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Chemical mixing in the bottom boundary layer of a eutrophic reservoir: The effects of internal seiching on nitrogen dynamics
Author(s) -
Deemer Bridget R.,
Henderson Stephen M.,
Harrison John A.
Publication year - 2015
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 - 10.1002/lno.10125
Subject(s) - thermocline , advection , internal wave , stratification (seeds) , denitrification , water column , eutrophication , halocline , boundary layer , geology , bottom water , seiche , atmospheric sciences , environmental science , nitrogen , oceanography , chemistry , mechanics , thermodynamics , seed dormancy , physics , germination , botany , organic chemistry , salinity , dormancy , biology , nutrient
In lakes and reservoirs, the bottom boundary layer (BBL) mediates chemical fluxes between sediments and the overlying water column. At the internal shoreline, where the thermocline contacts the lakebed, the motions of internal waves can create fluctuating redox conditions and dynamic physical forcing that may support ecologically important reactions such as denitrification. We characterized physical and chemical dynamics within the internal shoreline of a eutrophic reservoir during the spring and early summer of 2012 (18 May to 18 July). An internal seiche was found to generate quasi‐periodic fluctuations (periods about 12–24 h) in BBL stratification, temperature, and redox conditions. To examine possible implications for chemical mixing and microbial processing, differences between vertically offset, simultaneous BBL measurements of velocity, temperature, N 2 , and N 2 O were made over 23 h. Vertical differences in BBL temperature, N 2 , and N 2 O formed and collapsed during the wave cycle, with the largest differences occurring following the arrival of an internal bore. Through much of the wave cycle, chemical differences were explained by physical advection and mixing. However, chemical differences measured after bore arrival were not explained by advection, possibly owing to local production of N 2 and N 2 O. These results highlight the dynamic physical environment within the internal shoreline, and the potential of this zone to contribute to system wide denitrification and nitrous oxide production.