Nitrogen cycling processes and microbial community composition in bed sediments in the Yukon River at Pilot Station

Abstract

Information on the contribution of nitrogen (N)-cycling processes in bed sediments to river nutrient fluxes in large northern latitude river systems is limited. This study examined the relationship between N-cycling processes in bed sediments and N speciation and loading in the Yukon River near its mouth at the Bering Sea. We conducted laboratory bioassays to measure N-cycling processes in sediment samples collected over distinct water cycle seasons. In conjunction, the microbial community composition in the bed sediments using genes involved in N-cycling (narG, napA, nosZ, and amoA) and 16S rRNA gene pyrosequences was examined. Temporal variation was observed in net N mineralization, nitrate uptake, and denitrification rate potentials and correlated strongly with sediment carbon (C) and extractable N content and microbial community composition rather than with river water nutrient concentrations. The C content of the bed sediment was notably impacted by the spring flood, ranging from 1.1% in the midst of an ice-jam to 0.1% immediately after ice-out, suggesting a buildup of organic material (OM) prior to scouring of the bed sediments during ice break up. The dominant members of the microbial community that explained differences in N-processing rates belonged to the genera Crenothrix, Flavobacterium, and the family of Comamonadaceae. Our results suggest that biogeochemical processing rates in the bed sediments appear to be more coupled to hydrology, nutrient availability in the sediments, and microbial community composition rather than river nutrient concentrations at Pilot Station.

Importance of the Colmation Layer in the Transport and Removal of Cyanobacteria, Viruses, and Dissolved Organic Carbon during Natural Lake-Bank Filtration

“…The Quantitative Insights into Microbial Ecology (QIIME) pipeline was used to process sequence data. Sequence reads (>400 base pairs) were processed as previously described (Repert et al, 2014). Taxonomic assignments were made using the Greengenes database (gg_13_8 release) using UCLUST (DeSantis et al, 2006; Edgar, 2010).…”

Seasonal and Spatial Variation in the Location and Reactivity of a Nitrate‐Contaminated Groundwater Discharge Zone in a Lakebed

“…DOC was determined using a platinum-catalyzed wet persulfate oxidation method (Aiken, 1992). Nitrous oxide was determined using a headspace equilibration method and an electron-capture-equipped gas chromatograph (Repert et al, 2014). Sediment C content, KCl-extractable NH 4 + , and sediment-specific surface area were determined as previously described (Stoliker et al, 2016).…”

How network structure can affect nitrogen removal by streams

“…Benthic community composition, in particular, the relative abundance of dentitrifying bacteria that respire NO À 3 , may be an important driver of N removal by streams (Repert, Underwood, Smith, & Song, 2014). Stream bacterial communities are shaped by both their local environments and upstream processes, as well as out-of-network dispersal to a lesser extent; thus, they are inherently linked to the organisation and hydrology of stream networks (Widder et al, 2014).…”