CHANGES IN THE OPTICAL PROPERTIES OF DISSOLVED ORGANIC CARBON DURING CANOPY INTERACTION AND SHALLOW SOIL INFILTRATION, PALMERTON, PA

Organic carbon mobility and transformation in hillslope soils governs the biolability and net export of carbon from forested watersheds. The changes in the concentration and optical properties of dissolved organic carbon were monitored at five stages: rainfall, throughfall, shallow soil water, deep soil water, and groundwater. These samples were collected by rainfall collectors, throughfall collectors, leafwash technique, lysimeters and grab samples from streams at the Lehigh Gap Nature Center in Palmerton, PA. Fluorescence was quantified across a range of excitation wavelengths and used to construct an excitation-emission matrix (EEM). Elemental chemistry was measured using inductively coupled plasma mass spectrometry.

Preliminary analysis of the EEM data from one site is explained below. Rainfall showed a low overall fluorescence intensity and peaks that indicated the presence of terrestrial humic recalcitrant and terrestrial humic labile organic matter. Throughfall showed an extremely high fluorescence intensity in the wavelengths typically attributed to tryptophan and tyrosine, indicating that throughfall mobilized these compounds as it passed through the canopy. The leafwash data displayed a similar fluorescence intensity pattern to the throughfall but had a much lower intensity, most likely due to the washing procedure, which limited contact time with a few leaves instead of interaction with the entire canopy. The lysimeter data showed that the largest peaks were in the regions of terrestrial humic recalcitrant and labile carbon. The water from the spring at the site had only one very small peak with a low overall fluorescence intensity, supporting removal of carbon along the flowpath into groundwater.