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Physical and biological contributions to metalimnetic oxygen maxima in lakes
Author(s) -
Wilkinson Grace M.,
Cole Jonathan J.,
Pace Michael L.,
Johnson Robert A.,
Kleinhans Maxwell J.
Publication year - 2015
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.1002/lno.10022
Subject(s) - thermocline , environmental science , autotroph , supersaturation , maxima , oxygen , saturation (graph theory) , atmospheric sciences , ecosystem , hypoxia (environmental) , hydrology (agriculture) , ecology , chemistry , biology , geology , genetics , mathematics , geotechnical engineering , organic chemistry , combinatorics , performance art , bacteria , art history , art
Many lakes have positive, heterograde vertical oxygen (O 2 ) profiles with a metalimnetic maximum usually assumed to be the result of biological O 2 production. However, supersaturated metalimnetic O 2 maxima are formed by biological processes (net photosynthetic production of O 2 ) and physical processes (warming of gasses trapped below the thermocline). Although the mechanisms contributing to supersaturated metalimnetic O 2 peaks are understood, the contribution of biological vs. physical processes is not well known in lakes. To examine these contributions, we measured O 2 and argon (Ar) saturation anomalies in the metalimnia of 17 lakes. Unlike O 2 , Ar is biologically inert and, therefore, can be used to quantify physical processes. There was a positive Ar anomaly at the depth of the O 2 maximum in every lake. On average, only 14% of the O 2 maximum could be attributed solely to biological production of O 2, but this percentage varied widely among lakes. Additionally, in a subset of lakes, the relative saturation of O 2 at the metalimnetic maximum was lower than Ar due to net biological consumption, creating a weaker O 2 maximum than would be expected based on the physical processes alone. Some lakes were sampled multiple times during summer and net ecosystem production (NEP) was also calculated. There were many instances of positive NEP in the metalimnion; however, net autotrophy was usually transient instead of persistent. Overall, biological production of O 2 alone is not responsible for metalimnetic O 2 maxima as both physical and biological processes contribute substantially to the formation and persistence of O 2 maxima in lakes.