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Buffer strips are unanimously recognised by researchers as an effective tool for reducing diffuse pollution coming from agricultural fields in the lowlands, but there are contrasting reports about the minimum width to obtain satisfactory results. Since narrow buffers are the more suitable for the Italian territory, we studied the pollution control of a 6 m wide buffer.

The experiment was carried out during the period December 1997-June 1999 in N-E Italy, monitoring the quality of subsurface water entering and exiting a buffer composed of a strip of grass (5 m wide) and a line of woodland vegetation (1 m wide at the foot of the trees). 28 samplings for a total of 448 samples were taken, measuring the following parameters: pH, ECw, NO3-N, bromides, dissolved P, herbicides (terbuthylazine, alachlor, nicosulfuron, pendimethalin, linuron).

Using bromide as tracer, the biological processes of nitrate decomposition have been detected. Dissolved phosphorus concentrations were markedly reduced passing through the buffer and in most cases exiting water satisfied the limit for avoiding eutrophication. A positive effect was also detected on ECw (reduced by 25%), while pH was not significantly modified. Finally, the abatement of herbicide concentration varied between 60 and 90%, depending on the chemical considered.

The results show the environmental value of water quality protection of this narrow buffer strip. The data also suggest that its zone of influence might be bigger than its simple width. The abatement was also efficient during winter.