Leaf Leachate Chemistry: Regional Variation Across Three Watersheds in the Northeastern United States

Abstract:

During the autumn, leaf leachate plays a significant and influential role in a forested ecosystem’s hydrologic and biogeochemical cycles. As trees prepare for winter dormancy and future spring growth, they undergo resorption, senescence, and leaf abscission. How do these phenological changes affect the dissolved organic matter (DOM) chemistry of leaf leachates? Despite numerous studies into the factors that affect resorption efficiencies and the DOM signatures of leaf-litter leachate, little work has been done to look at the temporal effects of leaf-litter leachate on multiple watersheds in a region. In order to gain a better understanding of the physiological functional ecology of leaves in autumn in different watersheds, we examined changes in fluorescent DOM (FDOM) of Fagus grandifolia (American beech) leaf leachate from field sites in Maryland, Rhode Island, and Vermont. At each site, leaves were collected during three distinct phenological stages: fresh, senescing, and fresh litter. Leaves were collected at each site during their respective peaks for each phenological phase and then were sequentially measured, dried, and submerged in Nanopure deionized water. Leachate samples were analyzed for macronutrient concentrations and FDOM indexes, including specific ultraviolent absorbance at 254nm, humification index, spectral slope ratio, percent protein-like fluorescence, fluorescence index, and biological index. Preliminary results from Maryland suggest that, throughout autumn, the percent protein-like fluorescence and spectral slope ratio both decrease, fluorescence index remains relatively constant, and the humification index tends to increase. By investigating the temporal ecological roles of leaf-litter leachate in three different watersheds, we will be able to more accurately determine the effects of autumnal leaf changes on watersheds at the regional scale.