Conservation Atlas of Wetlands in the St. Lawrence Valley (1993-1994)

The main purpose of the Conservation Atlas of Wetlands is to develop a portrait of the wetlands of the St. Lawrence Valley using innovative mapping methods in order to favor bird conservation by helping land managers to make decisions about land use and bird habitat conservation. Another objective was to develop methods needed to allow a monitoring of the St. Lawrence Valley wetlands and make a link to a potential national mapping project of that type as an indicator on environment quality in Canada.

The Atlas is considered a large-scale project because of the area covered, the great variability in the area’s characteristics and the various types of wetlands encountered. Using Canadian RADARSAT satellite images, along with other sources of information available (e.g., digital hydrological and hypsometric data) and data from Landsat-TM images, the mapping has required certain adjustments and the use of innovative methods. Achieving the objectives set at the start of the project in the spring of 1999 has resulted in the following products:

• A global mosaic of the distribution of wetlands in southern Québec
• A 1:50 000 scale map showing the location of wetlands in each of the area’s regional county municipalities (RCMs)
• Descriptive statistics on wetlands' characteristics (number, category, average area, etc.) to complement the maps,
• Information and links to to sites that promote wetland conservation.

In the last few years, the Canadian Wildlife Service of Environment Canada has been carrying out a project to map natural habitats using Landsat-TM imagery. This mapping has been used to apply methods for analysing landscape features in a large area of southern Québec in order to ensure adequate habitat protection and development. As a follow-up to the project, the CWS decided to produce an Atlas of wetlands in the St. Lawrence Valley. The CWS’s work has shown that multispectral imagery does not provide all the information needed to differentiate between some wetlands. For example, forested wetlands and flooded forests can be confused with other forested areas. To increase the accuracy of wetland identification, it was decided that radar imagery should be incorporated into the project. Research carried out in Canada and abroad is attempting to show that this imagery, when acquired at the right time, can help to differentiate wetlands and map agricultural land and grasslands.

Mapping and appropriate wetland monitoring require remote sensing tools that are independent of cloud cover and sensitive to soil humidity. Equipped with SAR (Synthetic Aperture Radar) captors capable of providing high-resolution images unaffected by daytime and nighttime weather conditions, the Canadian RADARSAT satellite is able to map the exact boundaries of wetlands.

Phase I: image acquisition

Image acquisition took place between April 27, 1999 and June 11, 1999. The Data Acquisition Division of the Canada Centre for Remote Sensing established an acquisition plan based on various criteria, i.e., image acquisition had to take place in the ascending mode to eliminate the dew effect, it had to be carried out in a short time period (after flooding but before the dry spells of summer) and it had to offer the possibility of producing a mosaic for a large portion of the territory. Thirty-four images were finally acquired, 28 in fine mode and 6 in standard mode.

Following this acquisition, a partnership agreement between Environment Canada, the Canadian Space Agency and the Geography Department of the University of Montréal was signed. In the project’s first phase, Landsat-TM images were used to mask certain soil types, which resulted in the production of a mosaic of RADARSAT images of southern Québec and preliminary image classification results. Although the product was generally satisfactory, it was felt that the mosaic image and the classified RADARSAT images could be improved.

Phase II: a classification method development

The CWS thus developed a new classification method that combines several formats of RADARSAT images (texture, homogeneity and contrast indices) with the decorrelated Landsat-TM image and a digital elevation model. Several hundreds ground control points were used as basic information to guide tree analysis. The preliminary results at test sites proved the method’s efficiency for these types of images. The wetlands of 68 RCMs in the St. Lawrence Valley could thus be classified.

Phase III: final validation of maps

Another phase of our work was the final validation of the Atlas maps. This was made possible through extensive consultation with Quebec wetlands experts (see the list of financial and technical partners in the Acknowledgements section). In all, over 60 hours of consultation took place with more than 30 experts in the various regions of Southern Québec. This final phase of the mapping project was dubbed “Operation Open House.”

A complete series of 1:50 000 scale maps, drawn up according to the boundaries of the topographical maps (UTM co-ordinates), was printed out so that the various experts could examine them and, if necessary, signal any errors and plot the required corrections. It should be noted that there are two possible sources of discrepancies. Errors may have occurred during the image classification process, or may be a result of changes to wetlands since the two series of satellite images used for this project were taken (1993-1994 and 1999). We have assigned a specific code in the map legend for areas where such changes have occurred so that, until a second map is produced in the coming years, the reader can get an idea of the dynamics of these habitats and the major areas of change (disappearance or degradation of wetlands) resulting from various human activities.

Phase IV: towards interactivity

A fourth phase now allows to produce a map for the sector of their choice through the interactive mapping procedure and improve the database by adding supplementary information.

Citation

Bélanger, L., M. Grenier, 2003. Atlas de conservation des terres humides. Environnement Canada, Service canadien de la faune, région du Québec