Spatial and temporal dynamics of nitrogen in a mountainous watershed
Abstract
Mountainous watersheds are characterized by substantial heterogeneity in geomorphology, soil texture, and vegetation that determine hydrological flow paths and residence times through distinct catchment subsystems. Despite advances in understanding the spatial and temporal drivers of biogeochemical cycling within snowmelt-dominated ecosystems, knowledge gaps remain. Here we describe ongoing work employing a combination field and laboratory approaches alongside multi-scale modeling to characterize and quantify the sources, transformations, and sinks of nitrogen, a major limiting nutrient, within the East River (CO) watershed. This work focuses on two distinct spatial scales, a hillslope to floodplain transect, and across the whole watershed. At the hillslope scale, we employ a combination of geochemistry, isotope geochemistry and molecular microbiology to identify and quantify specific mechanisms regulating the input (e.g., nitrogen fixation, Mancos shale weathering, or atmospheric deposition), retention (plant and microbial accumulation), transformation (mineralization, nitrification) and loss (denitrification or hydrological export) of nitrogen across temporal aridity gradients (capturing baseflow, snowmelt, drought, and monsoonal precipitation). At the scale of the watershed we use a semi-distributed mechanistic model to ask the question of how broad features of the landscape (e.g., topography, river sinuosity, soil properties) and biology determine the export of nitrogen (as NO3- or organic nitrogen) during distinct periods of the hydrograph. Our model output is benchmarked against high-resolution nitrate and organic nitrogen flux data collected along the East River and major tributaries over 3+ years. Overall, this work intends to improve understanding of the feedback between hydrological perturbation (in the formation and loss of snowpack) and biogeochemical processes to improve predictions of nitrogen export at the watershed scale.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B53K2207B
- Keywords:
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- 0444 Evolutionary geobiology;
- BIOGEOSCIENCESDE: 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCESDE: 0469 Nitrogen cycling;
- BIOGEOSCIENCESDE: 4870 Stable isotopes;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL