The Peace–Athabasca Delta, covering over 5,000 km2, is one of the largest inland freshwater deltas in the world. Made up of two large central lakes and over 1,000 small lakes and wetlands,59 it is of international importance for waterbirds, bison, and fish.4 The delta's dynamics are driven largely by short– and long–term fluctuations in water levels, including occasional spring floods caused by ice jams60, 61 and summer open–water floods, with intervals of drying between flood events.62 Studies have found recent ice–jam and flood frequency to be within the range of historical variability and intervals.63-65 Nevertheless, although the delta has experienced several major ice–jam and open–water flooding episodes since the 1940s,66 the most recent occurring in 1997,60, 64 landscape analyses have found a significant overall drying trend from 1945 to 2001 in which wet communities declined in extent while dry communities increased.63, 67
Determining the cause of landscape change is difficult because the delta is constantly changing – driven by climate, hydrology, and deltaic processes, all of which are variable and influenced by natural and anthropogenic factors.63, 65, 66 Influences over the past 45 years include:60, 62, 66, 68-72
- a warmer, drier climate;
- the prevention of a natural change in the course of the Athabasca River in 1972 and the natural occurrence of a channel breakthrough in 1982;
- flow regulation, including the construction of the Bennett Dam on the Peace River in 1968, and subsequent weirs on outflow channels built in 1975–76 in response to concerns about changes in connected lake levels;
- land use changes and development, including forestry, agriculture, and oil sands extraction;
- growing water uses; and
- cultural changes.
A projected reduction in ice–jam flood frequency over the next century due to climate change may result in further drying,73 and additional upstream development may add additional stress to the delta's ecosystem.
Mamawi Creek, Peace–Athabasca Delta
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