S.K. Mantel and N.W.J. Muller (South Africa)
Caseless versus cased caddisflies, reduced low flows, environmental water quality, instream flow needs
This paper investigates the cumulative impacts of small dams on trichopteran larvae in foothill-gravel streams of two South African regions – Western Cape and Mpumalanga. Previous research by the authors found reduced river discharge during low flow periods and an increase in total dissolved salts at sites with large number of small dams in their catchment. Additionally, a decrease in Average Score per Taxon (an indirect measure of river health based on invertebrate families) was noted and further analyses confirmed differences in invertebrate communities. Regional differences were noted for trichopteran taxa that were absent at sites with high level of small dam impact in the Western Cape, but were less affected in Mpumalanga. This might reflect the regional differences in climate as the Western Cape is a temperate winter rainfall region in contrast to Mpumalanga which is a tropical summer rainfall area. Additional variation in taxon specific response to water quantity, quality and possibly habitat modification were noted. This paper investigates the observed differences in the context of our ecological knowledge of caddisfly families (cased versus caseless) and suggests future areas of research including development of a diagnostic biotic index to distinguish small dam impacts from other forms of anthropogenic impacts.
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