Effects of Acidic Deposition

Acid deposition and its effects on ecosystems is a long-standing research interest.  Acid deposition is elevated concentrations of strong acids deposited to the Earth’s surface as a result to emissions of fossil fuels. Acid deposition has acidified soil and water in sensitive regions resulting in adverse effects on aquatic organisms and trees. Emissions of acidifying air pollutants peaked in the U.S. and have decreased markedly in recent decades, due to air quality legislation and rules. With Zhengwei Wang, a researcher from the Chinese Academy of Sciences, a synthesis of acid deposition and its effects was published in the Encyclopedia of Water: Science, Technology, and Society (Driscoll and Wang 2020).

We completed an analysis of target loads of acidity for soil and streams of forest watershed in the Adirondacks (Shao et al. 2020, McDonnell et al. in review; Figure 1). Target loads are a determination of levels of atmospheric deposition, below which will alleviate adverse ecosystem effects for a specific time period. There were several innovative aspects to this work. We determined site specific targets for soil and stream recovery based on the sites inherent sensitivity. For stream response, we developed a procedure to extrapolate the stream target load to hydrologic conditions of interest (e.g., spring high flow, summer low flow). Finally, we applied biological algorithms to determine the target load necessary to protect regional fisheries.

Figure 1.  Location of watersheds in the Adirondack Park of exceedance of projected Target Load (TL) for attaining site-specific stream ANC (left) and soil base saturation = 12% (right) by year 2050.    

I have initiated a new critical loads project with funding from the Electric Power Research Institute. Working with Sonoma Technologies and partnering with a joint federal agency task force, including EPA, Research Triangle International, the National Park Service and the US Forest Service (US FS), we are applying machine learning techniques to the USFS Forest Inventory Analysis to quantify critical loads of sulfur and nitrogen deposition for tree health for the US. This is an exciting project and may establish an approach that will be used to determine a secondary air quality standard for sulfur and nitrogen. This work will continue through 2021. This project opens up new opportunities for research involving machine learning techniques.

I have expanded my research on acid deposition effects to contrast with agricultural amendments of sulfur. In developed countries, continued calls to reduce sulfur emissions arising from fossil fuel combustion are mitigating the largest manipulation of the global sulfur cycle to date. However, anthropogenic modification of the global sulfur cycle continues. Currently, high rates of sulfur applications to economically important crops at local-to-regional scales represents a major perturbation to the global sulfur cycle. Long-term sulfur additions to crop lands likely result in many of the same consequences for soil health and aquatic ecosystems observed in forested regions historically impacted by acid rain, yet this cascade of effects has not been broadly explored. 

Over the past few years, I have worked with Eve-Lyn Hinckley (University of Colorado) to characterize and quantify effects of agricultural application of sulfur on ecosystems, contrasting these with the well-established effects of atmospheric sulfur deposition (i.e., acid rain).  We found that with decreases in atmospheric sulfur deposition, fertilizer sulfur application rates have increased to make up this change in inputs. The sulfur addition rate for agricultural applications is more intense at the local scale but the areal extent is smaller than for atmospheric sulfur deposition. However, over the coterminous U.S. the total application of agricultural sulfur amendments is comparable to that experienced from atmospheric deposition (Hinckley et al, 2020). This work will continue as we examine the roles of climate, hydrology, fertilizer application rates and other element cycles in modifying sulfur processes and flows within and down gradient of agricultural source areas. Following the publication of Hinckley et al. (2020), we were contacted by a group from Switzerland working on a similar issue that we addressed for sulfur for selenium.  This has resulted in a new collaboration and paper, involving the first global model of atmospheric selenium (Feinberg et al. in review)

I have expanded my research on acid deposition effects to contrast these with agricultural amendments of sulfur. In developed countries, continued calls to reduce sulfur emissions arising from fossil fuel combustion are mitigating the largest manipulation of the global sulfur cycle to date. However, anthropogenic modification of the global sulfur cycle continues. Currently, high rates of sulfur applications to economically important crops at local-to-regional scales represents a major perturbation to the global sulfur cycle. Long-term sulfur additions to crop lands likely result in many of the same consequences for soil health and aquatic ecosystems observed in forested regions historically impacted by acid rain, yet this cascade of effects has not been broadly explored.

