Stratigraphy and genesis of the Lake Sixteen peatland, northern Michigan

Abstract

The Lake Sixteen peatland is a 400-ha mire consisting principally of low-shrub (Chamaedaphne) bog and lesser areas of tree-covered (Picea – Larix) bog and sedge fen adjacent to a 55-ha alkaline lake. The sediments consist of the following superimposed deposits: gyttja, sedge peat, and Sphagnum–ericad–sedge peat. Near the edges of the peatland, highly humified, sometimes woody peat is present as the basal layer instead of gyttja. Radiocarbon-dated pollen stratigraphies from the lake and four sites in the peatland have elucidated the temporal relationships of the various sediment units and the developmental history of the peatland. During the mid-Holocene, probably in response to a change to cooler, moister climate, early Lake Sixteen underwent an expansion resulting in the deposition of gyttja over an increasingly larger area. About 3000 years BP, a sedge fen developed on the edge of the lake. Low-shrub bog replaced the sedge vegetation as the fen mat expanded into the lake. Swamping of bordering forests also allowed expansion of bog vegetation outward from the basin. Hydrological changes accompanying peat accumulation probably promoted vegetational changes within the peatland and the centrifugal spread of bog vegetation through swamping.