AME 24:129-142 (2001)  -  doi:10.3354/ame024129

Immobilization and bacterial utilization of dissolved organic carbon entering the riparian zone of the alpine Enns River, Austria

Albert Brugger1, Bernhard Wett2, Ingrid Kolar1, Bettina Reitner1, Gerhard J. Herndl3,*

1Department of Marine Biology, Institute of Ecology and Conservation Biology, University of Vienna (IECB), Althanstr. 14, PO Box 285, 1091 Vienna, Austria
2Institute of Environmental Technology, University of Innsbruck, Technikerstr. 13, 6020 Innsbruck, Austria
3Department of Biological Oceanography, Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, The Netherlands
*Corresponding author. E-mail:

ABSTRACT: In order to understand the factors controlling the removal of riverine dissolved organic carbon (DOC) in the riparian zone of an alpine river, concentrations of DOC and dissolved oxygen, as well as bacterial abundance and production, were determined in interstitial waters of an experimental bank filtration site of the Enns River, Austria. Four porewater stations exhibiting differing sedimentologic and hydrologic characteristics were sampled over an annual cycle. We found that concentrations of DOC, oxygen, bacterial biomass and production decreased significantly within the first meter from the sediment water interface. Differences in the grain size distribution among the sampling stations led to spatial heterogeneity in the permeability of the riparian sediments and in the hydraulic residence time of the infiltrating river water, resulting in specific patterns in DOC immobilization and microbial respiration. Porewater bacterial abundance and production and apparent microbial oxygen consumption were positively correlated with the hydraulic residence time of the infiltrating water. DOC occasionally accumulated in the shallow porewater layers during the winter. During the summer, DOC infiltrating from the river surface potentially explained only 36 ± 25\#000 of the apparent interstitial oxygen consumption. This suggests that particulate organic carbon (POC) contributes substantially to the microbial organic carbon supply in the hyporheic zone. We conclude that the availability of POC rather than DOC infiltration determines hyporheic microbial metabolism.

KEY WORDS: Hyporheic bacteria · POC · DOC · Respiration · Sediment · Bank filtration · Enns River

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