Evaluating solute dynamics and methane transformation in high-elevation Rocky Mountain fens using a transporter-transformer framework

Abstract

Peat wetlands at high latitudes have been a key focus for geochemical and hydrologic research due to their roles in carbon storage and greenhouse gas emissions. At the local scale, fens facilitate nutrient cycling and methane production via microbial processes. At the watershed scale, their distribution and hydrologic connectivity with surface waters can substantially influence water quality. However, the role of mid-latitude montane fens in moderating watershed functions remains understudied, despite their susceptibility to pronounced redox shifts driven by high-elevation seasonal dynamics.

We conducted a comprehensive analysis of (1) base cations, (2) biologically active, redox-sensitive nutrients and metals, and (3) carbon compounds in Rocky Mountain fens and surface waters along an elevational gradient in the East River watershed (Upper Gunnison Basin, Colorado, USA). Our aim was to evaluate whether fens act as passive transporters or active transformers of these solute groups. Fen base cation chemistry was largely indistinguishable from surface water and groundwater, suggesting transport-dominated behavior controlled by bedrock lithology. In contrast, anoxic conditions in fens produced distinct redox-sensitive nutrient signatures. A quasi-linear relationship between Cl-normalized NO₃²⁻ and PO₄³⁻ in high-elevation fens and surface waters suggests a possible mixing signal originating from nutrient-enriched fen waters and more dilute surface or groundwater sources. Stable isotope data for dissolved methane, unlike conservative cations, indicate active carbon transformation via methanogenesis, with limited microbial methane oxidation.

Collectively, our study offers an integrated assessment of the aqueous geochemistry of montane fens and their potential to modulate surface water chemistry across mid-latitude alpine watersheds.