Stimulating Denitrification in Agricultural Headwater Streams Using Elemental Sulfur

The extensive use of nitrogen fertilizers in agriculture has led to widespread eutrophication. We explored sulfur-based autotrophic denitrification in agricultural headwater streams as means to remove nitrogen near the source. A stream mesocosm, simulating a headwater drainage ditch, was amended with elemental sulfur chips. Nitrate removal efficiencies were as high as 99%, corresponding to effluent concentrations below 1 mg/L NO3−-N. However, nitrate removals decreased over time, concurrent with accumulation of biomass on the bed surface. A model was developed to describe the hydraulic and biological reactions taking place within the mesocosm. The model captured trends in bulk liquid nitrate concentrations but provided reasonable accuracy only when using a high diffusive exchange coefficient. This result suggests advective exchange with the bulk may be significant and biological activity is limited to the top few millimeters of the sulfur bed. Results suggest this approach is promising, although further research under more realistic conditions is needed.