Hydrological controls on subsurface shale bedrock-nitrogen release and export from a mountainous watershed hillslope
Abstract
The nitrogen (N) originally contained in plants and organisms, then trapped in sedimentary rocks (rock-N or petrogenic-N) during rock formation, has previously been found as a "new" source of N that reenters the Earth's surface ecosystems. Numerous coarse scale models have been developed to estimate the rates of rock-N release based on mass balance through tectonic uplift and surface denudation. Field measurements have shown that the released rock-N is a significant nutrient source for forest ecosystems. Rock-N has been recognized as a source of high nitrate concentrations in some seeps, streams and rivers. However, the important processes of rock-N weathering release and transport occurring below the ground surface are largely unknown. These processes are revealed through a set of innovative long-term measurements at a hillslope transect in a mountainous watershed underlain by shale bedrock. The findings that will be presented include the following. (1) The vertical location of subsurface rock-N release and its dependence on the seasonally fluctuating water table. (2) The dominant speciation of the N in porewaters and their hydro-biogeochemical controls. (3) The directedly measured rates of subsurface N export. (4) Snowmelt delivered quantities of dissolved N from soil to subsurface waters. Measurements of D14C-DOC content, d15N/ d18O-NO3- isotope compositions, and DOM compound classes and abundance (FTICR MS) support our conclusions. We suggest that these findings are applicable to other shale hillslopes of mountainous watersheds.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H21J1878W
- Keywords:
-
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0466 Modeling;
- BIOGEOSCIENCES;
- 1828 Groundwater hydraulics;
- HYDROLOGY;
- 1849 Numerical approximations and analysis;
- HYDROLOGY