Effects of Acidic Deposition

Acid deposition and its effects is a long-standing research interest. Acid deposition is elevated concentrations of strong acids that are deposited to the Earth’s surface as a result to emissions of fossil fuels. This input has resulted in adverse effects on aquatic organisms and trees. Emissions of acidifying air pollutants have peaked in the U.S. and have decreased in recent decades due to air quality legislation and rules. With the help of Zhengwei Wang, a visiting scholar from the Chinese Academy of Sciences, a synthesis of acid deposition and its effects was completed for the Encyclopedia of Water: Science, Technology, and Society (Driscoll and Wang in press).

With the New York State Department of Environmental Conservation and the Adirondack Lakes Survey Corporation and the U.S. Environmental Protection Agency, we monitor the chemistry and fisheries of 52 lakes in the Adirondacks. Our work shows that inputs of acid deposition have decreased markedly in recent years due to air emission control programs (Figure 1) and this has resulted in some improvements in the chemistry of acid impacted streams and lakes in the Northeast (Figure 2).

Figure 1. Relationships between national emissions of sulfur dioxide and nitrogen oxides and concentrations of sulfate and nitrate in precipitation at Huntington Forest in the Adirondacks. Atmospheric deposition of sulfate and nitrate have decreased markedly in response to emission controls. Also shown are estimates of pre-anthropogenic precipitation concentrations and projected emissions for 2030.

 

 

 

Figure 2. Map of long-term trends in acid neutralizing capacity in surface waters in mountainous areas of the eastern U.S. Acid neutralizing capacity is a measure of the sensitivity of waters to acid inputs. Note that acid neutralizing capacity in surface waters in New York and New England are decreasing in response to decreases in sulfur dioxide emissions and acidic deposition. In contrast many sites in the Southeast are continuing to acidify due to desorption of sulfate previously retained on soil under conditions of high atmospheric deposition.

An unintended consequence of decreases in acid deposition is a phenomenon called “browning”.  Browning is an increase in the mobilization of dissolved organic matter from soil to surface waters.  This process is evident in many Adirondack lakes and other waters in the eastern U.S.  Browning has important water quality implications, including increased transport of nutrients and trace metals, increases in water treatment costs and changes in the thermal stratification of lakes.  Yaskira Mota, a MS student, is examining how browning is influencing the thermal stratification of lakes in the Adirondacks.

In addition to these monitoring and modeling activities, we have been working on strategies and experiments to mitigate effects of acid deposition. We have an ongoing study at the Hubbard Brook Experimental Forest, NH examining the effects of calcium supply on the structure and function of the northern forest, through experimental addition of wollastonite (CaSiO3) to a watershed. Weiyao Gu (recent MS student working under Chris Johnson) conducted an analysis of the long-term response of soil solutions and stream water to the calcium silicate addition at Hubbard Brook (Gu et al. 2017)

Current Work on Acid Rain

References:

Driscoll, C. T. and Z. Wang. In press. Ecosystem effects of acidic deposition. Chapter in Encyclopedia of Water Science, Technology and Society.

Gu, W., C. T. Driscoll, S. Shao and C. Johnson. 2017. Aluminum is more tightly bound in soil after wollastonite treatment to a forest watershed. Forest Ecology and Management, 397: 57-66. doi: 10.1016/j.foreco.2017.04.035.