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Between a rock and a hard place: the chemistry, biology, and lability of glacial meltwaters in the American West




Fegel, Timothy Scott, author
Baron, Jill, advisor
Hall, Edward, advisor
Gooseff, Michael, committee member

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Glaciers and rock glaciers supply water and nutrients to headwater mountain lakes and streams across all regions of the American West. The resulting changes in volume, timing, and chemistry of meltwater discharged by these features appears to be having significant effects on the adjacent alpine headwater ecosystems they feed. Whereas both glaciers and rock glaciers are sources of seasonal meltwater, sediment, and solutes to headwater ecosystems, differences in meltwater characteristics between glacial types, and its affect on biological productivity, is poorly documented. Here we present a comparative study of the metal, nutrient, and microbial characteristics of glacial and rock glacial influence on headwater ecosystems in three mountain ranges of the contiguous U.S.: the Cascade Mountains, Rocky Mountains, and Sierra Nevada. Several meltwater characteristics (water temperature, conductivity, pH, heavy metals, nutrients, complexity of dissolved organic matter (DOM), and bacterial richness and diversity) differed significantly between glacier and rock glacier meltwaters, while other characteristics (Ca2+, Fe3+, SiO2 concentrations, reactive nitrogen, and microbial processing of DOM) showed distinct charcteristics between mountain ranges regardless of meltwater source. Some characteristics were affected both by glacier type and mountain range (e.g. temperature, ammonium (NH4+) and nitrate (NO3-) concentrations, bacterial diversity). Glaciers and rock glaciers had similar carbon concentrations, but differed in the structural composition of their DOM. Incubations of DOM from glaciers and rock glaciers with a common subalpine bacterial assemblage were conducted to examine how observed differences in meltwater chemistry controlled bacterial productivity and metabolism. DOM pools from glaciers and rock glaciers were similar in size and chemical diversity, but differed in the chemical compounds they contained. Glacier meltwaters had higher proportions of bioavailable compounds compared with rock glaciers. A smaller portion of DOM from rock glaciers was bioavailable, but both glacial types are enriching alpine headwaters with bioavailable DOM that can support heterotrophic production. Due to the high numbers of rock glaciers and the accelerating loss of low latitude glaciers, the results presented here suggest that rock glacier meltwaters may be representative of what future biogeochemical inputs will be in currently ice-glaciated watersheds.


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