Spatial and temporal variability of stable isotopes and biological parameters for the Danube River in Serbia

This paper presents the results of hydrological, physicochemical, biological, and isotopic investigations of the Danube River along the stretch through Serbian territory conducted during four campaigns in September and November 2007, September 2008 and April 2009. The stable isotope values exhibited significant changes both in the Danube (−10.7 to−9.5‰ for δ18O and−73.7 to−67.1 ‰ for δ2H) and in its tributaries (−9.1 to−8.5‰ for δ18O and−69.4 to−59.4‰ for δ2H) depending on the time of survey, which could be partly attributed to the influences of seasonal effects. Results emphasise the dominant role of tributaries inflows from aquifers along the Danube. The very narrow range of δ13CPOC (from−28.9 to−27.4 ‰) was associated with relatively high C/N ratios (C/N>9), and together with δ15NTPN values, the date suggested that, in early spring, a major fraction of particulate organic matter was derived from allochthonous matter. An orthogonal varimax rotation of the principal components analysis identified four la...