The chemistry of surface water in prairie ponds

Water analyses from 80 small prairie ponds, 0.17 to 89.8 hectares, in Manitoba and Saskatchewan between 1967 to 1972 exhibited two basic ionic dominance patterns HCO₃ > SO₄ > Cl and SO₄ > HCO₃ > Cl. The order of SO₄ and Cl were reversed in 40 percent of the bicarbonate ponds below 500 µmhos/cm. At salinities above 12,000 µmhos/cm, Cl exceeds SO₄ in several wetlands. Temporary wetlands were characterised by Ca > K > Mg > Na / HCO₃ > Cl > SO₄, semi-permanent ponds Mg > Ca > Na > K / SO₄ > HCO₃ > Cl while the permanent pond structure was Ca > Mg > Na > K / HCO₃ > SO₄ > Cl.Conductivities of the wetlands studied ranged from 47 to 23,000 µmhos / cm.Seasonal changes in salinity varied within and between pond types as well as from year to year. The average salinity increase within season in temporary ponds was 67 percent, 63 percent in semi-permanent ponds and 20 percent for permanent ponds. These changes were affected by evaporation, transpiration, see-page and precipitation patterns. Ionic dominance patterns did not change within a season although Mg, K and HCO₃ increased at higher rates than Ca, Na, CI and SO₄.Temporary wetlands are slightly acidic, averaging pH 6.8 while semi-permanent and permanent ponds were alkaline, pH range 7.1 to 9.2. No stratification of pH with depth and minimal diurnal variation was recorded.At two study areas, Bradwell and St. Denis fhe following ranges (micrograms/litre) were recorded: 3 to 630 PO₄-P, 10 to 650 NO₃-N, 5 to 630 TDFe, 1 to 13 TDCu and 1 to 27 TDZn. Colour was 5 to 190 Hazen units at St. Denis and 10 to 110 for Bradwell.Two herbicides, 2,4-D and 2,4,5-T were detected at levels of 4 to 111 and 1.4 to 13.5 micrograms/litre, respectively, from 15 ponds at St. Denis.