Periphyton and phytoplankton samples were collected monthly at five sites in the Sacramento River between May 1972 and April 1973. Periphyton were analyzed for species identification and biomass, and phytoplankton were analyzed for species identification and concentrations. The results were used to assess biological water-quality conditions in the river and to compare phytoplankton types and concentrations at three sites with those in 1960-61.
Diatoms were the dominant group in both numbers and types of periphyton and phytoplankton. The number of genera and frequency of occurrence of periphyton increased downstream. The periphyton biomass decreased downstream and with succeeding monthly sampling periods. The highest productivity was at site B, below Red Bluff, probably because the Red Bluff Diversion Dam provides optimum conditions for periphyton growth. The decreasing productivity downstream is probably a function of higher sediment concentrations. The periphyton biomass ranged from 0.00 to 0.56 grams per square meter per day throughout the study period.
Phytoplankton concentrations and diversity increased downstream. The highest phytoplankton concentration was 980 organisms per milliliter at site D, above Knights Landing, in September. The diversity indices ranged from 0.95 to 3.88 for all sites throughout the study period. Fewer phytoplankton genera were collected in 1972-73 than in 1960-61, but the generic composition was similar. Total phytoplankton concentrations were nearly always higher in 1960-61 than in 1972-73. Green algal concentrations were significantly higher (p<0.05) at site C and diatoms were significantly higher at all three sites in 1960-61. Blue-green algal concentrations were higher in 1972-73, but differences between the two time intervals were not significant.
