Abstract
A deep chlorophyll layer (DCL) is a common feature of many deep, oligotrophic lakes including Lake Superior. Mechanisms generating and maintaining DCLs are variable across lakes, and seasonal patterns and relationships of DCL structure to physical variables are not well described. Using vertical profile data for physical and biological variables from western and central Lake Superior, we described seasonal patterns in DCL structure and other physical and biological parameters and applied linear mixed-effects models to determine how different physical factors (surface temperature, thermocline depth, and 1% photosynthetically active radiation (PAR) depth) affect the depth, thickness, maximum concentration, and integrated chlorophyll of the DCL. We observed clear seasonal patterns in the development and degradation of the DCL that coincide with seasonal changes in light and temperature. Modeling analysis using linear mixed-effects models showed that the DCL thickness was best predicted by surface temperature (R2 = 0.51) followed by thermocline depth (R2 = 0.36), and the deep chlorophyll maximum (DCM) concentration was best predicted by surface temperature (R2 = 0.26). The 1% PAR depth was not implicated as an important predictor, but observations from seasonal data suggest that it plays a role in the depth of the DCM. While no relationship was found between surface temperature and DCL-integrated chlorophyll, DCL thickness decreased and DCM concentration increased with increasing surface temperature, which could have implications for productivity in the DCL as the lake continues to warm.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1615-1624 |
| Number of pages | 10 |
| Journal | Journal of Great Lakes Research |
| Volume | 46 |
| Issue number | 6 |
| DOIs | |
| State | Published - Dec 2020 |
Bibliographical note
Funding Information:Funding: This work was supported by the National Science Foundation [grant numbers 0352291 , 0927512 ]; the State of Minnesota, Legislative and Citizens Commission on Minnesota Resources M.L. 2013, Ch52, Sec 2, Subd05f; and a subcontract from the Jet Propulsion Laboratory, California Institute of Technology, under the contract with the National Aeronautics and Space Administration.
Funding Information:
Funding: This work was supported by the National Science Foundation [grant numbers 0352291, 0927512]; the State of Minnesota, Legislative and Citizens Commission on Minnesota Resources M.L. 2013, Ch52, Sec 2, Subd05f; and a subcontract from the Jet Propulsion Laboratory, California Institute of Technology, under the contract with the National Aeronautics and Space Administration. Data were collected during the following projects ?The Nitrifying of Lake Superior and Its Intersections with the P and Fe Cycles? (NILSS) (https://www.bco-dmo.org/dataset/655249/data), ?Sources and Sinks of Stoichiometrically Imbalanced Nitrate in the Laurentian Great Lakes? (SINC) (http://lod.bco-dmo.org/id/dataset/3632), and ?Legislative-Citizen Commission on Minnesota Resources? (LCCMR). All authors read and commented on the final manuscript. KLR performed data analyses and led the writing for this contribution. RWS provided some of the funding, led and participated in field data collections, and assisted with interpretation and writing. JAA also provided some of the funding, helped to develop the analytical methods, and provided feedback on the manuscript.
Publisher Copyright:
© 2020 International Association for Great Lakes Research
Keywords
- DCL
- DCM
- Deep chlorophyll maximum
- Light
- Temperature