BayCEER Workshop 2020

Distribution and activity of ammonia-oxidizing bacteria and archaea in sediments of a first-order stream influenced by local hydrological characteristics

Intensive agricultural activities have become a major contaminant source for lower-order streams. As a result, excessive nitrogen loads have been released to the environment from agricultural operations, garnering widespread attention in recent years. Lower-order streams adjacent to agricultural fields are a major receiver of nitrogen pollution. The stream sediment harbors complex and diverse microbial communities. Their activities play an essential role in controlling the water chemistry of the stream and receiving major water bodies. However, the capacity of lower-order streams, especially the stream sediment, on transforming nitrogen species under the influence of local hydrological settings have been largely ignored so far. In this study, we investigate the first-order stream Schönbrunnen, located near the city Tübingen, Baden-Württemberg. Stream water and sediment samples were collected longitudinally. Sediment samples were further differentiated by different depths (5 and 15 cm from the streambed). Besides the streamflow, hydrological data indicate prominent surface water infiltration and groundwater exfiltration along stream reaches during the sampling season. Our aim is to understand the impact of local hydrological characteristics on nitrifying microbial communities in respective sediments. Therefore, quantitative PCR (qPCR), 16S rRNA genes sequencing and microcosm incubation have been conducted to find out how local hydrological characteristics affect the distribution and activity of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in the sediments. Our results indicate that 1. sediment microbial communities are dominant contributors to ammonia oxidation rather than stream water microbial communities. 2. Despite a much higher in-situ abundance of AOA, higher reactivity and potential of ammonium oxidation was attributable mostly to bacteria rather than archaea. 3. Hot-spots of nitrification are located at stream reaches where water gaining and losing happens.