WetlandWater Level Dynamics Associated with Recent Drought Conditions inSouthwestern Michigan

Thobaben, E.T. and S.K. Hamilton

Presented at the ASM at Snowbird (2000-08-02 to 2017-12-05 )

Most wetlands exhibit seasonal water level fluctuations as a result of winter and spring hydrologic inputs and summer drydown by evapotranspiration. In addition to the seasonal dynamics, climatic variation can produce marked interannual variability. We monitored water levels in a set of wetlands in southwestern Michigan that spans the range of hydrologic conditions common to the area. Measurements began in 1996 or 1998, and the region has experienced exceptionally dry conditions since 1998. The cumulative effects of multiple years of below-average precipitation and high summer evaporation rates explain the recent water level declines. On a seasonal time scale, water source information is a strong determinant of wetland water level fluctuations; more groundwater-fed wetlands exhibit less within-year variability than more precipitation-fed wetlands. Interannual water level variability is better explained by a measure of landscape position. Wetlands located farthest from the Kalamazoo River, the regional topographic low, have exhibited the most substantial water level decreases. Exceptionally high precipitation in May 2000 has partly alleviated some of the recent drought effects. A 43-year water level record for a local lake provides an historical context for the recent drydown event, demonstrating that local water levels in late 1999 were lower than they had been in over 30 years. On annual time scales, the existence of significant groundwater inputs confers hydrologic stability to some local wetland systems. However, landscape position is a much stronger predictor of which wetlands will dry down most during drought periods.

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