Denitrification in sediments of a Lake Erie coastal wetland (Old Woman Creek, Huron, Ohio, USA)

Denitrification in Old Woman Creek estuary (Lake Erie) sediments was measured by an in vitro N-2-flux method with intact cores and by an in situ chamber method. In both methods, nitrogen gas, the end product of denitrification, was measured directly by gas chromatography. The in situ approach allowed measurement of denitrification directly over short time intervals but its use was limited to shallow depths. Denitrification rates measured with in situ chambers agreed well with those from in vitro intact cores where temperatures in the estuary remained constant. However the two methods could not be accurately compared during the spring where temperature increased rapidly because of the 4-day pre-incubation time needed for sparging for the in vitro method. In vitro denitrification rates ranged from ca 40 to 135 mu mole N-2 m(-2) h(-1) in October 1993 and from 66 to 428 mu mole N-2 m(-2) h(-1) in May and July, 1994. Oxygen consumption rates in these experiments ranged from 0.71 to 3.0 mmole O-2 m(-2) h(-1). Denitrification rates tended to decrease among the flow axis but differences among stations were usually, not significant In situ N-2 accumulation rates ranged from 45 mu mole N(2)m(-2) h(-1) in dark chambers during October 1993 up to apparent values of 2,100 mu mole N-2 m(-2) h(-1) in May 1994, immediately after the water temperature had rapidly increased to 27 degrees C, These calculated values included gas-solubility corrections due to the water-temperature increases. In situ measurements of denitrification rates in transparent chambers were 76-79% higher than rates measured in a similar dark chamber. The results suggest that denitrification is an important sink for-nitrogen in Old Woman Creek estuary and that environmental conditions such as temperature, light, and available substrate affect denitrification rates.