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