ACETYLENE REDUCTION (NITROGEN FIXATION) IN WISCONSIN LAKES1

Abstract

Acetylene reduction has been used as an index of the nitrogen‐fixing capacity of the phytoplankton of representative oligotrophic and eutrophic lakes in Wisconsin. Acetylene reduction was not measurable in samples from oligotrophic Crystal Lake but was vigorous in samples from eutrophicated lakes. The activity during the season fluctuated widely with the development of blooms of nitrogen‐fixing blue‐green algae; no activity was demonstrated during winter months. Activity and population generally decreased with depth. Acetylene reduction was low in early morning, rose to a peak at noon, and then declined.