A depth-resolved hillslope to floodplain budget for nitrogen within a high-altitude mountainous watershed
Abstract
Hillslope topography exerts a strong control on the distribution and transit time of water and, as a consequence, nitrogen availability, and plant growth. Here we bring together a series of complementary biogeochemical (pore/groundwater chemistry, leaf litter, soil organic matter), isotopic, vegetation surveys and remote sensing measurements, with models to better constrain nitrogen stocks and fluxes within a single spatio-temporal budget. We focus our analysis on a representative montane hillslope-toeslope-floodplaint transect within a snowmelt-dominated watershed of the Upper Colorado River Basin. At each point along this transect, we collected measurements across a bedrock to canopy gradient over several years that span historical high and low snowpack depths.
Here we show that across the hillslope-floodplain transect total nitrogen and total dissolved nitrogen declined with depth. Total dissolved nitrogen and nitrate concentrations showed a subsurface peak at the soil-saprolite boundary, likely attributable to infiltration from shallower soils and the weathering of the nitrogen-rich Mancos shale underlying these soils. Moreover, our coupled approach improves estimation of different nitrogen stocks. For example, remote sensing technology provides a powerful way to estimate biochemical properties. Using airborne hyper-spectral imaging in conjunction with field measurements and machine learning approaches, we estimate leaf nitrogen content across the transect, with observed spatial patterns largely driven by topography and plant functional types. Subsurface groundwater nitrogen fluxes from hillslopes to toeslopes, and floodplains to rivers were estimated by using spatially extensive measurements of groundwater chemistry combined with modeled advective fluxes. By combining resources and datasets from different methods and disciplines, we showcase the power of a community approach to developing a detailed nitrogen budget.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.B12H1150B