(Open Access) 20th Century Atmospheric Deposition and Acidification Trends in Lakes of the Sierra Nevada, California, USA (2014) | Andrea M. Heard

Q: What are the contributions mentioned in the paper "20th century atmospheric deposition and acidification trends in lakes of the sierra nevada, california, usa" ?

The authors investigated multiple lines of evidence to determine if observed and paleo-reconstructed changes in acid neutralizing capacity ( ANC ) in Sierra Nevada lakes were the result of changes in 20th century atmospheric deposition. The authors conclude that ANC depletion at Moat and Emerald lakes was principally caused by acid deposition, and recovery in ANC after 1970 can be attributed to the United States Clean Air Act.

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Title

20th century atmospheric deposition and acidification trends in lakes of the Sierra Nevada,

California, USA.

Permalink

https://escholarship.org/uc/item/8j33v5vf

Journal

Environmental science & technology, 48(17)

ISSN

0013-936X

Authors

Heard, Andrea M

Sickman, James O

Rose, Neil L

et al.

Publication Date

2014-09-01

DOI

10.1021/es500934s

Peer reviewed

eScholarship.org Powered by the California Digital Library

University of California

20th Century Atmospheric Deposition and Acidiﬁcation Trends in

Lakes of the Sierra Nevada, California, USA

Andrea M. Heard,*

,†,‡

James O. Sickman,

†

Neil L. Rose,

Danuta M. Bennett,

∥

Delores M. Lucero,

†

John M. Melack,

∥,⊥

and Jason H. Curtis

†

Department of Environmental Sciences, University of California, Riverside, California 92521, United States

‡

National Park Service, 47050 Generals Highway, Three Rivers, California 93271, United States

Environmental Change Research Centre, University College London, Gower Street, London WC1E 6BT, U.K.

∥

Marine Science Institute and

⊥

Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara,

California 93106-6150, United States

Department of Geological Sciences, University of Florida, Gainesville, Florida 32611, United States

Supporting Information

ABSTRACT: We investigated multiple lines of evidence to determine if

observed and paleo-reconstructed changes in acid neutralizing capacity (ANC)

in Sierra Nevada lakes were the result of changes in 20th century atmospheric

deposition. Spheroidal carbonaceous particles (SCPs) (indicator of anthro-

pogenic atmospheric deposition) and biogenic silica and δ

C (productivity

proxies) in lake sediments, nitrogen and sulfur emission inventories, climate

variables, and long-term hydrochemistry records were compared to

reconstructed ANC trends in Moat Lake. The initial decline in ANC at

Moat Lake occurred between 1920 and 1930, when hydrogen ion deposition

was approximately 74 eq ha

−1

, and ANC recovered between 1970 and

2005. Reconstructed ANC in Moat Lake was negatively correlated with SCPs

and sulfur dioxide emissions (p = 0.031 and p = 0.009). Reconstructed ANC

patterns were not correlated with climate, productivity, or nitrogen oxide

emissions. Late 20th century recovery of ANC at Moat Lake is supported by increasing ANC and decreasing sulfate in Emerald

Lake between 1983 and 2011 (p < 0.0001). We conclude that ANC depletion at Moat and Emerald lakes was principally caused

by acid deposition, and recovery in ANC after 1970 can be attributed to the United States Clean Air Act.

■

INTRODUCTION

Mountain lakes are sensitive indicators of environmental

change and are especially useful for detecting changes from

regional-scale stressors including air pollution. Sensitivity of

aquatic ecosystems to atmospheric deposition of sulfate and

nitrate is well documented throughout the northern hemi-

sphere.

1−3

Adverse eﬀects from acidiﬁcation include chronic or

episodic depression of acid neutralizing capacity (ANC) and

changes in the structure of biotic communities.

4,5

Associated

nutrient inputs are contributing to long-term eutrophication

and shifts in nutrient limitation and phytoplankton commun-

ities.

6−8

At the same time, climate change is altering hydrologic

and water temperature regimes, which may further contribute

to variability in productivity and algal community shifts.

