Assessment and monitoring of lakes in Europe

Different Biological Quality Elements (BQEs) are being used to assess the ecological status of lakes in Europe: fish, benthic invertebrates, macrophytes/phytobenthos and phytoplankton. The different responses of these BQEs to different stressors require the use of several BQEs in order to assess the multiple impacts by multiple stressors (Table 1). In brief:

• Phytoplankton and macrophytes show strong responses to eutrophication pressure.
• Littoral benthic invertebrates clearly respond to morphological shoreline degradation, and macrophytes to water level fluctuations.
• Fish assemblages show less clear signals to individual pressures, but may be good indicators of climate warming.

  Table 1

Phytoplankton is highly sensitive to eutrophication pressure, based on the statistical analyses using all regional data sets (Table 2). The best common metric, with high sensitivity, is the Phytoplankton Trophic Index, which includes both taxonomic composition data as well as chlorophyll a. These two metrics have been combined into a common metric for the intercalibration of phytoplankton methods with successful results in both the Northern GIG and the Central-Baltic GIG. Cyanobacterial blooms are common in all eutrophied lakes across Europe. The risk that the WHO health alert threshold for cyanobacteria biovolume (1-2 mg/l) would be exceeded is 10% at a total-P concentration of 20 µg L-1 and 30% at 40 µg L-1.

The best metric for macrophytes indicating eutrophication pressure is the intercalibration common metric for taxonomic composition (ICM; Table 2), which has also been used for intercalibrating macrophyte methods in the same GIGs.

Other metrics for phytoplankton and macrophytes responding to eutrophication have also been tested within WISER, such as cyanobacteria abundance and macrophyte growing depth. These metrics also show highly significant relationships with nutrient pressures and may be easier to communicate to the public and water managers. A shift from macrophytes to cyanobacteria highlights an important functional shift that can greatly affect the use of freshwaters for recreation, swimming or as a reservoir for potable water.

Macrophytes also responded clearly to hydromorphological pressure, in terms of water level fluctuations in regulated lakes in the Northern countries. The macrophytes water level fluctuation index (Wlc) has a clear threshold response concerning the indicator taxa e.g. Isoetes corresponding to ca. 3.5 m water level fluctuations. Thus, this metric is a very promising tool to define ecological potential in heavily modified water bodies.

Littoral macroinvertebrates respond clearly to modification and degradation of shoreline habitats in lakes. Two new multimetric indexes have been developed within WISER, including several single metrics, such as the number of taxa of mayflies, stoneflies, caddisflies, water beetles, mussels, dragon-flies, relative abundance of the functional groups like gatherers or collectors, or classes of chironomids, and Margalef diversity. Number of Macroinvertebrate species and fraction of individuals feeding on particulate organic matter were lower at both intermediately and strongly modified lake margins than at unmodified margins in 64% of 44 lakes. Another multimetric index based on littoral macroinvertebrates also responds to a combination of pressures from eutrophication and morphological modifications (Table 2).

For fish, the best metrics to assess eutrophication impacts are biomass per unit effort (BPUE) (r² = 0.19), catch per unit effort (CPUE) (r² = 0.18) and relative number of omnivorous individuals (OMNI) (r² = 0.18), but none of these have been used for the final stage of intercalibration of national methods. Fish has however been shown to respond to climate warming with cold-water species like arctic char being pushed further north and towards higher altitudes, while warm-water species like many cyprinids increase in dominance and widen their biogeographical range. Warm lakes were dominated by small-sized individuals, whereas in cold lakes the relative proportion of large-sized fish increased. The dominance of small fish in warm lakes was primarily the consequence of an increase in juvenile fish.

  Table 2

Operational monitoring and assessment of ecological status in lakes should be based on the most sensitive quality elements to different pressures. WISER evidence supports that the botanical BQEs (phytoplankton and macrophytes) are well suited to assess lake eutrophication impacts. Effects of measures to restore eutrophied lakes can only be seen when the total phosphorus concentration is reduced to less than 100 µg/l. For hydromorphological pressure, macrophytes respond well to water level fluctuations in northern regulated lakes and may thus be used as a tool to set environmental goals for heavily modified water bodies. Littoral macroinvertebrates have been shown to sensitively assess impacts of morphological alterations to lake shores. Fish should be monitored to assess impacts of climate warming.

More detailed analysis and results are being presented in various deliverables and are available for download in our results & deliverable section.

Brauns, M., Garcia, X.-F., N. Walz & M.T. Pusch 2007. Effects of human shoreline development on littoral invertebrates in lowland lakes. Journal of Applied Ecology, 44, 1138-1144

Emmrich, M., Brucet, S., Ritterbusch, D., Mehner, T., 2011. Size spectra of lake fish assemblages: responses along gradients of general environmental factors and intensity of lake-use. Freshwater Biology 56: 2316-2333

Kolada A, Hellsten S, Søndergaard M, Mjelde M, Dudley B, van Geest G, Goldsmith B, Davidson T, Bennion, H, Nõges P & Bertrin V, WISER Deliverable D3.2-3: Report on the most suitable lake macrophyte based assessment methods for impacts of eutrophication and water level fluctuations. March 2011.

Mischke U, Carvalho L, McDonald C, Skjelbred B, Lyche Solheim A, Phillips G, de Hoyos C, Borics G, Moe J & Pahissa J. 2011. WISER Deliverable D3.1-2: Report on phytoplankton bloom metrics, March 2011

Caussé, S., Gevrey, M., Pédron, S., Brucet, S., Holmgren, K., Emmrich, M., De Bortoli, J. and Argillier, C. 2011: Fish indicators for ecological status assessment of lakes affected by eutrophication and hydromorphological pressures. WISER Deliverable D3.4-4, September 2011.

Phillips G, Skjelbred B, Morabito G, Carvalho L, Lyche Solheim A, Andersen T, Mischke U, de Hoyos C & Borics G. 2010. WISER Deliverable D3.1-1: Report on phytoplankton composition metrics, including a common metric approach for use in intercalibration by all GIGs, Aug 2010.

Jeppesen, E., Meerhoff, M., Holmgren, K., Gonzalez-Bergonzoni, I., Teixeira-de Mello, F., Declerck, S.A.J., De Meester, L., Søndergaard, M., Lauridsen, T.L., Bjerring, R., Conde-Porcuna, J.M., Mazzeo, N., Iglesias, C., Reizenstein, M., Malmquist, H.J., Liu, Z., Balayla, D. and Lazzaro, X., 2010. Impacts of climate warming on lake fish community structure and potential effects on ecosystem function. Hydrobiologia (2010) 646: 73-90.