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Groundwater nitrogen composition and transformation within a moorland catchment, mid-Wales

Lapworth, D. J.; Shand, P.; Abesser, C.; Darling, W. G.; Haria, A. H.; Evans, C. D.; Reynolds, B.. 2008 Groundwater nitrogen composition and transformation within a moorland catchment, mid-Wales. Science of the Total Environment, 390 (1). 241-254. 10.1016/j.scitotenv.2007.09.043

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Abstract/Summary

The importance of upland groundwater systems in providing a medium for nitrogen transformations and processes along flow paths is investigated within the Afon Gwy moorland catchment, Plynlimon, mid-Wales. Dissolved organic nitrogen (DON) was found to be the most abundant form of dissolved nitrogen (N) in most soils and groundwaters, accounting for between 47 and 72% of total dissolved nitrogen in shallow groundwater samples and up to 80% in deeper groundwaters. Groundwater DON may also be an important source of bio-available N in surface waters and marine systems fed by upland catchments. A conceptual model of N processes is proposed based on a detailed study along a transect of nested boreholes and soil suction samplers within the interfluve zone. Shallow groundwater N speciation reflects the soilwater N speciation implying a rapid transport mechanism and good connectivity between the soil and groundwater systems. Median nitrate concentrations were an order of magnitude lower within the soil zone (< 5–31 μg/L) than in the shallow groundwaters (86–746 μg/L). Given the rapid hydrostatic response of the groundwater level within the soil zone, the shallow groundwater system is both a source and sink for dissolved N. Results from dissolved N2O, N2/Ar ratios and dissolved N chemistry suggests that microbial N transformations (denitrification and nitrification) may play an important role in controlling the spatial variation in soil and groundwater N speciation. Reducing conditions within the groundwater and saturated soils of the wet-flush zones on the lower hillslopes, a result of relatively impermeable drift deposits, are also important in controlling N speciation and transformation processes.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.scitotenv.2007.09.043
Programmes: CEH Programmes pre-2009 publications > Biogeochemistry
BGS Programmes 2008 > Groundwater resources
CEH Sections: Emmett
Harding (to July 2011)
ISSN: 0048-9697
Additional Keywords: Dissolved Organic Nitrogen (DON), Groundwater, Denitrification, Nitrification, Nitrate, Transformations, Upland catchments
NORA Subject Terms: Ecology and Environment
Hydrology
Date made live: 09 Jan 2008 11:50
URI: http://nora.nerc.ac.uk/id/eprint/1745

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