9,10

The Clean Air Act and Amendments (CAAA) is the primary

policy for improving air quality and reducing atmospheric

deposition in the United States (US). The legislation targets

decreases in acid deposition and the recovery of surface waters

from acidiﬁcation and prohibits deterioration of air quality in

national parks and wilderness areas, where a large proportion of

western mountain lakes occur. Chemical recovery of lakes from

acid deposition has been attributed to the CAAA, although

most of the published research and success stories have been in

the northeastern US where negative ecological eﬀects have

been most notable and acid deposition has received the most

attention.

11,12

Recently, western land management agencies

have been adopting the critical load (CL) as a policy approach

to further protect mountain lakes from air pollution.

ACLisa

quantitative estimate of an input or exposure to a pollutant at

which unacceptable impacts occur to sensitive ecosystem

components.

Paleolimnological research suggests that Sierra Nevada lakes

may have been aﬀected by acid deposition as early as 1920.

Sickman et al.

reconstructed the last 1600 years of ANC using

diatom inference models in Moat Lake, a subalpine lake located

in the Sierra Nevada, and observed a decrease in ANC from

1920 to 1970. ANC increased after 1970 and returned to pre-

1920 levels by 2005. The causes underlying Moat Lake ANC

patterns are uncertain, but it is possible that the CL for acid

Received: February 23, 2014

Revised: July 28, 2014

Accepted: July 31, 2014

Published: July 31, 2014

Article

pubs.acs.org/est

deposition was exceeded well before regular monitoring in the

1980s. Sierra Nevada lakes have been aﬀected by other stressors

during the 20th century such as nutrient inputs, climate change,

and non-native ﬁsh species so additional information is needed

to understand the primary drivers of ANC change.

Multiproxy approaches can aid interpretation of the Moat

Lake ANC reconstruction.

Spheroidal carbonaceous particles

(SCPs) found in lake sediments have been used to investigate

historic atmospheric deposition.

SCPs are porous spheroids

composed primarily of elemental carbon that are chemically

resistant and well-preserved.

They are unambiguous

indicators of anthropogenic atmospheric deposition because

they are produced only by industrial combustion of fossil fuels;

there are no natural sources. Biogenic silica (BSi) and δ

C are

proxies for algal productivity and are used to assess eﬀects of

nutrient inputs and climate change on aquatic ecosystems.

19,20

Paleolimnological studies are further strengthened by compar-

ison with long-term climate and lake chemistry data.

The primary goal of our research was to determine if the

ANC changes observed in Moat Lake

are a result of acid

deposition. In our study we synthesize multiple lines of

evidence, including measurements of SCPs, BSi, and δ

Cin

lake sediments, emission inventories for oxides of sulfur (S) and

nitrogen (N), climate, and long-term hydrochemistry records to

test the hypothesis that high elevation lakes in the Sierra

Nevada were aﬀ ected by atmospheric deposition early in the

20th century. Using these analyses we evaluate the eﬀectiveness

of the CAAA in protecting Sierra Nevada lakes and contribute

to the development of air pollution standards, including CLs.

■

METHODS

We analyzed SCPs, BSi, and δ

C in Moat Lake sediments from

the same core where Sickman et al.

reconstructed ANC. Moat

Lake is located on the eastern slope of the Sierra Nevada,

California, United States of America on Humboldt-Toiyabe

National Forest at 3224 m (Figure S1). It has a maximum

depth of 7 m, lake surface area of 2.8 ha, and watershed area of

59 ha. The bedrock geology of the watershed is dominated by

metasedimentary rocks including quartzite and argillite. To

increase our spatial understanding of atmospheric deposition

and ANC chemistry in the Sierra Nevada, we also investigated

SCP patterns at Pear and Emerald lakes and hydrochemistry

trends at Emerald Lake. Pear and Emerald lakes are located in

adjacent watersheds on the western side of the Sierra Nevada in

Sequoia National Park at 2904 and 2800 m, respectively. Pear

Lake has a maximum depth of 24 m, lake surface area of 7.3 ha,

and watershed area of 136 ha. Emerald Lake has a maximum

depth of 10 m, lake surface area of 2.7 ha, and watershed area of

120 ha. The bedrock geology of both watersheds is dominated

by granite and granodiorite. Less than 10% of the three

watersheds are vegetated.

At Moat Lake we used a rod-corer to collect a 210 cm core in

September 2008 and ﬁeld sectioned the core at 1 cm

intervals.

