A 450-year record of environmental change from Castle Lake, California (USA), inferred from diatoms and organic geochemi
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ORIGINAL PAPER
A 450-year record of environmental change from Castle Lake, California (USA), inferred from diatoms and organic geochemistry Paula J. Noble . Gary A. McGaughey . Michael R. Rosen . Christopher C. Fuller . Marco A. Aquino-Lo´pez . Sudeep Chandra
Received: 11 December 2019 / Accepted: 6 October 2020 Springer Nature B.V. 2020
Abstract A 39-cm sediment core from Castle Lake, California (USA) spans the last * 450 years and was analyzed for diatoms and organic geochemistry (d15N, d13C, and C:N), with the goal of determining sensitivity to natural climate variation and twentieth century anthropogenic effects. Castle Lake is a subalpine, nitrogen-limited lake with * 5 months of annual ice cover. Human impacts include light recreational use, past fish stocking, and experimental use by the Castle Lake Research Station. The base of the core Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10933-020-00160-y) contains supplementary material, which is available to authorized users. P. J. Noble (&) G. A. McGaughey Department of Geological Sciences and Engineering, University of Nevada, Reno, NV 89557, USA e-mail: [email protected] G. A. McGaughey e-mail: [email protected] P. J. Noble M. R. Rosen S. Chandra Global Water Center, University of Nevada, Reno, NV 89557, USA e-mail: [email protected] S. Chandra e-mail: [email protected]
(below 32 cm; pre mid-1700s) represents the period of maximum ice cover. In contrast, the end of the Little Ice Age (mid 1700s–early 1800s) is dominated by cyclotelloids (mostly Discostella stelligera), indicating significant open-water periods, a condition that persisted into the early 1900s. Cyclotelloids began to decline in the 1960s and were replaced by the Fragilaria tenera grp. (peak in 1970s), succeeded by Asterionella formosa (peak * 2010), and accompanied by a reduction in d15N values and a decrease in C:N that may represent increased atmospheric nitrogen deposition. Another anthropogenic signal was discerned in the core and was interpreted to be the result of an ammonium nitrate fertilization experiment C. C. Fuller US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA e-mail: [email protected] M. A. Aquino-Lo´pez Arts and Humanities Institute, Maynooth University, Maynooth, Co. Kildare, Ireland e-mail: [email protected] S. Chandra Department of Biology, University of Nevada, Reno, NV 89557, USA
M. R. Rosen US Geological Survey, California Water Science Center, 2730 N. Deer Run Road, Carson City, NV 89701, USA
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J Paleolimnol
of the epilimnion that was conducted in 1980 and 1981. This signal was manifested in the core largely by a negative excursion in d15N, possibly caused by fractionation during denitrification in surface sediment. A phytoplankton monitoring dataset collected by the Castle Lake Research Station from 1967 to 1984 corroborates the timing of increased araphid euplanktonic species in the 1970s, and increases in two benthic diatoms (
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