Necessity for Decontamination of Filters in C^{14} Measured Rates of Photosynthesis in Fresh Waters

Extracellular deposition of C { 14} can lead to large errors in estimates of photosynthesis in many aquatic situations where C { 14} techniques are employed. Of the available pre—radioassay techniques for the removal of extracelluar deposition, exposure to fumes of concentrated HC1 for a brief period is superior. Loss of radioactivity upon treatment differs among lakes, seasonally, and between illuminated and dark samples. Exposure of desiccated filters to fumes of concentrated HCl for a 10—min period is suggested as a standard procedure prior to assays of radioactivity.