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Changes in the Biogeochemistry of Potassium following a Whole-Tree Harvest

Dep. of Civil and Environmental Engineering, Syracuse Univ., 220 Hinds Hall, Syracuse, NY 13244

Timothy J. Fahey

Dep. of Natural Resources, 8 Fernow Hall, Cornell Univ., Ithaca, NY 14853

Gene E. Likens

Inst. of Ecosystem Studies, Box AB, Millbrook, NY 11545

Thomas G. Siccama

Forestry and Environmental Studies, Greeley Lab., Yale Univ., New Haven, CT 06520

*Corresponding author (ctdrisco{at}mailbox.syr.edu).

ABSTRACT

A whole-tree harvest (WTH) was conducted at the Hubbard Brook Experimental Forest, New Hampshire, in 1983–1984 to evaluate changes in the loss and supply of nutrients such as K in response to clear-cutting. The WTH removed 554 mmol m^–2 associated with forest biomass. During the first 2 yr following the WTH, there were marked increases in concentrations and fluxes of K in drainage waters (stream efflux 24 mmol m^–2 yr^–1), coinciding with elevated losses of NO₃^–. While these losses decreased within 3 yr, concentrations and fluxes of K remained high in Bs2 horizon soil water and streamwater (10.5 mmol m^–2 yr^–1) for 10 yr relative to the reference watershed (4.8 mmol m^–2 yr^–1). Soil exchangeable K pools increased within 3 yr after the WTH. In the high-elevation zone of the watershed, soil pools returned to near-preharvest values after 8 yr. In the remainder of the watershed, exchangeable K pools decreased after 8 yr but remained about 20% above preharvest pools. The increase in exchangeable K in the mineral soil probably contributes to the long-term pattern of elevated K concentrations in streamwater after the WTH. Although stream and WTH removal of K (8.5 mmol m^–2 yr^–1) was large in comparison to preharvest exchangeable K pools (284 mmol_c m^–2), the increased release of K from mineralization of soil organic matter and weathering resulted in an increase in K on the soil exchange complex (43 mmol m^–2 yr^–1 in the first 8 yr). The increase in exchangeable K provided an available pool of K for the regrowing vegetation.

Received for publication February 1, 1995.