Denitrification in Lake 227 During Summer Stratification

Abstract

In situ denitrification in Lake 227 was assayed by using 15N-labeled NO3− during summer stratification periods in 1973, 1974, and 1975. Dissolved oxygen and NO3− concentrations were the main factors controlling denitrification in the water column and in sediments. The epilimnetic sediment–water interface was a more significant site of natural denitrification when compared to the oxygen-limiting (dissolved oxygen less than 0.2 mg/L) thermocline and the anoxic hypolimnion. Epilimnetic sediment denitrification rates averaged about 15 mg N∙m−2∙d−1. Nearly all of the NO3− that mixed into the surficial sediments was denitrified. Alone, epilimnetic denitrification removed 1.4% of the NO3− added annually. Below the euphotic zone, sediments would provide an efficient sink for NO3−-N without simultaneous initiation of eutrophication.Key words: denitrification, nitrogen sink, nitrate in lakes, experimental lakes, summer stratification