Phytoplankton Abundance and Generic Composition Data for the Potomac River and Estuary, Maryland

Phytoplankton of the Potomac River and Estuary were counted and identified to the generic level. Double-blind precision tests for an individual counter yielded a standard deviation that was * 10 percent of the mean. Differences between three counters exceeded * 10 percent, and a curve could be fit to calibration counts to yield correlation coefficients of 0.70 to 0.86 between counters. Counters identified the same genera that comprised the highest and second highest percentages of the population in 88 percent of the calibration samples.