A Multiscale Approach for Representing Integrated Hydro-Biogeochemical Processes Across Terrestrial Aquatic Interfaces


Jianqiu Zheng1* (jianqiu.zheng@pnnl.gov), Bing Li1, Wei Huang2, Teri O’Meara2, Xingyuan Chen1, Nicholas Ward1, Ben Bond-Lamberty1, Patrick Megonigal3, Michael Weintraub4, Ken Kemner5, Pamela Weisenhorn5, Peter Thornton2, Vanessa Bailey1


1Pacific Northwest National Laboratory, Richland, WA; 2Oak Ridge National Laboratory, Oak Ridge, TN; 3Smithsonian Environmental Research Center, Edgewater, MD; 4University of Toledo, Toledo, OH; 5Argonne National Laboratory, Lemont, IL



The aquatic interfaces exposing terrestrial soils to oxic-anoxic regime shifts are hotspots of biogeochemical processes that are extremely sensitive to hydrological cycles and other external drivers. Interactions among water movement, physical heterogeneity, plant and microbial function regulate the transformations and fluxes of carbon (C), nutrients, and redox sensitive compounds. However, researchers lack a consistent, mechanistic modeling framework of these interactions or their scale dependency of hydrological, vegetation, and soil biogeochemistry that regulate whole-ecosystem function across terrestrial-aquatic interfaces (TAIs). Researchers present a new modeling framework that connects a molecularly resolved biogeochemical model (AquaMEND) with surface and subsurface reactive transport modeling capabilities (via ATS- PFLOTRAN) and the E3SM Land Model (ELM) to enable coupled process modeling across the soil-water-vegetation continuum. AquaMEND is a versatile biogeochemical model for solving dynamic coupling of organics, minerals and microbes from molecular to reaction and site scales. Leveraging bioenergetics as the central tenet governing microbial metabolic activities and C and nutrient fluxes, AquaMEND employs a flexible stoichiometry approach that accounts for microbial physiological traits, diversity of C substrate and dynamics of electron acceptors. High resolution FTICR-MS-based metabolomic data and metagenomes are used to generate energy balance for various reactions, which are further controlled by aqueous phase chemistry dynamically simulated in AquaMEND. Together, AquaMEND generates thermodynamically constrained reaction networks to provide ATS-PFLOTRAN and ELM with lumped descriptions of the rates and efficiency of C and nutrient transformations. The resulting reaction networks and kinects are then tested in PFLOTRAN and incorporated into ATS-PFLOTRAN for coupled hydrologic and biogeochemical modeling across upland-to-wetland transects.

Hydrological dynamics introduced by precipitation and tidal dynamics regulate solute distribution and oxygen dynamics, which exert additional controls on biogeochemical reactions. The coupling between hydro-biogeochemistry and vegetation dynamics is further realized through a three-column module of ELM, in which the impact of water level and salinity at the coastal TAI are explicitly represented for a C3 sedge (Schoenoplectus americanus, low marsh) and a C4 grass (Spartina patens, high marsh) plant functional types. Through the coupling of AquaMEND, ATS-PFLOTRAN and ELM, local reactions, site-scale properties, and their interactions are fully integrated to enhance advanced modeling of coupled hydro-biogeochemical processes for holistic, predictive understanding of coastal TAI systems.