Collapse of the Onrus palmiet peatland: understanding anthropogenic impact interactions driving wetland degradation at landscape scale

This paper documents the origin and dynamics of a palmiet peatland in the Western Cape Province, South Africa, in the context of landscape development since the Last Glacial Maximum. This timeframe incorporates a key period of geomorphological development leading up to and including the Holocene. From this contextual foundation, the paper analyses anthropogenic impact interactions that led to peatland degradation and continue to impede natural recovery, providing a framework for a broader, transferable approach to understanding recent drivers of riverine landscape change. Peatland degradation has been driven by a combination of on-site alteration of wetland structure and function through agricultural drains, road crossings and alien vegetation invasion, and alteration of the hydrological regime of the Onrus River by De Bos Dam. The development of full longitudinal sediment connectivity within a previously unchanneled valley bottom, observed at Onrus and other palmiet peatlands, is a potential indicator that regional riverine landscape behaviour has transitioned beyond the range of variability characteristic of the Holocene, and a new, highly transformed landscape is emerging. In practical terms, the collapse of the peatland is an early warning that anthropogenic development is exceeding the capacity of the landscape to provide resources, and high-level, coordinated management intervention is needed.