United States Department of Agriculture / Forest Service

Rocky Mountain Research Station

General Technical Report RMRS-GTR-248WWW

November 2010

Lake and Bulk Sampling Chemistry, NADP, and 

IMPROVE Air Quality Data Analysis on the 

Bridger-Teton National Forest (USFS Region 4)

Jill Grenon

Terry Svalberg

Ted Porwoll

Mark Story
Available only online at http://www.fs.fed.us/rm/pubs/rmrs_gtr248.html

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Grenon, Jill; Svalberg, Terry; Porwoll, Ted; Story, Mark. 2010. Lake and bulk 

sampling chemistry, NADP, and IMPROVE air quality data analysis on the 

Bridger-Teton National Forest (USFS Region 4). Gen. Tech. Rep. RMRS-GTR248WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 44 p.

Abstract

Air quality monitoring data from several programs in and around the Bridger-Teton 

(B-T) National Forest—National Atmospheric Deposition Program (NADP), longterm lake monitoring, long-term bulk precipitation monitoring (both snow and 

rain), and Interagency Monitoring of Protected Visual Environments (IMPROVE)—

were analyzed in this report. Trends were analyzed using non-parametric tests 

and seasonality was taken into account when possible. Nitrate (NO3

-

) showed 

seasonal increasing trends in all sampled lake inlets, in atmospheric deposition at 

NADP sites and bulk sampling sites, and at two visibility sites. NADP sites showed 

consistent decreasing trends for both deposition and concentrations in SO4

2-, Na+, 

Mg2+, and Cl- and increasing trends in NH4

+ and inorganic nitrogen deposition. 

Lake and bulk deposition chemistry data showed increasing trends in cations and 

decreasing trends in Cl-

. Bulk deposition sites showed an increasing trend in NH4

+. 

Standard Visual Range (SVR) showed an increasing trend and extinction showed 

a decreasing trend at all IMPROVE sites analyzed. In conclusion, considerations 

were listed regarding current and future air quality monitoring on the B-T National 

Forest.

Keywords: Bridger-Teton National Forest, NADP, IMPROVE, long-term lake 

chemistry, bulk deposition, air quality trends, nitrogen deposition

Authors

Jill Grenon—Air Quality Specialist/Botanist, USFS Region 4, Bridger-Teton 

National Forest.

Terry Svalberg—Air Quality Specialist, USFS Region 4, Bridger-Teton 

National Forest.

Ted Porwoll—Air Quality Technician, USFS Region 4, Bridger-Teton 

National Forest.

Mark Story—Hydrologist, USFS Region 1, Gallatin National Forest.

Cover Photo: Two of the four lakes in the Bridger-Teton NF that were sampled 

for this report: Black Joe Lake (foreground, lower left); and Deep Lake (upper 

middle); (Forest Service photo).
Contents

Introduction.....................................................................................................................1

Analysis Methods.............................................................................................................2

National Atmospheric Deposition Program (NADP)........................................................3

NADP Concentration Trends ..................................................................................... 4

NADP Deposition Trends .......................................................................................... 9

NADP Discussion.................................................................................................... 15

Bulk Deposition .............................................................................................................16

Bulk Deposition Discussion..................................................................................... 19

Long-Term Lake Monitoring...........................................................................................19

Lake Trend Discussion............................................................................................. 29

IMPROVE (Interagency Monitoring of Protected 

Visual Environments)..................................................................................................30

IMPROVE Discussion.............................................................................................. 34

Conclusions....................................................................................................................34

Considerations...............................................................................................................35

Acknowledgments..........................................................................................................36

References .....................................................................................................................36

Appendix........................................................................................................................39

USDA Forest Service RMRS-GTR-248WWW. 2010. 1

Introduction

The Bridger-Teton (B-T) National Forest is the second largest National Forest in the 

United States (outside of Alaska), embracing over 3.4 million acres in western Wyoming 

including 1.2 million acres of Class I and II Wilderness areas (fig. 1). The B-T is connected 

to the southern end of the 20-million acre Greater Yellowstone Ecosystem. The B-T has 

over 1,500 lakes, 2,000+ miles of trails, seven of the largest Glaciers in the lower 48 States, 

many high peaks (more than 13,000 ft elevation), and an abundance and variety of flora and 

fauna. Increasing atmospheric emissions associated with human population, vehicles, and 

expansion of oil and gas development and production pose a potential to affect air quality 

in the B-T National Forest.

Figure 1—Bridger-Teton and Shoshone National Forests Air Quality Monitoring sites.

^_

^_

^_

^_

^_

^_

^_

^_

^_

^_

^_

^_

£¤26

£¤191

£¤189

BRIDGER - TETON

NATIONAL

FOREST

Pinedale

Big Piney

Dubois

Lander

SHOSHONE

NATIONAL

FOREST

WIND RIVER

INDIAN RESERVATION

Sinks Canyon

LaBarge

Bridger

Wilderness

Fitzpatrick

Wilderness

Popo Agie

Wilderness

Pinedale

Deep Lake

Ross Lake

South Pass

Hobbs Lake

Gypsum Creek

Black Joe Lake

Upper Frozen Lake Upper Saddlebag Lake

VICINITY MAP BRIDGER-TETON NF

& SHOSHONE NF

AIR QUALITY

MONITORING SITES

0 2 4 6 8 10 E Miles

BAG - 6/04/10

Legend

Air Monitoring Sites

^_ CASTNET

^_ IMPROVE

^_ Long-term lake monitoring

^_ NADP

^_ Long-term lake monitoring and Bulk Deposition

Airsheds of Concern

Class I - Wilderness Areas

Class II - Wilderness areas
2 USDA Forest Service RMRS-GTR-248WWW. 2010.

The Clean Air Act (http://www.epa.gov/air/caa/) requires the Forest Service to protect 

air quality related values (AQRVs) in Class I Wilderness Areas (those wilderness areas in 

existence as of August 7, 1977, that are larger than 5,000 acres). Those Wilderness areas that 

are not designated as Class I also have management goals identified in the 1964 Wilderness 

Act (http://www.wilderness.net/index.cfm?fuse=NWPS&sec=legisAct). A large piece of 

wilderness air protection stems from the Prevention of Significant Deterioration (PSD) 

provisions of The Clean Air Act. State legislation, regional haze rules, and PSD regulations 

determine how States conduct the air-quality regulatory process (more information can be 

found at: http://www.epa.gov/air/oaq_caa.html/ and http://www.epa.index.html).

In compliance with the Clean Air Act, the B-T National Forest participates in four 

different types of air quality monitoring programs: National Atmospheric Deposition 

Program (NADP) (http://nadp.sws.uiuc.edu), long-term lake monitoring, bulk deposition 

monitoring (wet and dry deposition), and the Interagency Monitoring of Protected Visual 

Environments (IMPROVE). These programs collect data on wet precipitation chemistry, 

lake chemistry, bulk precipitation chemistry, and visibility with the goal to monitor forest health and make practical regional haze progress to restore background conditions by 

2064. The purpose of this report is to analyze existing air quality data to gain a more 

complete understanding of regional and local trends in air quality and to better understand 

possible effects to the B-T National Forest and, more specifically, the Bridger Wilderness. 

This report is intended to provide useful information for understanding and managing air 

quality in southwest Wyoming, including natural gas field exploration and development 

effects on air quality related resources. This report provides air quality information and 

associated resource information for NEPA, PSD, and document baseline for trends relative 

to climate change effects.

Analysis Methods

Methods for analysis followed the Data Analysis Protocol (DAP) for long-term lake 

monitoring (Gurrieri 2006), which was derived from the statistical, graphical, and protocol development methods of Gilbert (1987), Helsel and Hirsch (1992), and Ward and 

others (1990). Trends were tested using the Kruskall-Wallis test for seasonality, the MannKendall, and the seasonal Mann-Kendall tests. These nonparametric tests work well with 

monotonic trends. They do not require normally distributed data and are much more resistant to outliers and missing data than parametric tests (Gurrieri 2006).

The null hypothesis for this analysis (Ho

) is no significant trend (in lake, NADP, 

IMPROVE, or the bulk variables tested) observed over time. The alternative hypothesis 

(H1

) means that a significant increasing or decreasing trend is found over time. As suggested in the DAP, only data with eight or more observations were tested for trends (Gurrieri 

2006). Figure 2 shows a flow diagram of the Data Analysis Protocol that was used to analyze trends in long-term monitoring data and to guide the data analysis found in this report.

The data and statistical analysis for this paper was generated using SAS software, 

Version 9.1.3 of the SAS System for Windows. (Copyright © 2009 SAS Institute Inc. 

SAS and all other SAS Institute Inc. product or service names are registered trademarks or 

trademarks of SAS Institute Inc., Cary, NC, USA.) After the data were imported into SAS, 

the Kruskal-Wallis test was run for each variable to see if there was a difference among 

seasons (seasonal data only). If seasonal differences were statistically significant at α = 

0.05 level, then the seasonal Mann-Kendall test was run. If seasonal data were not statistically different, then the Mann-Kendall test was run on the annual data. The Mann-Kendall 

and seasonal Mann-Kendall tests report whether or not a trend exists, they do not evaluate 

the magnitude of the trend. The Mann-Kendall test also was used to analyze trends within 

individual seasons.
USDA Forest Service RMRS-GTR-248WWW. 2010. 3

The Mann-Kendall and seasonal Mann-Kendall use α to quantify the probability that 

a trend exists. For this report the α (alpha) level for statistical significance was set at α = 

0.1. A value of α = 0.1 means there is a 10 percent possibility of falsely rejecting the null 

hypothesis that no trend exists (Salmi and others 2002). We set the p-value significance at 

0.1 to allow a wider extent of trend detection. The Sen’s slope estimator shows the magnitude not the significance of a trend. This magnitude depends on the units of measure 

and can be a negative or positive value depending on whether the trend is decreasing or 

increasing, respectively. It is important to note that a decreasing trend may represent either 

an improvement or degradation in environmental quality depending on the context. All 

graphs in this report, unless noted otherwise, illustrate statistically significant trends, but 

only selected significant trends are graphed (for space conserving purposes).

National Atmospheric Deposition Program (NADP)

The NADP was initiated in 1978 to monitor geographic and temporal trends in the 

chemical composition of wet deposition (rain and snow) with the primary purpose of acid 

rain benchmark monitoring. The program was prompted by scientific evidence and public 

concern in the 1970s that acid rain could be damaging to aquatic ecosystems throughout 

the United States. The program grew steadily though the early 1980s and has stabilized 

at about 200 sites. The NADP network data is used by a wide variety of scientists and 

resource managers to evaluate wet deposition to and its effects on agriculture, forests, 

rangelands, freshwater streams and lakes, and cultural resources. All of the NADP sites 

are operated according to NADP protocols (http://nadp.sws.uiuc.edu/documentation/completeness.asp). Sample buckets are exchanged each Tuesday throughout the calendar year 

and the samples are shipped to the Central Analytical Lab (CAL) at the Illinois State Water 

Survey for chemical analysis.

Both annual and seasonal NADP data were downloaded from the NADP website (http://

nadp.sws.uiuc.edu) for the following five sites: Gypsum Creek (WY98), Murphy Ridge 

(UT08), Pinedale (WY06), Sinks Canyon (WY02), and South Pass (WY97). Figure 3 

shows the locations of NADP sites for all of Wyoming including all the sites analyzed 

in this report. Gypsum Creek and Pinedale are both on the west side of the Wind River 

Range and are operated by the Forest Service (established in 1982) and BLM (established 

in 1984) respectively. Sinks Canyon (established 1984) and South Pass, established 1985) 

are located on the Washakie District of the Shoshone National Forest and operated by 

BLM and the Forest Service respectively. Murphy Ridge (established in 1986) is located in 

Figure 2—Flow diagram depicting temporal trend analysis protocol (Gurrieri 2006).
4 USDA Forest Service RMRS-GTR-248WWW. 2010.

Utah on the border of Wyoming and operated by the British Petroleum-Amoco Production 

Company. The elevation of the five NADP sites that were analyzed range from 2,146 m 

at Murphy Ridge to 2,524 m at South Pass; none of the sites are in designated wilderness 

areas.

