Delta Marsh Field Station (University of Manitoba) Occasional Publication No. 4. November [MBEN] Manitoba Eco-Network Wetlands in Manitoba. [Water Tabloid Newsletter]. Winnipeg, (MB): [cited 2011 April 20]. [MBEN] Manitoba Eco-Network Around the Lake Winnipeg Watershed. [Water Tabloid Newsletter]. Winnipeg, (MB): [cited 2011 April 20].