Data for: TIME RESOLVED DATA UNVEILS THE COMPLEX DOM DYNAMICS IN A MEDITERRANEAN RIVER
The dataset includes information on dissolved organic matter concentration (DOC) and quality (CDOM, FDOM) in the Arno River (Italy) in 2014 and 2015, together with water temperature and river discharge on the sampling dates. Weekly samples were collected from a station located in the lower part of the river, the closest point to the mouth, not influenced by seawater. Methods: Surface (upper 1m) water samples were collected in the center of the river from a bridge using an acid-washed Teflon sampler. Water temperature was measured by a portable Hanna 9033 probe (Hanna Instruments Inc., USA); Daily average river discharge are available from the Regional Hydrological Service (www.sir.toscana.it); Samples for DOM analyses were collected into acid-washed polycarbonate bottles (Nalgene) and kept refrigerated and in the dark until filtration. Samples were filtered through a 0.2 μm pore size filter (Whatman Polycap, 6705-3602 capsules) and dispensed into 3 x 60 ml acid-washed polycarbonate (Nalgene) bottles, used as analytical replicates. DOC, CDOM, and FDOM were immediately measured after filtration. DOC was measured by high-temperature catalytic oxidation using a Shimadzu Total Organic Carbon analyzer (TOC-Vcsn). The instrument performance was verified by comparison with DOC Consensus Reference Waters (Hansell, 2005) (CRM Batch #13 nominal concentration of 41-44 μM; measured concentration 42.3 ± 0.9 μM, n=88) Absorbance spectra (230 to 700 nm) were measured using a Jasco UV-visible spectrophotometer (Mod-7850) with a 10 cm quartz cuvette. Fluorescence excitation-emission Matrixes (EEMs) were obtained using the Aqualog spectrofluorometer (Horiba). Excitation ranged between 250 and 450 nm at 5 nm increment, emission was recorded between 212 and 620 nm every 0.8 nm with an integration time of 5 seconds. The EEMs were subtracted by the EEM of Milli-Q water and corrected for the inner-filter effect. Rayleigh and Raman scatter peaks were removed by using the monotone cubic interpolation and EEMs were normalized by the integrated Raman band of Milli-Q water (λex= 350 nm; λex= 371-428 nm). PARAFAC analysis (drEEM Toolbox) resulted in a 5-component model. Samples for Heterotrophic Prokaryotes Abundance (HPA) were fixed for 10 min with a mix of paraformaldehyde (PF, 1%) and glutaraldehyde (GL, 0.05%), frozen in liquid N2 and stored at -80 °C until the analysis. Once thawed, samples were stained with SYBR Green (Invitrogen Milan, Italy) 10-3 dilution of stock solution for 15 min at room temperature. Heterotrophic prokaryotes (HP) cell concentrations were estimated using a FACSVerse flow cytometer (BD BioSciences Inc, Frankyn Lakes, USA) equipped with a 488 nm Ar laser and standard filter set. Data analysis was performed using the FCS Express software and HP discriminated from other particles based on scatter and green fluorescence from SYBR Green.