NADP data were analyzed for trends in annual concentrations (μeq/L) and deposition 

(kg/ha) and for trends within each season. For the seasonal data, winter includes January, 

February, and March; spring includes April, May, and June; summer includes July, August, 

and September; and fall includes October, November, and December. These seasons are 

the same as seasons 1 to 4 in the IMPROVE data discussed later in this report. Trends are 

reported in order of annual and seasonal concentrations followed by annual and seasonal 

deposition. The full period of record available at the time of analysis was used to analyze 

each site and was site dependent with beginning data between 1982 and 1987 and the latest 

data available between 2006 and 2008.

NADP Concentration Trends

Each site was analyzed for trends in volume weighted mean (VWM) concentrations 

(μeq/L), lab specific conductance (Lcond)(μS/cm), Ca2+, Cl-, K+, Mg2+, Na+, NH4

+, NO3-

, 

lab H+ (LH), and SO4

2-. Annual trends are shown in table 1. Lab H+ at Murphy Ridge and 

Na-

 at Sinks Canyon did not show an overall difference among seasons (table 1). Trends 

for each season are shown in tables 2 through 6. Annual precipitation (cm) at NADP sites 

are shown for the years 1982 to 2008 for the purpose of general background information 

(fig. 4). Selected annual concentration trends are shown in figures 5 to 8.

Figure 3—NADP sites in and near WY: WY08 Yellowstone NP, WY98 Gypsum Creek, WY06 

Pinedale, WY02 Sinks Canyon, WY97 South Pass City, WY00 Snowy Range, WY96 Nash Fork, 

WY99 Newcastle, UT08 Murphy Ridge, and CO22 Pawnee.
USDA Forest Service RMRS-GTR-248WWW. 2010. 5

Table 1—NADP: VWM concentrations, Mann-Kendall test for annual trends at five NADP sites: ss represents the 

Sen’s slope estimate (the negative sign represents a decreasing slope); p represents p-value; red numbers equal 

significant trends when p<0.1. Seasonality was taken into account when appropriate.

Gypsum Creek Murphy Ridge Pinedale Sinks Canyon South Pass

WY98 UT08 WY06 WY02 WY97

Variable

(μeq/L/yr) ss p ss p ss p ss p ss p

Ca2+ -0.033 0.239 -0.172 0.162 -0.05 0.164 0 0.99 0.112 0.132

Mg2+ -0.033 <0.001 -0.082 0.004 -0.046 <0.001 -0.033 0.012 -0.014 0.121

K+ -0.001 0.691 -0.008 0.192 0 0.343 0.002 0.477 0.007 0.092

Na+ -0.104 <0.001 -0.221 <0.001 -0.145 <0.001 -0.098 0.005 -0.075 <0.001

NH4

+ 0.177 <0.001 0.257 0.009 0.166 0.002 0.187 <0.001 0.146 0.005

NO3

- 0.031 0.523 0.049 0.678 0.11 0.182 0.007 0.901 0.103 0.082

SO4

2- -0.177 <0.001 -0.423 <0.001 -0.262 <0.001 -0.261 <0.001 -0.22 <0.001

Cl- -<0.001 <0.001 -0.187 <0.001 -0.102 <0.001 -0.061 <0.001 -0.074 <0.001

LH -0.047 0.283 -0.179 0.071 0.023 0.965 -0.075 0.011 -0.123 0.009

Lcond -0.041 0.027 -0.166 <0.001 -0.029 0.075 -0.05 0.003 -0.019 0.299

Table 2—NADP: VWM concentrations, Mann-Kendall outputs for seasonal trends, Gypsum Creek

(WY 98): ss represents Sen’s slope estimator (the negative sign signifies a decreasing slope); 

p represents p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(μeq/L) ss p ss p ss p ss p

Ca2+ -0.040 0.037 -0.066 0.710 -0.166 0.509 0.073 0.382

Mg2+ -0.034 <0.001 -0.049 0.253 -0.060 0.119 -0.009 0.595

K+ -0.009 0.003 0.003 0.747 0.006 0.771 0.010 0.113

Na+ -0.119 0.003 -0.073 0.137 -0.087 0.032 -0.116 0.009

NH4

+ 0.024 0.456 0.166 0.039 0.623 0.008 0.333 <0.001

NO3

- -0.020 0.710 0.044 0.637 0.118 0.711 0.087 0.413

SO4

2- -0.187 <0.001 -0.222 0.172 -0.190 0.139 -0.111 0.267

Cl- -0.111 <0.001 -0.098 0.002 -0.141 0.010 -0.078 0.003

LH -0.010 0.901 -0.055 0.442 -0.092 0.355 -0.051 0.792

Lcond -0.072 0.003 -0.045 0.333 -0.027 0.853 -0.006 0.874

Table 3—NADP: VWM concentrations, Mann-Kendall outputs for seasonal trends, Murphy Ridge

(UT08): ss represents Sen’s slope estimator (the negative sign signifies a decreasing slope); 

p represents p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(μeq/L) ss p ss p ss p ss p

Ca2+ -0.109 0.352 -0.364 0.342 -0.160 0.756 -0.112 0.612

Mg2+ -0.073 0.075 -0.131 0.107 -0.082 0.271 -0.060 0.258

K+ -0.029 0.037 -0.009 0.509 0.006 0.821 0.000 0.955

Na+ -0.577 0.002 -0.171 0.205 -0.149 0.090 -0.157 0.012

NH4

+ 0.044 0.843 0.234 0.291 0.796 0.055 0.409 0.048

NO3

- 0.108 0.652 -0.069 0.526 0.178 0.592 0.109 0.612

SO4

2- -0.411 0.009 -0.447 0.065 -0.333 0.128 -0.463 0.024

Cl- -0.456 <0.001 -0.219 0.028 -0.157 0.045 -0.110 0.024

LH 0.006 0.955 -0.098 0.383 -0.060 0.612 -0.270 0.015

Lcond -0.216 0.021 -0.172 0.146 -0.070 0.367 -0.191 0.037
6 USDA Forest Service RMRS-GTR-248WWW. 2010.

Table 6—NADP: VWM concentrations, Mann-Kendall outputs for seasonal trends, South Pass 

(WY97): ss represents Sen’s slope estimator (the negative sign signifies a decreasing slope); 

p represents p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(μeq/L) ss p ss p ss p ss p

Ca2+ -0.125 0.057 0.252 0.009 0.024 0.874 0.349 0.045

Mg2+ -0.041 0.002 0.016 0.411 -0.037 0.195 0.015 0.711

K+ -0.002 0.299 0.013 0.059 0.011 0.369 0.011 0.130

Na+ -0.196 <0.001 0.008 0.804 -0.126 0.048 -0.053 0.039

NH4

+ 0.021 0.916 0.194 0.087 0.433 0.054 0.203 0.045

NO3

- -0.023 0.369 0.138 0.165 0.146 0.413 0.188 0.035

SO4

2- -0.269 0.001 -0.239 0.130 -0.254 0.187 -0.062 0.597

Cl- -0.131 0 -0.038 0.233 -0.093 0.008 -0.035 0.077

LH 0.056 0.916 -0.183 0.011 -0.184 0.316 -0.113 0.170

Lcond -0.067 0.107 -0.009 0.691 -0.044 0.635 0.024 0.673

Table 5—NADP: VWM concentrations, Mann-Kendall outputs for seasonal trends, Sinks Canyon 

(WY02): ss represents Sen’s slope estimator (the negative sign signifies a decreasing slope); 

p represents p-value; red numbers equal significant trends when p<0.1. Na+ trends are shown 

even though there was no overall significance between seasons.

Winter Spring Summer Fall

Variable

(μeq/L) ss p ss p ss p ss p

Ca2+ -0.066 0.243 0.315 0.045 -0.263 0.244 0.075 0.710

Mg2+ -0.042 0.005 0.018 0.518 -0.098 0.078 -0.036 0.297

K+ -0.005 0.128 0.007 0.061 -0.005 0.673 0.005 0.129

Na+ -0.117 0.002 -0.033 0.309 -0.098 0.018 -0.069 0.059

NH4

+ 0.042 0.568 0.226 0.031 0.319 0.097 0.306 0.001

NO3

- -0.097 0.254 -0.005 0.882 -0.004 0.980 0.191 0.102

SO4

2- -0.197 0.004 -0.248 0.012 -0.535 0.024 -0.253 0.074

Cl- -0.078 <0.001 -0.035 0.063 -0.101 0.009 -0.052 0.009

LH 0.006 0.980 -0.128 0.009 -0.173 0.157 -0.069 0.286

Lcond -0.069 0.015 -0.044 0.078 -0.110 0.244 -0.027 0.568

Table 4—NADP: VWM concentrations, Mann-Kendall outputs for seasonal trends, Pinedale 

(WY06): ss represents Sen’s slope estimator (the negative sign signifies a decreasing slope); 

p represents p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(μeq/L) ss p ss p ss p ss p

Ca2+ -0.150 0.010 -0.141 0.478 0.075 0.791 0.102 0.843

Mg2+ -0.059 <0.001 -0.055 0.103 -0.062 0.225 -0.025 0.151

K+ -0.013 0.001 0.003 0.544 0.016 0.440 0.002 0.860

Na+ -0.328 0 -0.144 0.070 -0.072 0.186 -0.122 <0.001

NH4

+ 0.00 0.659 0.222 0.052 0.680 0.004 0.246 0.071

NO3

- 0.011 0.724 0.054 0.707 0.325 0.234 0.251 0.146

SO4

2- -0.296 <0.001 -0.336 0.033 -0.290 0.134 -0.121 0.234

Cl- -0.173 <0.001 -0.085 0.033 -0.078 0.186 -0.064 0.023

LH 0.261 0.009 -0.050 0.440 -0.214 0.064 0.035 1.000

Lcond -0.043 0.098 -0.038 0.338 -0.074 0.355 0.023 1.000
USDA Forest Service RMRS-GTR-248WWW. 2010. 7

Figure 4—Annual precipitation in centimeters from 1982 to 2007 at Gypsum Creek (GC), Murphy 

Ridge (MR), Pinedale (PI), Sinks Canyon (SC),and South Pass (SP).

Figure 5—Annual NH4

+ concentration (μeq/L) trends from 1982 to 2007 at Gypsum Creek (GC), 

Murphy Ridge (MR), Pinedale (PI), Sinks Canyon (SC),and South Pass (SP).

Figure 6—Annual SO4

2- concentration (μeq/L) trends from 1982 to 2007 at Gypsum Creek (GC), 

Murphy Ridge (MR), Pinedale (PI), Sinks Canyon (SC),and South Pass (SP).
8 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 7—Annual NO3

-

 concentration (μeq/L) trend at South Pass (SP) NADP site from 1985 to 2007.

Figure 8—Annual Cl-

 concentration (μeq/L) trends from 1982 to 2007 at Gypsum Creek (GC), Murphy 

Ridge (MR), Pinedale (PI), Sinks Canyon (SC),and South Pass (SP).
USDA Forest Service RMRS-GTR-248WWW. 2010. 9

NADP Deposition Trends

Each site was analyzed for trends in deposition (kg/ha) for Ca2+, Cl-, K+, Mg2+, Na+, 

NH4

+, NO3-

, total measured inorganic nitrogen (IN), and SO4

2-. Annual trends (with seasonality taken into account) are shown in table 7. Trends for each season are shown in tables 8 

to 12, and selected trends are shown in figures 9 through 21. The graphs focus on depicting 

trends in N and S.

Table 7—NADP: Deposition, Seasonal Mann-Kendall output for annual trends at five NADP sites: ss represents Sen’s 

slope estimator (the negative sign signifies a decreasing slope); p represents p-value; red numbers equal significant 

trends when p<0.1.

