Model Assessment of Biogeochemical Controls on Dissolved Organic Carbon Partitioning in an Acid Organic Soil

Abstract

A chemical model (constructed in the ORCHESTRA modeling framework) of an organic soil horizon was used to describe soil solution data (10 cm depth) and assess if seasonal variations in soil solution dissolved organic carbon (DOC) could be explained by purely abiotic (geochemical controls) mechanisms or whether factors related to biological activity are needed. The NICA-Donnan equation is used to describe the competitive binding of protons and cations and the charge on soil organic matter. Controls on organic matter solubility are surface charge and a parameter, gamma, that accounts for the distribution of humic molecules between hydrophobic and hydrophilic fractions. Calculations show that the variations in solute chemistry alone are not sufficient to account for the observed variations of DOC, but factors that alter gamma, such as biological activity, are. Assuming that DOC in organic soils is derived from soluble humic material and that gamma is modified seasonally due to biological activity (with monthly soil temperature used as a surrogate for biological activity) we are able to model the observed seasonality of soil solution DOC over a 10-year period. Furthermore, with modeled DOC coupled to other geochemical processes we also model soil solution pH and Al concentrations.

An Analysis of Terrestrial and Aquatic Environmental Controls of Riverine Dissolved Organic Carbon in the Conterminous United States

“…In line with previous site-level investigations [57,58], our analyses highlight the important role of soil properties in determining DOC concentrations. For example, soil organic matter has significant impacts on DOC concentrations [59,60] at the national scale and in major three water resource regions ( Table 2).…”

Modeling dissolved organic carbon in temperate forest soils: TRIPLEX-DOC model development and validation

“…The key innovations compared to previous DOC models (Neff and Asner, 2001;Michalzik et al, 2003;Lumsdon et al, 2005) are that TRIPLEX-DOC is the first DOC cycling model to explicitly include land cover type effects for Table 2. Results of sensitivity of key variables to changes in climatic variables for different-aged temperate pine stands used in this study.…”

“…Michalzik et al (2003) relied on 14 C data to determine the age of soil organic matter. Lumsdon et al (2005) simulated changing organic matter solubility as a function of competitive cation adsorption and hydrophobicity in a single soil horizon. Although these DOC models reasonably simulate soil DOC dynamics, they are currently incapable of investigating the potential impacts of land use change on the fate of DOC, such as forest management practices.…”

Cross-scale ensemble projections of dissolved organic carbon dynamics in boreal forest streams

“…Similarly, both DyDOC (Michalzik et al 2003) and the DOC model proposed by Neff and Asner (2001) are explicit models of processes in the soil phase, which have been useful for predicting soil solution carbon, but their lack of detailed processes occurring in streams might undermine their applicability outside this range. The strength of the model proposed by Lumsdon et al (2005) is its focus on organic carbon solubility in the soil. The Mire DOC model proposed by Yurova et al (2008), works well for peaty wetlands, but might not be able to give a credible representation of the contrasting mechanisms controlling DOC in forest streams.…”