Bacterioplankton in Lake Michigan: Dynamics, Controls, and Significance to Carbon Flux

• Published in: Limnology and oceanography Vol. 32; no. 5; pp. 1017 - 1033
• Main Authors: Scavia, Donald, Laird, Gwenyth A.
• Format: Journal Article
• Language: English
• Published: Waco, TX American Society of Limnology and Oceanography 01-09-1987
• Subjects: Animal, plant and microbial ecology; Bacteria; Bacterioplankton; Biological and medical sciences; Carbon; Chlorophylls; Delta cells; Freshwater; Fundamental and applied biological sciences. Psychology; Lakes; Microbial ecology; Phytoplankton; Production estimates; Sea water; Surface water; Various environments (extraatmospheric space, air, water); USA, Michigan L; Productivity; Temperature; Growth rate; United States; Fresh water; Loss rate; Environmental factor; Microflora; Spatial variation; North America; Carbon; Numeration; Seasonal variation; America; Lakes; Bacteria; Population dynamics
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.1987.32.5.1017

Lake Michigan bacterial production, based on [3H-methyl]thymidine (TdR) incorporation and empirically determined conversion factors (5-25 × 109cells nmol-1), decreased with distance from shore (thicksim 2× over 30 km), was higher at night (1.4 ×-2.2 ×), and decreased with depth (thicksim 10 × over 100 m). TdR-based growth rates were consistent with independent antibiotic- and dilution-based estimates. Population size varied little and appeared controlled by balanced growth (0.02-0.33 h-1) and grazing (0.039-0.12 h-1). Growth correlated with tempreature only below 10circC. Cell size ranged from 0.015 to 0.072 μ m3. Carbon content averaged 0.154 ± 0.047 pg C μ m-3. Net annual carbon production was 142 g C m-2 yr-1. Summer averages were 28.9 (epilimnion), 10.4 (10-35 m), 1.6 (hypolimnion) μ g C liter-1 d-1, and 652 mg C m-2 d-1 for the water column. Flux to microconsumers averaged 8.4 μ g C liter-1 d-1 in the summer epilimnion. Annual areal bacterial carbon demand is met by autotrophic production only if little of the latter is lost by other means. This suggests that external loads are needed, our conversion factors are high, or autotrophic production is underestimated. Although only small adjustments of those factors will satisfy the annual balance, the summer imbalance is still too large. We suggest that temporal and spatial disequilibrium of labile organic carbon supply and bacterial use is responsible for the apparent discrepancy during summer.