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Distribution of microbial activity, methanogenic archaea and type I and II methanotrophs were studied in a small lowland stream Sitka in Czech Republic. The methanogens and methanotrophic bacteria were detected using FISH with 16 S rRNA-targeted oligonucleotide probes. The highest microbial density was obtained in the upper sediment layer 0-25 cm; this zone corresponded also to that of the highest metabolic activity, as indicated by the methanogenic potential, methanotrophic activity, INT and FDA profiles. Both methanogenic archaea and aerobic methanotrophs were found at all localities along the longitudinal stream profile. The proportion of these groups to the DAPI-stained cells was quite consistent and varied only slightly but a higher proportion to the DAPI-stained cells in the deeper sediment layer 25-50 cm was observed. On average 23.4% of DAPI-stained cells were detected by FISH with a probe for methanogens while type I methanotrophs reached ~ 21.4% and type II methanotrophs 11.9%, respectively. The percentage of DAPI-stained cells hybridizing with methanotroph-specific probes was generally higher for type I than type II. Our data show that the methanogenic archaea and aerobic methanotrophs can be numerically dominant components of the hyporheic biofilm community and affect CH4 cycling in river sediments.

Greenhouse gas emissions from a small lowland stream in the Czech Republic were quantified using three methods. Emissions from the sediments measured with the static chamber method averaged 1.0 ± 0.1 g CO2 m-2d-1, 6.5 ± 1.5 mg CH4 m-2d-1 and 0.31 ± 0.04 mg N2O m-2d-1, while calculated fluxes of gases across the air-water interface were much higher, in average 9.1 ± 0.7 g CO2 m-2 d-1, 39.2 ± 3.6 mg CH4 m-2d-1 and 10.4 ± 1.6 mg N2O m-2 d-1. In addition, emissions measured using the floating chamber method averaged 3.7 ± 0.3 g CO2 m-2 d-1, 16.0 ± 3.4 mg CH4 m-2d-1 and 1.7 ± 0.2 mg N2O m-2d-1. No relationship between temperature and gas emissions into the atmosphere was found. Gas fluxes across the air-water interface were significantly correlated with surface water concentrations, but emissions from the sediments showed no relationship with those concentrations in either the surface or interstitial water. Regardless of the method used, our results suggest that the Sitka stream is a source of gases into the atmosphere, and losses of carbon and nitrogen such as the fluxes of these greenhouse gases out into the ecosystem can participate significantly in river self-purification.

Distribution of dissolved oxygen, nitrate, sulphate, carbon dioxide and dissolved organic carbon (DOC), acetate and lactate was studied in the stream and interstitial water along the subsurface flowpath in the hyporheic zone of a small lowland stream. Sediments were found to act as a source of nitrous oxide and methane. Interstitial methane concentrations were significantly much higher in comparison to those from surface water, and were significantly lower in the relatively well oxygenated downwelling zone than in the rather anoxic upwelling zone. The interstitial concentrations of O2, NO3−1and SO4−2showed significant decline along the subsurface flowpath, while concentrations of CO2, N2O, DOC, acetate and lactate remained unchanged. In addition to field measurements, ex situincubation of sediments was carried out in the laboratory. Maximal methane production was found in the incubation assay using acetate (mean value 380 µg CH4kg DW−1d−1). Mean value of the denitrification potential was 1.1 mg N2O kg DW−1d−1. Nitrous oxide production potential reached 71–100% of denitrification potential. Our results demonstrate that respiration of oxygen, nitrate, sulphate and methanogenesis may coexist within the hyporheic zone and that anaerobic metabolism is an important pathway in organic carbon cycling in the Sitka stream sediments. Copyright © 2005 John Wiley & Sons, Ltd.

Alder leaves and catkins were placed in a small stream, then retrieved in weekly intervals, and rates of release of dissolved organic carbon (DOC) and substantial DOC characteristics were determined. Decomposition rates of leaves and catkins were 0.026 d–1 and 0.011 d–1 on the streambed, and 0.017 d–1 and 0.009 d–1 in the sediments, respectively, during 5 weeks of decomposition. The rate of DOC release from leaves declined from 18.0% d–1 to 0.7% d–1, and had a higher proportion of low molecular weight compounds, more saturated and contained larger humic molecules than DOC from catkins, which rate of release declined from 10.6% d–1 to 0.1% d–1. In initial stages of the decomposition, leaf material produced more biodegradable DOC (BDOC) than catkins. During the period of low leaf litter input, DOC released from catkins can become an important instream source of labile DOC. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Two types of particulate organic materials, pure cellulose and alder catkins from common alder (Alnus glutinosa), were used to determine and compare decomposition rates of POM in two zones of a small lowland stream – the surface water and the hyporheic sediments. Generally, decomposition rates of both POM types incubated within the hyporheic sediments were relatively very slow (k = 0.002–0.005 d–1) compared to that in the surface water (k = 0.02 d–1). Breakdown of both POM types was clearly influenced by water temperature. Invertebrates found on samples of both cellulose and alder catkins, incubated within the hyporheic zone, had much lower species richness compared to samples from the surface water. In the surface water, the dominant species on both materials was the amphipod Rivulogammarus roeselii. Hyporheic samples were dominated by chironomid larvae and tubificids.

Methane concentrations and selected chemical parameters in interstitial water were examined along subsurface flowpath in two subsystems (hyporheic and parafluvial sediments) in the Sitka stream, Czech Republic. Interstitial methane concentrations exhibited a distinct spatial pattern. In the hyporheic downwelling zone where the sediments are relatively well oxygenated due to high hydrologic exchange with the surface water, low interstitial methane concentrations, averaging 9.3 μg CH4/l, were found. In contrast, upwelling sediments and parafluvial sediments (active channel sediments lateral to the wetted channel) had significantly higher methane concentrations (p < 0.05, and p < 0.01, respectively), averaging 43.2 μg CH4/l and 160.5 μg CH4/l, respectively. Dissolved oxygen was the highest where surface water entered hyporheic/parafluvial sediments and decreased with water residence time in the sediments (p < 0.01). Nitrate concentrations decreased along the flowpath and were significantly lower at downstream end of the riffle (p < 0.001). Sulfate concentrations also show a slight decline with the water residence time, but differences were not significant. Effect of both nitrate and sulfate on methanogenesis is also discussed. The interstitial methane concentration significantly increased with surface water temperature (p < 0.001) and was negatively correlated with redox potential (p < 0.01) and dissolved oxygen (p < 0.05).