Retention and removal of nitrogen and phosphorus i

Authors: Tamara K Harms Sarah M Ludwig

Publish Date: 2016/01/21

Volume: 127, Issue: 2-3, Pages: 291-304

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Abstract

Interaction of hydrologic and biogeochemical processes on hillslopes may contribute significantly to export of nutrients from soils to stream networks yet hillslopes remain poorly understood components of catchments In the arctic hillslopes are underlain by permafrost and drained by zeroorder channels called water tracks that contain perennial subsurface flow We conducted in situ experiments to measure retention of inorganic nitrogen N and phosphorus P by saturated soils of water tracks and investigated the roles of water residence time flowpath depth and substrate availability in determining the balance of reaction and transport of nutrients Net retention of P was observed in 46  of experiments and net retention or removal of nitrate textNO 3 was observed in 57  of experiments whereas net retention of ammonium textNH 4 + occurred in only 16  of experiments performed Net production of textNH 4 + occurred in 42  of experiments was more frequently observed than retention and was most rapid where water residence time was shortest P retention was enhanced by P availability suggesting strong capacity to buffer downslope fluxes of inorganic P in water tracks Net retention or removal of textNO 3 tended to occur in shallow flowpaths but was not detected in deeper soils Strong retention of inorganic P by saturated arctic soils indicates that hillslopes contribute to regulating the flux of P to downstream ecosystems whereas weaker retention of inorganic N particularly where flows are deep or rapid suggests that increased discharge from hillslopes and deeper thaw will contribute to increased export of NWe thank C Cook D Fjare M Jaeger J Jones and R Risser for assistance in the field E Longano for contributions to laboratory analyses and J Stuckey for preparation of Fig 1 We acknowledge two anonymous reviewers for comments that improved the manuscript This work was supported by the National Science Foundation OPP1108200

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