GEOCHEMISTRY OF FROST AFFECTED SOIL, ROCKY MOUNTAIN NATION PARK, COLORADO

The nutrient movement in frost affected tundra soils can influence high altitude plant communities and alter the trophic status of alpine lakes and streams. To evaluate the geochemistry of soil pore water in tundra soils, intact soil core samples were collected in Rocky Mountain National Park, Colorado. Core samples were kept frozen at -5^oC until use, at which time the cores were warmed to 18^oC. Columns were leached with low ionic strength water, and leachates were collected using a fraction collector. Leachates were analyzed for Ca, Mg, K, Na, Cu, Zn, Mn, SO₄^2-, PO₄^3-, pH, and LMWOA. After leaching, the columns were drained, and frozen at -5^oC for five days. Six sequential freeze thaw cycles (FTC) were used, the first three cycles involved a thaw, leach, drain, freeze cycle (-5^o C, 5 days), the last three cycles involved thaw, leach, saturated column, freeze cycle (-5^o C, 5 days).

Leachate analysis showed that P leaching was correlated to elevated Mn and oxalic acid concentration in solution. Release of P into solution may be attributed to the dissolution of the manganese oxide solid phases adsorbing P, and competitive adsorption of P and oxalate for surface adsorption sites resulting in P leaching. Eluent P and Mn concentration in leachates were observed to decrease for the drained FTC, and increase for the water saturated FTC. Copper and Zn were leached from the columns with metal concentrations being influenced by the water content of the FTC. Magnesium leachate concentration decreased during the saturated FTC, while Ca showed no definite leaching pattern for either freeze thaw-cycle.

Chemical speciation of collected leachates indicated considerable metal complexation with oxalate, with Cu-oxalate complexes ranging from 4 to 62% of total Cu, and Zn-oxalate complexes ranging from 4 to 21% of total Zn. The extent of metal-oxalate complexation correlated with oxalic acid concentration in the leachates. The identification and quantification of aqueous complexes can be used to elucidate the mechanisms by which P is released and transported in tundra soils.