Original scientific paper
https://doi.org/10.15255/KUI.2026.006
Determination of Organic Matter Content in Surface Waters in Varaždin County
Anita Ptiček Siročić
; University of Zagreb Faculty of Geotechnical Engineering, Hallerova aleja 7, 42 000 Varaždin, Croatia
*
Mladen Šiljeg
; University of Zagreb Faculty of Geotechnical Engineering, Hallerova aleja 7, 42 000 Varaždin, Croatia
Dijana Begić Šinjori
; Institute of Public Health Varaždin, I. Meštrovića 1/11, 42 000 Varaždin, Croatia
* Corresponding author.
Abstract
Key parameters for assessing the level of surface-water pollution include total organic carbon (TOC), potassium permanganate consumption (KMnO₄), and biochemical oxygen demand (BOD₅), as they provide insight into the quantity and nature of organic matter present, as well as its impact on oxygen consumption in the aquatic ecosystem. In this study, surface water samples were analysed at five different locations in Varaždin County from April 2023 to March 2024, monitoring the seasonal variability of these organic loading indicators. The results indicate increased organic loading during the summer months, with the highest TOC values recorded at the Lonja (14.3 mg l⁻¹) and Ljuba voda (16.7 mg l⁻¹) sites. The seasonal dynamics of BOD₅ and KMnO₄ consumption suggest a mixed origin of organic pollution, the intensity of which increases during the warmer part of the year due to enhanced biological activity and runoff from surrounding surfaces. The BOD₅/TOC ratios at the Korušćak (0.65) and Presečno (0.64) locations indicate a predominance of biodegradable organic matter, which is consistent with the occasional increases in BOD₅ during the summer months when enhanced biological activity accelerates the transformation of the organic load.
Keywords
surface waters; organic load; total organic carbon (TOC); biochemical oxygen demand (BOD₅); potassium permanganate
Hrčak ID:
351410
URI
Publication date:
13.11.2026.
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