IN-SITU OPTICAL SENSORS REVEAL HOT MOMENTS OF DISSOLVED ORGANIC MATTER EXPORT IN SLEEPERS RIVER RESEARCH WATERSHED, VERMONT

River systems serve as net carbon exporters from land to the ocean, fueling downstream aquatic ecosystem food webs. Optical properties of stream water can be used as proxies for dissolved organic carbon (DOC) concentration and can characterize DOC composition, reactivity, and source to improve our understanding of ecological processes. In-situ measurement of spectral attenuation and fluorescence using fifteen-minute interval data logging allows greater temporal resolution than laboratory studies. Multiparameter water quality sondes (Eureka Manta), fluorometers (Turner Designs Cyclops) and spectrophotometers (s::can spectrolyser) were deployed at sites nested within the Sleepers River Research Watershed in Vermont in 2017. We coupled these measurements with field sampling campaigns and laboratory analysis for DOC, Excitation-Emission Fluorescence Matrices, spectral attenuation, and ions. The data loggers recorded optical properties responding to discharge events and laboratory results show a nonlinear, hysteretic relationship between discharge and DOC where peak DOC lags peak discharge. This hysteresis is predicted to be controlled by multiple flow paths and DOC sources (i.e. groundwater, overland flow). We conclude that continuous in-situ observations of stream water optical properties can be used to inform ecological processes and test new hypotheses concerning dissolved organic matter dynamics in watersheds.