Gypsum Creek Murphy Ridge Pinedale Sinks Canyon South Pass

WY98 UT08 WY06 WY02 WY97

Variable

(kg/ha) ss p ss p ss p ss p ss p

Ca2+ 0 0.651 0 0.759 -0.002 0.002 -<0.001 0.389 0.003 0.115

Mg2+ -<0.001 0.06 -<0.001 0.076 -<0.001 <0.001 -<0.001 0.002 0 0.532

K+ <0.001 0.088 0 0.933 -<0.001 0.041 0 0.583 <0.001 0.025

Na+ -0.001 0.001 -0.002 <0.001 -0.003 <0.001 -0.002 <0.001 -0.002 0.002

NH4

+ 0.003 <0.001 0.001 0.023 0.001 0.045 0.003 0.001 0.003 0.003

NO3

- 0.007 0.003 0.005 0.165 0 0.744 0.002 0.434 0.009 0.153

Cl- -0.002 <0.001 -0.003 <0.001 -0.003 <0.001 -0.003 <0.001 -0.003 <0.001

SO4

2- -0.003 0.115 -0.006 0.005 -0.01 <0.001 -0.011 <0.001 -0.011 0.003

IN 0.004 <0.001 0.003 0.06 0.001 0.426 0.002 0.058 0.004 0.012

Table 8—NADP: Deposition, Mann-Kendall outputs for trends, Gypsum Creek (WY 98): ss 

represents Sen’s slope estimator (the negative sign signifies a decreasing slope); p represents 

p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(kg/ha) ss p ss p ss p ss p

Ca2+ 0 0.575 0 0.881 -0.001 0.771 0.002 0.411

Mg2+ -<0.001 0.203 -<0.001 0.214 -<0.001 0.290 0 0.936

Cl- -0.002 0.056 -0.003 0.012 -0.004 0.026 -0.002 0.059

K+ -<0.001 0.148 <0.001 0.156 <0.001 0.355 <0.001 0.009

Na+ -<0.001 0.059 -<0.001 0.637 -0.002 0.068 -0.002 0.030

NH4

+ 0.001 0.006 0.003 0.135 0.011 0.011 0.008 <0.001

NO3

- 0.006 0.024 0.002 0.710 0.008 0.398 0.017 0.019

IN 0.002 0.009 0.003 0.517 0.010 0.047 0.008 0.003

SO4

2- -0.002 0.116 -0.006 0.297 -0.003 0.492 <0.001 0.812
10 USDA Forest Service RMRS-GTR-248WWW. 2010.

Table 9—NADP: Deposition, Mann-Kendall outputs for seasonal trends, Murphy Ridge (UT08): ss 

represents Sen’s slope estimator (the negative sign signifies a decreasing slope); 

p represents p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(kg/ha) ss p ss p ss p ss p

Ca2+ 0 0.840 -0.002 0.561 0 0.888 0 0.977

Mg2+ -<0.001 0.277 -<0.001 0.195 -<0.001 0.651 -<0.001 0.551

K+ -<0.001 0.245 -<0.001 0.791 <0.001 0.232 0 0.955

Na+ -0.002 0.009 -0.002 0.256 -0.001 0.224 -0.002 0.010

NH4

+ <0.001 0.250 0 1 0.007 0.054 0.003 0.133

NO3

- 0.007 0.085 -0.007 0.509 0.011 0.150 0.004 0.735

Cl- -0.003 0.009 -0.003 0.076 -0.003 0.202 -0.001 0.166

SO4

2- -0.003 0.246 -0.011 0.154 -0.007 0.158 -0.008 0.127

IN 0.002 0.098 -0.003 0.771 0.010 0.108 0.003 0.396

Table 11—NADP: Deposition, Mann-Kendall outputs for seasonal trends, Sinks Canyon (WY02): ss 

represents Sen’s slope estimator (the negative sign signifies a decreasing slope); p represents 

p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(kg/ha) ss p ss p ss p ss p

Ca2+ -<0.001 0.300 0.007 0.157 -0.006 0.022 0 0.881

Mg2+ -<0.001 0.023 <0.001 0.804 -0.001 0.002 -<0.001 0.263

K+ -<0.001 0.236 <0.001 0.106 -<0.001 0.709 <0.001 0.295

Na+ -0.002 0.001 -<0.001 0.619 -0.002 0.008 -0.002 0.027

NH4

+ 0 0.347 0.006 0.180 0.004 0.187 0.006 0.007

NO3

- 0 0.822 0.002 0.843 -0.006 0.413 0.015 0.053

Cl- -0.002 <0.001 -0.003 0.036 -0.004 0.003 -0.002 0.003

SO4

2- -0.006 0.030 -0.015 0.118 -0.023 0.015 -0.009 0.253

IN 0 0.615 0.004 0.471 0.002 0.691 0.007 0.037

Table 10—NADP: Deposition, Mann-Kendall outputs for seasonal trends, Pinedale (WY06): 

ss represents Sen’s slope estimator (the negative sign signifies a decreasing slope); 

p represents p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(kg/ha) ss p ss p ss p ss p

Ca2+ -0.002 0.006 -0.004 0.203 -0.004 0.081 0 0.773

Mg2+ -<0.001 <0.001 -0.001 0.035 -0.001 <0.001 -<0.001 0.072

K+ -<0.001 0.008 -<0.001 0.530 -<0.001 0.774 0 0.642

Na+ -0.003 <0.001 -0.003 0.027 -0.003 <0.001 -0.002 0.002

NH4

+ 0 0.501 0.001 0.738 0.004 0.093 0.004 0.009

NO3

- <0.001 0.895 -0.007 0.326 -0.008 0.261 0.012 0.098

Cl- -0.003 <0.001 -0.003 0.002 -0.005 <0.001 -0.002 0.005

SO4

2- -0.007 <0.001 -0.020 0.012 -0.026 <0.001 -0.006 0.061

IN 0 0.548 -0.002 0.517 0.002 0.479 0.006 0.027
USDA Forest Service RMRS-GTR-248WWW. 2010. 11

Table 12— NADP: Deposition, Mann-Kendall outputs for seasonal trends, South Pass (WY97): 

ss represents Sen’s slope estimator (the negative sign signifies a decreasing slope); 

p represents p-value; red numbers equal significant trends when p<0.1.

Winter Spring Summer Fall

Variable

(kg/ha) ss p ss p ss p ss p

Ca2+ 0 0.458 0.011 0.018 -0.003 0.443 0.006 0.026

Mg2+ -<0.001 0.076 <0.001 0.243 -<0.001 0.060 -<0.001 0.265

K+ <0.001 0.853 <0.001 0.013 <0.001 0.791 <0.001 0.072

Na+ -0.004 0.007 <0.001 0.862 -0.003 0.008 -<0.001 0.256

NH4

+ 0.001 0.611 0.004 0.065 0.004 0.153 0.004 0.031

NO3

- 0.003 0.711 0.010 0.188 0 1 0.018 0.057

Cl- -0.004 0.002 -0.001 0.292 -0.003 0.001 -0.001 0.241

SO4

2- -0.012 0.061 -0.006 0.518 -0.020 0.020 -0.008 0.328

IN 0.002 0.916 0.006 0.030 0.003 0.354 0.008 0.053

Figure 9—Gypsum Creek (WY98) NADP site winter nitrogen deposition from 1985-2008. 

IN represents measured winter inorganic nitrogen.

Figure 10—Gypsum Creek (WY98) NADP site summer nitrogen deposition from 1985-2007. 

IN represents measured inorganic nitrogen.
12 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 11—Gypsum Creek (WY98) NADP site fall nitrogen deposition from 1987-2007. IN represents 

measured inorganic nitrogen.

Figure 12—Murphy Ridge (UT08) NADP site winter nitrogen deposition from 1987-2008. 

IN represents measured inorganic nitrogen.

Figure 13—Murphy Ridge (UT08) NADP site summer NH4

+ deposition from 1986-2007.

Figure 14—Pinedale (WY06) NADP site summer NH4

+ deposition from 1982-2007.

0 

0.05 

0.1 

0.15 

0.2 

0.25 

0.3 

0.35 

0.4 

0.45 

1982 

1984 1986 

1988 1990 1992 

1994 1996 

1998 2000 2002 

2004 2006 

kg/ha 

NH4 
USDA Forest Service RMRS-GTR-248WWW. 2010. 13

0 

0.2 

0.4 

0.6 

0.8 

1 

1.2 

1.4 

1.6 

1.8 

2 

1984 

1988 1992 1996 2000 

2004 

2008 

kg/ha/yr 

Winter 

Spring 

Summer 

Fall 

Figure 15—Pinedale (WY06) NADP site fall nitrogen deposition from 1982-2007. IN represents 

measured inorganic nitrogen.

Figure 16—Pinedale (WY06) NADP site seasonal SO4

2- deposition from 1982-2008.

Figure 17—Sinks Canyon (WY02) NADP site fall nitrogen deposition from 1985-2007. IN represents 

measured inorganic Nitrogen.

Figure 18—Sinks Canyon (WY02) NADP site seasonal SO4

2- deposition from 1985-2008.
14 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 21—South Pass (WY97) NADP site seasonal SO4

2- deposition from 1985-2008.

Figure 19—South Pass (WY97) NADP site spring nitrogen deposition from 1985-2008. IN represents 

measured inorganic nitrogen.

Figure 20—South Pass (WY97) NADP site fall nitrogen deposition 1985-2007. IN represents measured 

inorganic nitrogen.
USDA Forest Service RMRS-GTR-248WWW. 2010. 15

NADP Discussion

NADP reports precipitation chemistry for weekly snow and rain; therefore, the calculated deposition amounts only represent wet deposition. Total deposition also includes dry 

and fog deposition. In the Northern Rocky Mountains, dry deposition can be a substantial 

component of total deposition. Data from the EPA Clean Air Status and Trends Network 

(CASTNET) (http://www.epa.gov/castnet/) estimates dry deposition of inorganic nitrogen 

in this area to account for about 25 to 33 percent of total deposition (Ingersoll and others 

2008).

The NADP samplers (Aerochem Metrics) were designed to collect rainfall in relatively 

calm environments. The sampler and buckets are not 100 percent efficient at collecting 

samples in environments that are windy and or/snow-laden (such as that found in and 

around the Wind River Range). Winter conditions often pose difficulties for data collection 

(i.e., iced solar panels, burned out or frozen motors, and difficulties with site accessibility) 

(Goodison and others 1998; Yang and others 2000).

Ammonia concentration and deposition increased at all NADP sites that were analyzed. 

Consistent increases in ammonia concentration and deposition have been documented 

over much of the western United States (Fenn and others 2003; NADP data report 2007). 

Ingersoll and others (2008), Bevenger (2008), and Grenon and Story (2009) also documented a moderately significant upward trend in NH4

+ concentration at NADP sites in the 

Northern Rockies. Results of the analysis by Bevenger (2008) are included in the Appendix. 

Analysis of NADP trends from 1985 to 2002 and from 2002 to 2004 documented nationwide NH4

+ increases, particularly in agriculture areas of the Midwest and western United 

States (Lehmann and others 2005, 2007). Fenn and others (2003) evaluated NO3

-

 and NH4

+

concentrations at NADP sites in Oregon and Washington and found that concentrations 

have been increasing since monitoring began in 1980. Campbell (2004) indicates that for 

the Intermountain West, ammonia makes up about one third of the total nitrogen deposition 

at many sites. The increase in atmospheric NH4

+ has been attributed to fertilizer production 

and volatilization from animal feedlots, waste lagoons, and land-based waste application.

Gypsum Creek (WY98) and South Pass (WY97) showed increasing trends in annual 

NO3

- deposition and concentration respectively. All NADP sites had at least one season 

in which there was an increasing trend in NO3

-

. In general, NO3

-

 concentrations have decreased in the Northeast and Midwest due to the 1990 Clean Air Act amendments that 

mandated emission reductions for stationary sources (EPA 2008). Concentrations in the 

Rocky Mountains have generally increased, particularly around urban areas (Fenn and others 2003; Lehmann and others 2005), for example, NO3

- in wet deposition is elevated in the 

Colorado Front Range (Nanus and others 2008).

Annual inorganic nitrogen (IN) deposition revealed statistically significant increasing 

trends at all the NADP sites except at Pinedale, Wyoming. All sites had at least one season 

in which IN deposition increased. The increase in IN is due primarily to the increase in 

NH4

+. An increase in IN can act as a fertilizer and enrich sensitive ecosystems, cause acidification to soils, and eutrophication to aquatic systems.

