Patch-scale controls on denitrification in stream bed sediments
Denitrification is usually considered one of the most important processes controlling nitrogen loads in streams and rivers because it has the capability of permanently removing fixed nitrogen. Denitrification requires an electron donor (such as DOC) and nitrate, which is often abundant in agriculturally impacted systems. However, it is inhibited by oxygen and therefore occurs primarily in sediments where the supply and delivery of these substrates might be more limited. The goal of this study was to assess the interaction of chemical, biological and physical controls on in-stream denitrification. The influence of stream velocities, sediment grain size, carbon content and reactivity, hyporheic exchange, benthic algal coverage and microbial community distribution and activity were evaluated in sediment cores collected from two small streams in the Upper Illinois River watershed, where elevated loads of nitrogen species are commonly observed. This study tests our hypothesis that in-situ denitrification rates are controlled by a balance of physical mechanisms of substrate delivery and biologically controlled processes that alter porewater concentrations of essential and inhibitory substrates, which are controlled in turn by both physical and biological properties of the sediment.
