AIMS Talladega Absorbance Spectral Fingerprint at Watershed Outlet (AIMS_SE_TAL_SCAN)

This study was conducted in the Talladega research watershed (outlet location: 33.76219799, -85.59550775) in the Talladega National Forest (Cleburne County, AL, USA). The watershed drains a non-perennial unnamed tributary of Pendergrass Creek, and contains 0.92 km^2 of mixed coniferous and deciduous forest in the Piedmont Upland physiographic section. Located near Anniston, AL, the watershed spans an elevation range from 345 to 456 m above sea level and is a tributary to the Coosa River (within the larger Mobile-Tombigbee basin). The region has a humid subtropical climate, with mean daily January and July air temperatures of 5.3°C and 25.3°C respectively, and mean annual precipitation of 1,400 mm/yr.

These data were collected in support of the core sampling goals of the Aquatic Intermittency effects on Microbiomes in Streams (AIMS) Project. Between 15 September 2021 and 26 September 2023, we also deployed a s::can spectro::lyser V3 UV-Vis spectrophotometer (Messtechnik GmbH, Vienna, Austria) to measure light absorbance at wavelengths from 190 to 750 nm at 2.5 nm intervals every 15 minutes. These absorbance spectra were turbidity-compensated using a s::can proprietary algorithm. Due to the complexity of the absorbance spectra time series generated by the submersible UV-Vis spectrophotometer, we used a simplified data quality assurance method to filter out erroneous absorbance spectra. We used error codes recorded on the instrument, field notes, and water-level and turbidity data from the watershed outlet to help remove all spectra during periods of instrument malfunction, burial, and desiccation. We further filtered the absorbance data time series by first selecting three wavelengths (200 nm, 255 nm, 400 nm) to be representative of the entire UV-VIS absorbance spectra. We removed entire recorded spectra when 1) absorbance values at a given time point were negative at 200 or 255 nm and 2) when absorbance values at a given time point exceeded three standard deviations of the rolling mean absorbance values at 200, 255, or 400 nm.