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Diversity and ecological function of benthic nitrate reducing populations along an estuarine nitrate gradient


Eutrophication of estuarine and coastal ecosystems due to increased anthropogenic inputs of nitrogen is an increasing problem. Benthic microbial processes influence nitrogen loads particularly by denitrification removing up to 50% of the load. However, a product of nitrate reduction is the greenhouse gas nitrous oxide. Understanding the benthic processes involved in the removal of nitrogen, or the formation of nitrous oxide, is important for the management and reduction of nutrient load to coastal waters and greenhouse gases emissions. Nitrate reduction in estuarine sediments is mediated by two main functional groups of bacteria.

Bacterial denitrifiers reduce nitrate or nitrite to gases subsequently lost from the aquatic environment, while nitrate ammonifier s reduce nitrate to ammonium that remains in the system. The first step in both processes is identical (nitrate reduction to nitrite) and is catalysed by one of the two types of nitrate reductase enzyme (NAR and NAP) that show different physiological roles depending on the bacterial functional group involved and environmental conditions.

Aim is to study the spatial distribution and seasonal changes of genes coding for NAR and NAP, and their expression level, in the benthic nitrate reducing community along an estuarine nitrate concentration gradient and relate these to process rates. To accomplish this, the researcher will apply modern molecular (eg. real time PCR) and biogeochemical (eg. stable isotopes) techniques in an inter-disciplinary way that will strengthen his scientific skills. The results will allow to test the hypotheses that changes in the concentrations of electron acceptors result in differences in the distribution of functional genes and groups of nitrate reducers along an estuary and that differences in rates and relative importance of key nitrogen processes along an estuarine gradient are related with changes in the expression of the corresponding functional genes.

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Wivenhoe Park
Reino Unido

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