Oxygen use by Nitrification in the Hypolimnion and Sediments of Lake Erie
Nitrification is an oxygen consumptive process, consuming 2 mol of oxygen permol of ammonium oxidized. Hypolimnion
and sediment sampleswere collected during the summers of 2008–2010 in Lake Erie to determine the
total oxygen consumption and oxygen consumption fromnitrification by blocking nitrification with selective inhibitors.
Oxygen consumption by nitrification in the hypolimnion was 3.7 ± 2.9 (mean ± 1 SD) μmol O2/L/d,
with nitrification accounting for 32.6 ± 22.1% of the total oxygen consumption. Nitrification in the hypolimnion
contributed more to oxygen consumption in the eastern sites than western sites and was lowest in September.
The nitrification rate did not correlatewith environmental factors such as oxygen, nitrate or ammonium, or nitrifier
numbers. Oxygen consumption by nitrification in sediment slurries was 7.1 ± 5.8 μmol O2/g/d, with nitrification
accounting for 27.0 ± 19.2% of the total oxygen consumption with the lowest rates in July and the lowest
percentages in June. Oxygen consumption by nitrification in intact sediment coreswas 682 ± 61.1 μmol O2/m/d
with nitrification accounting for 30.4 ± 10.7% of the total oxygen consumption. Nitrification rates in intact cores
were generally highest in September. The proportion of oxygen consumed by nitrification corresponds closely
with what would be predicted from complete oxidation of a Redfield molecule (23%).While nitrification is unlikely
to be the dominant oxygen consumptive process, the rates observed in Lake Eriewere sufficient to theoretically
deplete a large portion of the hypolimnetic oxygen pool during the stratified period.