Modeling the carbon cycling in aquatic environments is relevant for predicting the detritus processing capacity in metal-affected environments. Considering the potential toxic effect of Zn and Pb on microbial metabolism, we hypothesize that the presence of these metals decreases decomposition rates of macrophytes detritus. We examined the anaerobic decomposition of Hedychium coronarium and Urochloa subquadripara in presence of Zn and Pb at 15 and 25°C. The mass decay was parameterized by first-order kinetic model. The higher concentration of Zn promoted reduction on mineralization of particulate organic carbon (POC) in the U. subquadripara and H. coronarium detritus. The Q 10 (H. coronarium: 0.95 to 1.75 and U. subquadripara: 1.26 to 1.59) showed a positive effect of temperature increasing during macrophytes anaerobic degradation. Considering the metal type and concentration, the high Zn concentration acted as a driving force over POC decay and consequently affecting the yields in the plant detritus mineralization processes since the decrease in POC degradation was effective due to adsorption of metals in this detritus fraction. The use of mathematical models was suitable tool that allows predicting carbon turnover in an ecosystem submitted to an episode of metal contamination.