Of Microbes and Men: Determining Sources of Nitrate in a High Alpine Catchment in the Front Range of Colorado and Science Outreach on Alpine Hydrology

Hafich, Katya Anna

Graduate Thesis Or Dissertation

Of Microbes and Men: Determining Sources of Nitrate in a High Alpine Catchment in the Front Range of Colorado and Science Outreach on Alpine Hydrology Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/vt150j602

Abstract

High elevation ecosystems throughout the Colorado Front Range are undergoing a shift from nitrogen-limited systems to nitrogen-saturated systems, resulting in changes in alpine biota and water quality. Nitrate concentrations are increasing in surface water of the Green Lakes Valley (GLV) by 0.27 µmol L^-1 per year, but atmospheric deposition of dissolved inorganic nitrogen (DIN = NH_4⁺ + NO₃^- ) has recently curtailed due to drought, leaving a gap in our understanding of the source of the increased export of nitrate. Current research suggests multiple theories to explain increased N suggested; increasing nitrogen deposition in precipitation, changing climate, melting cryosphere, and changing microbial communities. Research from GLV points to microbial hotspots of nitrification in barren soils, talus and rock glaciers—not atmospheric deposition—as the primary source of nitrate in surface waters. Increased nitrate levels could be also attributed to melting ice features (permafrost, Arikaree glacier, and a rock glacier) in GLV, which increases hydrologic connectivity that transports nitrate to surface waters in late summer. In this study, we aim to address this gap in understanding by employing a novel triple isotope method for the first time in an alpine catchment to quantify the terrestrial and atmospheric contribution of nitrate to numerous water types in GLV. The Δ¹⁷O--NO₃⁻ measurement retains an atmospheric signature through microbial processing, enabling us to directly measure atmospheric nitrate in the system. Results show that nitrate in surface waters, including talus, soil water and rock glacier melt, is more than 75% terrestrial, with the strongest atmospheric signals present during snowmelt. These results suggest that efforts to curtail nitrogen emissions may be too little too late, as alpine catchment biogeochemistry has transitioned to a net nitrification system that is compromising water quality at high elevations. Still, a decrease in nitrogen emissions could have positive effect, hence we address the public awareness of the changes occurring in alpine hydrology with ScienceLIVE curriculum for K-12 students. The unit on Alpine Hydrology utilizes videos, social media, and lesson plans to educate students about the nitrogen cycle, glaciers, and hydrologic flowpaths.

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