Snowpack Ion Accumulation and Loss in a Basin Draining to Lake Superior

Stottlemyer, Robert

The objective of this study was to relate winter precipitation ionic inputs, snowpack retention, and change in first-order stream chemistry with spring snowpack melt, using winter 1982-1983 precipitation inputs in a 176 hectare watershed on the Keweenaw Peninsula of Michigan. Results are provided and discussed based on these objectives. An unusually low snowpack during the study year limits the results of this study to the local region. The objective of this study was to relate winter precipitation ionic inputs, snowpack retention, and change in first-order stream chemistry with spring snowpack melt. During winter 1982-83, measurement of preci~itation inputs, snowpack concentration and loading, and streamwater concentration and discharge of Ca +, K+, H +, N03-, and sol- from a 176-ha watershed reveals that only H+ might be lost from the snowpack before first thaw. Above-freezing soil temperature beneath the snowpack may be a factor in H+ loss. An initial1-d thaw resulted in loss of over one third (6 eq·ha-1) of the snowpack Ca2+. Over one half the snowpack load of K+, H +, N03-, and SO/-, was lost in a subsequent midwinter freeze-thaw period. Snowpack loading of ionic species was reduced by 70-90% before peak spring melting and stream discharge. Ecosystem H+ retention and biological uptake of N03- further mitigate ionic "pulses" in streamwater. Sulfate discharge exceeds bulk inputs, which suggests significant dry deposition input and little forest soil retention of this anion. The snowpack was relatively small, which limits wider application of these results to the region.

Snowpack Ion Accumulation and Loss in a Basin Draining to Lake Superior

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