THE FLORIDA STATE UNIVERSITY ARTS AND SCIENCES ...

50ºC (36ºF - 122ºF) (Brady & Weil, 2002; Poulin et al., 2006). While there are no studies
reviewed to show the possibility of denitrification above 50ºC (122ºF), it is theoretically
possible where bacteria have evolved to cope with specific environmental conditions.
Researchers assume that reaction rates double for every 10ºC (50ºF) increase in
temperature (Arrhenius rate law). Since groundwater temperature generally reflective of
the average temperature of the region, it may be therefore be difficult to observe a
relationship between temperature and denitrification rates in groundwater in a specific
area.
Nevertheless Robertson et al. (2000, 2008) demonstrate a correlation between water
temperature and denitrification rates in a permeable reactive barrier system.
Denitrification is observed at temperatures as low as 2ºC (36ºF). Robertson et al. (2000)
reported a denitrification rate of 5 mg-N/l/day for a temperature range of 2 ºC (36 ºF) -
5ºC (41ºF) and 15–30 mg-N/l/ day for a temperature range of 10ºC (50ºF) - 20ºC (68ºF).
Pfenning and McMahon (1996) demonstrated that lowering temperatures by 18ºC (65ºF)
result in a 77 % decrease in the rates of denitrification. This shows that there is a direct
correlation between temperature and the rate of denitrification.
Christiansen and Cho (1983) reported that abiotic denitrification of nitrite by soluble
organic matter can occur in frozen soil. At one field site, Cannavo et al. (2004) observed
that, unlike CO2 levels, N2O levels in soil are independent of temperature; the authors
ascribed this to aerobic denitrifying fungi that are much more tolerant of low
temperatures than bacteria.
Changes in the denitrification rate due to seasonal temperature variations may be masked
by deviations in the rate of organic carbon flux. For example, Cannavo et al. (2004)
found that freeze–thaw cycles increase the flux of carbon to the unsaturated zone and can
create anaerobic micro-environments in which denitrification can become established.
The observed increase in the denitrification rate with an increase in temperature varies
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