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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Jun 2019

Submitted as: research article | 04 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

A microtopographic signature of life: Ecohydrologic feedbacks structure wetland microtopography

Jacob S. Diamond1, Daniel L. McLaughlin1, Robert A. Slesak2, and Atticus Stovall3 Jacob S. Diamond et al.
  • 1School of Forest Resources and Environmental Conservation, Virginia Tech, Blacksburg, 24060, USA
  • 2Minnesota Forest Resources Council, St. Paul, 55108, USA
  • 3NASA Goddard Space Flight Center, Greenbelt, 20771, USA

Abstract. Microtopography in wetlands can be a visually striking landscape feature, and also critically influences biogeochemical processes at both the scale of its observation (10−2–102m2) and at aggregate scales (102–104m2). However, relatively little is known about how microtopography develops in wetlands or the factors that influence its structure and pattern. For example, wetland vegetation appears to have a strong affinity to elevated microsites, but the degree to which wetland vegetation simply preferentially occupies elevated microsites (“hummocks”) versus the degree to which wetland vegetation reinforces and maintains these elevated microsites is not clear. Growing research across different ecosystems suggests that such reinforcing processes may be common between plants and their environment, resulting in self-organized patch features, like hummocks. Here, we made use of landscape ecology techniques and diagnostics to evaluate the plausibility of plant-environment feedback mechanisms in the maintenance of wetland microtopography. Using a novel terrestrial laser scanning dataset, we were able to quantify the sizing and spatial distribution of hummocks in 10 black ash (Fraxinus nigra Marshall) wetlands in northern Minnesota, U.S.A. We observed clear elevation bimodality in our wettest sites, indicating microsite divergence into two states: elevated hummocks and base elevation hollows. We coupled the TLS dataset to a three-year water table record and soil-depth measurements, and showed that hummock height is largely predicted by mean water table depth, with little influence of subsurface microtopography on surface microtopography. We further show that hummocks in wetter sites exhibit regular spatial patterning in contrast to hummocks in drier sites, which exhibit more random spatial arrangements. We show that hummock size distributions (perimeters, areas, and volumes) are lognormal, and that hummocks exhibit a characteristic patch area of approximately 1 m2 across sites. Finally, we show that hummocks may be responsible for increased reactive surface area in black ash wetlands by up to 32 %, and may also influence surface water dynamics through modulation of specific yield by up to 30 %. We suggest that vegetation develops and maintains hummocks in response to anaerobic stresses from saturated soils, leading to a microtopographic signature of life.

Jacob S. Diamond et al.
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Jacob S. Diamond et al.
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