The Pear and Emerald cores were collected in the

summer of 2003 as part of the Western Airborne Contaminants

Assessment Project (WACAP) using a gravity corer ﬁtted with

a Plexiglas tube and ﬁeld sectioned at 0.5 cm intervals.

The

chronology of the Moat Lake core was established with

210

and

C dating

and the Pear and Emerald lake cores using

210

Pb dating.

SCPs (gDM

−1

) were analyzed in the Moat, Pear, and

Emerald cores per methods in Rose,

and diatom BSi (mg g

−1

)

and δ

C(‰) of bulk organic matter were analyzed in the

Moat core per methods in Conley and Schelske

and

Sickman.

Methods are described in the SI.

Sickman et al.

described the methods and results for the

Moat Lake ANC reconstruction based on a diatom inference

model. In this paper we compare the Moat Lake ANC

reconstruction to SCP sediment proﬁles (Moat, Emerald, and

Pear lakes) and 20th century sulfur dioxide (SO

) and nitrogen

oxide (NO

) emissions estimated by the EPA

and Smith et

al.

National emissions (1900−2012) were used as regional

data were only available back to 1990, and we have provided a

Kendall correlation analysis of national and regional emissions

in the SI to demonstrate that national emissions provide a good

proxy for understanding multidecadal trends. ANC variations

are strongly inﬂuenced by precipitation and snow water

equivalent (SWE) and to a lesser extent by temperature

which aﬀects snowpack dynamics and watershed weathering

rates.

Using available long-term records, we compared ANC

changes to mean annual air temperature and precipitation, and

April 1st SWE. Temperature and precipitation data were

obtained for the Sierra climate region, as deﬁned by Abatzoglou

et al.,

from the Western Regional Climate Center’s California

Climate Tracker (http://www.wrcc.dri.edu/monitor/cal-mon/

SWE data were examined from two snow courses: (i)

Donner Summit located near Lake Tahoe (39.3100 N,

120.3380 W) (1910−2011) and (ii) Virginia Lakes located

near Moat Lake (38.0570 N, 119.2470 W) (1947−2011)

(http://cdec.water.ca.gov). Climate data were analyzed using

the Mann-Kendall (MK) test for trend

with Theil-Sen slope

estimator.

29,30

Correlations among variables were tested using

Pearson and principal component analysis (PCA).

We investigated trends for 30 years (1982−2012) of sulfate

chemistry and 28 years (1983−2011) of fall ANC and base

cation (BC) chemistry from Emerald Lake. Sampling and

laboratory methods are described in Melack et al.

Sulfate

trends were analyzed using the Seasonal Kendall test (SKT)

with Theil-Sen slope estimator

29,30

and compared to sulfate

deposition trends from the National Atmospheric Deposition

Program site CA75 in Sequoia National Park (http://nadp.sws.

uiuc.edu/). Deposition trends were analyzed using the MK

test with Theil-Sen slope estimator,

29,30

and correlations

between lake chemistry and deposition were analyzed using a

Kendall tau. We used two approaches to test for ANC and BC

trends that control for the eﬀect of SWE as the correlation

between these variables and SWE coupled with the high annual

variability of SWE makes it challenging to detect temporal

trends. Method (i) is computing the residuals for the SWE-

ANC linear regression, plotting them in chronological order,

and computing a linear regression between residuals and year

and (ii) is using multiple linear regression (MLR) to predict

ANC using year and SWE as explanatory variables.

We used

the residuals approach (i) to test for BC trends.

We calculated a CL for acid deposition by hindcasting

deposition rates back to the time period when changes in

diatom communities and reconstructed ANC were initially

observed by Sickman et al.

We assumed acid deposition to be

the sum of nitrate and sulfate, estimated deposition rates for

these constituents separately, and then summed them.

Hindcasting methods are based on Baron

and described in

the SI section.

