Bacterial production along a river-to-ocean continuum in central Chile: implications for organic matter cycling

We examined how variation in bacterial abundance (BA), biomass (BB), and production (BP) along a river-ocean continuum might be related to the large heterogeneity of potential controlling factors upon different scenarios of river flow and coastal upwelling in the adjacent ocean. Between late July 2010 and January 2011, representing winter, spring, and summer conditions, we sampled 7 stations along the Biobio River in Central Chile (36 degrees S), and almost simultaneously, the adjacent ocean. BP along the river ranged from 3.1 to 168.4 mu g C l(-1) d(-1), with the highest values associated with the more anthropogenically influenced areas, where highest nitrate (NO3-) and dissolved organic carbon (DOC) were also observed. High bacterial growth rates (BGR) were observed along the river, but BA and BB were relatively low in comparison to the coastal ocean, probably associated with a strong top-down control along the river. The most isotopically depleted DOC (delta C-13-DOC, -30 to -33%) was also observed in anthropogenically influenced areas, but unequivocal signatures suggest that DOC represented many different terrestrial sources with different isotopic composition, which supported BP along the river. BP estimates along the river plume ranged from 0.7 to 81 mu g C l(-1) d(-1). The delta C-13-DOC distribution along the river-ocean continuum indicated that riverine flux of organic matter dramatically influenced the composition of DOC in this coastal upwelling area. During summer - when river flow was extremely low, coastal upwelling events were recurrent, and high chlorophyll a was enhanced - riverine DOC might not have contributed significantly to carbon pools in this coastal area. The temporal scale of river plume impacts on BP might vary with the magnitude of river discharge and wind-induced coastal upwelling events.