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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Earth Sci. | doi: 10.3389/feart.2019.00063

Mineral weathering and podzolization control acid neutralization and streamwater chemistry gradients in upland glaciated catchments, northeastern USA

  • 1Northern Research Station, Forest Service (USDA), United States
  • 2Department of Forest Serources and Environmental Conservation and Virginia Water Resources Research Center, Virginia Tech, United States
  • 3Department of Plant and Soil Science, University of Vermont, United States
  • 4Northern Resarch Station, USDA Forest Service and Center for the Environment, Plymouth State University, United States
  • 5Department of Natural Resources and the Environment, University of New Hampshire, United States

Headwater streams in the White Mountains, NH, USA have been shown to have downstream gradients of increasing pH and concentrations of base cations coupled with decreasing concentrations of aluminum. A two-stage acid neutralization model involving shallow soil exchange processes in headwaters coupled with deeper mineral weathering downstream had been proposed to explain these gradients. We conducted synoptic sampling of three headwater catchments in this region that showed variations in this longitudinal pattern, ranging from streams that remain acidic throughout their length to streams with circumneutral pH beginning at their source. To explain these differences, we mapped soils using a hydropedologic approach that emphasizes the influence of groundwater saturation frequency and water table regime on soil formation processes. Stream segments with lower pH and base cation concentrations, coupled with higher concentrations of dissolved organic carbon, aluminum, and in one case iron, were in subcatchments mapped with shallow to bedrock soils where eluvial soil forming processes dominated. In contrast, stream segments with higher pH and base cation concentrations coupled with low concentrations of dissolved organic carbon and aluminum were associated with subcatchments with deeper soils where illuvial processes were more dominant. Concentrations of sodium and silicon were relatively uniform across these gradients. Coupled with the higher concentrations of dissolved aluminum and small pools of exchangeable aluminum in the areas of bedrock outcrops and shallow soils, these data suggest that primary mineral dissolution is an important process influencing upper stream reaches. Some stream reaches with obvious groundwater springs show a more abrupt transition suggesting that neutralization along deeper flowpaths may play a role as well. These data suggest a new three stage model of stream chemistry evolution with introduction of organic acids by frequent flushing of organic soils on shallow bedrock along ridge areas, acidic reaches controlled by shallow mineral weathering processes coupled with eluvial soil development, giving way to downstream reaches influenced by illuviation as organometallic complexes precipitate in spodic soil horizons. This new model highlights differences in critical zone evolution along hillslopes in glaciated catchments with implications for understanding gradients in water quality, soil fertility, and response and recovery from disturbances.

Keywords: critical Zone, Streamwater, Groundwater, Soil development, Podzolization, mineral weathering, catchment

Received: 27 Jul 2018; Accepted: 14 Mar 2019.

Edited by:

Samuel Abiven, University of Zurich, Switzerland

Reviewed by:

Pamela L. Sullivan, University of Kansas, United States
Jason Austin, University of Georgia, United States  

Copyright: © 2019 Bailey, McGuire, Ross, Green and Fraser. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Scott W. Bailey, Northern Research Station, Forest Service (USDA), Newtown Square, United States, swbailey@fs.fed.us