20th Century Atmospheric Deposition and Acidification Trends in Lakes of the Sierra Nevada, California, USA
TL;DR: It is concluded 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.
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 anthropogenic atmospheric deposition) and biogenic silica and δ13C (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 yr–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 increasin...
Summary (2 min read)
- Mountain lakes are sensitive indicators of environmental change and are especially useful for detecting changes from regional-scale stressors including air pollution.
- 16 Spheroidal carbonaceous particles (SCPs) found in lake sediments have been used to investigate historic atmospheric deposition.
- Biogenic silica (BSi) and δ 13 C are proxies for algal productivity and are used to assess effects of nutrient inputs and climate change on aquatic ecosystems.
- The primary goal of their research was to determine if the ANC changes observed in Moat Lake 15 are a result of acid deposition.
- Using these analyses the authors evaluate the effectiveness of the CAAA in protecting Sierra Nevada lakes and contribute to the development of air pollution standards, including CLs.
- The bedrock geology of the watershed is dominated by metasedimentary rocks including quartzite and argillite.
- 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.
- 26 Using available long-term records, the authors compared ANC changes to mean annual air temperature and precipitation, and April 1st SWE.
- 29, 30 Correlations among variables were tested using Pearson and principal component analysis (PCA).
- Deposition trends were analyzed using the MK 28 test with Theil-Sen slope estimator, 29, 30 and correlations between lake chemistry and deposition were analyzed using a Kendall tau.
- 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.
Environmental Science & Technology
- The first axis was positively correlated with air quality indices (NO x and SO 2 emissions) and temperature and negatively correlated with ANC and precipitation indices.
- Temperature and NO x emissions both increased throughout the 20th century but diverge after 2000 when NO x begins to decline as temperature continues to increase.
- The 95% confidence interval for the slope fell between 0.042 and 0.236 further supporting a nonzero change in the residuals through time.
- SCP profiles in Moat and Pear lakes have similar patterns.
- SCPs at their study sites reached maximum concentrations during the decades of the 1960s to 1980s which is consistent with sites in the northwestern US and Rocky Mountains 21 (Table S4 ).
- Precipitation slightly increased and SWE slightly decreased, although trends are weak (tau <0.08) and the 95% confidence intervals for the slopes include zero.the authors.the authors.
- The strong coherence between ANC, SCPs, and SO 2 emissions and late 20th century NO x emissions, coupled with the lack of coherence between ANC and climate, support their conclusion that changes in 20th century ANC are primarily driven by atmospheric deposition.
- The increasing ANC trend in Emerald Lake observed over the last three decades is consistent with the late 20th century recovery of ANC in Moat Lake and suggests recovery of acid sensitive lakes in the Sierra Nevada is ongoing.
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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" ?
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.