Studies Show Acid Rain May Make Trees Thirstier

The U.S. Forest Service has been involved in a decades long experiment to study how forests react to acid rain. As the climate changes, the plants and animals around us are adjusting to new patterns and changes in their environment just as humans are.

The Forest Service created an artificial environment in a forest in West Virginia to study how acid rain could influence the growth, and behavior of the forest as a whole. Known as the Fernow Experimental Forest near Parsons, West Virginia, the forest is 34 hectares in size and was chosen partially because of its characteristic watershed.


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The forest has been doused with a chemical cocktail that mimics the sulfur and nitrogen properties of acid rain. The study began in 1989 and the forest is treated with the chemicals three times a year.

What is Acid Rain? 

Acid rain is the byproduct of agriculture, industry, and the burning of fossil fuels. These emissions not only cause the release of carbon dioxide into the atmosphere, but other compounds as well. Sulfur and nitrogen are two such compounds that result from mankind’s development; when these chemicals are released into the air, they can be caught up in clouds and become part of the Earth’s water cycle.

Origins of acid rain.  Image: US EPA

Origins of acid rain. Image: US EPA

One of the findings of the study was that acid rain can make the plants in the affected area need more water. When acid rain falls, it leaches other important minerals out of the soil and away from the trees that need those minerals to survive. One such mineral is calcium, which plants need in order to retain water in their roots, trunks, stems, and leaves.

Affects of Acid Rain on Water Uptake in Forests

The study has also taken a deeper look at the effect acid rain can have on the forest’s watershed. In most of the years of the study, the experimental forest used 5% more water than a nearby forest that wasn’t treated with acidifying chemicals. In two of the years of the study, this number jumped up to 10%. In total, the amount of water that was estimated to be soaked up by the acidified forest was 13.6 million liters per year.

In this study, forests treated with acid rain components leached more minerals from the soil which in turn affected the ability of trees to retain moisture.  The thickness of the lines and sizes of the pools show relative differences between the control and treatment tree plots.  Figure:  Lanning et al., 2019.

In this study, forests treated with acid rain components leached more minerals from the soil which in turn affected the ability of trees to retain moisture. The thickness of the lines and sizes of the pools show relative differences between the control and treatment tree plots. Figure: Lanning et al., 2019.

Soil samples taken during the study showed falling calcium levels in the soil of the forest as compared to the levels in a nearby untreated forest. However, this data could predate the study, as calcium is slow to replenish in soil.

Additionally, each forest is unique in its composition of soil, plant, and animal life. What is true of the acidification of the Fernow Experimental Forest may not be true of a forest with a different makeup.

Future Implications

As our world changes, it’s important for us to understand how we are affecting the trees, water, and earth around us. As the study continues, scientists will better be able to find answers to questions about our evolving world and how we can manage some of the unintended consequences of industrialization.

Study

Lanning, M., Wang, L., Scanlon, T. M., Vadeboncoeur, M. A., Adams, M. B., Epstein, H. E., & Druckenbrod, D. (2019). Intensified vegetation water use under acid deposition. Science Advances, 5(7), eaav5168. DOI: 10.1126/sciadv.aav5168

Wilke, Carolyn. Decades of dumping acid suggest acid rain may make trees thirstier. 5 August, 2019. Retrieved from https://www.sciencenews.org/article/decades-dumping-acid-suggest-acid-rain-may-make-trees-thirstier

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