The role of dust on snow and other aeolian inputs in biogeochemical cycling in barren, alpine catchments
Poster Number:
185
Presenter/Primary Author:
Natalie Mladenov Many alpine areas are experiencing deglaciation and biogeochemical changes driven by temperature rise and changes in atmospheric deposition. It has been suggested that observed increases in nitrate export from high-elevation catchments in the Colorado Rocky Mountains are the result of warmer temperatures that are melting ice in glaciers and rock glaciers. Recent evidence also points to the importance of microbial processes, such as ammonification and nitrification, for the observed N export. Despite the high microbial activity measured in barren alpine soils, these environments are also severely carbon-limited, and it is unclear how the microbes obtain the carbon and energy necessary to sustain life. The C budget for alpine catchments is not well constrained, and mounting evidence suggests that allochthonous delivery of C and other nutrients may be extremely important.
Atmospheric aerosol transport is one vector for the delivery of C and other nutrients to alpine areas. Given phosphorus (P) limitation or co-limitation in many alpine areas, dust-derived and other atmospheric P inputs are also expected to be important. Using a long term dataset (2002 – 2010) of weekly atmospheric wet deposition and snowpack chemistry, we evaluated the magnitude of atmospheric deposition of C and nutrients to the Green Lake 4 catchment, an alpine site at Niwot Ridge in the Colorado Rocky Mountains. We found that atmospheric dissolved organic carbon (DOC) loadings ranged from 2 to 6 kg ha-1 yr-1and volume weighted mean DOC concentrations reached peaks as high at 6 to 10 mg L-1 every summer. In contrast, total dissolved phosphorus and calcium concentrations in wet deposition were highest in the spring when atmospheric dust inputs are typically highest. Interestingly, high DOC concentrations were also recorded during spring or late winter “dust-in-snow” events, which may reflect an association of dissolved organic matter with dust. Our C budget estimates for the Green Lake 4 catchment demonstate that wet and dry deposition represent an input of approximately 17 kg C kg ha-1 yr-1 that could be as high as 24 kg ha-1 yr-1 in high dust years. We also calculated that the export of P from GL4 (at 6 kg P yr-1) was much lower than the input of P from atmospheric deposition (34 kg P yr-1), suggesting that P is taken up in catchment soils and lakes. Atmospheric P inputs may therefore be important for meeting the P demand of heterotrophic microbial populations in the barren talus soils of Niwot Ridge.
The examination of atmospheric inputs presented here is the first step in evaluating a cascade of processes that may drive microbial nitrification, soil formation, and increased nitrate export from the Green Lake 4 catchment (Figure 1). We are also assessing the bioavailability of atmospheric inputs for soil microbial communities, evaluating the quantity and quality of water draining glaciers in the catchment, and refining our understanding heterotrophic and autotrophic microbial processes underway in the soils and snowpack in the Green Lake 4 catchment and other alpine catchments.
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