Organic matter in the bulk precipitations in Zagreb and Šibenik, Croatia

Dissolved organic carbon (DOC), surface active substances (SAS) and copper complexing capacity (CuCC) were studied in bulk precipitations collected periodically from 2003 to 2007 in the continental city of Croatia (Zagreb: n = 27) and in the city at the Adriatic coast (Šibenik: n = 38). DOC concentrations (Zagreb: 0.67–4.03 mgC/L with average concentration of 1.93 ± 0.76 mgC/L; Šibenik: 0.44–4.13 mgC/L with average concentration of 1.83 ± 0.83 mgC/L) are similar to those measured in other samples of continental rainwater in the northern hemisphere. The concentrations of SAS in samples from Zagreb ranged from 0.055 to 0.45 eq. Triton-X-100 mg/L with average concentration of (0.14 ± 0.06) eq. Triton-X-100 mg/L. SAS fractions were of a similar range in Šibenik (0.02–0.60 eq. Triton-X-100 mg/L) with an average concentration of 0.11 ± 0.06 eq. Triton-X-100 mg/L. However, the lowest values of SAS (between 0.02 and 0.04 eq. Triton-X-100 mg/L) were observed only in Šibenik (27%). We have estimated that the higher pH values were responsible for lower surface activity of organic matter in bulk samples from Šibenik. DOC may form complexes that control the transport and solubility of heavy metals in natural water. CuCC measured in Šibenik in the range 0.066–1.4 μM Cu2+ was in general higher, compared to the one in Zagreb (0.010–0.586 μM Cu2+) which is the result of biogenically driven organic contribution to the precipitation, especially in the warmer period of the year.