The present research evaluates the sensitivity of the terrestrial and aquatic ecosystems to acid precipitation in western Ungava, Quebec. PH values of the acid-sediment mixtures were used to classify the sediments according to their capacity to neutralize acid. The carbonate and the silt and clay content of the sediments are considered as the main controlling factors of their neutralization properties. Average acid neutralizing capacity (ANC) values were calculated for 14 sites. PH values, determined from the neutralization characteristics at each site, were used to classify the sites on a pH scale, presumably a sensitivity scale. On this scale, the least sensitive site, with pH remaining above 7, is from the coast of Hudson Strait where the sediment is a clayey fossiliferous glaciomarine diamicton. Of higher but still relatively low sensitivity, with pH remaining above 4.5, are two sites below the Tyrrell Sea marine limit, where the sediments are predominantly shell-bearing raised littoral deposits. Of high sensitivity, with pH below 4.5, are the remaining sites either below or above marine limit. Those below the marine limit have sediments mostly devoid of shell material. Those above the marine limit have till as the predominant type of sediment. By comparison to pH values determined for samples collected further south, namely in the Chibougamau-Lac Mistassini region, in the Thetford Mines region, and in northeastern Ontario, the group of samples with pH remaining above 7 may be qualified as showiny low sensitivity, those with pH between 7 and 4.5, of intermediate sensitivity, and finally those with pH below 4.5 of high sensitivity. It is concluded that ANC determinations can provide an adequate means of quantitative comparisons between widely separated regions and could possibly be used as one index of terrain sensitivity. Full assessment of terrestrial sensitivity to acid precipitation must also consider the hydrogeological characteristics at different localities. For instance, in those parts of Ungava where the permafrost table is near the surface, the saturation of the thawed upper layer prevents significant infiltration thereby limiting the possibility of neutralizing acid rain, regardless of the ANC characteristics of the sediments.
HO- and OH-, Reason and Tradition
