Challenged by a Climate Oscillation: Hydrology and Management of a Terminal Lake and Wetland Through the 20th Century

ABSTRACT About one‐quarter of global lands include closed watersheds that drain to terminal, endorheic or saline lakes, where evaporation provides the outflow. In southwestern Alberta, Canada, the terminal Frank Lake and associated wetlands support prolific waterfowl and other wildlife. Like other prairie potholes in the North American Great Plains, Frank Lake displayed extensive variation through the 20th Century. It rose and expanded through wet intervals in the early 1900s, and again around 1950, which prompted the excavation of drainage canals to reduce flooding of adjacent agricultural lands. The lake dried up with the 1930s drought, and again in the 1980s, prompting augmentation with municipal and agro‐industrial wastewater. This stabilised the lake level, but outflows in wet years contribute downstream contamination from the effluents. To characterise the system hydrology, we derived Frank Lake levels from historical reports, lake level monitoring, aerial photographs and observations. Lake levels were correlated with local temperature, precipitation and the integrative standardised precipitation evapotranspiration index (SPEI), including multiple‐year influences. The strongest correspondence was with the Pacific Decadal Oscillation (PDO) and a stepwise regression model with the 3‐year PDO and 2‐year SPEI accounted for 72% of the 2.5 m variation in the Frank Lake levels through the 20th century. The lake also rose in years with cold springtime weather when rain and snowmelt contributed surface runoff rather than infiltration due to the frozen ground. The management of this system was challenged by the alternating wet and dry cycles, which prompted the opposing interventions of drainage versus augmentation. Similar interventions have been implemented at other terminal lakes in western North America and elsewhere and their management should similarly recognise the natural variation that accompanies climate oscillation. Finally, with hydroclimatic responsivity, terminal lakes can provide sentinels to analyse cumulative hydrological consequences from human activities combined with climatic variation and change.