Seasonal Variation and Processing of Vascular Plant Organic Matter in Tropical Montane Catchments as Reflected by Riverine DOC Compositions

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Tropical systems face increasing pressure from land-use change in developing countries as well as unknown effects of imminent climate change. The concentration and composition of riverine dissolved organic carbon (DOC) serves as an integrator of terrestrial processes on timescales relevant to land-use change and climate change. Whereas most tropical rivers are challenging to study due to their remote locations and limited infrastructure, this project will take advantage of existing infrastructure and ongoing studies in the Luquillo Critical Zone Observatory (CZO) in Puerto Rico. Specifically, the investigator will measure the composition and concentration of biomarkers for higher plants, lignin-derived phenols, on weekly samples over the course of one year from two rivers that drain catchments of similar vegetation but contrasting lithologies and erosion rates with the goal of characterizing seasonal, event-driven, and catchment differences in DOC composition and concentration. Results will be compare and contrasted with a similar dataset from a temperate agricultural watershed to investigate partitioning effects, the effects of hydrologic flowpaths during low and high discharge, and the use of carbon-normalized yields of lignin as an endmember for DOC sources. This project will help to establish carbon cycling baseline measurements within these rivers, hence the societal impact will be an increased ability to understand impending climate and land-use changes in sensitive tropical systems. In addition, this is an investigation of fundamental processes within watersheds that are likely to be generalizable to nearly any DOC studies on rivers, hence results will have broad impact toward future studies. Results from this project will be presented at scientific meetings and published in peer-reviewed journals. The PI, Hernes, teaches undergraduate and graduate classes that cover various aspects of the global carbon cycle, climate change, and river biogeochemistry, and data collected from this project will be used to demonstrate important processes that are susceptible to changing state factors. Incorporation of active research into course curriculums increases the enthusiasm of both the instructor and the students, frequently leading to undergraduate internships. One such undergraduate from a group under-represented in science will participate in the laboratory analyses of samples and will have the opportunity to present results at undergraduate research forums on campus. Results will be posted on research websites and data contributed to appropriate national and international data bases associated with the Luquillo CZO for widespread use.