Salinization consequences in running waters : the use of a ‘sentinel substrate' as bioassessment method

Salinization has been disturbing increasing numbers of inland waterways, and new analytical tools are needed to survey water quality and to assess the impact of salinization. Researchers have developed new protocols that reduce the number and type of samples required to reduce the cost of existing assessment methods. Our study contributes to this effort with the primary objective of identifying a single, unique river-bottom substrate that could be sampled to detect the impact of rising salinity on macroinvertebrate assemblages. We hoped to define a new concept of sentinel substrate, a substrate with an invertebrate assemblage that would signal an environmental impact (in this case increasing salinity) and that could be used at the site scale to assess that impact. We worked on the Meurthe River, which presents a significant salinity gradient (from 0.2 to 2.6 g/L) over a 19-km section of river in which all other physicochemical variables remain stable. We sampled substrates present at each of 4 sites along the salinity gradient in 2002 and described the effects of rising salinity on the structure (richness, diversity, and dominance) of the macroinvertebrate assemblage in each substrate type. Only the assemblage in pebbles adequately reflected site-level responses. Moreover, only assemblages in pebbles satisfied important criteria such as widespread availability, low variability among seasons, and high invertebrate diversity