Reduction in agricultural non-point source pollution in the first year following establishment of an integrated grass/tree filter strip system in southern Quebec (Canada)

摘要

Vegetative buffer strips represent a possible approach for filtering the pollutants transported in runoff before the water reaches watercourses. Nevertheless, the effectiveness of these filter strip systems is often low in the first year after establishment because of the limited vegetation cover. The goal of this project was to evaluate the initial effectiveness of an integrated grass/tree strip system in filtering runoff and drainage water from grain corn fields fertilized with liquid swine manure. The experimental site consisted of four random blocks each comprising three plots (i.e. treatments T1-T2-T3). The effectiveness of the grass treatment (T2) and the grass/poplar tree treatment (T3), compared with the control plot with no vegetative strip (T1), was determined for each water quality parameter (total suspended solids (TSS), phosphorus, nitrogen, Escherichia coli) based on the total annual loads exported from the plots. The results obtained in the first year after the experimental layout was established in 2004 indicate that the grassed strips T2 reduced runoff water (R) volumes by 40%, TSS by 87%, total P by 86%, dissolved P by 64%, NH sub(4) by 57%, NO sub(3) by 33% and E. coli by 48% whereas the grass/tree strips T3 reduced runoff volumes by 35%, TSS by 85%, total P by 85%, dissolved P by 57%, NH sub(4) by 47%, NO sub(3) by 30% and E. coli by 57%. The drainage water (D) volumes measured for the plots containing vegetative strips (T2 and T3) increased by 16% and 8%, respectively, compared with the control plot (T1). The increased drainage water volume also corresponded to increased total P of 418%, dissolved P of 23% and E. coli of 24% for treatment T2; and increases of 347%, 27% and 18%, respectively, for treatment T3. By contrast, the NH sub(4) and NO sub(3) loads in drainage water were reduced by 8% and 63% in T2 and by 11% and 68% in T3. Overall, taking into account the total loads exported in runoff and drainage water (R+D), the vegetative filter strips system T2-T3 reduced water volumes by about 15%, TSS by 85%, total P by 75%, dissolved P by 30%, NH sub(4) by 50%, NO sub(3) by 60% and E. coli by 25% in agricultural non-point source pollution associated with liquid swine manure spread in the corn plots. The addition of young (two-years-old) poplars in treatment T3 did not bring about a significant increase in the filtering capacity of the grassed strip system in this first year of monitoring.