The relevance of scavenging kinetics to modeling of sediment‐water interactions in natural waters1,1

Abstract

The uptake of radioactive trace metals by suspended particles in natural aquatic systems is often slow and the time constants for scavenging are of the same order of magnitude as the residence times of particles in the water column. Therefore, models simulating removal of radioactive trace metals from water to sediments in shallow aquatic systems with short particle residence times need to include sorption (i.e. scavenging) kinetics. We present a numerical kinetic transport model designed to simulate tracer movements from a well mixed water column where particles are generated by both primary production and sediment resuspension processes. Tracers are allowed to penetrate into underlying sediments by diffusion and particle and porewater mixing. All model parameters can be experimentally determined either in the ecosystem itself or in separate laboratory experiments. Model simulations of three kinds of experiments are presented: tracer diffusion in benthic flux chambers, and tracer removal in marine mesocosms and in lacustrine limnocorrals. Limited sensitivity analyses and simulations of actual experiments indicate that under conditions of particle cycling in the sediments and the water, tracer removal can be affected and—in the case of high particle fluxes, as in summer—even be limited by the slow kinetics of tracer uptake by suspended particles. The model is also useful in identifying and quantifying critical pathways in the complicated web of interrelated processes of an aquatic ecosystem.