Significant decreasing trends in SO4

2- concentration and deposition were detected at 

all sites except for deposition at Gypsum Creek (WY97). This pattern is consistent with 

Lehmann (2005) who documented sulfate decreases in the 1985 to 2002 period at all of the 

NADP sites in the western United States. The EPA has documented a national decrease in 

SO2 emissions of 43 percent from 1990 to 2007 and 24 percent from 2001 to 2007 (EPA 

2008). Oxidation of SO2 emissions can lead to SO4

2- formation and deposition (Kellogg and 

others 1972); concentrations of the two S species often closely track each other (Debell and 

others 2006). The Yellowstone NP NADP site had a 27 percent decrease in net SO2 deposition from 1990 to 1999 (EPA 2008). This widespread decrease in SO2

 emissions and resulting 

SO4

2- deposition is largely a result of the Clean Air Act of 1990 (http://www.epa.gov/air/caa/) 
16 USDA Forest Service RMRS-GTR-248WWW. 2010.

emission reduction provisions amendment, the Highway Low Sulfur Diesel Rule (http://epa.

gov/cleandiesel/documents/420f04034.htm), and the closure and/or emission reductions of 

several smelters and coal burning power plants in the western United States.

All of the NADP sites showed statistically significant decreasing trends in Cl-

, Na+, and 

Mg2+ for both concentration and deposition (except for South Pass which did not show 

trends for Mg2+). Recent trends in Colorado report 9 of 10 high elevation (over 2,700 

meters) NADP sites had statistically significant decreasing Na+ and Cl- (p≤0.01) (Mast, 

and others 2010). These findings also are consistent with reported declines in base cations 

for the eastern United States, other parts of the Northern Rockies, and parts of Europe. 

(Grenon and Story 2009; Hedin and others 1994). The trends in Na+ and Cl-

 may also be 

caused, in part, by changes in protocols. In 1994 a change was made in the type of filter 

used for NADP protocol/procedures at the CAL (Lynch and others 1996). Both of these 

changes may account for a portion of the cation and anion decreases observed, but not all. 

Emission decreases or other environmental factors may contribute to cation and anion decreases, but this trend is not, at present, entirely explainable.

Bulk Deposition

The bulk deposition program in the Bridger Wilderness was established at four sites 

in 1985: Hobbs Lake, Black Joe Lake, Lester Pass, and Indian Park. All four sites were 

developed to establish a high elevation deposition for the Bridger Wilderness. The sites at 

Hobbs and Black Joe Lakes were initiated to investigate possible cause-and-effect relationships between atmospheric deposition and surface water chemistry since both lakes are 

part of the B-T long-term lake monitoring program. In 1985 bulk precipitation collectors 

were established at three NADP sites in and around the Wind River Mountains, (Gypsum 

Creek WY98, South Pass WY97, and Pinedale WY06), to determine a correlation among 

the NADP collectors. These three co-located bulk collectors and the Lester Pass and Indian 

Park bulk collectors were discontinued in 1991 since the precipitation chemistry from 

these sites corresponded well with the Hobbs Lake bulk collector. Current bulk deposition sampling locations evaluated in this report are shown in figure 1. Bulk deposition 

chemical analysis is done at the USFS Air Resource Management (ARM) Laboratory in 

Fort Collins, Colorado (http://www.fs.fed.us/waterlab/). The sites are sampled about every 

2 weeks in the summer, and every 4 weeks in the winter. The summer season generally runs 

from July to October and the winter season from November to June. The bulk precipitation 

program calculates deposition based on concentrations of Ca2+, Mg2+, K+, Na+, Cl-, NH4

+, 

nitrogen(N) as NH4

+, NO3-

, N as NO3

-

, Total N, SO4

2-, S as SO42-, and precipitation (cm). 

Annual trends from the data analysis are shown in table 13 and graphs are depicted in figures 22 to 26.
USDA Forest Service RMRS-GTR-248WWW. 2010. 17

Table 13—Bulk deposition: Mann-Kendall output for annual trends at Hobbs Lake and 

Black Joe Lake sites (rain and snow). Red numbers equal significant trends when 

p<0.1. A negative Sen’s slope represents a decreasing slope.

Hobbs Lake Black Joe Lake

Variable (kg/ha) Sen’s slope p-value Sen’s slope p-value

Ca2+ 0.078 0.009 0.087 0.011

Mg2+ 0.013 0.008 0.013 <0.001

K+ 0.004 0.711 0.004 0.459

Na+ -0.007 0.615 -0.001 0.916

Cl- -0.03 0.010 -0.020 0.019

NH4

+ 0.042 0.002 0.041 0.035

N as NH4

+ 0.027 0.002 0.026 0.035

NO3

- 0.124 0.007 0.151 0.065

N as NO3

- 0.028 0.007 0.034 0.065

Total N 0.055 0.005 0.061 0.027

SO4

2- 0.052 0.224 -<0.001 1

S as SO4

2- 0.017 0.224 -<0.001 1

Precipitation 1.458 0.027 0.150 0.792

Figure 22—Annual NH4

+ trends from Hobbs and Black Joe bulk deposition sites from 1986-2008.

Figure 23—Annual NO3

-

 trends from Hobbs and Black Joe bulk deposition sites from 1986-2008.
18 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 26—Annual Cl-

 trends from Hobbs and Black Joe bulk deposition sites from 1986-2008.

Figure 24—Total annual nitrogen trends from Hobbs and Black Joe bulk deposition sites from 1986-

2008.

Figure 25—Annual precipitation amount (cm) at Hobbs and Black Joe bulk deposition sites from1986-

2008. Only Hobbs had a statistically significant trend.
USDA Forest Service RMRS-GTR-248WWW. 2010. 19

Bulk Deposition Discussion

The Hobbs bulk deposition site generally has slightly higher annual precipitation averages than the Black Joe site. Reduced precipitation at the bulk deposition sites in the early 

2000s, especially at the Black Joe site, which may have influenced deposition amounts.

Bulk deposition trends of decreasing Cl-

 and increasing Mg2+, Ca2+, NH4

+, and NO3-

 are 

consistent with the long-term lake and NADP data analyses. The consistent statistically significant increasing trends in nitrogen are particularly notable. Annual nitrogen deposition 

in terms of both NO3

-

 and NH4

+ at the bulk sampling sites is higher than deposition at the 

NADP sites (see NADP website for annual deposition amounts). Annual NO3

-

 deposition 

at the NADP sites analyzed tends to average around 1.5-3.5 kg/ha/yr sometimes exceeding 

an annual average of 4 kg/ha/yr (South Pass City WY97 site). This may be due in part to 

the sampling equipment. The bulk samplers collect both wet and dry deposition whereas 

the NADP sites collect only wet deposition. In the drier climates of the West, dry deposition is thought to account for a significant proportion of total deposition. As mentioned 

above, data from CASTNET samplers estimate total nitrogen dry deposition in the Rockies 

to be about 25 percent to 33 percent of total deposition (Ingersoll and others 2008). This 

still does not account for the discrepancy in annual nitrogen deposition amounts recorded 

by the two monitoring programs. The bulk sampler sites are located 760 m higher than 

the NADP sites. Higher elevations in the Rocky Mountains typically experience higher 

precipitation and, therefore, higher wet deposition (Baron and others 2000). Also, the bulk 

collectors have an open design that allows for insects, plant debris, and other material to 

fall or get blown into the collectors. The open design also allows for evaporation, which 

has the potential to concentrate the chemical constituents that are measured. Bird droppings sometimes end up in the collectors; as a precaution, samples that show abnormally 

high phosphate levels are discarded in the screening process.

SO4

2- deposition at the bulk sites did not show any trends in annual deposition. This 

coincides with the SO4

2- concentration findings in the lake data, but opposes the decreasing trends in annual SO4

2- deposition found at the NADP sites in the B-T and opposes the 

nation-wide trends of decreasing SO4

2- mentioned above.

Long-Term Lake Monitoring

The lake monitoring program on the B-T National Forest began in 1984. The four lakes 

(Black Joe, Hobbs, Upper Frozen, and Deep lakes) (fig. 1) that are currently monitored were 

chosen based on elevation (above 2,900 meters), size (greater than 15 acres), and low acid 

neutralization capacity (ANC) (table 14). Chemical analyses are conducted at the USFS Air 

Resource Management (ARM) Laboratory in Fort Collins, Colorado (http://www.fs.fed.us/

waterlab/). Lake data for the B-T National Forest can be obtained from the USFS NRIS-Air 

database for chemistry of lakes, streams, and bulk deposition on and near the National Forests 

(http://www.fs.fed.us/waterdata/). The lake sampling followed protocols highlighted in the 

Bridger-Teton National Forest Wind River Mountains Air Quality Monitoring Program 

Table 14—Lakes: Physical features of sampled lakes.

Lake Elevation (m) Depth (m) Area of lake (acres)

Black Joe 3,121 28.9 80.4

Deep 3,218 27.0 60.5

Hobbs 3,083 18.3 17.3

Upper Frozen 3,487 42.9 23.5
20 USDA Forest Service RMRS-GTR-248WWW. 2010.

Methods Manual (USDA FS 2002). Lakes were typically sampled three times per year 

at the inlet and outlet. Season 1 is after ice begins to break up (May to July 21). Season 

2 was taken mid- to late summer when the lakes are stratified (July 22 to August 31). 

Season 3 sample was taken closest to lake freeze-up after fall overturn (September 1 to 

mid November). In addition epilimnion and hypolimnion samples were collected during 

season 2.

Samples are marked “regular” (those taken every time), “duplicate” (taken every couple 

samples), and “blank” (deionized water). In the data analysis, duplicate samples were averaged with their corresponding regular sample if the concentrations were within 10 percent 

of each other. If not, then the preceding and following samples were averaged and the 

sample data closest to the value of the newly averaged sample was used (see Appendix). 

Data from blanks were used for QA/QC in the lab and were not included in the analysis 

for this report. Missing data were left blank. The revised data sets were used for the SAS 

analysis. The long-term lake monitoring program has used three labs throughout its duration. The B-T lake monitoring program started with the USGS lab in Denver, Colorado, 

and then switched to the CAL lab in Illinois in the late 1980s. A switch was again made in 

1996 to the current ARM lab in Fort Collins, Colorado. Split samples were sent to the CAL 

and ARM for 2 years to ensure a smooth transition of QA/QC.

Data from Black Joe, Hobbs, Deep (fig. 27), and Upper Frozen lakes were analyzed for 

trends in concentrations of lab specific conductance (Lcond), ANC (acid neutralizing capacity μeq/L), Ca2+, Cl-

 , K+, Mg2+, Na+, NH4

+, NO3-

, lab pH, and SO4

2- (all in μeq/L). Data 

from each lake was analyzed for annual trends in chemistry at the lake inlet, outlet, epilimnion, and hypolimnion. Tables 15 and 16 show results from epilimnion and hypolimnion 

analysis respectively. Figures 28 to 31 show trends in the hypolimnion. Due to its remote 

location, Upper Frozen Lake is sampled once a year at the outlet during season 2. Tabular 

and graphical information for Upper Frozen Lake are found in table 17 and figures 32 to 33. 

Inlet and outlet datasets from Black Joe, Hobbs, and Deep lakes had enough observations 

to analyze for seasonality and to analyze for trends within each season (tables 18 to 25 and 

figs. 22 to 26 and 28 to 43).

Figure 27—Deep Lake, one of the long-term lakes sampled by the Bridger-Teton National Forest since 

1984 (photo by Hank Williams).
USDA Forest Service RMRS-GTR-248WWW. 2010. 21

Table 15—Lakes: Epilimnion, Mann-Kendall output for annual trends at three lakes: p represents 

p-value; red numbers equal significant trends when p<0.1. A negative Sen’s slope represents a 

decreasing slope.

