Diversity and abundance of dissimilatory nitrogen reducers present in the sediments of the Paulina polder tidal mudflat, the Netherlands

Anthropogenic activities (use of synthetic N fertilizers, use of N-fixing crops, …) have altered the nitrogen cycle substantially in aquatic environments leading to increased amounts of inorganic nitrogen (mainly nitrate) in estuaries, rivers, streams and coastal marine waters. Estuarine sediments play a significant role in the removal of this anthropogenically derived inorganic nitrogen via benthic nitrate reduction. In this study, we will assess the diversity and quantify the abundance of three different groups of dissimilatory nitrate reducers present in estuarine sediments of the Paulina Polder tidal flat, namely those involved in denitrification, dissimilatory nitrate reduction to ammonium (DNRA) and anammox. Sediment samples were collected from sediments without (visible) biofilm. The potential presence of these nitrate removal processes was verified by amplification of specific functional markers (nirK/nirS, NrfA and hzsA) acting as proxies for bacteria involved in these processes. Currently, we are pyrosequencing obtained amplicons and 16S rRNA amplicons for an in-depth specific and general community structure analysis of the bacterial components to get an idea of (a) the bacterial diversity involved in these different nitrate removal processes and (b) the general bacterial diversity present in Paulina estuarine sediments. In addition we are examining the relative abundance ratios of these three processes using qPCR to obtain an idea about the dominant nitrate removal process in this type of sediment