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Controls on nitrogen flux in alpine/subalpine watersheds of Colorado

Water Resources Research

By:
, ORCID iD , , , and ORCID iD
https://doi.org/10.1029/1999WR900283

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Abstract

High‐altitude watersheds in the Front Range of Colorado show symptoms of advanced stages of nitrogen excess, despite having less nitrogen in atmospheric deposition than other regions where watersheds retain nitrogen. In two alpine/subalpine subbasins of the Loch Vale watershed, atmospheric deposition of NO3 plus NH4+ was 3.2–5.5 kg N ha−1, and watershed export was 1.8–3.9 kg N ha−1 for water years 1992–1997. Annual N export increased in years with greater input of N, but most of the additional N was retained in the watershed, indicating that parts of the ecosystem are nitrogen‐limited. Dissolved inorganic nitrogen (DIN) concentrations were greatest in subsurface water of talus landscapes, where mineralization and nitrification augment high rates of atmospheric deposition of N. Tundra landscapes had moderately high DIN concentrations, whereas forest and wetland landscapes had low concentrations, indicating little export of nitrogen from these landscapes. Between the two subbasins the catchment of Icy Brook had greater retention of nitrogen than that of Andrews Creek because of landscape and hydrologic characteristics that favor greater N assimilation in both the terrestrial and aquatic ecosystems. These results suggest that export of N from alpine/subalpine watersheds is caused by a combination of direct flushing of N from atmospheric deposition and release of N from ecosystem biogeochemical processes (N cycling). Sensitivity of alpine ecosystems in the western United States to atmospheric deposition of N is a function of landscape heterogeneity, hydrologic flow paths, and climatic extremes that limit primary productivity and microbial activity, which, in turn, control retention and release of nitrogen. Conceptual and mechanistic models of N excess that have been developed for forested ecosystems need to be modified in order to predict the response of alpine ecosystems to future changes in climate and atmospheric deposition of N.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Controls on nitrogen flux in alpine/subalpine watersheds of Colorado
Series title:
Water Resources Research
DOI:
10.1029/1999WR900283
Volume:
36
Issue:
1
Year Published:
2000
Language:
English
Publisher:
American Geophysical Union
Contributing office(s):
Fort Collins Science Center
Description:
11 p.
First page:
37
Last page:
47