Insights into Allogenic and Autogenic Controls on the Nature and Distribution of Bog Islands in Patterned Peatlands

Large-scale allogenic and autogenic controls of bog genesis are generally well understood, with bogs forming where there is sufficient precipitation, and limited losses to evapotranspiration, groundwater recharge, and lateral runoff (allogenic) to maintain high water tables, which in turn allows for the slow decomposition of organic matter which yields soil hydraulic properties (autogenic) that also help maintain high water tables. Unknown is why small bog islands (1 to < 50,000 m²; <1 to ~ 150 m diameter) found within large fen complexes occur where they do. Were there allogenic factors such as a small depression or mounds in the post-glacial (clay surface) landscape that gave an advantage to early successional ecological processes helping keep, or shed, water sooner than the surrounding landscape? Within a large peatland complex in Manitoba, Canada, detailed measurements of 9 northern plateau bog islands of various sizes (606 m² to 5609 m²) were made in two orthogonal transects (fen through bog to fen) including: clay elevation, water table, hydraulic conductivity, bulk density, pH and electrical conductivity. Most results followed known differences between fens and bogs (e.g., domed water table and surface in bog, lower pH). Interestingly, and counter to our hypothesis, no difference was observed in the average clay elevation beneath fens vs. bogs; however, the terrain ruggedness index (TRI) was significantly different, with bogs having a TRI nearly, or more than, double the fens, suggesting that microtopography in the post-glacial landscape may have played an important allogenic role in encouraging early successional ecological processes.