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

Increasing stoichiometric imbalance in North America’s largest lake: Nitrification in Lake Superior
Increasing stoichiometric imbalance in North America’s largest lake: Nitrification in Lake Superior
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.
0094-8276
L10406
Sterner, Robert W.
c3db9594-619e-4fb9-a6f7-42f7b0bb0cd1
Anagnostou, Eleni
4527c274-f765-44ce-89ab-0e437aa3d870
Brovold, Sandra
8f240d87-43af-4813-b5d6-a89e525c98e2
Bullerjahn, George S.
eeb7e94d-9b40-4330-acac-f7175c6c82fc
Finlay, Jacques C.
fd1fd733-599a-497b-b405-3af6f4e92d09
Kumar, Sanjeev
72adbe62-7c8b-4430-aab6-6e54e94b2a91
McKay, R. Michael L.
4a42e8b4-e48f-4063-89d4-ab5bc51efe55
Sherrell, Robert M.
251b287a-1ac0-48aa-a422-edeed2427c22
Sterner, Robert W.
c3db9594-619e-4fb9-a6f7-42f7b0bb0cd1
Anagnostou, Eleni
4527c274-f765-44ce-89ab-0e437aa3d870
Brovold, Sandra
8f240d87-43af-4813-b5d6-a89e525c98e2
Bullerjahn, George S.
eeb7e94d-9b40-4330-acac-f7175c6c82fc
Finlay, Jacques C.
fd1fd733-599a-497b-b405-3af6f4e92d09
Kumar, Sanjeev
72adbe62-7c8b-4430-aab6-6e54e94b2a91
McKay, R. Michael L.
4a42e8b4-e48f-4063-89d4-ab5bc51efe55
Sherrell, Robert M.
251b287a-1ac0-48aa-a422-edeed2427c22

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).

Record type: Article

Abstract

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.

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Published date: 2007
Organisations: Geochemistry

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Local EPrints ID: 339953
URI: http://eprints.soton.ac.uk/id/eprint/339953
ISSN: 0094-8276
PURE UUID: add4dc49-4606-4023-86cd-3f6864ad5660

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Date deposited: 06 Jun 2012 12:36
Last modified: 16 Dec 2019 20:38

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Contributors

Author: Robert W. Sterner
Author: Eleni Anagnostou
Author: Sandra Brovold
Author: George S. Bullerjahn
Author: Jacques C. Finlay
Author: Sanjeev Kumar
Author: R. Michael L. McKay
Author: Robert M. Sherrell

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