ECOSYSTEM ECOLOGY Nathaniel E. Ostrom Hunter J. Carrick Michael R. Twiss Leah Piwinski Evaluation of primary production in Lake Erie by multiple proxies Received: 26 July 2004 / Accepted: 26 January 2005 Ó Springer-Verlag 2005 Abstract Direct measurements of rates of primary pro- duction in Lake Erie are few and uncertainties surround rate measurements based on radiocarbon and the light– dark bottle incubation methods. For these reasons, we conducted a series of simultaneous primary productivity measurements in Lake Erie in July and August of 2003, based on incubation with [ 14 C]-NaHCO 3 , the light–dark bottle method, and incubation with 18 O enriched water. Significant differences in the rates of primary production obtained by incubations with [ 18 O]-H 2 O (0.19– 34.60 mmol-O 2 m 3 h 1 ), [ 14 C]-NaHCO 3 (0.03– 90.50 mmol-C m 3 h 1 ), and light–dark bottles (0.06– 60.78 mmol-O 2 m 3 h 1 ) were evident in six out of nine comparisons. Within the epilimnion, [ 18 O]-H 2 O rates of primary production were significantly different from rates based on [ 14 C]-NaHCO 3 and light–dark bottles in all four comparisons and lower rates were obtained in three out of four comparisons. Eutrophic conditions in Sandusky Bay, Lake Erie were evident from the high primary production rates of 20.50–34.60 mmol- O 2 m 3 h 1 ([ 18 O]-H 2 O), 34.39–90.50 mmol-C m 3 h 1 ([ 14 C]-NaHCO 3 ), and 46.66–60.78 mmol-O 2 m 3 h 1 (light–dark bottle). The photosynthetic quotient (PQ), or ratio of O 2 production to CO 2 consumption during photosynthesis, averaged 0.64±0.33 and 1.93±1.93, respectively, based on a comparison of [ 18 O]-H 2 O to [ 14 C]-NaHCO 3 rates or light–dark bottle to [ 14 C]-NaH- CO 3 production rates, respectively, demonstrating that photosynthesis in Lake Erie communities primarily fol- lows expected stochiometric trends. The average of the ratio of production rates based on incubation with [ 18 O]- H 2 O relative to those obtained by the light–dark incu- bation method was 0.66±0.33, indicating a tendency for the [ 18 O]-H 2 O method to provide slightly lower esti- mates of production in Lake Erie. Lower estimates of primary production based on [ 18 O]-H 2 O incubation relative to the other two approaches is most likely a consequence of consumption of labeled O 2 within the cell or dilution of label by the release of O 2 from supersaturated cells. This latter effect may be particu- larly characteristic of eutrophic environments. Keywords Photosynthesis Photosynthetic quotient Oxygen isotopes Lake Erie Carbon-14 Introduction For over 50 years, radiocarbon has been extensively used to evaluate rates of photosynthesis in aquatic eco- systems (Steeman-Nielsen 1952); however, uncertainty remains as to whether or not this technique provides an accurate indication of gross primary production (Howarth and Michaels 2000; Laws et al. 2000; Moigis 2000 and references therein). Artifacts associated with the [ 14 C]-NaHCO 3 incubation method include bottle effects (growth of bacteria and phytoplankton on bottle walls, lack of stirring or advection, exclusion of grazers, and so on), loss of label as CO 2 and/or dissolved organic carbon, and assimilation of unlabeled respired CO 2 (Ir- win 1991; Collos et al. 1993; Howarth and Michaels 2000). For these reasons, the consensus of the scientific community appears to be that short-term incubations (several hours or less) provide a reasonable estimate of Communicated by Jim Ehleringer N. E. Ostrom (&) L. Piwinski Department of Geological Sciences, Michigan State University, East Lansing, MI, 48824 USA E-mail: ostromn@msu.edu Tel.: +1-517-3554661 Fax: +1-517-3538787 N. E. Ostrom Center for Global Change and Earth Observations, Michigan State University, East Lansing, MI, 48824 USA H. J. Carrick School of Forest Resources, Pennsylvania State University, 8B Ferguson Building, University Park, PA, 16802 USA M. R. Twiss Department of Biology, Clarkson University, Potsdam, NY, 13699-5805 USA Oecologia (2005) DOI 10.1007/s00442-005-0032-5