Abstract
Reactive Transport Models (RTMs) are essential for understanding and
predicting intertwined ecohydrological and biogeochemical processes on
land and in rivers. While traditional RTMs have focused primarily on
subsurface processes, recent RTMs integrate hydrological and
biogeochemical interactions between land surface and subsurface. These
emergent, watershed-scale RTMs are often spatially explicit and require
large amount of data and extensive computational expertise. There is
however a pressing need to create parsimonious models that require less
data and are accessible to scientists with less computational
background. Here we introduce BioRT-HBV 1.0 (hereafter BioRT), a
watershed-scale, hydro-biogeochemical model that builds upon the widely
used, bucket-type HBV model (Hydrologiska Bryåns Vattenavdelning), known
for its simplicity and minimal data requirements. BioRT uses the
conceptual structure and hydrology output of HBV to simulate processes
including solute transport and biogeochemical reactions driven by
reaction thermodynamics and kinetics. These reactions include, for
example, chemical weathering, soil respiration, and nutrient
transformation. This paper presents the model structure and governing
equations, demonstrates its utility with examples simulating carbon and
nitrogen processes in a headwater catchment. As shown in the examples,
when constrained by data, BioRT can be used to illuminate the dynamics
of biogeochemical reactions in the invisible, arduous-to-measure
subsurface, and their connections to observed solute export in streams
and rivers. We posit that such parsimonious models increase model
accessibility to users without in-depth computational training. It also
can serve as an educational tool that promote pollination of ideas
across different fields and foster a more diverse, equal, and inclusive
user community.