Groundwater-fed wetland sediments and paleosols: It's all about water table

Gail M. Ashley, Daniel M. Deocampo, Julia Kahmann-Robinson, Steven G. Driese

Research output: Chapter in Book/Report/Conference proceedingChapter

19 Scopus citations


Wetlands are continental depositional environments and ecosystems that range between ephemerally wet to fully aquatic habitats, and, thus, the character of a wetland soil is directly related to the position of the water table over seasonal and longer timescales. The sediment and paleosol records of wetlands are products of a unique setting that can be both exposed to the atmosphere and water-saturated at the same time. Wetlands tend to occupy low-gradient portions of the landscape in places where the phreatic zone is at least ephemerally exposed at the surface, and hydrophytic vegetation has an opportunity to colonize. Groundwater-fed wetlands are an end member of a continuum of waterlogged environments and are associated with localized groundwater discharge (GWD); e.g., springs and seeps that can sustain permanent saturation. Research has tended to follow one of two parallel tracks: sedimentology or pedology. An objective of this paper is to bring these two separate lines of inquiry closer together. The signature of wetland pedogenesis includes redoximorphic features, enhanced hydrolytic alteration or dissolution of soluble phases, and preservation of biotic indicators of wetland habitats. Histosols (peats) and other hydric soils (indicated by gley color and reduced minerals like pyrite and siderite) are common in sites with a permanently high water table and anaerobic conditions. Illuvial clays, in contrast, record episodes in which wetlands dry out and drainage improves sufficiently for these features to form. A case study from Holocene-age Loboi Swamp, Kenya, illustrates the importance of integrating field observations and laboratory analyses. Wetland conditions were observed through thin section micromorphology, mineralogy, bulk geochemistry, and macro- and microfossils. The record of Loboi Swamp is characterized by the juxtaposition of features indicating episodes of soil saturation alternating with those indicating desiccation. In order to extract the most information recorded in groundwater-fed wetlands, soils and sediments should be studied as part of the larger spatial and climatic frameworks in which they occur.

Original languageEnglish (US)
Title of host publicationNew Frontiers In Paleopedology And Terrestrial Paleoclimatology
Subtitle of host publicationPaleosols And Soil Surface Analog Systems
PublisherSEPM Society for Sedimentary Geology
Number of pages15
ISBN (Print)9781565763227
StatePublished - 2013

Publication series

NameSEPM Special Publications

ASJC Scopus subject areas

  • Geology
  • Stratigraphy


  • Groundwater
  • Hydric soils
  • Micromorphology
  • Paleosol
  • Wetland


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