Do current European lake monitoring programmes reliably estimate phytoplankton community changes?

Hydrobiologia, Nov 2017

Many European lakes are monitored according to the EU Water Framework Directive (WFD), with focus on phytoplankton biomass and species composition. However, the low-frequency WFD monitoring may miss short-term phytoplankton changes. This is an important issue because short-term extreme meteorological events (heat waves and heavy rain) are predicted to increase in frequency and intensity with climate change. We used records from Lake Mondsee (Austria) from 2009 to 2015 to test if a reduction from monthly to seasonal sampling affected the average annual phytoplankton biovolume. Furthermore, we combined inverted light microscopy, FlowCAM and flow cytometry to estimate the effect of sampling during extreme events on average phytoplankton biovolume. Relative to monthly sampling, seasonal sampling significantly overestimated phytoplankton biomass. A heat wave in 2015 and two episodes of heavy rain in 2015 and 2016 caused species-specific changes; biovolumes of chlorophytes and the filamentous cyanobacterium Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek increased significantly during the heat wave. Using live material with FlowCAM and flow cytometry, we detected small and fragile cells and colonies that were either ignored or underrepresented by analysing fixed samples with light microscopy. We suggest a modified sampling and analysis strategy to capture short-term changes within the phytoplankton community.

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Do current European lake monitoring programmes reliably estimate phytoplankton community changes?

Do current European lake monitoring programmes reliably estimate phytoplankton community changes? Victoria Bergkemper 0 1 . Thomas Weisse 0 1 0 Water Framework Directive Flow cytometry Lake Mondsee 1 V. Bergkemper (&) T. Weisse Research Department for Limnology, University of Innsbruck , Mondseestraße 9, 5310 Mondsee , Austria Many European lakes are monitored according to the EU Water Framework Directive (WFD), with focus on phytoplankton biomass and species composition. However, the low-frequency WFD monitoring may miss short-term phytoplankton changes. This is an important issue because short-term extreme meteorological events (heat waves and heavy rain) are predicted to increase in frequency and intensity with climate change. We used records from Lake Mondsee (Austria) from 2009 to 2015 to test if a reduction from monthly to seasonal sampling affected the average annual phytoplankton biovolume. Furthermore, we combined inverted light microscopy, FlowCAM and flow cytometry to estimate the effect of sampling during extreme events on average phytoplankton biovolume. Relative to monthly sampling, seasonal sampling significantly overestimated phytoplankton biomass. A heat wave in 2015 and two episodes of heavy rain in 2015 and 2016 caused species-specific changes; biovolumes of chlorophytes and the filamentous cyanobacterium Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Koma´rek increased significantly during the heat wave. Using live material with FlowCAM and flow cytometry, we detected small and fragile cells and colonies that were either ignored or underrepresented by analysing fixed samples with light microscopy. We suggest a modified sampling and analysis strategy to capture short-term changes within the phytoplankton community. - Guest editors: Nico Salmaso, Orlane Anneville, Dietmar Straile & Pierluigi Viaroli / Large and deep perialpine lakes: ecological functions and resource management Introduction Phytoplankton plays a key role at the base of pelagic food webs and its biomass and species composition are directly related to the trophic state of water bodies. Therefore, phytoplankton is one of the four biological quality elements used for the assessment of the ecological status of European surface waters according to the European Union Directive 2000/60/EC (EC, 2000) better known as Water Framework Directive (WFD). The primary aims of the WFD are the maintenance and recovery of water quality and to ensure good surface and groundwater status by 2027 at the latest (Arle et al., 2016) . The WFD requires that phytoplankton species composition, abundance and biomass are measured to assess the ecological status of lakes. Additionally, most EU countries use assessment procedures that evaluate phytoplankton taxa in relation to nutrient conditions. In Austria, several metrics are calculated, i.e. phytoplankton biovolume, Chlorophyll a concentrations and a modified Brettum Index; (Brettum, 1989; Dokulil et al., 2005; Wolfram et al., 2015) , which eventually result in the ‘Ecological Quality Ratio’ [EQR; (van de Bund & Solimini 2007)]. The EQR is constrained to values ranging from zero (the worst possible status) to 1 (excellent) and evaluates the current ecological status relative to a reference condition, i.e. an undisturbed, quasi-pristine status for the respective water body. The ‘normalised Ecological quality ratio’ (nEQR) is the mean value of the metric converted to a normalised EQR scale, where the classes are equally spaced (e.g. the boundary value between moderate and good status is always 0.6 and the boundary value between good and high status is always 0.8) (http://dd.eionet.europa.eu/ dataelements/latest/resultNormalisedEQRValue). The EU member states are requested by the WFD to set up monitoring programmes to provide sufficient data for reliably assessing the status of the relevant quality element. The measurement frequencies depend on the water category (e.g. streams and rivers, lakes), the biological quality element (e.g. phytoplankton, macroinvertebrates, fish), and on the ecological status of the water body under consideration. Consequently, the selection of quality elements and the frequency of monitoring vary greatly between the EU member states (Hering et al., 2010; Pasztaleniec, 2016) . The WFD differentiates between surveillance monitoring, operational monitoring and investigative monitoring. Surveillance monitoring is performed for all biological, hydromorphological and physical and chemical quality elements, and investigative monitoring is carried out if the status of the water body is lower than good. Operational monitoring is used for assessing the status of those water bodies at risk of failing to meet their environmental objectives, and it is the most widespread monitoring tool. For operational monitoring, the minimum requirement for phytoplankton listed in Annex V of the WFD is twice per year, but most member states apply higher sampling frequencies. (...truncated)


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Victoria Bergkemper, Thomas Weisse. Do current European lake monitoring programmes reliably estimate phytoplankton community changes?, Hydrobiologia, 2017, pp. 1-20, DOI: 10.1007/s10750-017-3426-6