Seasonality of phosphorus and nitrate retention in riparian buffers

Measurement of the retention of dissolved nutrients in riparian areas with snowmelt runoff are much less common than for rainfall runoff, but low rates of uptake or the release of nutrients with snowmelt have been attributed to frozen soils, lower biotic uptake, and release of nutrients from senesced vegetation. In the research presented here, we evaluate whether the potential for uptake of dissolved reactive phosphorus (DRP) and NO3- differ significantly between snowmelt and summer seasons with flow through 13 riparian buffers downstream of cropland in Manitoba, Canada. Flow-through buffers in small channels are typical in this landscape, and pulsed releases of a conservative tracer and dissolved nutrients were used to measure uptake rates. Although mean uptake rates of NO3- were higher in summer than for snowmelt, responses varied widely. Aerial uptake rate of DRP showed a significant negative relationships with soil Olsen-P (r2 = 0.54, p < 0.001) and a P saturation index (r2 = 0.48, p < 0.001) across both seasons. Biological processes may be of greater importance for NO3- retention, but DRP retention appears to be driven by adsorption-desorption regardless of season. Olsen-P is identified as a good indicator of potential for release or retention of DRP in riparian buffers with fine-textured calcareous soils, for both snowmelt and summer seasons. Soil testing may be a good tool to aid in the siting of new buffers and to track the effectiveness of management interventions to remove P from riparian areas, such as harvest of vegetation.