Abstract

Terrestrially-derived dissolved organic matter (DOM) (composed of dissolved organic carbon (DOC) and nitrogen (DON)) flux and quality exert significant influence over carbon (C) and nitrogen (N) cycling, and related stream and soil ecologies. Yet, no study known to the author has simultaneously investigated all forest canopy-derived DOM inputs (throughfall, stemflow, and litter leachate) from trees of contrasting canopy structure to the soils of wooded ecosystems across temporal scales (annual, seasonal, and within-event scales). This dissertation attempts to fill this knowledge gap for a mid-latitude temperate deciduous forest by quantifying all canopy-derived annual, seasonal and intrastorm DOM fluxes, characterizing their relative aromaticity and molecular weight via UV-vis spectroscopic metrics (SUVA₂₅₄, E₂:E ₃, S_R), and estimating contributions to soil solution 1 meter from the stemflow infiltration pathway using end member mixing analysis (EMMA) for two trees of contrasting canopy structure (Liriodendron tulipifera L., tulip poplar, and Fagus grandifolia Ehrh., American beech). DOC concentrations and fluxes produced stronger seasonal patterns than DON for both species, especially in stemflow. Since seasonal DON fluxes were nearly negligible for both species in our study, diminished DOC:DON ratios were almost exclusively a result of seasonal DOC dynamics. Aromaticity and molecular weight of canopy-derived fluxes generally increased under leafless conditions, likely due to lignin-degradation byproducts from greater bark contact.

Litter leachate DOM fluxes were greatest of all monitored canopy-derived DOM fluxes. F. grandifolia canopy structure enhanced precipitation capture and washoff of dry deposited materials via stemflow, favoring spatially-concentrated, less aromatic, lighter weight DOM flux. Conversely, L. tulipifera' s canopy morphology enhanced chemical exchange, increasing hydrologic residence time for entrained rain droplets, favoring more aromatic, heavier, more diffuse throughfall DOM flux. EMMA results found stemflow and throughfall signatures in near-stem soil solutions under varying meteorological and catchment conditions, indicating these fluxes may move through soils relatively unaltered. EMMA event comparisons also indicate that drier catchment conditions and increased rainfall intensity may enhance the contributions of these canopy water sources. The results of this study show the structure of above-ground plant biomass and precipitation within canopies can drastically influence DOM enrichment, flux and quality to the soils and (potentially) down-gradient watershed compartments.

Supported by US-NSF EAR-0809205, BCS-1003047.

Citation

Van Stan, J.T. (2012): Controls and dynamics of canopy-derived dissolved organic matter from co-dominant broadleaved deciduous canopies to the soil of a temperate catchment in the northeastern United States. Publications in Climatology 64: 1-96.