Supplement of Drivers of CO2 emissions during the dry phase in Mediterranean and Temperate ponds

Table S1. Summary of CO2 fluxes by season. For each pond, the table shows the mean ± standard deviation (SD) of CO2, the observed range ( maximum to minimum) values and the number of samples (N). -- Table S2. Comparison of environmental variables between climate regions. Results of Mann–Whitney U tests comparing the distributions of values between Mediterranean and Temperate ponds. Statistically significant differences (p < 0.05) are highlighted in bold. -- Figure S1. Relationship between sediment water content, temperature and CO2 fluxes. The plot shows the standardized relationship between sediment temperature and water content with CO2 fluxes during the dry phase. Each point represents an individual observation, colour-coded by variable (orange = sediment temperature and blue = water content). Fitted quadratic regression lines depict the non-linear trends in the data. -- Figure S2. PARAFAC-extracted components of dissolved organic matter by season (summer and autumn). C1 represents terrestrial humic-like substances (yellow), C2 humic-like (blue), and C3 tryptophan-like substances (green). -- Figure S3. ANOVA results for dissolved organic matter components by climate regions (a) and seasons (b). C1 = terrestrial humic-like (yellow), C2 = humic-like (blue), and C3 = tryptophan-like (green). Asterisks (**) indicate significant differences between groups, p < 0.01; n.s. denotes non-significant differences. -- Figure S4. Scatterplots with fitted linear regressions (dashed lines) and 95% confidence intervals (grey shaded areas) showing the relationship between hydroperiod length and the concentration of three DOM components: C1 = terrestrial humic-like (yellow), C2 = humic-like (blue) and C3 = tryptophan-like (green). Each dot represents an individual pond measurement. -- Figure S5. Relationship between CO2 fluxes and the relative concentration (%) of fluorescent DOM components, grouped as terrestrial humic-like, humic-like, and tryptophan-like compounds. Each point represents the average CO2 flux from a pond during the dry phase (summer or autumn). Lines show linear regressions with 95% confidence intervals (shaded areas), with blue indicating summer data and orange indicating autumn. Asterisks above each panel denote the significance of the interaction between component concentration and season on linear models: *** p < 0.001; * p < 0.05, n.s. denotes nonsignificant differences. -- Figure S6. Principal Component Analysis (PCA) showing the distribution of ponds and the main environmental variables driving their separation. Points are coloured by country: Spain (yellow), Denmark (blue), Germany (green) and Belgium (orange), as indicated in the legend. Ellipses represent the confidence intervals for the climate groups: Mediterranean (orange) and Temperate (green). Each dot corresponds to an individual pond measurement. -- Figure S7. Excitation-Emission Spectra (EEM) of the dissolved organic matter components (C1, C2, C3) identified through PARAFAC analysis. -- Table S3. Tucker congruence coefficients (TCC = 0.99) with published spectra from OpenFluor.org, including matching PARAFAC models and the corresponding components from related studies. -- Table S4. Fluorescence peaks of dissolved organic matter location and classification by Coble (1996). -- Table S5. Fluorescence components of dissolved organic matter: chemical interpretation and sources. -- References