Using diatoms and physical and chemical parameters to monitor cow-pasture impact in peat cores from mountain mires

Peatlands play a crucial role in carbon (C) sequestration and biodiversity conservation. However, these environments are highly vulnerable, and Europe has lost >60 % of its peatland habitat in recent decades. Cattle grazing and trampling contribute to peatland degradation, which generally result in a shift from moss-dominated vegetation to vascular plants and in lower C sequestration rates. Overgrazing poses also a significant threat to habitat integrity and biodiversity, especially in the Alpine area, where close-to-pristine mires with high ecological integrity are becoming extremely rare. Thus, a more in depth understanding of how cattle grazing and trampling are threatening Alpine mires is strongly needed for a sustainable management and conservation of these habitats. The objective of this study was to examine the impact of grazing on the physical, chemical, and biological characteristics of peat, with a focus on diatoms. To answer such a question, seven 50-cm deep cores were collected from mires located in the Adamello-Brenta Nature Park (North of Italy) along a grazing-induced disturbance gradient. Results indicated that grazing primarily affected at least the upper 15 cm of the peat, resulting in increased density and reduced water content, due to compaction, and lower C-to‑nitrogen ratio, possibly caused by both cow manure inputs and increased peat mineralization. Moreover, almost 200 diatom taxa were recorded across the 7 cores, with several of them falling under threat categories in the Red List for central Europe. The higher percentage of eutraphentic species in highly-grazed areas was related to the increase in nutrients caused by cattle manure. Finally, intense grazing increased the share of taxa that are more likely to survive in environments with unstable water availability (= aerial species). We showed that diatom data, supported by physical and chemical parameters, can be a refined tool to inform mire protection and rehabilitation.