Photodegraded dissolved organic matter from peak freshet river discharge as a substrate for bacterial production in a lake-rich great Arctic delta

Jolie A.L. Gareis, Lance F.W. Lesack
2018 Arctic Science  
11 Lake-rich Arctic river deltas are recharged with terrigenous dissolved organic matter 12 (DOM) during the yearly peak water period corresponding with the solstice (24 h d -1 solar 13 irradiance). Bacteria-free DOM collected during peak Mackenzie River discharge was exposed 14 to sunlight for up to 14 d in June 2010. As solar exposure increased, carbon and lignin 15 concentrations declined (10% and 42% respectively after 14 d), as did DOM absorptivity (62% 16 after 14 d), aromaticity, and
more » ... romaticity, and molecular weight. Photochemical changes were on par with those 17 normally observed in Mackenzie Delta lakes over the entire open-water season. When irradiated 18 freshet DOM was provided as a substrate, no significant differences were observed in 19 community-level metabolism among five bacterial communities from representative delta 20 habitats. However, bacterial abundance was significantly greater when non-irradiated (0 d) 21 rather than irradiated DOM (7 or 14 d) was provided, while cell-specific metabolic measures 22 revealed that per-cell bacterial production and growth efficiency were significantly greater when 23 communities were provided irradiated substrate. This complex response to rapid DOM 24 photodegradation may result from the production of inhibitory reactive oxygen species (ROS), 25 along with shifts in bacterial community composition to species that are better able to tolerate 26 ROS, or metabolize the labile photodegraded DOM. 27 28
doi:10.1139/as-2017-0055 fatcat:ui2drxnozbfovasp3wt32ra4ti