wAbstract
@The interaction between microbially-mediated nitrogen cycling
and catchment hydrology affects the amount and isotopic composition
of nitrate exported from catchments in drainage waters. Dominant
microbial and hydrological influences were investigated using
Β15NNO3 and
Β18ONO3 of
nitrate from the Wensum catchment in East Anglia, eastern England;
a 570 km2 lowland agricultural catchment. Samples were
collected from catchment waters, precipitation, dry deposition,
agricultural fertiliser and sewage effluent. Catchment water nitrate
concentration and isotopic composition can be explained by microbially-mediated
cycling of nitrogen inputs through nitrification to denitrification,
resulting in a reduced nitrate load exported from the Wensum catchment.
Seasonal, transient and through-year constant isotopic signals
from nitrogen cycling processes reflect the influence of dynamic
and stable hydrological factors. A three-member mass-balance mixing
model demonstrates an increasing influence from Chalk groundwater
downstream in the Wensum headwaters, and the displacement of shallow
groundwater into the river by runoff explains the isotopic and
hydrochemical stability seen in the river Wensum under varying
flow conditions. Together this demonstrates a powerful application
of a dual isotope and hydrological approach in the understanding
of an agricultural catchment's response to nitrogen loading.
Keywords: Nitrate; Stable isotopes; Nitrification; Denitrification;
Agricultural catchment; Hydrologyx
1. Introduction
2. Study site
3. Materials and methods
4. Results and discussion
@4.1. Nitrate sources and nitrogen cycling
@4.2. Wensum catchment waters nitrate: the nitrification-denitrification
continuum
@4.3. Wensum catchment water nitrate: nitrification
@4.4. Wensum catchment water nitrate: denitrification
@4.5. Denitrification during summer high flow: Cl-
and NO3- export
@4.6. Spatial evolution of 15NNO3 and 18ONO3 and nitrate concentration along the River Wensum
5. Conclusion
Acknowledgements
Appendix A. Supplementary material
References