Abstract
Rule curves dictating target water levels for management have been implemented in several water bodies in North America over the last 70 years or more. Anthropogenic alterations of water levels are known to affect several components of wetland ecosystems. Evaluating the influence of rule curves on biological components with simple performance indicators could help harmonize water level management with wetland integrity. We assessed the potential of using the probability of common loon nest viability as a performance indicator of long-term impacts of rule curves on nesting wetland birds. We analyzed the outcome of rule curves on the probability of loon nest viability in Rainy Lake and Namakan Reservoir, 2 regulated water bodies located along the Ontario-Minnesota border. The analysis was focused on 4 hydrological time series between 1950 and 2013: 2 sets of time series simulating rule curves used to manage the water bodies in the past decades (referred to as the 1970RC and 2000RC), one of the historical measured water levels, and one of computed natural water levels. The probability of loon nest viability under the 1970RC was 2× higher than under natural conditions in both water bodies. The probability was also 2× higher under the 2000RC than under the 1970RC in the Namakan Reservoir but not in Rainy Lake. The rule curves generally improved conditions for nesting loons in both water bodies. The presented performance indicator can be used to evaluate future rule curves before they are implemented in the Rainy-Namakan or other similar systems.
Highlights
Water levels (WL) in lakes and reservoirs naturally fluctuate according to hydrology and climate
We analyzed the outcome of rule curves on the probability of loon nest viability in Rainy Lake and Namakan Reservoir, 2 regulated water bodies located along the Ontario-Minnesota border
Predicted Probability of Loon Nest Viability (PLNV) and observed percentages of successful nests had similar trends between 2004 and 2006. This suggests that the model we developed was able to predict the relative differences in PLNV among year based on WL variations
Summary
Water levels (WL) in lakes and reservoirs naturally fluctuate according to hydrology and climate. Multiple characteristics of a WL regime, such as its amplitude, timing, and rate of variation, are often impacted by WL regulation [5], thereby resulting in changes to the biological aspects of the ecosystem, such as its suitability as a fish spawning habitat [7] or the distribution of wetlands [8]. Rule curves (RC) are guidelines dictating target WL of a managed water body for different times of year. They are used to determine the timing and magnitude of water supply and releases according to a management plan. Given the large number of species present in wetland ecosystems, evaluating the impacts of RCs on all species is unrealistic. One often focuses on a smaller selection of key species to develop performance indicators as a practical means to assess RC impacts [11] [12] [13]
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