Rates and controls of nitrification in a large oligotrophic lake

• DOI: 10.4319/lo.2013.58.1.0276
• Publication Date: 2012-12-08T07:29:31Z
• Authors: Gaston E. Small; George S. Bullerjahn; Robert W. Sterner; Benjamin F. N. Beall; Sandra Brovold; Jacques C. Finlay; Robert M. L. McKay; Maitreyee Mukherjee
• Keywords: Epilimnion; Nitrogen Cycle

Recent discoveries have altered prevailing paradigms concerning the conditions under which nitrification takes place and organisms responsible for in aquatic ecosystems. In Lake Superior, nitrate () concentrations increased fivefold past century. Although previous evidence indicated that most is generated by within lake, important questions remain magnitude controls of nitrification, microbial groups are primarily this process. We measured water‐column rates western basin Superior during five research cruises from November 2009 to March 2011. Using situ bottle incubations at 10 depths, we quantified using both oxidation 15 N‐labeled ammonium uptake 14 C associated with nitrification. Average ranged 18–34 nmol N L −1 d across cruises, similar values reported coastal ocean, two orders lower than other lakes. Low observed epilimnion corresponded absence ammonium‐oxidizing archaea nitrite‐oxidizing bacteria. The > 50‐fold greater long‐term rise indicating actively cycling change ecosystem mediated internal dynamics.