Do buffers really reduce nitrogen and other chemicals loadings to streams?

Yes.

Nitrate concentrations are 90% lower and atrazine concentrations 70% lower in the soil water of the unsaturated zone (rooting zone) under the riparian buffers along Bear Creek than under adjacent crop fields. This may not mean that the buffer has removed all of that nitrogen or atrazine from the soil solution but it does represent a zone where nitrogen and atrazine have not been directly applied to the soil. Similarly, nitrate concentrations in the shallow groundwater are reduced by as much as 90% within the buffers, though this is very much influenced by site geology. Where the shallow groundwater moves in a narrow zone near the surface, significant reductions may be expected but where it lies in a wider zone and moves well below the rooting zone significantly less reduction can occur.

Understanding site geology is very important to understanding buffer function. In some agricultural regions, agricultural drainage tiles bring water from distant upland portions of the watershed directly to the stream channel, short-circuiting the buffer. In some regions this tile water may provide the major baseflow for the stream. In that case buffers themselves are ineffective at removing pollutant chemicals from the tile water. The Multispecies Riparian Buffer Management System provides an integrated management approach by including constructed wetlands that can be designed to intercept and treat tile water and therefore improve stream water quality.