ELSEVIER Ecological Modelling 91 (1996) 169-181 |[ll nlOliBILm6 Development of a sediment redox potential model for the assessment of postdepositional metal mobility Seok S. Park a,1 Peter R. Jaff6 b,, Department of Eneironmental Science, Kangwon National Universi~,, Chuncheon, Kangwon-do, 200-701, South Korea b Water Resources Program, Department of CiL'il Engineering and Operations Research, Princeton Universio', Princeton, NJ 08544, USA Received 23 May 1995; accepted 10 October 1995 Abstract A numerical model was developed to simulate the vertical profile of the redox potential in benthic sediments. The benthic sediments were subdivided vertically into six zones, each with different microbial and chemical reactions: aerobic respiration, denitrification, manganese reduction, iron reduction, sulfate reduction, and methanogenesis. Microbial degrada- tion of organic matter and subsequent chemical reactions of interest were formulated using stoichiometric relationships and considering the vertical advective/dispersive transport in the sediments. The kinetics of utilization of the different electron acceptors during the biodegradation of the organic matter were described by a Monod-type formulation. Eleven coupled differential equations were derived and solved interactively utilizing an iterative multistep numerical method. The model input parameters include the rate of solid deposition, concentrations of electron acceptors in the water overlaying the sediments, activities of the benthic fauna, and molecular diffusion. The model simulates the redox potential as well as eleven chemical constituents in the sediments, three solids (particulate organic matter, manganese oxide, and iron oxide), and eight dissolved species (oxygen, nitrate, sulfate, ammonia, dissolved manganese, dissolved iron, sulfide, and methane). The model demonstrated that accurate estimates of the flux of primary electron acceptors and donors from the overlying water to the benthic sediments is important to determine the redox conditions in sediments. Bioturbation and the rate of pore-water infiltration are processes that have a major influence on this flux. Keywords: Biodegradation; Metals; Nitrogen; Redox potential; Sediments; Sulphur 1. Introduction Benthic sediments can act either as a sink or a source for a wide variety of heavy metals and toxic chemicals in aquatic ecosystems. Benthic sediments are an important component of aquatic ecosystems, providing a habitat for many aquatic organisms. Therefore, sediment quality has been recognized as one of the most important criteria for the protection of water quality as well as of aquatic biota (Adams et al., 1992; Burton and Scott, 1992). * Corresponding author. Fax: (l) (609) 258 2799; e-mail: jaffe@princeton.edu ] Present address: Department of Environmental Science and Engineering, Ewha Womans University, Seoul, 120-750, South Korea. 0304-3800/96/$15.00 Copyright © 1996 Elsevier Science B,V. All rights reserved. SSDI 0304-3800(95)001 88-3