A reactive transport benchmark on heavy metal cycling in lake sediments

Abstract

Sediments are active recipients of anthropogenic inputs, including heavy metals, but may be difficult to interpret without the use of numerical models that capture sediment-metal interactions and provide an accurate representation of the intricately coupled sedimentological, geochemical, and biological processes. The focus of this study is to present a benchmark problem on heavy metal cycling in lake sediments and to compare reactive transport models (RTMs) in their treatment of the local-scale physical and biogeochemical processes. This benchmark problem has been developed based on a previously published reactive-diffusive model of metal transport in the sediments of Lake Coeur d'Alene, Idaho. Key processes included in this model are microbial reductive dissolution of iron hydroxides (i.e., ferrihydrite), the release of sorbed metals into pore water, reaction of these metals with biogenic sulfide to form sulfide minerals, and sedimentation driving the burial of ferrihydrite and other minerals. This benchmark thus considers a multicomponent biotic reaction network with multiple terminal electron acceptors (TEAs), Fickian diffusive transport, kinetic and equilibrium mineral precipitation and dissolution, aqueous and surface complexation, as well as (optionally) sedimentation. models are able to predict similar trends of TEAs and dissolved metal concentrations, as well as mineral abundances. TR and CF are further used to compare sedimentation and compaction test cases. Results with different sedimentation rates are captured by both models, but since the codes do not use the same formulation for compaction, the results differ for this test case. Although, both TR and CF adequately capture the trends of aqueous concentrations and mineral abundances, the difference in results highlights the need to consider further the conceptual and numerical models that link transport, biogeochemical reactions, and sedimentation.

Quantifying Geochemical Processes of Arsenic Mobility in Groundwater From an Inland Basin Using a Reactive Transport Model

“…3.5.3. Abiotic Reduction of Fe (III) Oxides by H 2 S Fe (III) oxides can be reduced via an abiotic path in sulfidic environments by H 2 S and S 0 , as described by equations (3) and (4) Water Resources Research are integrated as equation (5), with log K = 8.82 (Arora et al, 2015). Excess H 2 S could further precipitate with Fe (II) as mackinawite (FeS) (equation (6)).…”

Influence of hydrological, biogeochemical and temperature transients on subsurface carbon fluxes in a flood plain environment

“…Although simplistic, this representation of SOM and dissolved organic carbon has been used in other reactive transport studies (Hunter et al 1998;Van Breukelen et al 2004;Arora et al 2015b), and it is considered sufficient here as a first-order, semiquantitative approach to investigate the dominant controls on carbon dynamics at the site.…”

Reactive transport benchmarks for subsurface environmental simulation

“…The first (Benchmark problems for reactive transport modeling of the generation and attenuation of acid rock drainage [14]) uses reactive transport modeling to simulate the generation of acidity as a result of sulfide oxidation and its subsequent effect on metal mobility above and below the water table. The second benchmark focuses on metal accumulation and mobility in lake sediments downstream of mining operations (A reactive transport benchmark on heavy metal cycling in lake sediments [15]). The modeling assumes a 1D geometry that extends from the lake-sediment interface to depth and includes component problems with and without sediment burial.…”