Bacterial carbon production in Lake Erie is influenced by viruses and solar radiation

Abstract

Bacterial production is an integral recycling mechanism that facilitates carbon flow through aquatic food webs. Factors influencing bacterial activity therefore impact carbon flow. Although ecologists consider grazing and dissolved organic carbon flux to be the major regulators of bacterial activity, we explored two other important pressures. Virus-like particle abundance ranged from 3.7 × 1010to 37.9 × 1010·L-1in samples collected during August 1997 and July 1998. Bacterial abundance during these periods ranged from 1.8 × 109to 4.6 × 109·L-1. Based on electron microscopic analysis, viruses in Lake Erie would have been responsible for 12.1-23.4% of bacterial mortality and, in quasi-steady-state conditions, a comparable loss of bacterial productivity. In the central basin, solar radiation was also demonstrated to regulate bacterial productivity. Ultraviolet radiation (295-400 nm) was shown to inhibit bacterial productivity according to a cumulative exposure kinetic model, and biological weighting functions were derived to enable calculation of time- and depth-integrated photoinhibition. The daytime photoinhibitory loss of bacterial carbon production was estimated to be 14-30% over the upper 5 m, primarily due to ultraviolet radiation >320 nm. Viruses and sunlight are therefore of comparable importance as regulators of bacterial activity in this system.