Nitrate removal through microbial denitrification in riparian areas associated with
intensive agriculture
Cassie Leclair, David Burton, Glenn Stratton, and Gordon Brewster
Nova Scotia Agricultural College, Department of Environmental Sciences, Truro, Nova
Scotia, B2N 5E3
Riparian areas have a wide range of ecological benefits, including the capacity to remove
significant nitrate-N (NO3--N) loads entering from adjacent croplands. Microbial
denitrification is the main source of this N removal through the reduction of NO3- to
nitrous oxide (N2O) to N2 gas. Three conditions necessary for the complete reduction of
N2O to N2 gas include adequate soil moisture, for the development of anaerobic
conditions, available soil NO3-, and available soil organic carbon. Riparian zones
generally have optimum conditions that favour complete denitrification, relative to
croplands. Vegetative uptake of N in riparian zones is insignificant relative to removal
via denitrification, because N is temporarily stored in vegetation during the growing
season and returned to the soil as litter as plants die back in autumn. One objective of this
project was to determine where in the riparian area the most denitrification occurred. A
field study was conducted on the Thomas Brook Watershed in the Annapolis Valley,
Nova Scotia from May 2006-December 2007. Nitrous oxide emissions and soil NO3--N
concentrations were significantly (p<0.0001) higher in the cropland than riparian areas
for both years studied. No significant spatial differences were observed in denitrification.
Significant (p=0.0089) temporal differences in denitrification followed periods of high
soil moisture. The results of the canonical correlation analysis (CCA) showed
denitrification was primarily influenced by soil moisture, soil NO3--N concentrations, and
soil temperature. Overall, the data suggests NO3--N was the primary limiting factor to
N2O emissions, while soil moisture was the main controlling factor in denitrification.
Finally, the riparian area acted as an efficient buffer to NO3--N entering from the adjacent
cropland. The highest rate of complete denitrification (N2O to N2) occurred at the edge of
the riparian directly adjacent the cropland.