The USGS CAWSC Organic Matter Research Laboratory (OMRL) provides laboratory services and support to regional and national projects in the analysis of organic matter using the latest methods in absorbance and fluorescence spectroscopy. Optical measurements such as absorbance and fluorescence are used to gain insight into dissolved organic matter (DOM) composition, and can also serve as proxies for more expensive and difficult to obtain measurements. These techniques are relatively rapid and inexpensive and allow for the comprehensive tracking of DOM dynamics in aquatic ecosystems ranging from rivers and lakes to estuaries to open marine systems. Absorbance spectra and fluorescence matrices were simultaneously collected on filtered water samples at room temperature (21 °C) in an acid-cleaned 1 cm quartz cuvette using a spectrofluorometer equipped with a charge-coupled device (CCD) (Aqualog®, Horiba Instruments, New Jersey, U.S.A.). Excitation and absorbance scans were performed using a double-grating monochrometer, a 150 W Xenon arc lamp, a 5 nm bandpass, and a 1 s integration time at wavelengths of 240-800 nm. Emission spectra were collected with a CCD at approximately 2.3 nm (4 pixel) intervals at wavelengths of 245–800 nm. Excitation and absorbance wavelengths were scanned from low to high energy (i.e., VIS to UV) to reduce UV exposure of the sample, thus limiting the effects of photobleaching during analysis.
Data presented here were analyzed by the U.S Geological Survey California Water Science Center Organic Matter Research Lab, Sacramento CA. This release contains full spectra absorbance data measured on the Aqualog ® fluorometer January-December 2021.