Particulate organic carbon (POC) within the seston load is a basal resource of organic matter for stream ecosystems. However, of the few reported measurements of POC mineralization rates, most were made on POC collected from the benthos and performed over <24 hours.  We developed a method that kept particles in suspension and extended rate measurements to 30-40 days.  BOD bottles were filled with POC at elevated (5 to 10x) densities using particles collected and concentrated by tangential flow ultrafiltration.  Glass beads added to the BOD bottles prevented aggregation while the bottles were rotated around an axel to ensure that the particles were suspended. Replicate samples were periodically sacrificed for DO measurements.  We observed that suspended particles exhibited POC mineralization rates that were 5-fold higher than particles that were allowed to settle.  Mineralization rates peaked within a few days at 45.8 mg O₂ g initial POC^-1 day^-1 and then declined in the following weeks to 2.2 mg O₂ g initial POC^-1 day^-1.  The mineralization patterns are consistent with POC that is comprised of two or more lability classes.  Labile POC may be mineralized by bacteria within upstream reaches; more resistant POC may subsidize downstream ecosystems with carbon from the headwaters.