Increasing stoichiometric imbalance in North America’s largest lake: Nitrification in Lake Superior

Sterner, Robert W., Anagnostou, Eleni, Brovold, Sandra, Bullerjahn, George S., Finlay, Jacques C., Kumar, Sanjeev, McKay, R. Michael L. and Sherrell, Robert M. (2007) Increasing stoichiometric imbalance in North America’s largest lake: Nitrification in Lake Superior. Geophysical Research Letters, 34, L10406. (doi:10.1029/2006GL028861).


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Lake Superior has exhibited a continuous, century-long increase in nitrate whereas phosphate remains at very low levels. Increasing nitrate and low phosphate has led to a present-day severe stoichiometric imbalance; Lake Superior’s deepwater NO3 :PO43 molar ratio is 10,000, more than 600 times the mean requirement ratio for primary producers. We examine the rate of [NO3?] increase relative to budgets for NO3 and fixed N. Nitrate in Lake Superior has continued to rise since 1980, though possibly at a reduced rate. We constructed whole-lake NO3 and N budgets and found that NO3 must be generated in the lake at significant rates. Stable O isotope results indicate that most NO3 in the lake originated by in-lake oxidation. Nitrate in the lake is responding not just to NO3 loading but also to oxidation of reduced forms of nitrogen delivered to the lake. The increasing [NO3]:[PO43] stoichiometric imbalance in this large lake is largely determined by these in-situ processes.

Item Type: Article
Digital Object Identifier (DOI): doi:10.1029/2006GL028861
ISSNs: 0094-8276 (print)
Subjects: G Geography. Anthropology. Recreation > GC Oceanography
Q Science > QD Chemistry
Divisions : Faculty of Natural and Environmental Sciences > Ocean and Earth Science > Geochemistry
ePrint ID: 339953
Accepted Date and Publication Date:
Date Deposited: 06 Jun 2012 12:36
Last Modified: 31 Mar 2016 14:29

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