The relative potential of chemical dissolution driven erosion in limestone bedrock rivers

Identifying how chemical and physical bedrock erosion processes combine is crucial in understanding
how upland landscapes evolve through bedrock channel incision. It is well established that abrasion by
saltating bedload is a critical process and there is widespread recognition that dissolution of soluble
minerals in carbonate bedrock rivers is highly effective, but there has not been work directly quantifying
the relative rates of dissolution and abrasion on bedrock incision. Using a combination of laboratory
abrasion mill and bedrock cube mass loss experiments, this study assesses the role of dissolution and
abrasion across a range of environmental conditions. Laboratory cube experiments were run at three
temperature points and three pHs, while field cubes were places at different immersion frequencies in
Trout Beck, to see how these factors would affect mass loss. Results showed no difference in mass loss
between temperature bands, while pH was a statistically significant indicator of mass loss. The field
results showed that immersion time was not the main control on mass loss, with wetting and drying cycles
and acidic peat runoff having more control. To compare the contributions of abrasion and dissolution on
carbonate rocks, an abrasion mill was used with variable pH solutions, with and without sediment load. In
the mill experiments, similar mass loss rates were found for the mill run at pH 7 with bedload (abrasiondriven) and pH 3 with no bedload (dissolution-driven). In addition, the mill experimental runs found
evidence that the addition of abrasive tools led to an increase in chemical dissolution rates, while the
addition of dissolution did not increase abrasion rates. This study has shown that in low pH carbonate
bedrock channels dissolution has the potential to produce similar mass loss as physical processes,
challenging the widely accepted paradigm that physical processes are the main control on bedrock
channel incision.