Hydrobiogeochemical feedbacks across seasonal and decadal time-scales: implications for solute fate and transport in riverbed ecosystems
EMSL Project ID
50380
Abstract
Upland rivers host exceptionally strong linkages between the terrestrial and aquatic elemental cycles. Due to their abundance and tight connections with terrestrial ecosystems from which they receive dissolved organic carbon and other nutrients, these fluvial systems are major contributors to global carbon fluxes. Within these rivers, the hyporheic zone -- the shallow streambed region where surface water and groundwater mix -- represents a hotspot of biogeochemical activity due to converging surface water and groundwater flow paths that deliver limiting reactants to sediments. The extent of mixing between surface water and groundwater exerts a strong control on riverbed biogeochemistry; under snowmelt-driven high river discharge conditions, oxic river water penetrates deeper into riverbed sediments, whereas under low river discharge (base flow) conditions, the upwelling of reducing groundwater limits the depth of hyporheic mixing. Therefore, as environmental conditions change in upland catchments over annual and decadal time-scales, shifts in hydrology will affect riverbed biogeochemical conditions, while these sample environmental changes will also drive shifts in the chemistry of carbon being exported from such catchments. This proposal requests EMSL and JGI resources to determine the effects of dynamic hydrology on microbial carbon processing and export in hyporheic environments in a pristine, upland catchment in western Colorado. We hypothesize that seasonal changes in catchment hydrology will drive fluctuating redox conditions in riverbed ecosystems. Directly linked to these changes, we anticipate that more extensive carbon processing will occur under snowmelt-dominated peak discharge river conditions in spring and early-summer, while base flow conditions later in the calendar year will favor the accumulation of a wide range of carbon compounds in riverbed pore fluids. To investigate these concepts, we will utilize continuous in situ riverbed temperature and redox sensors coupled with discrete sampling campaigns to collect samples for high-resolution geochemical (carbon) analyses at EMSL. These data will be complemented by analyses utilizing JGI resources for both function (metagenomics) and activity (RNA-Seq) analyses of riverbed microbial communities. These datasets will subsequently be used in the development of 1D and 3D reactive transport models coupled to microbe-substrate interactions to quantify seasonal changes in chemical fluxes across the sediment-water interface, reaction rates per unit area of streambed, and forcings between hydrodynamics and biogeochemical dynamics. Finally, numerical sensitivity studies will be implemented to explore how biogeochemical parameters and solute fluxes respond to different hydrologic forcings, both now and as snowmelt dynamics evolve in the future.
Project Details
Project type
FICUS Research
Start Date
2018-10-01
End Date
2021-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members