Coupling hydrological and biogeochemical models to assess the role of landscape units on dissolved organic carbon transport

Abstract:

Catchment dissolved organic carbon (DOC) fluxes are governed by complex interactions involving hydrodynamic drivers which control biogeochemical processes generating DOC and regulate hydrological connectivity which, in turn, determines solute transport through the landscape to the stream network. Here, we present the application of a simple coupled hydrological-biogeochemical model to simulate daily streamwater DOC data to improve understanding of the dynamics of DOC fluxes from different landscape units to the aquatic environment. The model design allows the relative importance of DOC fluxes from the major landscape units (hillslopes, groundwater and saturation area) to be determined. The dynamic saturation zone contributed 84% (including 16% from the hillslope) of DOC to the stream, showing its disproportional influence over stream water chemistry which at maximum wetness comprises 40% of the area. The temporal connectivity of each of the landscape units was dependent on the antecedent conditions with a highly transient connection between the hillslope and valley bottom saturated area which was entirely disconnected during the driest periods. The groundwater contributions remained constant, but its relative importance increased during the driest periods. This work shows that predictive modelling is contingent upon conceptualising the non-linearity in hydrological connectivity, its relation to hydroclimatic factors and consequent role in the transport of DOC.