Modeling the mechanisms that control in‐stream dissolved organic carbon dynamics in upland and forested catchments

Abstract

[1] We present a new, process-based model of soil and stream water dissolved organic carbon (DOC): the Integrated Catchments Model for Carbon (INCA-C). INCA-C is the first model of DOC cycling to explicitly include effects of different land cover types, hydrological flow paths, in-soil carbon biogeochemistry, and surface water processes on in-stream DOC concentrations. It can be calibrated using only routinely available monitoring data. INCA-C simulates daily DOC concentrations over a period of years to decades. Sources, sinks, and transformation of solid and dissolved organic carbon in peat and forest soils, wetlands, and streams as well as organic carbon mineralization in stream waters are modeled. INCA-C is designed to be applied to natural and seminatural forested and peat-dominated catchments in boreal and temperate regions. Simulations at two forested catchments showed that seasonal and interannual patterns of DOC concentration could be modeled using climate-related parameters alone. A sensitivity analysis showed that model predictions were dependent on the mass of organic carbon in the soil and that in-soil process rates were dependent on soil moisture status. Sensitive rate coefficients in the model included those for organic carbon sorption and desorption and DOC mineralization in the soil. The model was also sensitive to the amount of litter fall. Our results show the importance of climate variability in controlling surface water DOC concentrations and suggest the need for further research on the mechanisms controlling production and consumption of DOC in soils.

Simulating Dissolved Organic Carbon Dynamics at the Swedish Integrated Monitoring Sites with the Integrated Catchments Model for Carbon, INCA-C

“…The model simulates the production, transformation and fluxes of carbon from soils to surface waters and operates on a daily time step. It has been applied to small, forested headwater catchments in Canada (Futter et al 2007) and Fennoscandia (Futter and de Wit 2008;Futter et al 2009) and to large, mixed land-use catchments in Canada (Oni et al 2010). …”

“…All water entering the lower soil box eventually enters the stream. The model is described more completely in Futter et al (2007). Daily time series of air temperature, precipitation, soil moisture deficit (SMD) and hydrologically effective rainfall (HER) data are needed to run INCA-C.…”

“…In INCA-C, modeled runoff is controlled by HER inputs and estimated parameters representing water residence times in the soil boxes. Flow in INCA-C is simulated using daily time series of HER, calibrated soil and groundwater residence times and calibrated stream velocity parameters (Futter et al 2007). …”

“…Key processes include organic carbon inputs through litterfall, sorption/desorption of organic carbon in organic and mineral soils, organic carbon mineralization and advective transport of material from soils to surface waters. All process rates are dependent on modeled soil temperature and moisture (Futter et al 2007). Soil temperature is modeled from air temperature using a relationship developed by Rankinen et al (2004) in which soil temperature is controlled by air temperature, insulating effects of snow cover, a soil thermal conductivity coefficient, heat capacity due to freeze/thaw and modeled soil temperature on the preceding day.…”

“…Equations 4 and 5 are simplified representations of effects of SAA on organic carbon sorption/desorption rates. The full equations are described in Futter et al (2007). Briefly, they have been modified to include the effect of soil water [SAA] on the rate at which DOC is precipitated to SOC.…”