AME 68:57-76 (2012)  -  DOI: https://doi.org/10.3354/ame01605

ABSTRACT: Arctic floodplain lakes of the Mackenzie River Delta receive large inputs of dissolved organic matter (DOM) and suspended particulates from allochthonous and autochthonous sources that may drive in situ formation of transparent exopolymer particles (TEP), and represent a complex combination of substrates for aquatic bacteria. During the open-water period of 2006, we tracked abundances of free-living bacteria versus those attached to TEP and to other non-TEP particles in 3 Delta lakes representing gradients of declining river-to-lake connection times, increasing levels of dissolved organic carbon (DOC), and declining total suspended solids (TSS). Total suspended bacteria (= free-living + TEP-attached + other-attached bacteria) were high in all lakes (~10⁶ to 10⁷ cells ml⁻¹) compared to tundra lakes, and most cells were particle-attached, despite the high DOC concentrations. Free-living bacteria were best related to DOC concentrations, but represented only 14% of total suspended bacteria. TEP-attached bacteria were best related to TEP mass, but represented only 9.6% of total suspended bacteria. Other-attached bacteria were best related to chromophoric DOM and TSS levels, and represented 76.5% of total suspended bacteria. Bacterial densities on TEP particles increased as TEP mass declined from lakes with strong river influence to the lakes with higher autochthonous DOC. However, bacterial density on non-TEP particles declined over the same gradient as the abundance of their substrate declined. These opposing gradients in bacterial density on particles of differing origin, combined with the high abundances of other-attached bacteria, suggest that TEP colonization is driven by the mass of particles available for colonization by free-living cells within the lakes, whereas non-TEP particles may mostly enter the lake waters pre-colonized with bacteria from terrestrial or benthic sources.

KEY WORDS: Particle-attached bacteria · Transparent exopolymer particles (TEP) · Arctic floodplain lakes · Arctic rivers · Carbon cycling · Allochthonous carbon · Particle colonization