Abstract
Small headwater streams interlink catchment soils with the river network. As water makes its way from the hillslopes to the stream, it may transport dissolved organic carbon (DOC) and potentially soil microbes into stream water. In this study, we aimed at quantifying the dynamic transfer of DOC and microbial life, namely bacteria from catchment soils into streams. We hypothesized that increased soil saturation enhances the lateral inflow of bacteria and DOC into streams. To address this hypothesis, we sampled six first order streams and three soil transects at two different depths located within the pre-alpine Oberer Seebach (OSB) catchment in Austria over a duration of 2 years. We found a strong variation in DOC concentrations (range 0.4–5.6 mg L−1) and bacterial abundances (range < 500,000–3,863,000 cells mL−1) measured by flow-cytometry. The highest values of DOC and bacterial cells occurred during high flow events. DOC concentration and bacterial abundance were correlated across all streams and seasons. In soils, DOC ranges were higher and were also correlated with bacterial abundance, while DOC concentrations were ∼ 10 times higher per bacterial cell than in streams. Overall we show that soils provide a dynamic inflow of bacteria and DOC to first order streams. Most probably, this results in a dynamic and reoccurring inoculation of small streams from catchment soils during runoff events. We propose that this dynamic microbial inoculation of small streams is potentially relevant for microbial community dynamics of downstream receiving waters.
Highlights
Small headwater streams are dynamic systems that interlink the terrestrial landscape with the fluvial network (Battin et al 2008; Richardson and Danehy 2007)
We investigated the relationship between dissolved organic carbon (DOC) concentration and bacterial abundance in stream and soil water (Fig. 5). Log10 DOC was found to be positively correlated with log10 bacterial abundance in stream water (r2 = 0.61, p < 0.001) and in soil water (r2 = 0.34, p < 0.05)
The major finding of this study is that the mobilization of bacteria from catchment soils to headwater streams is controlled by hydrological variability
Summary
Small headwater streams are dynamic systems that interlink the terrestrial landscape with the fluvial network (Battin et al 2008; Richardson and Danehy 2007). Headwater streams are influenced by environmental change (Wipfli et al 2007) The strong link they share with terrestrial environment affect in particular stream DOC concentrations that show fluctuations throughout the year—being lower during winter and higher during summer (Dawson et al 2008; Laudon et al 2011). These seasonal variations are influenced by discharge and temperature as secondary drivers that are sensitive to climate change (Köhler et al 2009; Sidle et al 2000). Similar to DOC, bacterial population dynamics, such as for example the bacterial
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