Stream and river networks represent the largest biogeochemical nexus between the continents, ocean and atmosphere. They metabolize dissolved organic carbon (DOC), which is one of the largest pools of reduced carbon (C) on Earth and a major intermediary to the global C cycle. DOC metabolism in stream and river networks remains poorly understood, which is particularly true for high-mountain streams. This is surprising given the increasing recognition that high-mountain streams are important for large-scale biogeochemistry. At the same time, high-mountain ecosystems are highly vulnerable to climate change, of which the most iconic consequence is the worldwide shrinkage of glaciers. The extreme 2022 summer has highlighted the unprecedented melting of mountain glaciers in the Swiss Alps and elsewhere. The impacts of glacier runoff on downstream network hydrology and DOC metabolism remain elusive to date.
The overall objective of C-NET_2 is to study DOC metabolism in high-mountain stream networks, with a focus on various glacier types (e.g., clean-ice glaciers versus rock glaciers ) that nurture both downstream hydrology and the organic C pool. C-NET_2 will center on the hydrological dynamics of stream networks and network-scale DOC removal and mineralization, with a focus on hyporheic processes. To this end, we propose to integrate the use of distributed sensors, field surveys and experiments, as well as modelling. This multi-faceted and interdisciplinary approach is imperative to move beyond the typical scale of a stream reach to encompass hydrological and biogeochemical processes at the scale of entire networks. C-NET_2 will focus on two glacierized catchments in the Swiss Alps.
Expected results and impact. C-NET_2 will advance stream biogeochemistry along the following lines: (a) It will increase our mechanistic understanding on the links between the hydrological dynamics (i.e., expansion and contraction) of stream networks and network-scale C cycling. (b) It will disclose the role of different mountain glacier types for downstream biogeochemistry. (c) It will unravel the relevance of hyporheic processes for DOC metabolism at network-scale - a critical step forward towards elucidating the role of stream ecosystems for large-scale C cycling. Collectively, these results will lead to a better appreciation of the downstream impacts of mountain glaciers for stream C cycling.