Microbial Planktonic Respiration in Lakes at North Temperate Lakes LTER 2001

Respiration of total plankton passing a 70 micron mesh, and bacteria passing a 1 micron mesh, calculated from loss of oxygen in lake water incubated at in situ temperatures. Oxygen concentration was determined using the Winkler reaction with azide modification. Final product concentration determined via spectrometry or titration with sodium thiosulfate. Titrations that may have overrun the endpoint were not included. The following equation for calculation of dissolved oxygen concentration from titration of Winkler end product with thiosulfate (from Wetzel, R. G. and G. E. Likens. 1991. Limnological Analyses, 2nd ed. Springer-Verlag, New York). Thiosulfate with a molarity of 0.20 N was used for all titrations. mg O2 L-1 = (ml titrant)*(molarity of thiosulfate)*(8000)/((ml of sample titrated)*((ml of bottle -3)/(ml of bottle))). The following equation is for calculation of dissolved oxygen calculation from spectophotometric analysis of Winkler reaction end product (from Roland, F., N. F. Caraco, J. J. Cole. 1999. Rapid and precise determination of dissolved organic oxygen by spectrophotometry: Evaluation of interference from color and turbidity. Limnol. Oceanogr. 44(4):1148-1154). mg O2 L-1 = absorbance at 430 nm (in units of cm-1) * 8.1-0.41 Sampling Frequency: fortnightly during ice-free season - every 6 weeks during ice-covered season Number of sites: 4