Voltammetric study of organic matter components in the upper reach of the Krka River, Croatia

The increased amount of organic matter (OM) accompanied with the development of hypoxia/anoxia and appearance of the sulphur species are indicators of eutrophication in natural waters. To predict biogeochemical and ecological changes, specific OM components in the Lake Brljan (the karst Krka River, Croatia ; station B and station B2 downstream) were studied during 2011 and in January 2012 using voltammetry. Surface‒active substances (eq. 0.018 to 0.150 mg dm-3 Triton‒X‒100) and Cu complexing capacity (54‒680 nmol dm-3) showed the highest values in surface water layer in May 2011 (B) and in November 2011 (B2), associated with the highest dissolved (0.505‒ 1.530 mg C dm-3) and particulate (0.051‒0.725 mg C dm-3) organic carbon and phytoplankton biomass. Autochthonously produced OM did not cause hypoxia/anoxia during the investigated period. Brljan's lake water could be characterised as oligotrophic with occasionally elevated OM concentration depending on season and Krka River water regime.