Relict charcoal hearth landscape and soil profile characteristics surrounding a mid-19th century Appalachian iron furnace

Across much of the Mid-Atlantic United States and Europe, relict charcoal hearths (RCHs) are a common landscape feature once used as a primary fuel source for iron smelting and quick-lime production. We investigated a landscape surrounding the Monroe Furnace in central Pennsylvania, which was in operation for around 17 years until 1846. This preliminary investigation explores landscape patterns of hearth placement in relation to the furnace and landscape position and resulting potential effect on soil moisture. We mapped RCHs using LiDAR derived hillshade models of varying aspects, elevation, and slope. We classified the different shapes of RCHs in relation to their geomorphic positions and modeled both a topographic and soil wetness index for selected hearths and off-hearth locations nearby. Two hearths were sampled in the field and their morphology and soil properties investigated.

Hearths that were constructed on flatter slope gradients are seemingly more circular in shape and have more equal axes whereas steep slopes have a more oval shape elongated in one axis with the slope direction. More circular hearths are on or near flatter hillslope positions (such as on summits or shoulders) whereas eye-like shaped hearths are on steeper hillslope positions (like backslopes).  Based on initial topographic wetness index data, hearths are not acting as sinks for flow but instead often cause water to flow around them leading to drier conditions within RCHs.

Trenches alongside the slope orthogonal direction of the two sampled RCHs show a single layered stratigraphy, i.e. both sides had only one continuous technogenic, charcoal rich layer. The downslope half of both sites had generally higher contents of macroscopic charcoal pieces as well as buried colluvial- and buried fossilized A-horizons underlying the charcoal rich layer. Both sites are not perfectly levelled, but slightly sloped. Buried B- and colluvial horizons show signs of heat induced reddening of iron oxides on the top few centimeters. Preliminary results suggest significant differences in soil chemical and physical properties of the technogenic layer in comparison to the adjacent forest soils.