■

RESULTS

SCPs were ﬁrst consistently detected in 1869 ± 96 in Moat

Lake, 1842 ± 33 in Pear Lake, and 1932 ± 10 in Emerald Lake

Environmental Science & Technology Article

dx.doi.org/10.1021/es500934s | Environ. Sci. Technol. 2014, 48, 10054−1006110055

(Figure 1). In Moat Lake a few SCPs were detectable prior to

industrial fossil fuel combustion. These SCPs may be

contamination-derived, although the core chronology suggests

limited contamination overtime. Following initial detection,

SCPs show an increasing trend at all three sites until maximum

SCP concentrations were reached in 1964 ± 6 at Emerald Lake

(1,500 gDM

−1

, 90% CI [910, 2100]), 1972 ± 9 at Pear Lake

(1,800 gDM

−1

, 90% CI[1200, 2400]), and 1988 ± 4 at Moat

Lake (2,400 gDM

−1

, 90% CI [1700, 3100]). A decreasing trend

in SCP concentrations was then observed through ca. 2000,

with the exception of Emerald Lake where SCPs decrease but

then increase again after 1999 ± 2. SCP concentrations

measured in surface sediments are 560 gDM

−1

, 90% CI [240,

870] in Pear, 590 gDM

−1

, 90% CI [260, 900] in Moat, and 860

gDM

−1

, 90% CI [480,1200] in Emerald.

Moat Lake BSi ranged from 175.1 to 227.9 mg g

−1

from 1834

± 277 to 2004 ± 3 (Figure 2). We observed an initial increase

between 1920 and 1930 and a second increase between 1980

and 2000. Sediment δ

C ranged from −22.3 to −21.4‰ from

ca. 1830 to ca. 1900 with no notable trend (Figure 2). We

observed an increasing trend in δ

C between 1900 and 2000

where δ

C ranged from −21.9 to −19.2‰. By 1990, δ

C had

increased from the most depleted value of −22.2‰ in 1903 ±

36 to −20.20‰. In the analysis we focus on δ

C trends from

before 1990 as sediment diagenesis complicates interpretation

of the most recent 10 years of sediment accumulation.

The PCA identiﬁed three principal components, which

together account for about 80% of the variance (Figure 3 and

Table S1). The ﬁrst axis was positively correlated with air

quality indices (NO

and SO

emissions) and temperature and

negatively correlated with ANC and precipitation indices. The

second axis positively correlated with phytoplankton produc-

tivity indices and negatively correlated with SCP and SO

emissions. The third axis was posit ively correlated with

precipitation indices.

The PCA and Pearson correlation demonstrated negative

correlations between ANC and SCPs (p = 0.031) and ANC and

emissions (p = 0.009) (Figure 3 and Table S2). Relatively

low levels of SCPs were observed in Moat Lake prior to any

notable change in ANC (Figure 1). A decreasing trend in ANC

began after 1920 and continued until the late 1970s. The ANC

decrease coincides with increasing concentrations of SCPs

between 1920 and 1980 and rising SO

emissions between

1920 and 1970. ANC in Moat switches to an increasing trend

within the same decade that SCPs and SO

emissions switch to

a decreasing trend. Pear and Emerald SCPs showed similar

declines between 1970 and 2000. Moat ANC patterns correlate

less with NO

emissions (p = 0.185), although the time series

suggests a stronger correlation after 1950 (Figure 4).

Figure 1. a) Moat Lake SCP concentrations and reconstructed ANC, b) Pear Lake SCP concentrations, and c) Emerald Lake SCP concentrations.

Figure 2. BSi and δ

C proﬁles for Moat Lake.

Environmental Science & Technology Article

dx.doi.org/10.1021/es500934s | Environ. Sci. Technol. 2014, 48, 10054−1006110056

The PCA and Pearson correlation indicate no direct

correlation between Moat Lake ANC and the climate variables

considered (Figure 3 and Table S2). Sierra Nevada air

temperature records demonstrate a 20th century warming

trend of 0.1 °C decade

−1

(p < 0.0001) (Figure 4). The ca. 1920

decrease in ANC coincided with a slight warming trend

observed during the same period. However, temperature

continued to rise through 2010, whereas the ANC trend in

Moat Lake reversed after 1980. There were no statistically

signiﬁcant trends in precipitation (p = 0.4129) or SWE

(Donner Summit: p = 0.257;Virginia Lakes: p = 0.4129), nor

were these variables correlated with ANC. Temperature was

more closely correlated with productivity (δ

C p = 0.007) and

emissions (p = 0.021). Temperature, δ

C, and BSi

increased throughout the 20th century. Temperature and NO

emissions both increased throughout the 20th century but

diverge after 2000 when NO

begins to decline as temperature

continues to increase.

