Carbonate bedrock channel erosion dynamics inhibit weathering effect on bedrock erodibility

The interplay of rock weathering and erosion processes controls rock erodibility throughout a bedrock channel cross-section. Existing models of these processes in bedrock river channels have been developed using observations largely from silicate lithologies, with rock erodibility increasing with height above the channel. The effects of the dissolution of soluble minerals in carbonate lithologies has been understudied. Here, we present a study of rock erodibility in two limestone bedrock channels in the North Pennines, UK. Patterns in rock erodibility were assessed using Schmidt hammer surveys conducted in 12 cross-sections and were analysed alongside calculations of bedrock inundation interval, observations of sediment transport from bedload impact plates and long-term estimates of limestone dissolution rates from environmental data and in-situ field observations. Results show that erosion via dissolution can result in similar patterns of rock erodibility observed in silicate channels where erosion outpaces weathering. Bedrock inundation interval is a key control on bedrock erodibility; where the channel margin is not regularly inundated by flow, weathering processes which weaken the rock are still present but may be locally offset by dissolution driven by soil seepage of low pH runoff which erodes weathered material. Long-term estimates of abrasion and dissolution rate are broadly equivalent at our study site further demonstrating the effectiveness of dissolution at eroding carbonate lithologies. Future studies of bedrock incision processes in carbonate landscapes should re-evaluate how mechanical erosion and dissolution are represented, and how sensitive the balance of these processes is to potential changes in inundation frequency and climate.