Estimation of the bulk atmospheric deposition of major and trace elements to a rural watershed

Despite the existence of many reports on the background deposition of contaminants in remote areas, very little is known about the total aerial inputs of major and trace elements to the entire surface of rural watersheds. In this work, the influence of the contribution from local nonpoint-sources of emission or resuspension (e.g. agricultural soil and road dust resuspension, direct emission from vehicle use, and small towns) on the background regional fluxes was evaluated in a small rural watershed of southern Quebec (Canada). A seasonal pattern was found for the background deposition of 28 major and trace elements, with spring and fall maxima as well as winter and midsummer minima mostly owing to agricultural practices and weather. The contribution from the Greater Montreal area, located 30 km to the west, was <5% of the background fluxes for all elements except Zn, Cu, Cd, and Mn. Although some of them do not constitute true inputs at the entire watershed level, a preliminary estimate of the local nonpoint-sources (e.g. agricultural soil resuspension, roads, small town) showed that the total aerial fluxes to the streams of the watershed could be considerably underestimated, owing mostly to agricultural soil resuspension source. Background-only deposition often represents a fraction of the total inputs to the waters of inhabited watersheds.