Dissolved organic matter composition in a peatland mesocosm experiment in Fäjemyr (Sweden) as PARAFAC components and specific ultraviolet absorbance

Peatland samples from the ombrotrophic bog Fäjemyr in southern Sweden (56°15′N, 13°33′E) were collected on June 15, 2017, and placed in experimental mesocosms as previously described [Salimi et al., 2021; Salimi and Scholz, 2021; 2022]. For this study, the response in pore water dissolved organic matter to manipulated climate and water levels were recorded during two years thereafter. Measurements were made monthly on 0.45 μm-filtered pore water from the peat mesocosms, but also on 0.45 μm-filtered samples from recipient surface water mesocosms. Absorbance scans and excitation-emission fluorescence matrices (EEMs) were collected on an Aqualog (Horiba Scientific) in a 1-cm quartz cuvette (2 s integration time) over 5 nm excitation wavelength increments from 230 to 800 nm and ~2 nm emission increments from 250 to 800 nm. The EEMs were blank-subtracted (deionized water), corrected for inner filter effects [Kothawala et al., 2013], normalized to the Raman area of deionized (Milli-Q) water [Lawaetz and Stedmon, 2009] and cropped to excitation range 250-450 nm and emission range 300-600 nm. Fluorescent components were identified with parallel factor analysis (PARAFAC) of corrected EEMs using the 6th release of drEEM toolbox [Murphy et al., 2013] in Matlab R2022a. Dissolved organic carbon concentration was analyzed through oxidative combustion-infrared analysis using a TOC analyzer (model TOC-V CPH-TNM-1, Shimadzu, Japan). Specific ultraviolet absorbance (SUVA) at a wavelength of 254 nm was calculated by dividing the absorbance coefficient at 254 nm by the DOC concentration. This study will be published by Berggren et al. in the <i>Journal of Physical Research - Biogeosciences</i> (conditionally accepted at the time of writing).<b>Included in this repository</b>Summary of PARAFAC component scores, DOC concentrations, SUVA and other experimental parameters (Data summary.xlsx)Metadata including method descriptions and Matlab code for PARAFAC modeling (Metadata and Matlab code.docx)The original EEMs read into Matlab, plus blank corrected and Raman area unit standardized EEMs (Xin.mat)The corrected EEMs after cropping and removal of scattering (Xcorr.mat)The graphical output of the split-half validation (Split-half.jpg)Contour plot images of the full model (PARAFAC_components.jpg)<b>References</b><br>Berggren M., S. Salimi, B. Sparkes, M. Scholz (2024), Climate impact on dissolved organic carbon composition in a north-temperate peatland and recipient surface water. <i>Journal of Geophysical Research - Biogeosciences</i>, ACCEPTED CONDITIONALLY.<br>Kothawala, D. N., K. R. Murphy, C. A. Stedmon, G. A. Weyhenmeyer, and L. J. Tranvik (2013), Inner filter correction of dissolved organic matter fluorescence, <i>Limnology and Oceanography-Methods</i>, 11, 616-630, doi:10.4319/lom.2013.11.616.Lawaetz, A. J., and C. A. Stedmon (2009), Fluorescence intensity calibration using the raman scatter peak of water, <i>Appl Spectrosc</i>, 63(8), 936-940, doi:Doi 10.1366/000370209788964548.Murphy, K. R., C. A. Stedmon, D. Graeber, and R. Bro (2013), Fluorescence spectroscopy and multi-way techniques. PARAFAC, <i>Anal Methods-Uk</i>, 5(23), 6557-6566, doi:10.1039/c3ay41160e.Salimi, S., M. Berggren, and M. Scholz (2021), Response of the peatland carbon dioxide sink function to future climate change scenarios and water level management, <i>Global Change Biology</i>, 27(20), 5154-5168, doi:10.1111/gcb.15753.Salimi, S., and M. Scholz (2021), Impact of future climate scenarios on peatland and constructed wetland water quality: A mesocosm experiment within climate chambers, <i>J. Environ. Manage.</i>, 289, 112459, doi:10.1016/j.jenvman.2021.112459.Salimi, S., and M. Scholz (2022), Importance of water level management for peatland outflow water quality in the face of climate change and drought, <i>Environ Sci Pollut Res Int</i>, 29(50), 75455-75470, doi:10.1007/s11356-022-20614-2.