DIEL CONCENTRATIONS AND HYSTERESIS BEHAVIORS OF MAJOR, MINOR, AND TRACE SOLUTES IN TAYLOR VALLEY, ANTARCTIC STREAMS

We have examined late austral summer diel hysteresis behaviors of discharge, pH, temperature, major cations and dissolved (<0.4 µm) As, Cu, Fe, Mn, and V within two Taylor Valley, Antarctic streams fed by melt from one glacier. Although streams had the same source water, they differed in their receipt of eolian material and their hyporheic-biological extent. The diurnal variation in flow was similar between the two streams and spanned more than an order of magnitude, similar to the diurnal flow variation associated with alpine snowmelt in temperate regions. However, both streams had distinct solute concentrations and hysteresis behavior. The western stream had generally greater mean solute concentrations than the eastern stream due to more abundant soluble eolian material. For example mean Ca2+ concentrations (104 µM) in the western stream were more than twice eastern stream concentrations (47 µM). However, the eastern stream had greater biomass and hyporheic area in exchange with the stream waters. Consequently, solutes in the western stream generally exhibited clockwise hysteresis with eolian particulates preferentially solubilizing in the rising limb, while the solutes in the eastern stream generally exhibited counterclockwise hysteresis more typical of groundwater or soil porewater exchange. In the eastern stream, dissolved V was an exception and exhibited clockwise hysteresis resulting from receiving elevated V concentrations from supraglacial headwaters. Detailed examinations of discharge related hysteresis (e.g. rotation direction and loop amplitude) of redox, pH, uv, and biologically sensitive trace and minor elements in streams are important to identifying their hydrochemical controls. In both Taylor Valley streams most major cations had significant negative relations with flow (i.e. dilution) with only small differences in rising and falling limb concentrations. Conversely, concentrations of dissolved Fe and Mn in the western stream and As and V in the eastern stream had greater differences between rising and falling limb concentrations and were therefore more sensitive to hydrologic dynamics than discharge amount.