Title

Iron in Eutrophic Clear Lake, California: Its Importance for Algal Nitrogen Fixation and Growth

Document Type

Article

Journal/Book Title/Conference

Canadian Journal of Fisheries and Aquatic Sciences

Volume

40

Issue

9

Publisher

National Research Council Canada

Publication Date

1983

First Page

1419

Last Page

1429

DOI

10.1139/f83-164

Abstract

Clear Lake, California, is warm, shallow, polymictic, and eutrophic. During 1975, levels of dissolved (< 0.45 μm) iron in all three basins of Clear Lake were always low (15–30 μg∙L−1) and decreased to 2 μg∙L−1 during the major bloom of Aphanizomenon flos-aquae. Nitrogen fixation (acetylene reduction) rates of the blue-green algal populations were stimulated as much as 500% above control levels by iron additions in laboratory and in situ large-volume bioassays. Carbon fixation rates and chlorophyll a levels were also significantly stimulated by iron additions, but usually less rapidly and to a lesser extent than N2 fixation. Additions of nitrate stimulated carbon fixation and chlorophyll production but inhibited increases in nitrogen fixation. Phosphate additions either had no effect or produced a mixture of stimulation or depression of all three variables. The bioassays indicate that the growth of blue-green algae and other algae in Clear Lake is usually directly limited by combined nitrogen and occasionally by iron or phosphorus. Low iron levels aggravate the effects of low nitrogen by limiting nitrogen fixation, thus reducing blue-green algal growth.

Comments

Originally published by the National Research Council - Canada. Abstract available through remote link. Subscription required to access article fulltext.