Studies of Cation Budgets in the Southern Appalachians on Four Experimental Watersheds with Contrasting Vegetation

Nutrient fluxes within and through watershed ecosystems at the Coweeta Hydrologic Laboratory are under study. This paper describes the annual budgets and seasonal fluctuations for selected cations. Concentrations and flux of cations moving through a hardwood forest stand, a weed to forest succession, a hardwood coppice stand and an eastern white pine stand on steep mountain topography are compared. Stream discharge was greater by 6% for the successional weed stand, and 10% for the second hardwood coppice, but 15% less for the young pine stand in contrast to pretreatment levels. Although concentrations for Ca ( ++), Mg ( ++), K + and Na + combined were usually less than 3.5 ppm, over 98% of the loss of each cation was in dissolved form on all four watersheds. Regression analysis showed that 50 to 60% of the variation in monthly weighted average concentration was accounted for by monthly discharge amounts. Annual losses of the four cations from the mature hardwood stand were in the amounts of approximately 7, 3, 5, and 10 kg/ha respectively for the Ca ( ++), Mg ( ++), K + and Na + . Annual budgets showed net changes to be —0.8, —2.0, and —4.3 kg/ha, respectively, for this mature hardwood ecosystem. In contrast, the weed stand lost significantly greater amounts, and the young pine and hardwood coppice watersheds showed a net gain in Ca ( ++) and significantly lower losses than the mature ecosystem for the other three ions. These budgets show that major alterations to these forest ecosystems are not now producing a substantial out—flux for these cations.