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O 2 reduction and denitrification rates in shallow aquifers
Author(s) -
Tesoriero Anthony J.,
Puckett Larry J.
Publication year - 2011
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2011wr010471
Subject(s) - denitrification , nitrate , aquifer , sulfate , groundwater , lithology , environmental chemistry , total organic carbon , sulfide , environmental science , chemistry , hydrology (agriculture) , nitrogen , geology , geochemistry , geotechnical engineering , organic chemistry
O 2 reduction and denitrification rates were determined in shallow aquifers of 12 study areas representing a wide range in sedimentary environments and climatic conditions. Zero‐ and first‐order rates were determined by relating reactant or product concentrations to apparent groundwater age. O 2 reduction rates varied widely within and between sites, with zero‐order rates ranging from <3 μmol L −1 yr −1 to more than 140 μmol L −1 yr −1 and first‐order rates ranging from 0.02 to 0.27 yr −1 . Moderate denitrification rates (10–100 μmol N L −1 yr −1 ; 0.06–0.30 yr −1 ) were observed in most areas with O 2 concentrations below 60 μmol L −1 , while higher rates (>100 μmol N L −1 yr −1 ; >0.36 yr −1 ) occur when changes in lithology result in a sharp increase in the supply of electron donors. Denitrification lag times (i.e., groundwater travel times prior to the onset of denitrification) ranged from <20 yr to >80 yr. The availability of electron donors is indicated as the primary factor affecting O 2 reduction rates. Concentrations of dissolved organic carbon (DOC) and/or sulfate (an indicator of sulfide oxidation) were positively correlated with groundwater age at sites with high O 2 reduction rates and negatively correlated at sites with lower rates. Furthermore, electron donors from recharging DOC are not sufficient to account for appreciable O 2 and nitrate reduction. These relations suggest that lithologic sources of DOC and sulfides are important sources of electrons at these sites but surface‐derived sources of DOC are not. A review of published rates suggests that denitrification tends to occur more quickly when linked with sulfide oxidation than with carbon oxidation.