Over the past few years, I have worked with Eve-Lyn Hinckley (University of Colorado) to characterize and quantify effects of agricultural application of sulfur on ecosystems, contrasting these with the well-established effects of atmospheric sulfur deposition (i.e., acid rain).  We found that with decreases in atmospheric sulfur deposition, fertilizer sulfur application rates have increased to make up this reduction. The sulfur addition rate for agricultural applications is more intense at the local scale but the areal extent is smaller than for atmospheric sulfur deposition. However, over the coterminous U.S. the total application of agricultural sulfur amendments is comparable to that experienced from atmospheric deposition. This analysis was recently published in the journal Nature Geoscience (Hinckley et al, 2020). We are planning a research project to examine the roles of climate, hydrology, and other element cycles in modifying sulfur processes and flows within and down gradient of agricultural source areas.

In addition to these monitoring and modeling activities, we have worked on strategies and experiments to mitigate effects of acid deposition. An ongoing study at the Hubbard Brook Experimental Forest, NH is examining the effects of calcium supply on the structure and function of the northern forest, through experimental addition of wollastonite (CaSiO3) to a forested watershed. In addition to mitigating the effects of acid deposition, there is interest in this experiment from the standpoint of a land-based carbon dioxide removal strategy by “enhanced mineral weathering”. The wollastonite addition experiment is the first catchment-scale enhanced mineral weathering experiment. A paper summarizing the effectiveness of “enhanced mineral weathering” in sequestering carbon is recently published Biogeosciences Discussions (Taylor et al., 2020).

Finally, 2020 is the 50th anniversary of the Clean Air Act.  To commemorate the accomplishments of this legislation, I helped organize a session at the annual meeting of the National Council for Science and the Environment (Washington D.C., January 2020) on “The Clean Air Act and the Science Policy Interface” in which the health and ecosystem effects, mitigation and future interactions with climate change were discussed for acid rain, mercury, and carbon.

References:

Driscoll, C. T. and Z. Wang. 2020. Ecosystem effects of acidic deposition. Chapter in online Encyclopedia of Water Science, Technology and Society. P. Maurice (Ed.). doi: 10.1002/9781119300762.wsts0043.

Feinberg, A., A. Stenke1, T. Peter, E. S. Hinckley, C. T. Driscoll, L. H. E. Winke. In review. Risk of declining atmospheric selenium and sulfur inputs to agricultural soils. Science.

Hinckley, E. S., J. T. Crawford, H. Fakhraei and C. T. Driscoll. 2020. A shift in sulfur-cycle manipulation from atmospheric emissions to agricultural additions. Nature Geoscience, 13:597–604. doi: 10.1038/s41561-020-0620-3.

McDonnell, T. C., C. T. Driscoll, T. J. Sullivan, D. A. Burns, B. P. Baldigo, S.  Shao. In review. Regional Target Loads of Atmospheric Nitrogen and Sulfur Deposition for the Protection of Stream and Watershed Soil Resources of the Adirondack Mountains, USA. Environmental Pollution.

Shao, S., C. T. Driscoll, T. Sullivan, D. A. Burns, B. Baldigo, G. Lawrence and T. McDonnell. 2020. The response of stream ecosystems in the Adirondack region of New York to historical and future changes in atmospheric deposition of sulfur and nitrogen. Science of Total Environment. 716:137113 doi:10.1016/j.scitotenv.2020.137113.

Taylor, L. L., C. T. Driscoll, P. M. Groffman, G. H. Rau, J. D. Blum and D. J. Beerling. 2020. Increased carbon capture by a silicate-treated forested watershed affected by acid deposition. Biogeosciences: Discussions, 2020:1-29. doi:10.5194/bg-2020-288.