Totally topography? Assessing the resilience of blanket peatlands to climate change using Winter’s concept of the ‘hydrologic landscape’ and the DigiBog model

Abstract:

In a landmark paper from 2000, T.C. Winter used the concept of ‘hydrological landscapes’ to consider how wetlands respond to climate change, in particular how they respond to episodes of climatic drying. He showed how hydro-geomorphological setting can have a critical role in wetland resilience. For example, wetlands dependent on groundwater seepage in mid-slope locations are more likely to lose key functions during periods of drought than are equivalent wetlands at the base of a slope. In essence, Winter’s model posits that wetland resilience to climate change is governed almost solely by their position in the landscape. We know, however, that peatlands can develop internal structures, such as zones of low-permeability peat, that alter their hydrological behaviour and potentially affect their resilience. For example, Lapen et al. (2005) found that lower-permeability peat formed at the edge of shallow peat domes within blanket bogs, reducing the rate at which water is lost to the margin, and allowing more peat to build up in the center of the dome. Here we use the DigiBog peatland development model to explore the relative importance of these external and internal controls on peatland resilience. We apply the model to real and hypothetical hillslopes under a range of climate forcings. We find that the model produces the right pattern of Holocene peatland development for a landscape in the Highlands of Scotland for which there are published peat thickness and basal-age data. The model shows too how particular landscape features, such as hollows, have different impacts on peatland resilience depending on their position relative to the hillslope divide, as predicted by Winter’s model. In addition, internal structures develop within the peat profile and these are sufficiently large to modify hydrological functioning and resilience. Nevertheless, the effect of these structures is often less important than landscape setting. Under sustained climatic drying blanket peatlands fragment, with peat eventually disappearing from the upper parts of hillslopes and sections with the steepest gradients, while in hollows at the base of hillslopes they may persist. Our simulations add new detail to coarser-scale climatic envelope models of blanket peatlands.