EEMs and PARAFAC in North Patagonia (Argentina): adapting to a methodology in continuous progress

GARCIA P.E.; GARCIA R.D; SOTO CÁRDENAS, C.; GEREA M.; REISSIG M.; PÉREZ, G.L.; DIÉGUEZ M.C; QUEIMALIÑOS, C.P.

Carqueiranne

Workshop; International Workshop on Organic Matter Spectroscopy (WOMS); 2018

WOMS

AbstractThe study of the fluorescent dissolved organic matter in Northwestern Patagonia through excitation emission matrices (EEMs) by our research group started in 2012. The first paper that we published using EEMs included six mountain lakes.The peak picking method was used due to the low number of EEMs collected, and three peaks were identified (Peak C, Peak A and Peak T) (García, P. et al., 2015a) (Figure 1). In this study, we deal not only with the low number of EEMs to perform PARAFAC analyses, but also low fluorescence was found in some samples. The next research deals with the terrestrial inputs of DOM in four headstreams in North Patagonia (García, R. et al., 2015b). In this opportunity, we were able to perform PARAFAC on 120 EEMs and a three-component model was validated through slit-half and random initialization (Figure 2). Two components were humic-like: C1 (peak A+ peak M) and C2 (peak A + peak C), and one was protein-like: C3 (peak T). This study highlighted the used of PARAFAC in order to identify underlying components such as C1 (A+M), that were not taken in consideration in the previous study. Continuing with the use of PARAFAC, we performed the analysis in samples on two neighboring shallow lakes during rainyand dry seasons (Soto Cárdenas et al., 2017). We collected 44 EEMs and, similar to previous findings, three-component model was validated: C1 (A+M), C2 (A+C) and C3 (T). At this point, we were almost convinced that only a three-component model could be achieved in the aquatic systems in our region. In order to identify different sources of DOM for a small catchment area, our research group performed experiments using DOM leached from soil and leaf litter. At this time, PARAFAC validated a four-component model (Figure 3) (García, R. et al., 2018) The first three components were previously found in different lakes and streams from the area, while C4 showed up as a new component. The C4 was composed of humic substances and resembles a "shifted" peak M. This component prevailed only in samples of leaf lecheates, reason why it was called Mleaf. This scientific contribution highlighted that DOM quality is affected by different sources and processes acting simultaneously and that must be taken into account when performing PARAFAC analysis.Evidently, PARAFAC is a useful tool to identifying fluorophores and at least three components were consistent through the freshwater DOM in North Patagonia. However, every dataset produces a unique set of components, making difficult to compare results across studies. Therefore, a combination of PARAFAC and peak picking seems to be the most conservative measurement in order to compare different types of environments in the same region. Consequently, we must use them carefully, particularly when we include in the analysis the DOM sources and different types of environments. Finally, we leave open for discussion which peaks should be "picked". References -Coble P.G. (1996) Characterization of marine and terrestrial DOM in seawater using excitation-emission matrix spectroscopy. Mar. Chem. 51, 325?46. -García, P.E., Diéguez, M.C., and Queimaliños, C.P. (2015) Landscape integration of North Patagonian mountain lakes: a first approach using characterization of dissolved organic matter. Lakes & Reserviors: Research and Managements 20(1), 19-32. -García, R.D., Reissig, M., Queimaliños, C.P., García, P.E., and Diéguez, M.C. (2015) Climate-driven terrestrial inputs in ultraoligotrophic mountain streams of Andean Patagonia revealed through chromophoric and fluorescent dissolved organic matter. Science of the total environment 521-522, 280-292. -Soto Cárdenas, C., Gerea, M., García, P.E., Perez, G.L., Diéguez, M.C., Rapacioli, R., Reissig, M., and Queimaliños, C.P. (2017) Interplay between climate and hydrogeomorphic features and their effect on the seasonal variation of dissolved organic matter in shallow temperate lakes of the Southern Andes (Patagonia, Argentina): a field study based on optical properties. Ecohydrology, e1872. -García, R.D., Diéguez, M.C., Gerea, M., Garcia, P.E., and Reissig, M. (2018) Characterisation and reactivity continuum of dissolved organic matter in forested headwater catchments of Andean Patagonia. Freshwater Biology 10.1111/fwb.13114.