Temperature and hydrologic controls on dissolved organic matter mobilization and transport within a forest topsoil

Variations in concentrations of dissolved organic matter (DOM) in streams and rivers reflect, in part, coupled biogeochemical and hydrological processes that govern DOM mobilization and transport through soils. We explore the effects of temperature and rainfall characteristics on the quantity and composition of DOM mobilized from laboratory columns packed with an unsaturated forest soil. Our observations demonstrate that changes in temperature and a five-month drought period affect the mass and structure of DOM mobilized during soil-water infiltration, while changes in rainfall intensity and hourly to daily changes in the frequency of rainfall affect only the mass of DOM mobilized. The spectroscopic analyses indicate that DOM mobilized at low temperature is less humified and tends to be less condensed and lower in molecular weight. The C:N ratios of effluent DOM decline with cumulative rainfall volume during successive rainfall events and decrease by an average of 36% owing to the extended drought period. A two-region model that accounts for rate-limited DOM desorption from soil-water interfaces present within inter-aggregate and intra-aggregate pore spaces closely describes the time-series data on total concentrations of DOM eluted from the soil columns during the rainfall events.