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This paper describes the application of a methodology, which primarily involves low-cost voltammetry, to rapidly track the reactivity (i.e. surfactant activity, SA) of dissolved organic carbon (DOC) in aquatic systems. The approach is based on the quantitative measurement of total surface activity (expressed as Triton-X-100 equivalent) of adsorbing organic compounds (AOCs) of amphiphilic and/or hydrophobic nature at the mercury electrode/electrolyte interface in natural water samples using phase-sensitive (out-of-phase) alternating current voltammetry (PSACV). The SA results were normalized to the DOC content. A graphical representation of DOC-normalized SA for different water systems allows a rough characterization and comparison of the DOC type at different scales (spatial, seasonal, temporal short- and long-term) and in extreme natural events such as different hydrological, meteorological, biological, and physical processes. The main idea is to demonstrate the capabilities of PSACV in the study of DOC in water systems. The presented methodology could be used in future research and monitoring studies, as PSACV is the only practical method available for the determination of surface active DOC in natural waters. [ABSTRACT FROM AUTHOR]

Organic matter (OM) has numerous geochemical and ecological functions in inland waters and can affect water quality. Different parameters of aquatic OM are measured with various methods as no single analytical tool can provide definitive structural or functional information about it. In the present paper we review different OM metrics used in the European Union (EU) lake surveillance monitoring programmes and assess their suitability to provide sufficient data about the brownification and enrichment with oxygen consuming substances in European lakes. In the EU Water Framework Directive (WFD), metrics of OM are not mandatory physico-chemical parameters, but only recommended parameters to characterize water transparency, oxygenation conditions or acidification status. Our analysis shows that, as lake OM is monitored under the WFD in only 14 countries, no Europe-wide conclusions on the situation regarding brownification and organic enrichment can be drawn based on these data. Applied parameters in lake surveillance monitoring programmes are biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), dissolved organic carbon (DOC), water colour (WCol), and yellow substance. Different national OM metrics used avoid getting a broad picture of lake OM concentration changes in Europe over the last decades. Furthermore, our results demonstrate that the possibilities to convert different OM parameters to each other are limited because empirical relationships between them are region-specific. OM sensors for continuous measurements and remote sensing surveys could improve the effectiveness of lake OM monitoring, especially its temporal and spatial representativeness. It would be highly suggested to include in lake monitoring programmes also methods (e.g. absorbance or fluorescence spectroscopy) allowing to characterize the composition of OM as it influences strongly the biogeochemical role of OM in lakes. [ABSTRACT FROM AUTHOR]