Black Joe Lake Hobbs Lake Deep Lake

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC 1.025 0.925 0.025 0.161 0.550 0.673

Ca2+ 0.936 0.012 -0.148 0.528 0.499 0.130

Cl- -0.046 0.216 -0.107 0.088 -0.041 0.107

Lcond 0.003 0.870 -0.115 0.025 0.006 0.709

H+ 0.001 0.469 0.005 0.027 0.001 0.747

K+ 0.090 0.044 -0.025 0.454 0.059 0.056

Mg2+ 0.128 0.440 -0.015 0.888 0.165 0.063

Na+ 0.373 0.003 0.259 0.015 0.310 0.008

NH4

+ 0.020 0.439 0.035 0.309 <0.001 0.743

NO3

- <0.001 0.253 -0.152 0003 0.000 0.013

Lab pH -0.006 0.440 -0.024 0.025 -0.004 0.519

SO4

2- 0.182 0.374 -0.039 0.544 0.058 0.980

Table 16—Lakes: Hypolimnion, Mann-Kendall output for annual trends at three lakes: p represents 

p-value; red numbers equal significant trends when p<0.1. A negative Sen’s slope represents a 

decreasing slope.

Black Joe Lake Hobbs Lake Deep Lake

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC 1.121 0.944 0.060 0.168 0.290 0.612

Ca2+ 0.921 0.068 0.075 0.691 0.257 0.888

Cl- -0.037 0.080 -0.090 0.062 -0.060 0.026

Lcond 0.003 0.657 -0.095 0.141 0.000 0.572

H+ 0.005 0.304 0.014 <0.001 0.009 0.159

K+ 0.127 0.015 0.012 0.944 0.055 0.195

Mg2+ 0.129 0.743 0.036 0.691 0.122 0.397

Na+ 0.284 0.058 0.232 0.023 0.082 0.910

NH4

+ 0.161 0.058 -0.015 0.356 0.068 0.006

NO3

- 0.037 0.574 -0.008 0.071 <0.001 0.005

Lab pH -0.012 0.025 -0.028 0.001 -0.018 0.030

SO4

2- 0.177 0.797 -0.059 0.414 -0.097 0.142

Figure 28—Annual hypolimnion NH4

+ trend at Black Joe and Deep lakes from 1984-2008.
22 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 31—Annual hypolimnion H+ trend at Hobbs Lake from 1984-2008.

Figure 29—Annual hypolimnion SO4

2- at Black Joe, Deep, and Hobbs lakes from 1984-2008.

Figure 30—Annual hypolimnion Cl- trend at Black Joe and Deep lakes from 1984-2008.

Table 17—Upper Frozen Lake: outlet, annual trends from MannKendall test. Red numbers equal significant trends when p<0.1. 

A negative Sen’s slope represents a decreasing slope.

Variable (μeq/L) Sen’s slope p- value

ANC 0.700 0.087

Ca2+ 1.148 0.013

Cl- -0.005 0.876

Lcond -0.004 0.938

H+ -0.072 0.005

K+ 0.084 0.029

Mg2+ 0.366 0.013

Na+ 0.526 0.119

NH4

+ -0.061 0.135

NO3

- -0.228 0.276

Lab pH 0.043 0.008

SO4

2- 0.264 0.029
USDA Forest Service RMRS-GTR-248WWW. 2010. 23

Figure 33—Upper Frozen Lake annual outlet SO4

2- trend from 1997-2008.

Figure 32—Upper Frozen Lake annual outlet ANC trend from 1997-2008.

Table 18—Lakes: Inlets, Seasonal Mann-Kendall output for annual trends at three lakes: p represents p-value 

and is significant when p<0.1. Numbers marked with an * mean those variables required the Seasonal 

Mann Kendall test for analysis; all other numbers come from the Mann-Kendall test. Bolded red numbers 

signify significant trends. A negative Sen’s slope represents a decreasing slope.

Black Joe Inlet Hobbs Inlet Deep Inlet

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC *0.959 *0.739 *0.407 *0.335 *0.859 *1

Ca2+ *1.236 *<0.001 *0 *1 *1.763 *<0.001

Cl- *-0.015 *0.567 *-0.093 *0.006 *-0.035 *0.224

Lcond *0.003 *0.861 *-0.097 *0.071 *0.067 *0.532

H+ 0.004 0.191 0.006 0.027 0.004 0.142

K+ *0.068 *0.024 0.024 0.441 *0.069 *0.018

Mg2+ *0.149 *0.032 *0.004 *0.821 *0.212 *0.003

Na+ *0.295 *<0.001 *0.270 *0.008 *0.350 *0.002

NH4

+ -0.004 0.926 0.091 0.036 0 1

NO3

- *0.203 *0.029 *-0.003 *0.277 *0.127 *0.272

LabpH -0.019 0.141 -0.025 0.014 -0.018 0.154

SO4

2- *0.290 *0.056 *-0.104 *0.259 *0.390 *0.128
24 USDA Forest Service RMRS-GTR-248WWW. 2010.

Table 19—Lakes: Outlets, Seasonal Mann-Kendall output for annual trends at three lakes: p represents 

p-value and is significant when p<0.1. Numbers marked with an * mean those variables required the 

Seasonal Mann Kendall test for analysis; all other numbers come from the Mann-Kendall test. Bolded 

red numbers signify significant trends. A negative Sen’s slope represents a decreasing slope.

Black Joe Outlet Hobbs Outlet Deep Outlet

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC 0.815 0.963 *-0.169 *0.017 0.891 0.726

Ca2+ 0.927 0.002 0.034 0.870 *0.811 *<0.001

Cl- -0.022 0.513 -0.084 0.068 -0.075 0.035

Lcond 0.007 0.852 -0.081 0.050 -0.018 0.743

H+ 0.003 0.129 0.005 0.168 0.003 0.129

K+ 0.072 0.03 -0.071 0.018 0.028 0.293

Mg2+ 0.210 0.003 0.014 0.779 0.200 <0.001

Na+ 0.461 <0.001 0.120 0.154 0.162 0.234

NH4

+ 0.061 0.093 0.037 0.065 0.000 1

NO3

- *0.010 0.870 -0.020 0.068 -0.009 0.130

LabpH -0.014 0.118 -0.018 0.141 -0.012 0.141

SO4

2- 0.310 0.118 0.031 0.640 0.008 0.926

Table 20—Lakes: Concentration, trends (three seasons) from Mann-Kendall test, Black Joe Lake 

inlet: p represents p-value; red numbers equal significant trends when p<0.1. A negative Sen’s 

slope represents a decreasing slope.

Black Joe Inlet

Season 1 Season 2 Season 3

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC 0.738 0.526 1.251 0.561 1 0.450

Ca2+ 0.413 0.492 2.046 0.012 1.435 0.090

Cl- -0.057 0.224 -0.015 0.692 0.038 0.450

Lcond -0.129 0.341 0 0.937 0.140 0.184

H+ 0.005 0.673 0.002 0.672 0.004 0.155

K+ 0.031 0.398 0.102 0.039 0.090 0.365

Mg2+ 0.082 0.561 0.048 0.578 0.483 0.006

Na+ 0.220 0.102 0.313 0.014 0.387 0.022

NH4

+ 0 0.495 0.026 0.523 -0.002 0.808

NO3

- 0.053 0.950 0.205 0.125 0.552 0.023

LabpH -0.011 0.616 -0.008 0.315 -0.015 0.165

SO4

2- -0.104 0.615 0.583 0.020 0.701 0.124

Table 21—Lakes: Concentration, trends (three seasons) from Mann-Kendall test, Black Joe Lake 

outlet: p represents p-value; red numbers equal significant trends when p<0.1. A negative Sen’s 

slope represents a decreasing slope.

Black Joe Outlet

Season 1 Season 2 Season 3

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC 0.652 1 0.982 0.309 0.086 0.039

Ca2+ 0.881 0.012 1.087 0.011 1.020 0.039

Cl- 0.015 0.853 -0.043 0.254 -0.054 0.197

Lcond 0 0.958 0.030 0.747 0.074 0.333

H+ 0.003 0.291 0.002 0.254 0.004 0.078

K+ 0.077 0.068 0.066 0.101 0.030 0.552

Mg2+ 0.215 0.003 0.061 0.637 0.267 0.005

Na+ 0.403 0.002 0.430 <0.001 0.458 0.006

NH4

+ 0.043 0.525 0 0.615 0 0.900

NO3

- 0.024 0.812 0.002 0.980 0.022 0.564

LabpH -0.011 0.278 -0.008 0.214 -0.018 0.070

SO4

2- 0.312 0.068 0.350 0.130 0.411 0.056
USDA Forest Service RMRS-GTR-248WWW. 2010. 25

Table 22—Lakes: Concentration, trends (three seasons) from Mann-Kendall test, Hobbs Lake inlet: 

p represents p-value; red numbers equal significant trends when p<0.1. A negative Sen’s slope 

represents a decreasing slope. Variables with only seven observations and are not statistically 

valid since at least eight observations are needed.

Hobbs Inlet

Season 1 Season 2 Season 3

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC 0.438 0.673 2.125 1 0.133 0.232

Ca2+ 0.244 0.691 0 1 -0.554 0.484

Cl- -0.085 0.087 -0.389 0.184 -0.146 0.052

Lcond -0.049 0.519 -0.460 0.640 -0.207 0.026

H+ 0.006 0.150 0.013 0.072 0.008 0.044

K+ -0.006 0.960 -0.068 0.585 0.142 0.248

Mg2+ 0.066 0.205 0.155 0.938 -0.281 0.090

Na+ 0.317 0.035 0.359 0.640 0.142 0.125

NH4

+ 0.111 0.039 0.263 0.085 -0.017 0.740

NO3

- -0.005 0.214 0.132 0.436 0.003 0.591

LabpH -0.019 0.150 -0.065 0.072 -0.033 0.044

SO4

2- -0.004 0.960 -0.541 0.043 -0.190 0.303

Table 23—Lakes: Seasonal concentration, trends from Mann-Kendall test, Hobbs Lake outlet: p 

represents p-value; red numbers equal significant trends when p<0.1. A negative Sen’s slope 

represents a decreasing slope.

Hobbs Outlet

Season 1 Season 2 Season 3

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC -0.055 0.197 -0.115 0.417 -0.727 0.036

Ca2+ 0.016 0.980 0.322 0.330 0.194 0.551

Cl- -0.084 0.130 -0.093 0.330 -0.103 0.054

Lcond -0.090 0.164 -0.100 0.475 0 1

H+ 0.006 0.254 0.004 0.330 0.003 0.726

K+ -0.041 0.157 -0.133 0.119 -0.007 0.806

Mg2+ -0.003 0.960 0.091 0.299 0.071 0.506

Na+ 0.249 0.074 0.189 0.183 0.136 0.381

NH4

+ 0 0.565 0.084 0.133 0.069 0.379

NO3

- -0.032 0.006 -0.015 0.579 0 0.547

LabpH -0.015 0.243 -0.015 0.346 -0.015 0.462

SO4

2- 0.015 0.862 0.043 0.627 0.069 0.624

Table 24—Lakes: Seasonal concentration, trends (three seasons) from Mann-Kendall test, Deep 

Lake inlet: p represents p-value; red numbers equal significant trends when p<0.1. A negative 

Sen’s slope represents a decreasing slope.

Deep Inlet

Season 1 Season 2 Season 3

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC 0.870 0.692 0.937 0.692 0.475 0.483

Ca2+ 0.832 0.323 2.745 0.002 1.580 0.093

Cl- -0.028 0.352 -0.038 0.444 -0.075 0.779

Lcond 0.015 0.693 0.172 0.178 0 1

H+ 0.005 0.632 0.001 0.653 0.002 0.362

K+ 0.051 0.382 0.075 0.091 0.083 0.132

Mg2+ 0.131 0.225 0.288 0.026 0.370 0.093

Na+ 0.382 0.016 0.340 0.125 0.315 0.160

NH4

+ 0 0.585 -0.014 0.488 -0.012 0.273

NO3

- 0.061 0.821 0.084 0.561 0.448 0.074

LabpH -0.014 0.632 -0.006 0.634 -0.009 0.123

SO4

2- 0.064 0.800 0.539 0.132 1.145 0.441
26 USDA Forest Service RMRS-GTR-248WWW. 2010.

Table 25—Lakes: seasonal concentration, trends (three seasons) from Mann-Kendall test, Deep 

Lake outlet: p represents p-value; red numbers equal significant trends when p<0.1. A negative 

Sen’s slope represents a decreasing slope.

