DOI: 10.2478/v10104-011-0003-x Vol. 10 No. 2-4, 347-354 2010 Ecohydrology for water ecosystems and society in Ethiopia RNA/DNA ratio as an indicator of the impact of long-term accumulative contamination for the assessment of river degradation – a pilot study. Mankiewicz-Boczek Joanna 1,2* , Kaczkowski Zbigniew 2 , Godowska Maja 1 , Maciej Zalewski 1,2 1 International Institute PAS – European Regional Centre for Ecohydrology under auspices of UNESCO, 3 Tylna Str., 90-364 Łódź, Poland * e-mail: j.mankiewicz@erce.unesco.lodz.pl 2 Department of Applied Ecology, University of Łódź, 12/16 Banacha Str., 90-237 Łódź, Poland Abstract To improve our understanding of the hierarchy of human induced modifications of the natural environment, with particular regard to the controlling strength of the habitat or chemical impacts, it was found to be appropriate to employ indicators at a molecular level. This paper examines the potential use of the analysis of the RNA/DNA ratio for the evaluation of the ecological status of two rivers of Central Poland. The study confirmed that analysis of the RNA/DNA ratio has the potential to be a sensitive indi- cator of river degradation. It is also a useful screening method for the evaluation of the impact of prolonged sub-lethal contamination of freshwater ecosystems dominated by tolerant fish species such as the perch, Perca fluviatilis L. Key words: nucleic acid, Perca fluviatilis L., water quality, ecohydrology. 1. Introduction The determination of good ecological status, as required by the European Water Framework Di- rective (WFD), includes both the chemical and bio- logical quality of waters. Freshwater ecosystems are subject to the whole range of impacts related to human population density (Wagner, Zalewski 2009). As a result, sustainability is most likely to be achieved using advanced integrated scien- ce approaches, such as Ecohydrology (Zalewski 2000, 2006). As most of the natural environment is now modified it is often difficult to decide to what extent the observed modification of animal and plant communities is due to habitat degrada- tion and how much to the effect of pollution. This is especially true in respect of the eurytopic and tolerant fish species that are usually dominant in the modified habitats of the “Anthropocene” world (Oberdorff, Hughes 1992; Meybeck 2003). To im- prove our understanding of the hierarchy of human induced modifications with regard to the control- ling strength of the habitat or chemical impacts, more sensitive indicators at the molecular level were tested in this study. The usefulness of the RNA concentration as an indicator of the growth of fish was established by Bulow (1970). Generally, the quantity of RNA is high in rapidly growing organisms (Bergeron 1997; Buckley et al. 1999) and any factors pre- venting or slowing growth are reflected by a reduc- tion in the quantity of RNA (Islam, Tanaka 2005). Growing organisms synthesize and accumulate the RNA needed for protein synthesis, whilst the quantity of DNA in most animal cells is believed to remain stable (Buckley et al. 1999). Conse-