Do organic matter metrics included in lake surveillance monitoring in Europe provide a broad picture of brownification and enrichment with oxygen consuming substances?

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 met- rics 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 con- ditions or acidification status. Our analysis shows that, as lake OM is monitored under the WFD in only 14 coun- tries, 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 ox- ygen 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 pic- ture 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.This research was supported by Estonian Ministry of Education and Research through the institutional project IUT 21-2 and personal research grant PUT777, by the MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), Contract No.: 603378 (http://www.mars-project.eu), by Estonian Science Founda tion grant ETF9102 and by national scholarship program Kristjan Jaak, which is funded and managed by Archimedes Foundation in collaboration with the Ministry of Education and Research.This research was supported by Estonian Ministry of Education and Research through the institutional project IUT 21-2 and personal research grant PUT777, by the MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), Contract No.: 603378 (http://www.mars-project.eu), by Estonian Science Foundation grant ETF9102 and by national scholarship program Kristjan Jaak, which is funded and managed by Archimedes Foundation in collaboration with the Ministry of Education and Research