Effects of Solid Phase Extraction on Stemflow DOM Properties

• Dillon Siple, Environmental Engineering, University of Delaware

• Yu-Ping Chin, Civil and Environmental Engineering, University of Delaware

Dissolved organic matter (DOM) are complex organic molecules that plays a role in the carbon cycle in soil and aquatic ecosystems. Trees are an important source for the terrestrial DOM, which can be released from live trees via stemflow.  Stemflow is meteoric water that flows over the tree bark after being intercepted by the canopy and is comprised of components found in DOM. This study attempts to look at stemflow DOM composition from 4 different tree species: Betula lenta L. (sweet birch), Fagus grandifolia Ehrh. (American beech), Liriodendron tulipifera L. (yellow poplar), and Pinus rigida Mill. (pitch pine) over the duration of the summer (June to end of August 2023).  Stemflow was collected during rain events using tubing along the trunk of the tree into clean polyethylene bags. Samples are collected and processed a day after the event. Solid phase extraction (SPE) was performed to isolate DOM, which was then analyzed by UV-Visible and fluorescence spectroscopy to characterize the chemical components that comprise its light absorbance and fluorescent properties. We examined these characteristics of the DOM isolate against the original unaltered stemflow DOM to assess from the components lost by the SPE process. The specific UV absorbance (SUVA254 and SUVA280) absorbance ratios at 250 and 365 nm (E2:E3), fluorescence index, humification index, biological index and freshness index were determined to be tree species-specific and also implies that SPE isolation biases stemflow DOM composition. Specifically, this study found that the SUVA254 and SUVA280 which typically correlates to the aromaticity, increased after SPE by 1.65x and 1.69x respectively with minor fluctuations between each run. My study show that the SPE isolation favors aromatic compounds more strongly than the other components in stemflow DOM. Future experiments involve correlating stemflow DOM to important compounds produced by trees such as lignins, which are highly aromatic structural compounds found in trees.