Deep Outlet

Season 1 Season 2 Season 3

Variable

(μeq/L) Sen’s slope p Sen’s slope p Sen’s slope p

ANC 0.983 0.976 0.880 0.611 -0.106 0.434

Ca2+ 0.925 0.030 0.893 0.013 0.620 0.138

Cl- -0.075 0.046 -0.062 0.114 -0.099 0.126

Lcond 0 1 -0.007 0.799 -0.037 0.509

H+ 0.005 0.608 -0.002 0.778 0.007 0.232

K+ 0.052 0.061 0.039 0.310 0.023 0.509

Mg2+ 0.227 0.103 0.132 0.032 0.367 0.004

Na+ 0.261 0.070 0.004 0.910 0.398 0.008

NH4

+ 0.078 0.198 0 1 -0.009 0.421

NO3

- 0.000 0.492 0 0.180 0 0.668

LabpH -0.011 0.629 0.005 0.756 -0.024 0.343

SO4

2- 0.012 0.976 0.017 0.651 -0.144 0.509

Figure 34—Black Joe inlet annual NO3

-

 trend for season 3 from 1984-2007.

Figure 35—Black Joe inlet annual SO4

2- trend for season 2 from1984-2007.
USDA Forest Service RMRS-GTR-248WWW. 2010. 27

Figure 36—Black Joe outlet annual SO4

2- trend for seasons from 1984-2007.

Figure 37—Black Joe outlet annual sodium trends through seasons from 1984-2008.

Figure 38—Hobbs inlet annual NH4

+ trends for seasons 1 and 2 from 1984-2008. Samples at the 0 

μeq/L represent values that were below lab detection limits.

Figure 39—Hobbs inlet annual SO4

2- trend for season 2 from 1984-2005. Line gaps are caused by 

years of missing data, which make it hard to extrapolate whether a trend is actually present.
28 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 40—Hobbs outlet annual NO3

-

 trend for season 1 from 1984-2008.

Figure 41—Hobbs outlet annual Cl- trend for season 3 from 1986-2008.

Figure 42—Deep Lake inlet annual NO3

-

 trend for season 3 from 1984-2008.

Figure 43—Deep Lake outlet annual Na+ trends for season 1 and 3 from 1984-2008.
USDA Forest Service RMRS-GTR-248WWW. 2010. 29

Lake Trend Discussion

More significant trends appeared in the seasonal inlet samples than the outlet samples, most likely due to Lake Watershed processes such as biological activity and mixing. 

Black Joe and Deep lakes may be particularly influenced by melting snowfields and bedrock weathering. Chemical concentrations in lakes may be influenced by weather and the 

time of year samples were collected since lake chemistry is increasingly influenced by 

groundwater after the snowmelt surge is over (Guerri 2010, personal communication).

Two trends in nitrogen concentration were present. First was the increase in NO3

-

 present for Black Joe and Deep Lakes for season 3. This trend is not as prevalent in other 

sections of the lakes that were sampled, which may be due to uptake of NO3

-

 by aquatic 

biota. An increasing trend in NO3

- concentration was also found in lakes that were sampled in the Shoshone National Forest (Bevenger 2008). USFS Region 1 (Montana and 

Idaho) Phase 3 lake sampling only reported one lake with a statistically significant increase trend in NO3

-

. It should be noted that the Region 1 lake monitoring program started 

9 years after Region 4 (Grenon and Story 2009). The inlet sampling locations, where most 

of the NO3

- trends have been detected, were not sampled in the Region 1 lakes. In the 

Rocky Mountains, many lakes may be at or near nitrogen saturation levels (Burns 2003 

and Campbell 2004) where lake nitrogen supply exceeds uptake. Increasing trends in nitrate concentrations have occurred in at least two water catchments in the Colorado Front 

Range (Williams and others 1996). In these two catchments, NO3

- levels have increased 

from below detection limits to about 10 μeq/L (0.62 mg/L). Nanus and others (2008) also 

reported a correlation between NO3

-

 (p<0.05) from lakes and NOx emissions within 300 

km from Rocky Mountain NP, Grand Teton NP, Great Sand Dunes NP, and Yellowstone 

NP with the strongest correlations in the central and southern Rockies in Colorado.

Ammonia (NH4

+) concentrations have also been increasing at Black Joe, Hobbs, and 

Deep lakes. Significant increasing trends were present in the hypolimnion at Black Joe 

and Deep lakes, the inlet and outlet at Hobbs Lake, and the outlet at Black Joe Lake. 

The lakes on the Shoshone National Forest were not analyzed for NH4

+ trends (Bevenger 

2008).

The major concern associated with increasing inorganic nitrogen in aquatic ecosystems 

is the potential to cause acidification (via increasing hydrogen ions) and/or eutrophication 

through increased primary producers (Camargo and Alonso 2007).

The data suggest an increasing trend in sulfate (SO4

2-) at Upper Frozen and Black Joe 

lakes. This is opposite the pattern of decreasing trends in SO4

2- concentrations observed in 

precipitation across the United States, including the trends found in the NADP data discussed above and in Hobbs Lake. SO4

2- concentrations in lake water may be influenced by 

internal weathering sources such as sulfur-bearing minerals in the bedrock (FeS2

), newly 

exposed bedrock due to melting snow fields (with the exception of Hobbs Lake), or local 

and/or regional emissions. In the neighboring Shoshone National Forest, Bevenger (2008) 

found no significant trends in SO4

2- at Saddlebag Lake and significant decreasing trends at 

Ross Lake for the outlet and hypolimnion. USFS Region 1 lake analysis revealed an overall lack of an SO4

2- trend, with only Stepping Stone Lake reporting a significant decreasing 

trend. On the other hand, some lakes in Colorado are exhibiting increases or no trend in 

SO4

2- concentrations when analyzed (Mast 2009, personal communication). The cause of 

the increased trend in SO4

2- in the B-T lakes is not readily understood.

Overall, cations (Na+,Ca2+, Mg2+, and K+) showed significant increases in concentrations over time in some portions of the lakes. A significant decreasing trend in the anion 

Cl- was found, most notably in the hypolimnion and outlet samples of Black Joe and Deep 

lakes.
30 USDA Forest Service RMRS-GTR-248WWW. 2010.

IMPROVE (Interagency Monitoring of Protected Visual 

Environments)

The IMPROVE program was established in 1985 as a tool to monitor and protect visibility 

in 156 Federal Class I areas (a stipulation from the 1977 amendments to the Clean Air Act). 

The goals of the IMPROVE network are to establish existing visibility conditions in Class 

I areas, to identify the pollutants that are impairing visibility, and to assess progress toward 

the national visibility goal of no manmade impairment in support of the Regional Haze Rule 

(IMPROVE information can be found at: http://vista.cira.colostate.edu/improve/).

Two IMPROVE sites in Wyoming have a sufficient period of record to run meaningful 

statistical analyses: YELL1 and YELL2 in Yellowstone National Park and BRID1 near the 

boundary of the Bridger Wilderness 10 miles east of Pinedale, Wyoming. Both sites were 

established in 1988. YELL1 was moved about a mile west from its original site in 1996 due to 

dust exposure, and the new site was named YELL2. The MOZI1 IMPROVE site was started in 

1994 and is located on Buffalo Pass northeast of Steamboat Springs, Colorado, and monitors 

the Mount Zirkel Wilderness. Data from MOZI1 was also analyzed to give a more regional 

perspective. Both MOZI1 and BRID1 are operated by the Forest Service and YELL2 is operated by the Park Service.

The IMPROVE data analyzed were sent directly from the Forest Service Visibility Data 

Analyst at CIRA (Cooperative Institute for Research in the Atmosphere, Fort Collins, 

Colorado), because the 2007 data were not yet available on their public website (http://

views.cira.colostate.edu). Seasonal data was used as part of the analysis when possible. 

The seasons are the same as those used in the NADP section where winter is defined as 

January, February, and March; spring as April, May, and June; summer as July, August, 

and September; and fall as October, November, and December. The analysis started with 

the first full year of NADP site establishment (1989). The Regional Haze Rule has strict 

data quality assurance guidelines to determine whether the data collected for a given year 

is adequate to represent the visibility conditions from that year. All data that did not meet 

these adequacy requirements were removed from the analysis.

Annual trends for BRID1, YELL1&2, and MOZI1 were analyzed for the arithmetic means of the following variables (the “E” signifies that the variable represents the 

atmospheric extinction due to the indicated species): ESO4

2+ (ammonium sulfate), ENO3-

(ammonium nitrate), EOMC (organic mass from carbon), ELAC (light-absorbing carbon 

or elemental carbon), ESoil (fine soil), ECM (coarse mass), ESalt (Sea salt), dv (deciview), 

VR (visual range), Rbext (sum of aerosol extinctions - ES04, ENO3, EOMC, ELAC, ESoil, 

ESalt, and ECM), and FMass (PM2.5). Seasonality was taken into account in all variables 

except ESalt, which is comparatively small and showed no seasonality. Annual trends for 

each season were also analyzed for all variables. Statistically significant trends are shown 

in tables 26 to 29 and figures 44 to 49.
USDA Forest Service RMRS-GTR-248WWW. 2010. 31

Table 26—IMPROVE: Visibility, Seasonal Mann-Kendalla output for annual trends at three sites: p represents 

p-value; red numbers equal significant trends when p<0.1. A negative Sen’s slope represents a 

decreasing slope. Decreasing trend indicates improving air quality except for VR. The period of record 

analyzed for BRID1 and YELL1&2 was 1988 to 2007, and MOZI1 was 1994 to 2007.

Variable (Mm-1) BRID 1 YELL 1&2 MOZI 1

(dv is dv and

VR is km) Sen’s slope p Sen’s slope p Sen’s slope p

dv -0.074 0.001 -0.105 0.007 -0.141 0.004

Rbext -0.118 0.009 -0.198 0.043 -0.264 0.020

ESO4

2- -0.039 0.011 -0.018 0.220 -0.083 0.020

ENO3

- 0.008 0.136 0.014 0.056 0.008 0.342

EOMC -0.019 0.511 -0.053 0.242 -0.042 0.299

ELAC 0.006 0.483 -0.028 0.032 -0.018 0.142

ESOIL -0.003 0.380 -0.018 0.002 -0.004 0.666

ECM -0.070 <0.001 -0.144 <0.001 -0.134 <0.001

VR 1.453 0.009 1.771 0.043 2.392 0.020

a

Sea salt was analyzed with the Mann Kendall test and no statistically significant trends were found.

Table 27—IMPROVE: Visibility, Mann-Kendall output for seasonal trends at BRID1: p represents p-value; 

ss represents Sen’s slope; red numbers equal significant trends when p<0.1. A negative Sen’s slope 

represents a decreasing slope. Decreasing trend indicates improving air quality except for VR. The period 

of record analyzed for BRID1 and YELL1&2 was 1988 to 2007, and MOZI1 was 1994 to 2007.

BRID1

Variable (Mm-1) Winter Spring Summer Fall

(dv is dv and

VR is km) ss p ss p ss p ss p

dv -0.062 0.060 -0.033 0.343 0.046 0.685 -0.163 <0.001

Rbext -0.101 0.113 -0.062 0.537 0.218 0.260 -0.299 <0.001

ESO4

2- -0.042 0.276 0.015 0.387 -0.045 0.017 -0.071 0.012

ENO3

- 0.029 0.060 0.006 0.537 0.005 0.444 -0.003 0.902

EOMC -0.027 0.198 0.038 0.434 0.306 0.096 -0.097 0.012

ELAC 0.006 0.621 0.017 0.266 0.017 0.344 -0.011 0.266

ESOIL 0.003 0.767 -0.001 0.967 <0.001 1 -0.007 0.064

ECM -0.057 0.023 -0.061 0.149 -0.044 0.053 -0.113 <0.001

VR 1.616 0.113 0.461 0.537 -1.263 0.260 4.120 <0.001

Table 28—IMPROVE: Visibility, Mann-Kendall output for seasonal trends at YELL1 & 2: p represents p-value; 

ss represents Sen’s slope; red numbers equal significant trends when p<0.1. A negative Sen’s slope 

represents a decreasing slope. Decreasing trend indicates improving air quality except for VR. The period 

of record analyzed for BRID1 and YELL1&2 was 1988 to 2007, and MOZI1 was 1994 to 2007.

