Chloride concentrations in growth rings of Taxodium distichum in a saltwater-intruded estuary

Element analysis by proton induced X-ray emission spectroscopy was performed on growth rings of baldcypress (Taxodium distichum) growing within the Cape Fear River estuary, North Carolina, USA. Trees from estuarine reaches heavily intruded by saltwater flooding contained larger concentrations of chloride, bromide, and sodium than did trees from less intruded reaches. At three intruded sites, trees nearest open water contained larger concentrations of these elements within outermost sapwood rings than did trees farther from open water and presumably flooded less often. Chloride was translocated from outer to inner sapwood rings of saltwater-intruded trees, resulting in larger concentrations within heartwood than within the inner sapwood. Chloride concentrations along the heartwood radius were used to estimate the position of the heartwood-sapwood interface during the beginning stages of intrusion, thus permitting historical estimates of the local onset of intrusion. Element analysis of the wood of baldcypress may aid assessments of tree growth and mortality in regions already subjected to saline flooding, and in coastal forests at risk from predicted sea level rises.