Dissertation/Thesis Abstract

Regional assessment of the sources and effects of acidic deposition on lake chemistry in alpine and subalpine watersheds of National Parks in the Rocky Mountains, United States
by Nanus, Leora, Ph.D., University of Colorado at Boulder, 2008, 170; 3315793
Abstract (Summary)

Acidic deposition can adversely affect sensitive aquatic habitats of alpine and subalpine watersheds. Studies were conducted to improve understanding of important controls on sources and effects of acidic deposition on lake chemistry across a regional scale in the United States Rocky Mountains. Relations between basin characteristics, acidic deposition, and lake concentrations of acid-neutralizing capacity (ANC), nitrate (NO3), sulfate (SO 4), and base cations were evaluated in five National Parks. Multivariate logistic regression models for ANC and NO3 had the best statistical outcome, with over 93% of lakes in the validation data correctly predicted. Modeling results indicate that elevation had the greatest influence on lake chemistry, followed by bedrock type, steep slopes, aspect, and high NO 3 and SO4 deposition. The most sensitive lakes to acidic deposition are located in the Southern Rockies. Over 33% of lakes in Colorado National Parks have a high probability for elevated NO3 and low base cation concentrations and are coincident with areas that have increasing rates of inorganic nitrogen deposition.

The significant correlation (p < 0.01) between lake NO3 concentrations and atmospheric NO3 deposition was evaluated using NO3 isotopes at 37 lakes and 7 precipitation sites. Lake NO 3 concentrations ranged from detection to 38 μeq/L, δ 18O (NO3) values ranged from -5.7 to +21.3 permil and δ 15N (NO3) values ranged from -6.6 to +4.6 permil. δ 15N (NO3) in precipitation and lakes overlap; however δ 15N (NO3) precipitation is more depleted than δ 15N(NO3) lakes, ranging from -5.5 to -2.0 permil. Regional patterns indicate that NO3 concentrations and δ15 N (NO3) values are more enriched in lakes and precipitation from the Southern Rockies and at higher elevations compared to the Northern Rockies and lower elevations. The correspondence of high NO3 and enriched δ15N (NO3) in precipitation with high NO3 and enriched δ15N (NO3) in lakes, suggests that deposition of inorganic N in wetfall may affect the amount of NO3 in lakes through a combination of direct and indirect processes such as enhanced nitrification.

Findings and modeling approaches presented in this dissertation may be used to improve long-term monitoring designs of alpine and subalpine watersheds in the Rocky Mountains and may be transferable to other remote mountain areas of the United States and the world.

Indexing (document details)
Advisor: Williams, Mark W.
Commitee: Beatty, Susan, Campbell, Donald, Milford, Jana, Tonnessen, Kathy
School: University of Colorado at Boulder
Department: Geography
School Location: United States -- Colorado
Source: DAI-A 69/07, Dissertation Abstracts International
Subjects: Geography, Geography, Hydrology, Environmental science
Keywords: Acidic deposition, Alpine, Atmospheric deposition, Lakes, National parks, Nitrate isotopes, Rocky Mountains, Watersheds
Publication Number: 3315793
ISBN: 978-0-549-67264-7
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