Nitrifying and denitrifying microbial communities and their relationship to nutrient fluxes and sediment geochemistry in the Derwent Estuary, Tasmania

Mineralisation, nitrification and denitrification in sediments are key processes that contribute to the removal of nitrogen from coastal waters. Together these processes are important in preventing the buildup of nitrogen, which can lead to eutrophication in estuarine systems. Spatial and temporal patterns in the composition of nitrifier (bacterial [AOB] and archaeal ammonia oxidizers [AOA]; amoA), denitrifier (nirS) and total bacterial and archaeal (16S rRNA gene) communities in sediment from the Derwent Estuary in southeast Tasmania, Australia, were contrasted with key environmental parameters and benthic nutrient fluxes. Spatial and temporal factors were significant in terms of shaping microbial community composition. Organic matter composition (C:N isotope ratios, %N and %C) was significantly related to the abundance of the different microbial guilds. There was a significant correlation between both the sediment nitrogen content and carbon stable isotope ratio with community composition for total bacteria, AOA and denitrifiers. Sediment chlorophyll a was significantly associated with AOB composition and carbon isotope ratio was related to total archaeal community composition.