CHANGES IN THE DELTA 13-C OF HUMIC SUBSTANCES FROM SOILS, SOIL WATER, GROUND, AND SURFACE WATER FROM A TALL-GRASS PRAIRIE WATERSHED, KONZA PRAIRIE RESEARCH NATURAL AREA, NEAR MANHATTAN, KS

Aquatic humic substances (AHS) derived from woody vegetation and warm season prairie grass yield distinct delta 13-C signatures that change as water flows off vegetation, passes through soils, and reaches ground and surface water in a prairie watershed. AHS are generally yellow-colored, high molecular weight, polyelectrolytic organic acids extractable from water using XAD resins or comparable procedures. AHS and soil humic substances are composed of humic acids (HA) that precipitate when the pH of a sample is lowered to 1.0, whereas, fulvic acids (FA) remain soluble. The delta 13-C values for vegetation leachates and through fall for FA and HA derived from woody vegetation (-25.76 to -28.33 o/oo, parts per thousand, relative to the PeeDee belemnite standard) differed from that derived mainly from warm season grasses (-15.06 to -16.77 o/oo). Going from the A to the C soil horizons beneath woody vegetation, delta 13-C values in HA and FA in soil water changed from -25.57 o/oo to -23.76 o/oo, possibly from the incorporation of carbon from soil HA and FA derived from prairie grass (-17.45 to -14.72 o/oo). The delta 13-C values in FA in soil water beneath grass changed from -18.45 o/oo in the A horizon to -19.51 o/oo in the C horizon. The delta 13-C values FA in groundwater collected from a spring and limestone aquifers sandwiched between beds of shale ranged from -21.25 to -21.10 o/oo. The delta 13-C values for HA and FA from Kings Creek and groundwater from a limestone bed intersected by the creek ranged from -21.59 to -23.22 o/oo. Groundwater and water from Kings Creek show the mixing of delta 13-C sources derived from grass and woody vegetation along differing flow paths rather indicating exclusive contributions from either vegetation source.