Persistent Nitrate in Alpine Waters with Changing Atmospheric Deposition and Warming Trends.

Nitrate concentrations in high-elevation lakes of the Colorado Front Range remain elevated despite declining trends in atmospherically deposited nitrate since 2000. The current source of this elevated nitrate in surface waters remains elusive, given shifts in additional nitrogen sources via glacial inputs and atmospheric ammonium deposition. We present the complete isotopic composition of nitrate (δN, δO, and ΔO) from a suite of nitrate-bearing source waters collected during the summers of 2017-2018 from two alpine ecosystems to constrain the provenance of elevated nitrate in surface waters during the summer open-water season.

Automated, High-resolution Mobile Collection System for the Nitrogen Isotopic Analysis of NOx.

Nitrogen oxides (NOx = NO + NO2) are a family of atmospheric trace gases that have great impact on the environment. NOx concentrations directly influence the oxidizing capacity of the atmosphere through interactions with ozone and hydroxyl radicals. The main sink of NOx is the formation and deposition of nitric acid, a component of acid rain and a bioavailable nutrient.