YELL 1&2

Variable (Mm-1) Winter Spring Summer Fall

(dv is dv and

VR is km) ss p ss p ss p ss p

dv -0.111 0.086 0.013 0.945 -0.092 0.127 -0.204 0.024

Rbext -0.179 0.150 0.016 1 -0.160 0.537 -0.385 0.024

ESO4

2- -0.032 0.537 0.086 0.086 -0.020 0.202 -0.078 0.064

ENO3

- 0.079 0.304 0.026 0.115 0.004 0.484 0.020 0.537

EOMC -0.091 0.005 -0.107 0.150 0.696 0.029 -0.165 0.034

ELAC -0.029 0.115 -0.014 0.304 <0.001 1 -0.057 0.016

ESOIL -0.005 0.304 -0.007 0.945 -0.051 0.009 -0.015 0.086

ECM -0.075 0.193 -0.027 0.945 -0.318 0.001 -0.100 0.047

VR 2.390 0.150 -0.157 1 0.666 0.537 4.217 0.024
32 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 44—BRID1 IMPROVE site winter extinction attributed to NO3

-

 from 1992-2007.

Figure 45—BRID1 IMPROVE site seasonal extinction attributed to SO4

2- trends from 1989-2007.

Table 29—IMPROVE: Visibility, Mann-Kendall output for seasonal trends at MOZI1; p represents p-value; 

ss represents Sen’s slope; red numbers equal significant trends when p<0.1. A negative Sen’s slope 

represents a decreasing slope. Decreasing trend indicates improving air quality except for VR. The 

period of record analyzed for BRID1 and YELL1&2 was 1988 to 2007, and MOZI1 was 1994 to 2007.

MOZI1

Variable (Mm-1) Wintera Spring Summer Fall

(dv is dv and

VR is km) ss p ss p ss p ss p

dv -0.321 0.009 -0.073 0.193 -0.026 0.756 -0.246 0.048

Rbext -0.472 0.004 -0.118 0.244 0.045 1 -0.359 0.175

ESO4

2- -0.053 0.174 0.003 0.945 -0.143 0.020 -0.132 0.175

ENO3

- -0.018 0.711 0.021 0.373 0.012 0.436 0.008 0.917

EOMC -0.175 0.019 -0.052 0.244 0.218 0.119 -0.042 0.466

ELAC -0.013 0.902 -0.016 0.451 -0.033 0.436 -0.018 0.348

ESOIL 0.010 0.386 0.009 0.732 -0.019 0.213 -0.011 0.466

ECM -0.183 0.035 -0.097 0.150 -0.109 0.043 -0.184 0.048

VR 8.027 0.004 1.087 0.244 -0.351 1 6.447 0.175

aWinter had only eight observations, which is the minimum number required by the DAP to recognize statistical 

significance.
USDA Forest Service RMRS-GTR-248WWW. 2010. 33

Figure 49—The 20% best and 20% worst annual average SVR at BRID1, MOZI1, and YELL1&2 

IMPROVE sites.

Figure 46—YELL1 & 2 IMPROVE site seasonal extinction attributed to SO4

2- trends from 1991-2007.

Figure 47—YELL1 & 2 IMPROVE site spring extinction attributed to NO3

- from 1997-2007. (This graph 

was included even though the NO3

-

 trend was not statistically significant at p<0.1.)

Figure 48—MOZI1 IMPROVE site summer extinction attributed to SO4

2- trend from 1995-2007.

50 

100 

150 

200 

250 

300 

350 

1989 1990 1991 1992 1993 

1994 

1995 1996 1997 1998 1999 2000 2001 2002 2003 

2004 

2005 2006 2007 

km 

BRID1 

MOZI1 

YELL1&2 

20% best SVR 

20% worst SVR 
34 USDA Forest Service RMRS-GTR-248WWW. 2010.

IMPROVE Discussion

The original IMPROVE site in Yellowstone National Park, YELL1, was moved in 1996 

due to dust exposure. Some decreasing trends in crustal components analyzed for YELL 1 

and YELL2 may be explained by monitor relocation.

The results from the IMPROVE data analysis show trends of increased average visibility across the region. This is consistent with visibility trends elsewhere in the western 

United States (Debell and others 2006; Grenon and Story 2009). A consistent reduction in 

dv and increase in VR occurred at all sites for most seasons observed. It should be noted 

that in some seasons the dv showed significant decreasing trends while the corresponding 

VR did not show significant increasing trends; this may be due to the logarithmic scale 

of dv, but the matter was not further investigated in this report. The analysis also found 

decreasing trends at all sites in Rbext and ECM along with a decreasing trend at some of 

the sites for SO4

2-, FMass, ELAC, and ESoil. The decrease in SO42- is consistent with the 

roughly 250,000 tons per year decrease in western electricity generating units (EGU) of 

SO2

 emissions since 1996.

A statistically significant increasing trend occurred in annual NO3

- at YELL1 and YELL2 

and BRID1 showed a significant increasing trend in NO3

- during the winter season. An increasing NO3

-

 trend in and around the B-T National Forest is opposite to the consistent 

decreasing NO3

- observed trend at IMPROVE sites found throughout Region 1 (Grenon 

and Story 2009). NOx emissions from the western United States have declined by roughly 

75,000 tons per year since 1996, which suggests that some new or other source of nitrate 

is counteracting the expected improvements in visibility. It is also possible that the NOx

reductions have occurred at facilities that do not impact Bridger and Yellowstone (fig. 1). 

The MOZI1 IMPROVE site in Colorado did not have a NO3

-

 trend.

These findings are generally consistent with EPA (2008) findings that no Class 1 

IMPROVE site had statistically significant upward trends for any of the extinction parameters evaluated (the noteworthy exception is the localized NO3

-

 increase trends discussed 

above).

Conclusions

This report is intended to provide useful information for better understanding and management of air quality in southwest Wyoming. This report provides air quality information 

and associated resource information for NEPA and PSD, and establishes a baseline for 

detection and characterization of effects from natural and anthropogenic emission sources 

and climate change. The Forest Service, Wyoming DEQ Air Quality Division, EPA, USGS, 

BLM, and universities regularly use the data from these monitoring programs for model 

validation and to assess the effectiveness of mitigation efforts—mostly associated with 

energy development—that are taking place in the local area and the region. Continued 

monitoring of these AQRVs is important for the agencies ability to demonstrate fulfillment 

of their responsibilities under the Clean Air and Wilderness Acts.

Analysis of the B-T NF air monitoring assessment documents a consistently increasing 

trend in nitrogen deposition. NH4

+ showed an increasing trend at all NADP sites, bulk deposition sites, and in lake concentrations, but the trend was less pronounced. NO3

- showed 

a increasing trend in lake samples, primarily the inlets and at both bulk deposition sites. 

A sporadic increasing NO3

-

 trend also was detected in deposition at NADP sites for some 

seasons. An increasing trend in NH4

+ is occurring over much of the western United States 

and may be partially due to increased agriculture emissions (feedlots, fertilizer, etc.).

This increasing deposition of nitrogen into the Bridger Wilderness is of concern. Total 

nitrogen deposition at the Hobbs Lake and Black Joe Lake sites have averaged 2.35 and 

2.66 kg/ha-1year-1 respectively over the last 22 years with min/max ranges of 1.23 to 4.3 kg/
USDA Forest Service RMRS-GTR-248WWW. 2010. 35

ha-1year-1. Using hindcasting of diatom communities, Baron (2006) found the background 

critical load—the level of atmospheric pollutant deposition or concentration above which 

negative ecosystem effects can occur—for nitrogen in the high alpine lakes of Rocky 

National Park to be about 1.5 kg/ha-1year-1. Saros and others (2010), using fossil diatom 

assemblages, determined a critical load for the Greater Yellowstone of 1.5 kg/ha-1year-1. 

In mixed conifer forests of California, Fenn and others (2008) suggest the critical load for 

nitrogen deposition among lichen communities to be around 3.1 kg/ha-1year-1. This data 

suggest that sensitive and pristine high-elevation (over 3,000 meters) lakes in the B-T 

could be near or at levels where adverse ecosystem effects may occur.

The overall decrease in SO4

2- at NADP sites analyzed is consistent with decreasing SO42-

trends in precipitation across the United States. This trend is most likely due to reductions 

of industrial sulfur emissions from power plants and the 1993 Highway Low Sulfur Diesel 

Rule (http://epa.gov/cleandiesel/documents/420f04034.htm). Sulfate concentration trends 

in the lake, bulk deposition samples, and IMPROVE data are not as clear. Black Joe and 

Upper Frozen lakes showed an increasing SO4

2- trend for some seasons. The bulk deposition sites had no sulfate trend.

Lake cations concentrations generally showed increasing trends especially for Ca2+ and 

Mg2+ while Cl-

 appears to be decreasing in lake concentrations. This is the same pattern 

found in the NADP and the bulk deposition data. The increase in base cations may be due to 

melting snowfields and glaciers and possibly an increase in bedrock weathering associated 

with climate change. However, in contrast, lakes in Montana showed overall decreasing 

trends in both anions and cations (Grenon and Story 2009). Visibility improvements, evidenced by increasing VR, decreased dv, and reduced light extinction were observed at all 

three of the IMPROVE sites.

EPA (1996) reports that the Rbext in northwestern United States urban regions peaks in 

the winter due to an increase in light scattering from ammonium nitrite and organics (presumably due to winter inversions). In the interior western United States, ammonium sulfate 

light scattering is unique in that it does not peak in the summer months as it does elsewhere 

but has been shown in Boise, Idaho, and Missoula, Montana, to peak in the coldest months 

(Debell and others 2006). The general decreasing Rbext trends in the Bridger Teton NF are 

consistent with the overall pattern of increasing VR in the northwestern United States.

The observed trends in this report should be used only as indicators of possible current 

and future changes in air quality and water chemistry. Because the periods of record for the 

datasets are relatively short, the trends identified may change in the future as more data is 

collected over time. Continued analysis will be required to evaluate trends and help determine their causes.

Considerations

Sampling lake sediment cores has potential to help understand trends of metal accumulation from atmospheric deposition sources (Baron and others 1986) and nitrogen critical 

loads (Baron 2006). Baron (2006) has explored the utility of examining high-elevation lake 

sediment cores and further investigating the relationship between shifting diatom communities, hindcasting nitrogen emissions, and then deriving critical loads. Analyzing metal 

concentrations, diatom diversity, and nitrogen concentration from sediment cores at one 

or more of the B-T lakes used for long-term monitoring could be diagnostic of long-term 

air quality trends and help determine critical load values for sensitive ecosystems in the 

Bridger-Teton National Forest.

 Additional analysis could be done with the NADP dataset to address trends at a site or 

regional level. Deposition from NADP sites could be assessed and used with other available 

data (such as the 1985-1991 co-located bulk / NADP collectors and the two discontinued 
36 USDA Forest Service RMRS-GTR-248WWW. 2010.

bulk sites) to help establish more accurate baseline values in order to predict N and S critical loads and to help guide decision making processes.

Preliminary review suggests that NO3

-

 concentrations in the Bridger Wilderness are 

much higher in the summer than winter at the bulk deposition sites (Svalberg and Porwoll 

2008). It would be useful to analyze the bulk data seasonally for both deposition and concentration of all variables analyzed. The winter portion could then be compared with the 

results from snowpack sampling.

IMPROVE monitoring provides an invaluable historic and current look at visibility 

conditions (including wildland fire smoke), which could be useful in assessing visibility 

impacts and for regional haze analysis. Due to the nitrogen and sulfate trend increases—

which are in contrast to predominant national trends—it is strongly recommended that all 

the USFS R4 IMPROVE sites continue to be re-analyzed for statistically validated trends. 

In the fall of 2009, a new IMPROVE site was added near Pinedale, Wyoming, near Boulder 

Lake. This site is significant because theoretical models predict the Boulder drainage to 

be a major “hotspot” for ozone and emission clustering in Sublette County. Data from the 

Boulder IMPROVE site should be compared with annual results from the other IMPROVE 

sites in the area.