Emerald Lake sulfate signiﬁcantly declined over the 30 year

monitoring period (Sen slope 95% CI: −0.080 to −0.053; p <

0.0001) as did annual sulfate deposition concentration (Sen

slope 95% CI: −0.273 to −0.088; p = 0001) and loading (Sen

slope 95% CI: −0.077 to −0.003; p = 0.0338) (Figure S2).

Emerald Lake sulfate concentrations were positively correlated

with deposition concentrations (tau = 0 .519; p < 0.0001) and

loading (tau = 0.262; p-value = 0.0470). The residuals from the

Emerald Lake SWE-ANC linear regression demonstrate a

concurrent increasing trend in ANC between 1983 and 2011

(slope = 0.139 μeq L

−1

; p = 0.006) (Figure 5). The 95%

conﬁdence interval for the slope fell between 0.042 and 0.236

further supporting a nonzero change in the residuals through

time. Over the 28 year record, ANC increased approximately 4

μeq L

−1

. MLR results conﬁrm that Year (p = 0.005) and SWE

(p < 0.001) are both signiﬁcant predictors of ANC (R

= 0.89)

and the coeﬃcient for Year is positive:

=− + −

NC 245 [(0.142)(Year)] [(0.00814)(SWE)]

(1)

The variable inﬂation factor for the MLR was 1.002 indicating

no signiﬁcant covariance between SWE and YEAR. We expect

SWE to be a signiﬁcant predictor as it controls ANC

concentrations through dilution when the snowpack melts.

The signiﬁcance of YEAR as a copredictor suggests an ANC

trend overtime. The residuals from the SWE-BC linear

regression indicate no signiﬁcant trend in base cations between

1983 and 2011 (p-value = 0.16 and 95% CI slope: −005 to

0.29) (Figure S3).

Mean nitrate and sulfate deposition from 1985−1999 at

Emerald Lake was 99 ± 17 eq ha

−1

and 52 ± 15 eq ha

−1

, respectively, and the sum of acid anions was 150 ± 30 eq

−1

(Table S3). The resulting hindcast model equation

used to compute historical nitrate deposition was

=×

−

Nitrate Deposition (8 10 )(e )

19 0.0232Year

(2)

Hindcasted sulfate deposition was modeled to match US

emissions records. We estimate that annual deposition varied

from 13 to 76 eq ha

−1

over the 20th century (Figure S4).

The CL was deﬁned as the rate of nitrate and sulfate

deposition during 1920−1930 as estimated from hindcasting

Figure 3. PCA plot for Moat Lake sediment, emissions, and climate

variables.

Figure 4. Time series graphs for a) Sierra Nevada mean annual air

temperature, b) Sierra Nevada mean annual precipitation, c) April 1st

SWE at Donner Summit (DNS) and Virginia Lakes (VGL), d)

national NO

and SO

emissions, and e) diatom reconstructed ANC at

Moat Lake. The slopes are reported as the 95% CI range.

Environmental Science & Technology Article

dx.doi.org/10.1021/es500934s | Environ. Sci. Technol. 2014, 48, 10054−1006110057

20th Century Atmospheric Deposition and Acidification Trends in Lakes of the Sierra Nevada, California, USA

Figures

Citations

Mountain lakes: Eyes on global environmental change

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On-road emissions of ammonia: An underappreciated source of atmospheric nitrogen deposition.

Long-Term Trends in Acid Neutralizing Capacity under Increasing Acidic Deposition: A Special Example of Eutrophic Taihu Lake, China.

Quantifying annual groundwater recharge and storage in the central Sierra Nevada using naturally-occurring 35S

References

Factors affecting water chemistry of alpine lakes

An organic geochemical record of Sierra Nevada climate since the LGM from Swamp Lake, Yosemite

Sierra Nevada, California

Reconstructing past eutrophication trends from diatoms and biogenic silica in the sediment and the pelagic zone of Lake Constance, Germany

Ecological responses to nutrients in streams and rivers of the Colorado mountains and foothills

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Q1. What are the contributions mentioned in the paper "20th century atmospheric deposition and acidification trends in lakes of the sierra nevada, california, usa" ?