Nutrient limitation of bacterioplankton growth in Lake Dillon, Colorado

Bacterioplankton biomass, production, and growth rate were measured over a 2-yr period in Lake Dillon, a mesotrophic Colorado reservoir. In addition, a multivariate statistical analysis and nutrient addition experiments were used to analyze the regulation of bacterioplankton growth in situ. Biomass ranged between 170 (winter) and 2,200 mg C m−2 (summer); production ranged from 10 (winter) to 625 mg C m 2 d−2 (summer); annual bacterioplankton production was 47 g C m−2 yr−1 in 1987 and 67 in 1988. Population growth rates ranged between 0.001 and 0.081 h−1. Growth rates in the epilimnion were substantially below estimated potential rates, suggesting severe nutrient limitation during the period of stratification. Population growth rates were highly correlated with P concentrations but not with dissolved organic C concentrations. Bacterioplankton growth in the summer epilimnion responded strongly to the addition of P alone or in combination with N or labile organic C. The field data show that bacterioplankton arc frequently without sufficient nutrients to sustain maximum growth; the experimental and statistical analyses indicate that P, rather than organic C, is the critical nutrient for bacterioplankton growth in this lake.