Examining the Role of Forest Soils in Conditioning Water

Research Issue

Scott Bailey preparing to sample streamwater during a highflow event on the Hubbard Brook Experimental Forest.

The chemical composition of water—its acidity or neutrality and the ions dissolved within—can greatly affect the life in and around it, from fish species and aquatic vegetation to its suitability as a source of drinking water. Traditional understanding of water chemistry within watersheds is that water is usually most acidic at its headwaters, and then decreases in acidity further along its course as other soil compounds and minerals neutralize it.

Researchers with the Northern Research Station and their colleagues are finding, however, that water chemistry can vary wildly during its journey through a watershed. And, furthermore, that variability can be fairly predictable based on a watershed’s topography, soil structure, and groundwater interactions.

Our Research

Researchers collected water samples throughout the length of several streams within three watershed areas of the Hubbard Brook Experimental Forest in central New Hampshire. They also gathered corresponding LiDAR data of the surrounding area to determine topography, which led to fairly accurate inferences about soil depth and dominant soil types. LiDAR is specialized laser technology, often shot from airplanes, that collects precise ground-level data and produces high-resolution maps. Meanwhile, belowground sensors collected data on groundwater interaction with the soil near the collection sites.

Scientists discovered a dynamic, yet predictable, interaction between groundwater and soil type that influenced the water’s chemistry at stream monitoring sites.

Expected Outcomes

For the purpose of the study and to put its findings into context, researchers defined soil types in a novel way: based on how groundwater interacted with it. Whereas, traditionally, soil might be classified as sandy, loamy, or clay, the researchers gave soils names based on the predominant groundwater process driving their formation: eluvial or illuvial.

Bedrock outcrops and the shallowest soils were eluvial in nature, meaning as groundwater passed through it, the groundwater dissolved metallic elements, such as iron and aluminum, along with  organic compounds. Surface water discharged from these sites was more concentrated with these dissolved materials and tended to be more acidic.

Other soils were illuvial in nature, accumulating organic matter and sequestering iron and aluminum ions as groundwater filtered through it. Stream water from these sites was higher in base elements, such as calcium, making its chemistry more neutral.

Researchers developed an algorithm that would allow land managers to map an entire watershed or forest using LiDAR imagery, and then make reasonable predictions about the water quality or chemistry at any given spot. This can help land managers focus restoration goals (such as increasing fish habitat) or recreation activities (such as swimming or fishing) in areas where the water chemistry would best support those goals or activities.

Research Results

Bailey, Scott W.; McGuire, Kevin J.; Ross, Donald S.; Green, Mark B.; Fraser, Olivia L. 2019. Mineral Weathering and Podzolization Control Acid Neutralization and Streamwater Chemistry Gradients in Upland Glaciated Catchments, Northeastern United States. Frontiers in Earth Science. 7: 296. 18 p. https://doi.org/10.3389/feart.2019.00063.

Zimmer, Margaret A.; Bailey, Scott W.; McGuire, Kevin J.; Bullen, Thomas D. 2013. Fine scale variations of surface water chemistry in an ephemeral to perennial drainage network. Hydrological Processes. 27(24): 3438-3451. https://doi.org/10.1002/hyp.9449.

Research Participants

Principal Investigator

  • Scott Bailey, USDA Forest Service Northern Research Station, Research Hydrologist

Research Partners

  • Last modified: January 4, 2021