GEOMORPHOLOGY AND WATERSHED SOIL TEXTURE INFLUENCES PEAT DEVELOPMENT, WATER CHEMISTRY, AND HYDROPERIOD IN WETLANDS OF WESTERN WISCONSIN’S CHIPPEWA MORAINE

Our study examines the effect that differences in wetland basin geomorphology and watershed soil texture have on soil development, water chemistry, and hydroperiod within the Chippewa Moraine of western Wisconsin. The Chippewa Moraine is a forested landscape of steep hummocks, kettles, and ice-walled lake plains formed between 18,000 and 15,000 years ago when the Chippewa Lobe of the Laurentide Ice Sheet reached its southernmost extent. The underlying glacial till in the study area tends to form low permeability soils that retain surface water. Within the moraine forest is a large variation in kettle size, from areas of numerous small kettles that hold ephemeral wetlands to areas of large kettles with permanent lakes.

We examined wetland dimensions, catchment size, and parent material in 57 wetlands scattered along a gradient from a high density of small ephemeral ponds to a mixture of small ephemeral and large permanent wetlands and lakes. We also measured peat depth, typical soil profiles, and water chemistry and hydroperiod attributes. Many of the ephemeral wetlands were too small to be mapped in the USDA Soil Survey. Geomorphological factors such as wetland and catchment size are more strongly related to water chemistry, hydrology, and peat development than they are to watershed soil texture. Wetlands with larger catchments had larger seasonal hydroperiod ranges. Wetlands that were larger in size had larger peat accumulations and correspondingly lower specific conductivities, most likely due to more stable (non-ephemeral) hydroperiods. The lack of relationship with wetland soil characteristics may be due to the short time of post-glacial soil and wetland development, and has implications for lake and wetland development within other glacial landscapes.