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Inorganic nitrogen transformations in the bed of the Shingobee River, Minnesota: Integrating hydrologic and biological processes using sediment perfusion cores
Author(s) -
Sheibley Richard W.,
Duff John H.,
Jackman Alan P.,
Triska Frank J.
Publication year - 2003
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2003.48.3.1129
Subject(s) - anoxic waters , denitrification , sediment , nitrification , groundwater , hyporheic zone , hydrology (agriculture) , environmental chemistry , nitrate , environmental science , water column , geology , nitrogen , chemistry , geomorphology , oceanography , geotechnical engineering , organic chemistry
Inorganic N transformations were examined in streambed sediments from the Shingobee River using sediment perfusion cores. The experimental design simulated groundwater‐stream water mixing within sediment cores, which provided a well‐defined one‐dimensional representation of in situ hydrologic conditions. Two distinct hydrologic and chemical settings were preserved in the sediment cores: the lowermost sediments, perfused with groundwater, remained anaerobic during the incubations, whereas the uppermost sediments, perfused with oxic water pumped from the overlying water column, simulated stream water penetration into the bed. The maintenance of oxic and anoxic zones formed a biologically active aerobic‐anaerobic interface. Ammonium (NH + 4 ) dissolved in groundwater was transported conservatively through the lower core zone but was removed as it mixed with aerated recycle water. Concurrently, a small quantity of nitrate (NO − 3 ) equaling ~25% of the NH + 4 loss was produced in the upper sediments. The NH + 4 and NO − 3 profiles in the uppermost sediments resulted from coupled nitrification‐denitrification, because assimilation and sorption were negligible. We hypothesize that anaerobic microsites within the aerated upper sediments supported denitrification. Rates of nitrification and denitrification in the perfusion cores ranged 42–209 and 53–160 mg N m −2 day −1 , respectively. The use of modified perfusion cores permitted the identification and quantification of N transformations and verified process control by surface water exchange into the shallow hyporheic zone of the Shingobee River.