Seminar

Abstract

Excess reactive nitrogen (Nr) deposition is occurring in sensitive ecosystems in the Rocky Mountains. In some high alpine lakes in Rocky Mountain and Grand Teton national parks, this deposition has passed critical thresholds and is causing biogeochemical changes. In these parks, Nr is a rich mix of inorganic and organic oxidized and reduced N compounds originating from an array of natural and anthropogenic sources. Current routine monitoring programs measure about half of the Nr deposition, missing important compounds including dry deposited ammonia and dry and wet deposited organic N (ON). The large missing fraction of the Nr deposition inhibits the ability to develop management goals and control strategies, and track progress towards these goals to remediate damaged and maintain healthy ecosystems.

To better understand the Nr composition and origin, field studies in Rocky Mountain NP were conducted in 2006 and 2009 as well as in Grand Teton in the summer of 2011. In Rocky Mountain NP, large contributions of wet-deposited ON and dry-deposited ammonia occurred during all seasons with 20% and 15% respective contributions over a year. The Nr originated from sources throughout the western United States, though sources in northeastern Colorado were the largest contributors and natural sources were also found to be important. Measurements of the total ambient ON compounds are still problematic; however, dry deposition of water soluble particulate ON was found to be a significant fraction of the deposited Nr in Rocky Mountain NP. In addition, measurements indicate that reduced ON gases could be a large contributor to the Nr deposition, particularly during biomass burning events. This presentation will discuss the results from these field studies and identify remaining information gaps and issues concerning organic and other N compounds and its origin in the Rocky Mountains.