HR: 16:30h
AN: B12F-03    [PDF]
TI: Interpreting Environmental Change and Nutrient Cycling Using Major Element and Strontium Isotope Ratios in Tree Rings
AU: * Ash, A W
EM: asha@umich.edu
AF: University of Michigan, Department of Geological Sciences 425 E University, Ann Arbor, MI 48109 United States
AU: Blum, J D
EM: jdblum@umich.edu
AF: University of Michigan, Department of Geological Sciences 425 E University, Ann Arbor, MI 48109 United States
AU: Eagar, C
EM: ceagar@fs.fed.us
AF: USDA Forest Service, 271 Mast Road, Durham, NH 03824 United States
AU: Fahey, T J
EM: tjf5@cornell.edu
AF: Cornell University, Department of Natural Resources 12 Fernow Hall, Ithaca, NY 14853 United States
AB: In northeastern US forest ecosystems affected by acid deposition, calcium and other base cations have been leached from the soil exchange complex thereby increasing the possibility that calcium could become a limiting nutrient and negatively affect ecosystem health. Three of the most significant contributions of calcium to the soil exchange complex are atmospheric deposition, silicate mineral weathering, and non-silicate weathering. Strontium isotope and Ca/Sr ratios can be used to identify the relative inputs from these sources and determine whether they have changed over time. Strontium isotopic compositions and Ca/Sr ratios of tree rings hold promise for interpreting and understanding changes in calcium sources and availability in forest ecosystems. However, before tree rings can be used as a reliable archive for environmental perturbations several important issues must be resolved. These include 1) the degree of differential uptake of Ca and Sr by different tree species, and 2) the degree of translocation of Ca and Sr between growth rings. A manipulation experiment at the Hubbard Brook Experimental Forest (HBEF), NH was conducted, in which wollastonite pellets were applied to an experimental watershed. The wollastonite, with Ca/Sr and 87Sr/86Sr ratios distinct from sources to the soil exchange complex, serves as an environmental tracer. By monitoring the uptake of wollastonite into foliage we demonstrate that the degree of fractionation between Ca and Sr is small and that Ca/Sr ratios provide a good monitor of Ca sources to trees. Uptake into roots of selected species suggests there is not significant physiological discrimination against strontium assimilation in favor of calcium. We also explored the degree of mobility of Ca and Sr once it is incorporated into growth increments by determining the presence of the tracer in older growth increments. We developed a multi-step chemical leaching procedure to isolate a reservoir of Ca in wood that represents Ca utilized by the tree during the time of cell wall formation. Applying these methods to tree cores of sugar maple and red spruce allows us to establish a long-term chemical record, indicating that there has been a significant change in calcium sources to northern forests over the past 80 years. In conjunction with decades of foliar, forest floor, and soil chemistry data at HBEF, and one of the longest watershed water chemistry records in the world, the dendrochemical record provides a powerful addition to our understanding of past watershed chemistry.
DE: 0345 Pollution--urban and regional (0305)
DE: 0400 Biogeosciences
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting