Using Riparian Buffer Strips to Manage Denitrification.

Riparian buffers are used to improve water quality in agricultural watersheds. Although multiple water quality benefits may be attributable to riparian buffers, the most common benefit is nitrate removal which can be through three main processes: vegetation uptake and storage in biomass; organic matter accumulation; and denitrification. Complete denitrification (reduction to di-nitrogen gas) is the most permanent of these removal processes. In many agricultural landscapes where nitrate creates water quality problems, enhanced drainage has either short-circuited the connectivity of runoff water and the riparian zone, decreased the residence time of water in the riparian zone, or both. Existing studies on management of denitrification in riparian buffers have generally taken a comparative approach where sites receiving different N and water loadings are compared for either nitrate disappearance or direct measurements of denitrification. Another approach has been to take management steps that would be expected to enhance denitrification such as enhancing water and nitrate input, increasing residence time, or both. Studies that have taken both the comparative and manipulative approach will be used to estimate the levels of enhanced denitrification that can be expected through riparian buffer management. The Riparian Ecosystem Management Model (REMM) will be used to illustrate the effects of soil and hydrologic properties of different sites on denitrification rates under different management regimes. Examples from existing managed and restored buffers will be used to illustrate the potential effects of increased soil organic matter, increased nitrate load, and /or increased water flow into the riparian buffer. The potential for incomplete denitrification and the production of nitrous oxide, a greenhouse gas, will also be discussed and both modeling and empirical approaches will be used to evaluate how management might affect nitrous oxide production in riparian buffers.