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Floodplain biogeochemical mosaics: A multidimensional view of alluvial soils
Author(s) -
Appling Alison P.,
Bernhardt Emily S.,
Stanford Jack A.
Publication year - 2014
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2013jg002543
Subject(s) - floodplain , environmental science , soil water , denitrification , alluvium , biogeochemistry , hydrology (agriculture) , biogeochemical cycle , total organic carbon , vegetation (pathology) , soil carbon , soil science , geology , nitrogen , ecology , environmental chemistry , oceanography , chemistry , geomorphology , geotechnical engineering , biology , medicine , organic chemistry , pathology
The alluvial floodplains of large rivers are exceptionally productive and dynamic ecosystems, characterized by a complex mosaic of vegetation at different successional stages overlying soils sorted by historic floods. Natural floodplains are widely credited with efficiently removing nitrogen from surface waters and accumulating carbon in biomass, yet very little floodplain research has examined carbon and nitrogen cycling below surficial soils. We evaluated the extent to which vegetation cover could be used to predict subsurface carbon and nitrogen dynamics and to estimate whole‐floodplain carbon storage and denitrification rates. We dug soil pits under three dominant vegetation communities on a gravel‐bedded floodplain in northwest Montana to the depth of the permanent water table (1–3 m). We compared depth profiles of total and dissolved carbon (C) and nitrogen (N), denitrification potentials (DEAs), organic particulates, moisture, and pH across vegetation types. Near‐surface soils (0–10 cm) of forests had larger C and N pools and DEAs than grasslands or gravel bars, but such vegetation effects dissipated within the upper ~50 cm of soil. At depth, spatial heterogeneity in carbon and nitrogen pools and fluxes depended instead on soil texture, and relatively high rates of DEA and carbon storage were measured in zones of buried organic debris. Although C storage and denitrification potential are generally low in subsurface soils, these deep soils might nonetheless contribute substantially to whole‐floodplain C storage and denitrification because of their large volume, high hydrologic connectivity, and heterogeneous biogeochemistry.