, Volume 42, Issue 1-2, pp 203-219

Precipitation and streamwater chemistry from undisturbed watersheds in the cascade mountains of Oregon

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Long-term records of precipitation and streamwater chemistry are rare; such records from forested watersheds relatively free of acidic deposition are even rarer. Precipitation and streamwater chemistry have been measured on two undisturbed forested watersheds at the H. J. Andrews Experimental Forest located on the western slopes of the Cascade Mountains of Oregon. Data from one watershed spans the period 1973–1985, the other 1969–1985. The mean annual pH of precipitation was 5.5 with a range of 4.7 to 6.0. HCO3 was the dominant anion; Ca2+ and Na+ were the dominant cations. The mean annual pH of streamwater was 7.3, and was dominated by HCO3 and Ca2+. These data contrast sharply with data from other calibrated watersheds in the north Cascade Mountains of Washington and British Columbia, and with data from New Hampshire and North Carolina where pH of precipitation averages 4.14 and 4.43, respectively, with SO4 2− the dominant anion.