This report did not review the lichen monitoring (St. Clair 2000) or the yearly USGS snow 

chemistry sampling network along the Rocky Mountains Continental Divide (Ingersoll and 

others 2008). Lichens are useful indicators of long term pollution impacts, and are typically sampled every 5 to 8 years. Lichens were sampled from the Bridger Wilderness in 

2004. Lichens can provide useful air quality information specifically on sulfur and nitrogen 

compounds and metals. Analyzed lichen data could provide a valuable addition to the lake 

chemistry, deposition, and visibility information in this report.

The USGS Rocky Mountain Snowpack Network provides the only air quality related 

sampling directly adjacent to some of the USFS Wilderness areas and is useful for winter bulk deposition analysis. It is recommended the USFS Region 4 continue support of 

and coordination with the USGS Snow Chemistry sampling program (Ingersoll and others 

2008).

Acknowledgments

Many people provided information and reviews and helped make this report possible: 

Scott Copeland (CIRA, Lander), Thomas Dzomba (USFS R1), Linda Geiser (USFS R6), 

Laurie Porth (USFS-RMRS), Alisa Mast (USGS), John Zachariassen (USFS-RMRS), and 

Cindy Swanson (USFS-RMRS).

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in sulfate and ammonium in US precipitation: Results from the National Atmospheric Deposition 

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USDA Forest Service RMRS-GTR-248WWW. 2010. 39

Appendix: Shoshone National Forest Air Quality Data Trend Analysis 

Greg Bevenger, Hydrologist, Shoshone NF, Cody, Wyoming 2008 

 In 2008, staff on the Shoshone National Forest conducted a comprehensive analysis 

of air quality monitoring data for the Forest portion of the Wind River Range. The data 

set that was analyzed was collected at the South Pass NADP site and Ross and Lower 

Saddlebag Lakes. The record dates back to 1986. 

 Data analysis protocols used for the NADP site and lakes assessment is identical to 

the protocols explained in the main body of this GTR. 

 South Pass NADP Site—Analysis of data collected between 1986 and 2006 (2007 

data was not yet available) was completed in early 2008. Both wet deposition and 

precipitation-weighted deposition data sets were analyzed. The analysis indicates change 

over time, with statistically significant upward or downward trend depending upon the 

parameter (Figures 1 through 4). 

 Ammonia (NH4) is on an upward trend and has basically doubled, but there are 

seasonal differences. The greatest deposition occurs during fall and winter. Potential 

sources of ammonia are upwind feedlots and machinery, e.g., drill rigs, that does not use 

catalytic converters. 

 Precipitation-weighted nitrate (NO3) deposition is on an upward trend for all four 

seasons. There is no statistically significant trend with wet deposition nitrate levels, but 

values have increased substantially for the winter, spring, and fall seasons. The 

differences between wet and precipitation-weighted deposition are explained by units of 

measure, i.e., volume by weight by period versus concentration by precipitation volume, 

respectively. The statistically insignificant trend in wet deposition is due to differences 

between seasons and variability within and across seasons. A potential source of nitrate is 

upwind emissions from oil and gas developments. 

 Sulfate (SO4) is on a downward trend through all seasons. Values have decreased by 

25-50%. The trend could be related to 1990s-era reductions in the use of high sulfur 

diesel fuel. Controls on emissions at refineries and coal-fired power plants, on a western 

U.S. regional basis, could also be a cause. 

 There is no trend with inorganic-nitrogen (Inorg-N) at the 95% confidence level but 

there is an upward trend at the 90% level. A potential source of inorganic nitrogen is 

upwind agricultural activities. 

 In addition to Forest Service uses, Wyoming Department of Environmental Quality 

and other agencies continually utilize data collected from this site. These data, along with 

data from other National Atmospheric Deposition Program sites in Wyoming, are used to 

model and track emissions and acid deposition across southwest Wyoming, which 

includes the Class I Fitzpatrick and Class II Popo Agie Wilderness areas on the Forest. 

Because of industrial development in southwest Wyoming and growth of several major 

cities upwind of the Forest, continued monitoring of this site is important relative to 

Forest managers being able to demonstrate compliance with the Clean Air and 

Wilderness Acts. 
40 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 1. South Pass NADP Site Wet Deposition Trend Analysis. 

Wet Deposition (kg/ha) 

Parameter Seasonality Season 1986 2006 Difference Change Trend Significant

NH4 Yes 

Winter 0.041 0.077 0.036 88% 

Up 0.05 Spring 0.122 0.206 0.084 69% 

Summer 0.141 0.194 0.053 38% 

Fall 0.060 0.139 0.079 132% 

 

NO3 Yes 

Winter 0.621 0.755 0.134 22% 

None -- Spring 0.823 1.170 0.347 42% 

Summer 0.910 0.892 -0.018 -2% 

Fall 0.415 0.863 0.448 108% 

 

SO4 Yes 

Winter 0.638 0.377 -0.261 -41% 

Down 0.01 Spring 0.900 0.643 -0.257 -29% 

Summer 0.950 0.508 -0.442 -47% 

Fall 0.599 0.410 -0.189 -32% 

 

Inorg-N Yes 

Winter 0.160 0.247 0.087 54% 

Up 0.10 Spring 0.282 0.406 0.124 44% 

Summer 0.353 0.377 0.024 7% 

Fall 0.148 0.316 0.168 114% 
USDA Forest Service RMRS-GTR-248WWW. 2010. 41
42 USDA Forest Service RMRS-GTR-248WWW. 2010.

Figure 4. South Pass NADP Site Precipitation-Weighted Deposition Trend Analysis. 

South Pass NADP Site Precipitation-Weighted Deposition

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Winter

Spring

Summer

Fall

Winter

Spring

Summer

Fall

Winter

Spring

Summer

Fall

mg/l

1986 2006

NH4

NO3

SO4

 Lower Saddlebag and Ross Lakes—Analysis of data collected between 1986 and 

2007 was completed in early 2008. The analysis indicates change over time, with 

statistically significant upward or downward trend depending upon the parameter, season, 

and lake sampling location (Figures 5 and 6). 

 Acid neutralizing capacity (ANC) is on a downward trend at both lakes. There is a 

greater change at Ross Lake. The change is occurring at all sampling locations, i.e., inlet, 

outlet, epilimnion, and hypolimnion. The inlet at both lakes exhibits seasonality, but the 

outlets do not. The change at Lower Saddlebag, at the outlet and hypolimnion, is 

statistically non-significant, while at Ross it is significant. 

 The commonly accepted threshold for ANC, when ANC values are greater than 25, is 

no more than a 10% change. Thus, the downward trend at Ross Lake is a significant 

concern. The downward trend at Lower Saddlebag is approaching the threshold level, so 

it is a concern as well. The downward trend in ANC at each lake may be due to the 

upward trend in nitrate (NO3) at both lakes. 

 Nitrate (NO3) is on an upward trend at the inlet of both lakes. Lower Saddlebag Lake 

exhibits seasonality, while Ross Lake does not. There is no trend at either lake at the 

outlet or epilimnion. The hypolimnion at Lower Saddlebag is on an upward trend while at 

Ross there is no trend. 

 The upward trend at the inlet of both lakes is a significant concern and could explain 

the downward trend in ANC. Since there is no trend at the lake outlets, it is possible the 

influx of nitrogen (N) is being used by aquatic biota (both plant and animal) living in the 

lakes. Increases at each lake in the hypolimnion are also a significant concern because 
USDA Forest Service RMRS-GTR-248WWW. 2010. 43

this zone is typically void of nitrogen. Thus, this increasing trend could be the enrichment 

phase of eutrophication, meaning these once stable lakes (in terms of N) are becoming 

acidified. NO3 sources could be emissions from upwind locations, such as oil and gas 

developments, or from what was stored in glaciers and large snow fields that have been 

rapidly melting over the last decade. 

 Sulfate (SO4) at Lower Saddlebag Lake does not exhibit a statistically significant 

change, but there has been a 20% decrease (approximately). SO4 is on a downward trend 

at Ross Lake at the inlet, outlet, and hypolimnion, but not the epilimnion. This trend at 

the Ross Lake inlet is not statistically significant, but it is statistically significant at the 

outlet and hypolimnion. Lower Saddlebag does not exhibit seasonality, but Ross does. 

 The downward trend could be related to 1990s-era reductions in the use of high sulfur 

diesel fuel. Controls on emissions at refineries and coal-fired power plants, on a western 

U.S. regional basis, could also be a cause. 

 In addition to Forest Service uses, Wyoming Department of Environmental Quality 

and other agencies continually utilize data collected from these lakes. These data, along 

with data from other lakes in the Wind River Mountain Range, are used to model and 

track emissions and acid deposition across southwest Wyoming, which includes the Class 

I Fitzpatrick and Class II Popo Agie Wilderness areas on the Forest. Because of industrial 

development in southwest Wyoming and growth of several major cities upwind of the 

Forest, continued monitoring of these lakes is important relative to Forest managers being 

able to demonstrate compliance with the Clean Air and Wilderness Acts. 

Figure 5. Lower Saddlebag Lake Trend Analysis. 

Lower Saddlebag Lake 

Parameter Location Seasonality Season 1986 2007 Difference Change Trend Significant 

ANC (ueq/l) 

Inlet Yes 

Spring 66 62 -4 -6% 

Summer 77 67 -10 -13% Down Yes 

Fall 71 75 4 6% 

Outlet No 

 

68 67 -1 -1% Down No 

Epilimnion N/A 73 69 -4 -5% Down Yes 

Hypolimnion N/A 76 68 -8 -10% Down No 

 

NO3 (mg/l) 

Inlet Yes 

Spring 0.126 0.784 0.658 522% 

Summer 0.079 0.434 0.355 449% Up Yes 

Fall 0.024 0.662 0.638 2658% 

Outlet Yes 

Spring 0.233 0.326 0.093 40% 

Summer 0.051 0.046 -0.005 -10% None -- 

Fall 0.034 0.037 0.003 9% 

Epilimnion N/A 0.011 0.014 0.003 27% None -- 

Hypolimnion N/A 0.001 0.201 0.200 20000% Up Yes 

 

SO4 (mg/l) Inlet No 1.030 0.838 -0.192 -19% None -- 
44 USDA Forest Service RMRS-GTR-248WWW. 2010.

Outlet No 

 

1.030 0.824 -0.206 -20% None -- 

Epilimnion N/A 0.969 0.816 -0.153 -16% None -- 

Hypolimnion N/A 0.975 0.971 -0.004 0% None -- 

Figure 6. Ross Lake Trend Analysis. 

Ross Lake 

Parameter Location Seasonality Season 1986 2007 Difference Change Trend Significant 

ANC (ueq/l) 

Inlet Yes 

Spring 74 59 -15 -20% 

Summer 66 50 -16 -25% Down Yes 

Fall 66 60 -6 -9% 

Outlet No 

 

69 61 -8 -11% Down Yes 

Epilimnion N/A Summer 76 55 -21 -28% Down Yes 

Hypolimnionn N/A Summer 74 65 -9 -12% Down Yes 

 

NO3 (mg/l) 

Inlet No 0.033 0.395 0.362 1097% Up Yes 

Outlet No 

 

0.022 0.049 0.027 123% None -- 

Epilimnion N/A Summer 0.014 0.079 0.065 464% None -- 

Hypolimnion N/A Summer 0.027 0.034 0.007 26% None -- 

 

SO4 (mg/l) 

Inlet Yes 

Spring 1.020 0.881 -0.139 -14% 

Summer 0.890 0.808 -0.082 -9% Down No 

Fall 1.020 0.698 -0.322 -32% 

Outlet Yes 

Spring 1.060 0.894 -0.166 -16% 

Summer 0.914 0.826 -0.088 -10% Down Yes 

Fall 0.963 0.872 -0.091 -9% 

Epilimnion N/A Summer 0.884 0.837 -0.047 -5% None -- 

Hypolimnion N/A Summer 1.050 0.926 -0.124 -12% Down Yes 
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