wAbstract
@We examined the effect of sustained stream bank seepage during
base flow conditions on the pore water nitrogen biogeochemistry
of two riparian zones in lowland agricultural areas in southern
Ontario, Canada. Nitrate, ammonium and dissolved oxygen concentrations
in riparian subsurface water over a two-year period showed well-organized
spatial patterns along stream bank seepage flow paths that extended
seasonally up to 25 m inland. High levels of dissolved oxygen
and NO3- in stream inflow were
depleted rapidly at the stream bank interface suggesting the occurrence
of aerobic microbial respiration followed by denitrification.
A zone of NH4+ accumulation persisted
in more anaerobic sediments inland from the bank margin, although
the magnitude and intensity of the pattern varied seasonally.
A bromide tracer and NO3- co-injection
at the stream bank interface indicated that bank seepage occurred
along preferential flow paths in a poorly sorted gravel layer
in the two riparian zones. Depletion of NO3-
in relation to co-injected bromide confirmed that the bank margin
was a hot spot of biogeochemical activity within the riparian
zone. Conceptual models of humid temperate riparian zones have
focused on nitrogen biogeochemistry in relation to hillslope to
stream hydrologic flow paths. However, our results suggest that
sustained stream bank inflow during low flow conditions can exert
a dominant control on riparian nitrogen cycling in lowland landscapes
where level riparian zones bounded by perennial streams receive
limited subsurface inflows from adjacent slopes.
Keywords: Nitrogen cycling; Groundwater; Riparian zone; Stream
bank seepage; denitrification; Nitrogen flushingx
Introduction
Study sites
Methods
Results
@Riparian subsurface hydrology
@Water chemistry
@@Nitrate
@@Ammonium
@@Dissolved oxygen
@Solute injections
Discussion
Conclusion
Acknowledgements
References