Modelling landscape controls on dissolved organic carbon sources and fluxes to streams

Abstract

Catchment dissolved organic carbon (DOC) fluxes are governed by complex interactions, which control biogeochemical processes generating DOC and hydrological connectivity, facilitating transport through the landscape to streams. This paper presents the development of a coupled hydrologicalbiogeochemical model for a northern watershed with organic-rich soils, to simulate daily DOC concentrations. The parsimonious model design allows the relative importance of DOC fluxes from the major landscape units (e.g. hillslopes, groundwater and riparian saturation area) to be determined. The dynamic extent of the saturated riparian zone, which at maximum wetness comprised 40 % of the drainage area, contributed 84 % of DOC to the stream, of which 16 % was derived from the hillslope soils. This shows the disproportional riparian influence on stream water chemistry and the importance of the non-linearity in hydrological connectivity. The temporal connectivity of each of the landscape units was dependent on antecedent moisture conditions, with highly transient connections between the hillslope and valley bottom saturated area, which were entirely disconnected during the driest periods. The groundwater contribution remained constant, but its relative importance increased during the driest periods. The study emphasises the importance of conceptualising hydrological connectivity and its relation to hydroclimatic factors, as well soil biogeochemical processes, when modelling stream water DOC.

Carbon and nutrient export regimes from headwater catchments to downstream reaches

“…Seasonal concentration variability is traditionally explained by the varying contribution of several conceptual compartments (end-members) with distinct chemical signatures , the contribution of these compartments to stream discharge being controlled by changing hydroclimatic conditions on a seasonal basis. In addition, biogeochemical processes controlled by temperature and by the convergence of reactants in reactive hotspots such as the riparian zone (Pinay et al, 2015;Tiwari et al, 2017;Dick et al, 2015) could lead to temporal variability in the concentrations within different conceptual compartments. Thus the interplay of hydrological and biogeochemical processes controls stream NO − 3 , DOC and SRP concentrations (Thomas et al, 2016).…”

“…Furthermore, biogeochemical processes take place in the riparian and upslope compartments, which may lead to additional seasonal variability linked to mobilization and/or retention of C, N and P sources. Biogeochemical processes are temperature dependent, and they are also influenced by residence time (Hrachowitz et al, 2016) and by the presence/absence of reactants in biogeochemical hotspots such as the riparian zone (Pinay et al, 2015;Tiwari et al, 2017;Dick et al, 2015). In this respect, high temperature and low flow velocity during the summer season (leading to high residence time in the riparian zone) provide favorable conditions for riparian denitrification and DOC and SRP mobilization.…”

“…A comparison of export regimes in contrasting catchments representing different landscape types can be performed to investigate the effect of, for example, contrasting dominant land use, dominant flow paths or climate (Outram et al, 2014;Dupas et al, 2017;Minaudo et al, 2017), sometimes aided by the use of models (e.g., Dupas et al, 2016a;Hartmann et al, 2016). In headwater catchments, several studies have highlighted the important role of landscape heterogeneity within hillslopes (Herndon et al, 2015;Musolff et al, 2017), notably the crucial role of reactive zones such as riparian wetlands (Dick et al, 2015;Pinay et al, 2015;Tiwari et al, 2017) in controlling solute export regimes.…”

Assessment on the Effect of Climate Change on Streamflow in the Source Region of the Yangtze River, China

“…The RMSE can reflect the dispersion of a data set and indicates less deviation when the RMSE approaching to 0. The KGE is a three dimensional decomposition of the NSE and evaluate the dynamics (R), bias (β) and variability (α) [45]. It displays a perfect simulation with the KGE value approaching to 1.…”

Aquatic DOC export from subarctic Atlantic blanket bog in Norway is controlled by seasalt deposition, temperature and precipitation

“…Atmospheric deposition of sulfate (Monteith et al 2007) and chloride (Moldan et al 2012) can lower DOC concentrations by suppressing organic matter solubility. Several models have managed to successfully describe DOC transport through soils taking into account most of the above processes (Michalzik et al 2003;Neff and Asner 2001), except for the chemical control of sorption-desorption DOC dynamics (Dick et al 2015). Process-based models have been developed specifically for peatlands carbon accumulation (Sulman et al 2012;Webster et al 2013;Wu et al 2012), which include water table effects on various process rates, but usually without taking into account lateral fluxes of water and DOC.…”