Wetland distribution and conversion in Southern Ontario

Abstract

Concern over the ongoing conversion of wetlands is growing. Information on the location, extent, and quality of remaining wetlands is needed to assist in developing future policy and management actions aimed at retaining wetland values. In addition, knowledge of wetland conversion rates and trends is important in assessing the current status of wetlands. To date, the availability of such information has been fragmentary and inconsistent. This study used available soil and land use data, supplemented by other information, to map southern Ontario wetlands and wetland conversion on 125 map sheets at a scale of 1:50 000. Analysis has revealed that before 1800, 2.38 million hectares (ha) of wetland were widely distributed throughout southern Ontario. By 1982, 0.93 million ha remained and were more prevalent in the northern parts of the study area. The original wetland area had been reduced by 61% overall, and by 68% south of the Precambrian Shield. Wetland decline since settlement has been most severe in southwestern Ontario where over 90% of the original wetlands have been converted to other uses. Areas in the Niagara Peninsula, along western Lake Ontario and in eastern Ontario have less than 20% of the original wetland area. From 1967 to 1982, 5.2% of the wetland area south of the Precambrian Shield was converted to other land uses. For the same period, some previously converted wetlands were allowed to revert to immature forest and scrubland, reducing the net decline of wetland area in 1982 to 1.8% of the 1967 wetland area. Kent County experienced the greatest reduction in wetland area between 1967 and 1982 with 26% of the 1967 wetland area being converted to other land uses. Conversion to agriculture accounted for most of the recent losses in all areas. Cottage development was a significant factor in the loss of lakeshore wetlands in central Ontario.