Biogeochemical signals in the outflow of glaciers and rock glaciers in the American West

Background/Question/Methods

Alpine glaciers in the American West are projected to be non-existent within the next 100 years. A better understanding of what the loss of these frozen masses will mean for mountain ecosystems is needed. Rock glaciers, which are heterogeneous periglacial masses of ice and lithic material that move through plastic deformation, are far more abundant than ice glaciers in the alpine regions of the western United States. However, there is little research on the biological and chemical signal of rock glaciers relative to ice glaciers. In particular, differences that may exist between microbial communities at their outflow may have the potential to alter reactive elements entering the ecosystem. In our comparative study of outflow chemistry and biology from 16 pairs of glaciers and rock glaciers across the Cascades, Sierra Nevada, and Rocky Mountains, We hypothesized that; 1. Physical and chemical bedrock weathering products will be greater from rock glaciers than ice glaciers, making more micronutrients available to the downstream freshwater ecosystem. 2. Differences in microbial communities between glaciers and rock glaciers may result in differential processing of reactive elements with the potential to affect the downstream ecosystem. Metals, nutrients, DOC, major ions, qPCR of the amoA gene and fluorescence scans of the CDOM were analyzed. 

Results/Conclusions

Preliminary results from samples collected in the late summer and fall of 2013 show significant differences in outflow chemistry between ice and rock glaciers. Although there was substantial variability, rock glaciers had higher temperatures, pH, silica, total dissolved nitrogen and metal ion content, and electrical conductivities than their respective study-paired ice glaciers. DOC values were low for both ice and rock glaciers, while structure of the dissolved organic matter, as observed in excitation-emission matrices, varied between paired rock-ice glacier sites, suggestive of microbial sourcing in ice glaciers , while DOM in rock glaciers was more representative of both microbial and terrestrially-derived sourcing. Ammonium levels were near or at detection limit for both types of features, however NO₃^- values varied between paired sites and appeared to be related to regional atmospheric depositional loads. Our preliminary analysis suggests meltwater from glaciers and rock glaciers are actively contributing metals and nutrients to downstream waters, and active microbial activity at the glacial terminus is shaping the nature of reactive elements that are delivered to headwater aquatic ecosystems As glaciers continue to ablate, interdisciplinary research will be critical to understanding of how loss of these cryosphere features will change alpine ecosystems.