US Long-Term Ecological Research Network
We sample at the deepest part of the lake using a peristaltic pump and tubing, monthly during open water and approximately every five weeks during ice cover. We collect two types of pH samples at each sampling depth: one in 20ml vials with cone cap inserts to exclude all air from the vial, and one in 125ml bottles to be air equilibrated before analysis.  The depths for sample collection are based on thermal stratification:  top and bottom of the epilimnion, mid thermocline, and top, middle,and bottom of the hypolimnion.  During mixis we sample at the surface, mid water column, and bottom.
 
We analyze for pH the same day that samples are collected, keeping them cold and dark until just before analysis. Samples are warmed to room temperature in a dark container, and the air equilibrated samples are bubbled with outside air for at least 15 minutes prior to measurement. We measure pH using a Radiometer combination pH electrode and Orion 4Star pH meter.
 
Protocol Log:  1981-1988 -- used a PHM84 Research pH meter.
     1986 -- began analyzing air equilibrated pH.
     1988 - July 2010 -- used an Orion model 720 pH meter. 
LTER Keywords
Protocol Format
Parameter
Protocol ID
param_pH1
Protocol Type
field & laboratory