Atmospheric Deposition of Nutrients, Pesticides,
and
Mercury in Rocky Mountain National Park, Colorado, 2002
By M. Alisa Mast, Donald H. Campbell, George P. Ingersoll, William T. Foreman, and David P. Krabbenhoft
USGS Water-Resources Investigations Report 03-4241, 15 p., 2 figs.
ONLINE ONLY
This document is available in pdf format:
WRIR 03-4241_ver1.1.pdf (6.6 MB)
Errata Sheet Version 1.1
(Requires Adobe Acrobat Reader)
The citation for this report, in USGS format, is as follows:
Mast, M. Alisa, Campbell, Donald H., Ingersoll, George P., Foreman, William
T., and Krabbenhoft, David P., 2003: U.S. Geological Survey Water-Resources
Investigations Report 03-4241, 15 p.
Abstract
Nutrients, current-use pesticides, and mercury were measured in atmospheric deposition during summer in Rocky Mountain National Park in Colorado to improve understanding of the type and magnitude of atmospheric contaminants being deposited in the park. Two deposition sites were established on the east side of the park: one at an elevation of 2,902 meters near Bear Lake for nutrients and pesticides, and one at an elevation of 3,159 meters in the Loch Vale watershed for mercury. Concentrations of nutrients in summer precipitation at Bear Lake ranged from less than 0.007 to 1.29 mg N/L (milligrams of nitrogen per liter) for ammonium and 0.17 to 4.59 mg N/L for nitrate and were similar to those measured at the Loch Vale National Atmospheric Deposition Network station, where nitrogen concentrations in precipitation are among the highest in the Rocky Mountains. Atrazine, dacthal, and carbaryl were the most frequently detected pesticides at Bear Lake, with carbaryl present at the highest concentrations (0.0079 to 0.0952 µg/L (micrograms per liter), followed by atrazine (less than 0.0070 to 0.0604 µg/L), and dacthal (0.0030 to 0.0093 µg/L). Mercury was detected in weekly bulk deposition samples from Loch Vale in concentrations ranging from 2.6 to 36.2 ng/L (nanograms per liter).
Concentrations in summer precipitation were combined with snowpack data from a separate study to estimate annual deposition rates of these contaminants in 2002. Annual bulk nitrogen deposition in 2002 was 2.28 kg N/ha (kilograms of nitrogen per hectare) at Bear Lake and 3.35 kg N/ha at Loch Vale. Comparison of wet and bulk deposition indicated that dry deposition may account for as much as 28 percent of annual nitrogen deposition, most of which was deposited during the summer months. Annual deposition rates for three pesticides were estimated as 45.8 mg/ha (milligrams per hectare) of atrazine, 14.2 mg/ha of dacthal, and 54.8 mg/ha of carbaryl. Because of much higher pesticide concentrations in summer precipitation than in winter snow, between 80 to 90 percent of the annual pesticide deposition occurs during summer. Mercury deposition to Loch Vale was estimated at 7.1 µg/m2 (micrograms per square meter) of which nearly 70 percent of the annual mercury deposition occurred during summer. Despite the fact that most precipitation at high-elevations falls during winter, these results emphasize the importance of monitoring precipitation chemistry during summer to improve estimates of contaminant deposition to high-elevation ecosystems in Rocky Mountain National Park.
Air-parcel back trajectories were calculated using an atmospheric transport model to identify potential source regions for contaminants reaching the park. The results indicate that during the winter, the most likely source of contami-nants is from areas northwest of the park, but during summer, contaminants are most likely coming from sources to the southwest and east.
Contents
Abstract
Introduction
Purpose and Scope
Acknowledgments
Study Methods
Atmospheric Deposition of Nutrients, Pesticides, and Mercury
Nutrients and Major Constituents
Nitrate Isotopes
Current-Use Pesticides
Mercury
Back Trajectory Models
Summary and Conclusions
References Cited
