Key points are not available for this paper at this time.
Weekly water samples were taken to measure stable isotope composition (δ 13 C and δ 15 N) of particulate organic matter (POM) in Lake Wauberg, Florida, from June 1994 to May 1995. The average δ 13 C of POM was ‐19.3%, consistent with an autochthonous origin from phytoplankton production, and exhibited a seasonal pattern that coincided with changes in water temperature, pH, CO 2 concentration, and phytoplankton biomass in the surface water. The 13 C enrichment in POM was attributed to reduced isotope fractionation due to carbon (C) limitation and the use of an isotopically heavy dissolved inorganic carbon pool supported mainly by atmospheric invasion and anaerobic respiration. Intermittent declines in δ 13 C of POM were related to the frequent collapses of phytoplankton blooms and increases in CO 2 concentration resulting from both increased community respiration and terrestrial loading. Average δ 15 N of POM was 1.3% and varied within a narrow range (20.1% to 2.5%). No significant correlation between phytoplankton biovolume and the δ 15 N of POM was found. The low δ 15 N is indicative of strong N 2 fixation, which is in line with the low concentration of dissolved inorganic nitrogen and the presence of high biovolume of N 2 ‐fixing cyanobacteria in the surface water. This study suggests that stable C isotopes are good proxies for surface water CO 2 concentration and primary production, while stable N isotopes can be used to indicate N 2 fixation.
Gu et al. (Wed,) studied this question.