Abstract for 1997 GLOBE Airlie Conference

Stream Response to Snowmelt and Rain

Roger C. Bales
Department of Hydrology and Water Resources
University of Arizona

Streams can experience dramatic and rapid changes
in chemical composition in the days following the
onset of snowmelt, or following a large rain. Large
inflows of dilute, acidic snowmelt or rainfall
runoff that has had little contact with soil
generally result in a lowering of stream pH,
alkalinity, dissolved solids and temperature. With
runoff from rain the largest effect may occur when
flows are highest, when dilution of stream water
with rainfall is greatest, With snowmelt the
greatest effect may begin well before peak flow,
since a large fraction of chemical species are
washed out of the snowpack with the first
meltwater. Spring snowmelt may also coincide with
the period when fish, zooplankton, amphibians or
macroinvertebrates are producing young. In the
early stages of life many aquatic organisms are
particularly sensitive to changing environmental
conditions, making spring runoff a critical period
in the life of a stream. We have field data from a
few well-studied streams that illustrate the
chemical changes associated with snowmelt or rain
runoff. GLOBE hydrology data, especially when
sampling is done weekly, can also capture in-stream
changes resulting from snowmelt and rainfall.