Estimating rates of wetland loss using power-law functions

Estimates of rates of wetland loss are important for understanding whether wetland policies meet their objectives. In Alberta, a no-net-area loss interim wetland policy was introduced in 1993. We tested the effectiveness of this interim wetland policy. A historical wetland inventory was established by generating a wetland inventory using digital topographic analysis and calculating a wetland-area vs. wetland-frequency power-law function from these data. Permanent wetland loss (topographic depression no longer exists) was calculated as the deviation from the historical wetland-inventory power-law function (representing the pre-settlement wetland inventory) and was estimated at 32.8% in number and 2.10% in area, with uncertainty estimates well below 1%. Temporary wetland loss (topographic depression remains on the landscape) was calculated as the difference between the historical wetland inventory and a time series of contemporary wetland inventories mapped from aerial photographs. Results indicate that as of 1993, 49.4% of the number of wetlands were temporarily lost (56.6% of wetland area), which increased in 2011 to 56.8% (68.0% of wetland area), with uncertainty estimates well below 1%. From 1993 to 2011, we estimated a rate of loss of 0.63% in wetland area/year. Wetland loss continued despite the introduction of the no-net-area-loss policy in 1993.