Nitrogen Limitation of Phytoplankton in a Spanish Karst Lake with a Deep Chlorophyll Maximum: A Nutrient Enrichment Bioassay Approach

Document Type

Article

Journal/Book Title/Conference

Journal of Plankton Research

Volume

25

Issue

4

Publisher

Oxford University Press

Publication Date

2003

Keywords

nitrogen limitation, phytoplankton, Spanish karst lake, deep chlorophyll maximum, nutrient enrichment, bioassay, approach

First Page

397

Last Page

404

Abstract

An in vitro nutrient addition bioassay was performed to test the relative inorganic nitrogen (N) and phosphorus (P) limitation of phytoplankton in a Spanish karst lake (El Tejo) during the last part of the stratification period, when nutrient limitation is most pronounced. Nutrient deficiency was tested in samples from three different layers of the lake: the epilimnion, metalimnion and oxic hypolimnion. Nitrogen additions, either without or combined with P, increased phytoplankton growth in all three strata, compared with controls or P treatments. This showed that N was the nutrient limiting phytoplankton growth in late summer–early fall. Since both hypolimnetic diffusion and groundwater fluxes of N-rich waters into the lake are much reduced during summer, N becomes the limiting nutrient as stratification advances. We suggest that in this Mediterranean area with low atmospheric deposition of anthropogenic N and in lakes relatively free of surface run-off, nutrient supply by atmospheric deposition might be a key factor in controlling nutrient deficiency for phytoplankton growth.

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