change in both the concept of water quality and its assessment throughout Europe. It has started a shift from the mindset of Europe’s water resource being a product which may be monitored chemically to ensure its suitability for human use to one that regards water as a heritage. A more holistic assessment by member states of functioning and structure of aquatic ecosystems is now legally required, which include the following biological elements: fish, phytoplankton, macrophytes and phytobenthos and benthic macroinvertebrates (Irvine et al. 2002; Heiskanen et al. 2004). For member-states this represents a highly complex task, as traditionally national and regional monitoring programs included only a subset of these elements.
Benthic invertebrates play an essential role in key processes within lake ecosystems (food chain dynamics, productivity, nutrient cycling and decomposition: Reice & Wohlenberg 1993). Benthic invertebrates form an important link between primary producers, detrital deposits and higher trophic levels in aquatic food webs (Brinkhurst 1974, Stoffels et al 2005). Hence,, any environmental changes in lakes, for example in nutrient concentrations, would be reflected by changes in the structure of the benthic invertebrate community (Carvalho et al. 2002). This means that benthic invertebrates may potentially indicate eutrophication, as planktonic communities, but in addition several other modes of lake degradation (see chapter 2). In consequence, the more holistic assessment based on benthic invertebrates is expected to result in different classifications than that based on planktonic communities, especially for lakes subjected to multiple impacts. The study of benthic invertebrates in lakes is traditionally segregated by depth zone: littoral, sub-littoral and profundal, see table 1, as these zones are generally colonized by distinct communities, which also respond in different ways to specific impacts on lakes (see next chapter)..
Recent extensive reviews of the current state-ofthe- art of ecological water quality assessment systems in Europe have revealed that, while practical (and WFD-compliant) assessment tools using macroinvertebrate parameters are already in use to assess the ecological quality of rivers, in many European countries there are currently no working macroinvertebrate assessment systems for lakes (Cardoso et al. 2005, Nõges et al. 2005).
Indeed, this has been recently identified as one of the major ecological ‘knowledge gaps’ impeding the full assessment of ecological quality of lakes as required by the WFD in a literature review carried out within the EU project REBECCA1 (Heiskanen and Solimini 2005). The current lack of knowledge is also limiting the fulfillment of the EU-wide intercalibration of the lake ecological quality assessment systems in Europe, and thus compromising the basis for setting the environmental objectives as required by the WFD, particularly concerning quantification of the ecosystem impacts of nutrient loading pressures (i.e. eutrophication), which is the most wide-spread pressure on surface water ecological quality in Europe (EEA, 2003).