DOI: 10.5061/dryad.hmgqnk9d9
title: Reproducible determination of dissolved organic matter photosensitivity: Data and code

description: This dataset includes absorbance and fluourescence spectra used to compare
 the sensitivity of dissolved organic matter to experimental
 photodegradation. Spectra represent time series of measurements collected
 during 20-hour lab photodegradations. Nearly all experiments consisted of
 60 absorbance and fluorescence measurements collected every 20 minutes as
 samples were exposed to simulated sunlight. A subset of these data were
 used to fit a parallel factor analysis (PARAFAC) model, onto which the
 entire data set was projected. Each experimental degradation fluorescence
 time series can then be expressed as relative change in PARAFAC component
 loadings, which are modeled with a  biexpontial decay function.
 Fitted biexponential decay parameters may be indicators of relative
 photo-sensitivity useful in studies of dissolved organic matter. The
 dataset here includes individual spectra exported after some processing,
 Matlab scripts used to further process data and fit the PARAFAC model,
 exported PARAFAC model loadings, R scripts used to fit biexponential decay
 models to loss of PARAFAC components during photodegradation and compare
 fitted biexponential parameters, and the plots and tables related to this
 analysis.
description: Fluorescence excitation-emission matrices (EEMs) and absorbance
 spectra were collected with an Horiba Jobin Yvon Aqualog
 spectrofluorometer using a quartz flow cell with 1 cm path length.
 Absorbance/excitation wavelengths ranged from 600-230 nm in 3 nm
 intervals. Fluorescence spectra were collected at each excitation
 wavlength over an 8 pixel CCD (roughly every 3.24 nm) across the same
 wavelength range. Integration time was 1 s using "medium" gain
 setting in the Aqualog control software. Measurements were collected every
 20 minutes using the "Sample Q" automatic measurement feature in
 the Aqualog software. Samples were continuously circulated between the
 spectrophotometer and a spiral exposure flow cell under an Oriel Sol2A
 solar simulator with a 1000 W Xe arc lamp equipped with a 1.5 air mass
 filter. Measurements were adjusted within the Aqualog software by
 subtracting a pure water blank, correcting fluorescence EEMs for inner
 filter effects, removing primary Rayleigh scatter, and normalizing each
 measurement by the integrated area under the Raman peak of water (347.5
 nm). Spectra were imported to Matlab (R2018a) using the script and
 toolboxes included here, which also removed  secondary Rayleigh scatter
 from EEMs. A subset of these data were fitted to a parallel factor
 analysis (PARAFAC) model onto which the entire dataset is projected, then
 model loadings for each EEM were exported (all using the drEEM toolbox)
 with the Matlab script. R (v. 3.6.0) was used to import model loadings and
 metadata and fit decay of PARAFAC components to an exponential decay model
 using the nlsLM function from the minpack.lm package. 
description: Matlab and R scripts have been annotated to improve
 interpretation. Required R libraries are noted at the top of the script. R
 script requires user to define location of directory containing data to
 import (character variable "datadir") and location of directory
 to save plots (character variable "plotdir"). Matlab analysis
 script requires the drEEM toolbox (Murphy K.R., Stedmon C.A., Graeber D.
 and R. Bro, Fluorescence spectroscopy and multi-way techniques. PARAFAC,
 Anal. Methods, 2013, DOI:10.1039/c3ay41160e.), available for download
 at http://dreem.openfluor.org/ at time of writing.