Report No DWI0144

INVESTIGATIONS OF IN-SlTU BACTERIAL DENITRIFICATION IN THE CONFINED CHALK AQUIFER IN NORFOLK AND NORTH LONDON WD/90/4

DWI0144

1990

SUMMARY

The ability of indigenous bacteria to denitrify groundwater in situ has important implications on the management of groundwater resources of British aquifers. The controls and limitations of this natural process need to be understood and, if possible, quantified in order to exploit it fully. In this study, bacteria have been identified in the confined Chalk aquifer in locations where only limited recent recharge has occurred and are therefore likely to be indigenous. Laboratory experiments show that these bacteria are capable of reducing nitrate to nitrogen gas and that they are versatile in their ability to utilise a range of carbon sources. The bacteria also appear to be capable of surviving in both low and high-nutrient environments.

Before nitrate can be removed bacteriologically from groundwater in aquifers, anaerobic conditions must prevail. Dissolved oxygen that is transported into the Chalk aquifer with nitrate is likely to be removed by the oxidation of ferrous iron, subsequent to which bacteriological denitrification is very likely to occur. However, the capacity of the system to continue to remove nitrate is likely to be controlled by the supply of organic carbon.

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