Tracing hydrologic flow paths in a small forested watershed using variations in 87Sr/86Sr, [Ca]/[Sr], [Ba]/[Sr] and δ18O.

Natural variations in ⁸⁷Sr/⁸⁶Sr, [Ca]/[Sr], [Ba]/[Sr], and δ¹⁸O were used to investigate changing hydrologic flow paths during storm events in an 11.8 ha first-order watershed of the Hubbard Brook Experimental Forest. Throughfall, soil water, and stream water were sampled during several storm events and a single snowmelt event. Throughfall had ⁸⁷Sr/⁸⁶Sr, [Ca]/[Sr], and δ¹⁸O values that were distinct from other water types. Soil water was highly variable in composition but could be separated into three distinct elevation zones in the watershed with ⁸⁷Sr/⁸⁶Sr and [Ba]/[Sr] both increasing with elevation in the watershed. Changes in ⁸⁷Sr/⁸⁶Sr, [Ba]/[Sr], and δ¹⁸O of stream water during storm events yielded complementary information about watershed hydrologic flow paths. Traditional hydrograph separation using δ¹⁸O values indicated that new water was only a small component of storm flow (9-18%), whereas ⁸⁷Sr/⁸⁶Sr and [Ba]/[Sr] ratios indicated that shallow subsurface flow (soil water) contributed significantly to storm flow in amounts up to 40%, depending on soil moisture conditions. [ABSTRACT FROM AUTHOR]