North South Shared Aquatic Resource

Assessing ecological quality of standing waters under the European Water Framework directive (2000/60/EC) requires inclusion of biological elements. For all surface waters this includes the “composition and abundance of benthic invertebrate fauna”. The use of benthic macroinvertebrates in river monitoring has a long tradition and is used routinely in many countries (Hellawell 1986; Metcalfe 1989; Rosenberg and Resh, 1993; Mason, 1996; Maitland, 1997). This reflects a view that invertebrates comprise a large number of species with a spectra of responses to environmental stresses; are principally sedentary, allowing effective spatial analyses of pollutants or disturbances; and have long life cycles conducive to assessment of short-term temporal disturbances (Reice and Wohlenberg, 1993). As well as direct toxic effects, invertebrate community structure can change with the addition of a pollutant at a sub-lethal concentration because of reduced competition, decreased resistance to predation and lowered reproductive success for the more sensitive organisms (Metcalfe, 1989). The tradition of including, or indeed relying, on metrics of the macroinvertebrate community for river monitoring programmes stems principally from a well established response to organic enrichment (Mason, 1996). In comparatively recent times this has included an assumed response to more general nutrient enrichment, as implicated from the use of BMWP water quality indices in the development of RIVPACS (River InVertebrate Prediction and Classification System) (Wright, 2000). In contrast to rivers, ecological assessment of lakes has focussed mainly on the response of open-water phytoplankton (usually measured as concentrations of chlorophyll a) to nutrient (mainly phosphorus) enrichment (O.E.C.D., 1982) and, to a lesser extent, that of profundal or sub-littoral invertebrate communities (Thienemann, 1931; Naumann, 1931; Saether, 1979; Lauritsen et al., 1985; Lang and Reymond, 1993, 1996; Dinsmore et al., 1999). The use of the profundal communities for lake assessment was the subject of an earlier review under NS Share and the profundal per se will not be addressed further in this review, other than where relevant to a particular point that is made in relation to the use of the littoral or sub-littoral fauna for lake assessment. Littoral invertebrates have also been used as a component in the assessment of acidification (Fjellheim and Raddum,