The Impact of Disturbances on the Trait-To-Function Relationships Underpinning Watershed Biogeochemical Cycling
Authors
Nick Bouskill1* (Nick Bouskill), Helen Weierbach1, Zelalem Mekonnen1, Matthias Sprenger1, Curtis Beutler2, Markus Bill1, Wendy Brown2, Baptiste Dafflon1, Wenming Dong1, Nicola Falco1, Taylor Maavara3, Michelle Newcomer1, Pat Sorensen1, Robin Thibaut1, Shi Wang1, Erica Woodburn1, Ken Williams1, Eoin Brodie1 (elbrodie@lbl.gov)
Institutions
1Lawrence Berkeley National Laboratory, Berkeley, CA; 2Rocky Mountain Biological Laboratory, Gothic, CO; 3University of Leeds, Leeds, U.K.
URLs
Abstract
Mountainous watersheds are characterized by strong gradients in functional traits, including vegetation, topography, geology, and geomorphology, which together determine nitrogen (N) retention, and release. Uncertainty remains as to how atmospheric warming within mountainous regions, which increases water limitation and the severity of drought, will impact trait-to-function relationships underpinning the N cycle. This contribution details recent and upcoming work examining, through integrated measurements, manipulations, and modeling, how disturbance in subalpine ecosystems uncouples trait-function relationships and feeds back on biogeochemical cycling. Researchers start by addressing how distinct watershed traits dictate the retention and release of N, by characterizing the N cycle in paired catchments within the East River watershed. The East River catchment, underlain by N-rich Mancos shale with a mixed land cover, exported ~3.5 times more nitrate than the conifer-dominated Coal Creek. The conservative N-cycle within Coal Creek is likely due to the abundance of conifer trees, and smaller riparian region, retaining more NO3- overall. The East River shows evidence of stronger biogeochemical cycling of N, where the aggregate export signal is regulated by physical and biogenic processes. To improve the characterization of the East River N cycle over time, researchers built a simple model of the terrestrial-aquatic N cycle predicated upon the most critical traits identified previously. Subsurface water residence times, which dictate transport or reactivity, are determined by coupling the model to ParFlow-CLM. Here, through a series of atmospheric warming experiments, researchers address how disturbance alters trait-to-function relationships, and subsequently N export. Researchers note that warming reduces hydrologic connectivity and impedes assimilation and transformation of N by plants and microbes. As such, exports of N from the East River catchment are predicted to decline under future climate conditions. However, distributions of traits (e.g., vegetation, microbial) are not static and more dynamic modeling approaches may be necessary to capture system adaptation to future climate conditions. Finally, in addition to pervasive water limitation, biogeochemical cycling can also be impacted by acute trait redistribution following pulse disturbance (e.g., wildfire, beetle outbreaks), or management (e.g., thinning, clear cutting) to coupled hydrological, ecological and biogeochemical processes. Researchers outline the plans to leverage proposed adaptative forest management activities within Trail Creek to address questions concerning how hydrologic connectivity and biogeochemical cycling change following abrupt shifts in trait distribution, and the consequences for downslope forest community resilience to drought, and biogeochemical cycling in riparian regions.