Stream channels in peatlands: The role of biological processes in controlling channel form

While some aspects of peatlands are well studied, understanding of the hydrology and geomorphology of the associated surface drainage networks is quite limited. This paper attempts to describe some of the basic attributes of stream channels in peatlands, and asks whether the form and the mechanisms behind development represent a significant departure from self-forming alluvial streams. We use three approaches to better understand these poorly studied systems: an examination of the geomorphology of Allequash Creek, Wisconsin; a survey of aerial photographs of similar peatland–stream complexes in northern Wisconsin; and a review of the existing literature on peat-influenced and wetland channels. Distinct features of Allequash Creek and other Wisconsin streams in peatlands include absence of mineral substrates, low width/depth ratio, presence of lateral pool-like structures along the channel margin, long straight reaches, and acute-angle bends. Further, the lateral location of the thalweg was apparently independent of planform or cross-sectional form, and no-flow zones often occurred along both edges of channel cross-sections. Collectively, these features represent a distinct departure from characteristic forms of alluvial channels. Deep peat samples from Allequash Creek and aerial photographs from other sites indicate that these streams represent remnant lake systems whose basins filled with peat. Thus, we suggest that the processes responsible for channel form in these low energy peatland systems are largely governed by groundwater hydrology and the biology of peat accumulation and decomposition. In this manner, biological forces — not just physical drivers such as channel discharge and sediment supply — are central to the understanding of stream geomorphology in peatlands.