RIPARIAN POPLAR TREE BUFFER IMPACT ON AGRICULTURAL NON-POINT SOURCE POLLUTION

J.L. Jordahl, L.A. Licht and J.L. Schnoor
Department of Civil and Environmental Engineering, University of Iowa, Iowa City, IA, 52242, 319-335-5178

ABSTRACT

The water quantity and quality of two adjacent agricultural watersheds were compared. The stream draining one watershed was farmed to the edge of the stream (unbuffered) and the stream draining the other watershed was "buffered" with 9 m (4 rows) of poplar trees on each side. The buffer was designed as a living filter to reduce agricultural non-point source pollution.

The pattern of nitrate concentration in the outflow of the watersheds in 1994 was similar to 1993; the buffered watershed consistently had lower nitrate levels. The nitrate concentration in the tile lines feeding each stream closely paralleled watershed outlet concentrations, showing that the tile line flow must be intercepted to fully control water quality at this site. Ground water nitrate levels in piezometer transects through the buffer showed generally low levels of nitrate, with a trend of decreasing nitrate concentration across the buffer from the field to the stream.

A section of the buffer which has been in place for 7 years was excavated to determine the distribution of macronutrients, micronutrients and carbon in the trees (leaves, stem, roots) and in the soil to a depth of 1.8 m. In addition, preliminary data was collected to determine the impact of the poplar buffer on rhizosphere microbial populations potentially important to bioremediation. Increased populations of heterotrophic and denitrifying organisms relative to the surrounding soil were observed in the rhizosphere of poplar.

Key words: nitrate, non-point source, phytoremediation