Document Type
Article
Journal/Book Title/Conference
Limnetica
Author ORCID Identifier
Wayne A. Wurtsbaugh https://orcid.org/0000-0002-1436-5225
Volume
40
Issue
2
Publisher
Asociacion Iberoamericana de Limnologia
Publication Date
7-20-2020
Journal Article Version
Accepted Manuscript
Keywords
deep chlorophyll maxima, DCM, diffusivity, tracer
First Page
309
Last Page
327
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Abstract
Deep-chlorophyll layers (DCL) in oligotrophic lakes contribute significantly to primary productivity, but the importance of this production for the rest of the food web and for other strata is unknown. In Laguna El Tejo, a sheltered 1.7-ha Spanish karst lake, chlorophyll levels were < 2 μg/L in the epilimnion but reached 10 μg/L in the metalimnion and upper hypolimnion where cyanobacterial picoplankton dominated. Particulate nitrogen levels were 2-14 times higher in the metalimnion than in the epilimnion and 42 % of the primary productivity occurred in the deeper strata where the DCL was located. To address the trophic importance of the high biomass and production in the deep chlorophyll layer, we injected 15NH4+ and rhodamine into a 0.5-m strata (15-16 m) in the metalimnion of the lake. The 15NH4+ taken up by the nitrogen-limited phytoplankton allowed us to measure the importance of biologically mediated transport whereas the rhodamine traced physical eddy diffusion. After 28 days 55 % of the 15N could be accounted for: 71 % remained in the metalimnetic seston (11-18 m), 10 % was in the hypolimnetic seston (18-20 m), 11 % was found above in the epilimnetic seston, and only 8 % had sedimented into the anoxic layer below 20 m. Only negligible amounts of rhodamine (corrected for degradation) moved beyond the 14-18 m strata in the lake, but bio-diffusivity of 15N was 3 times greater than the physically induced diffusivity of rhodamine. A mixing model indicated that the deep chlorophyll layer contributed only 1-2 % of the diet of epilimnetic macrozooplankton but 14-33 % of the diet of the meta-hypolimnetic zooplankton. The data indicate the overall importance for primary production and the sequestration of nutrients in the DCL, but relatively limited importance for the macrozooplankton in the lake.
Recommended Citation
Wayne A. Wurtsbaugh, María Rosa Miracle, Antonio Camacho, Javier Armengol and Eduardo Vicente 2021. Volumen 40(2): 309-327. DOI: 10.23818/limn.40.21
Comments
https://www.limnetica.net/en/node/1488