Ammonium (NH4) 
 PI: Zackary Johnson (Duke University) 
 Version History: 
   Dataset updated: 10 July 2014 (current version) 
   Original data:   25 Oct 2012 
 Note: 0 = mean of replicated samples was below detection limit  
       (Detection limits: 9 nM for POWOW1; 5 nM for POWOW2 and 3).