Atmospheric deposition at Turkey Lakes watershed

The chemistry of the atmospheric deposition is measured at the "CAPMoN" (Canadian Air and Precipitation Monitoring Network) site just outside the basin, while snowpack chemistry has been monitored at several locations (Figure 1).

Sulphuric acid is the predominant acid in "acid rain". Atmospheric deposition of sulphate (expressed as kg/ha) is a measure of the input of this acid to the basin. Two types of sulphate deposition are measured and shown in Figure 2. "Bulk" deposition is that accumulated in a continuously open collector and contains material that enters during both wet and dry periods. "Wet-only" deposition is measured using the CAPMoN collector which opens only when it is raining or snowing. Monthly bulk deposition of sulphate (fine red line in Figure 2) is highly variable because of the large variability in monthly precipitation quantity. Annual sulphate deposition (thick black and green lines in Figure 2) has declined throughout the period of study in the Turkey Lakes Watershed (TLW) reflecting reduced sulphur dioxide emissions from upwind sources.

Air concentrations of sulphur dioxide and other acidifying gases and particles are measured by drawing air through a filter located 10 m above the ground surface. Input of these acidifying gases and particles to the TLW occurs as "dry" deposition (i.e. during periods when it is not raining or snowing). Dry deposition is estimated by multiplying the measured air concentration values by a site-specific factor called a "deposition velocity". Dry deposition is ~ 40% of the annual total sulphate deposition at the TLW. Ground level ozone is also being measure at the CAPMoN site.