Riparian vegetation condition is associated with invertebrate assemblage composition in intermittent and humic streams

Abstract

Riparian vegetation is known to provide environmental benefits for aquatic ecosystems and is commonly used in the restoration of agricultural catchments. However, little information exists on the influence of riparian vegetation on the fauna of intermittent or humic (coloured) streams. We examined the ecological condition of riparian vegetation and its influence on stream fauna amongst humic and non-humic intermittent and perennial stream reaches in the Ellen Brook catchment, south west Western Australia. Permutation-tests showed that flow regime (Global R = 0.444, P < 0.001) and the presence/absence of riparian vegetation (Global R = 0.407, P < 0.001) were the most influential factors associated with invertebrate assemblage composition. Riparian vegetation influenced invertebrate assemblages through the provision of organic matter for food and habitat, and by shading stream channels, thereby limiting light and algal growth. This was illustrated by a higher proportion of algal grazers (Chironominae and Physidae) in unvegetated streams and more detritivores (Leptoceridae, Gripopterygidae, Ceinidae) in vegetated streams. Humic intermittent streams showed different invertebrate assemblages to non-humic intermittent streams; having fewer Cladocera and Chironomidae and more grazing gastropods (Physidae and Lynceidae). A significant proportion of the variation in invertebrate assemblages was associated with stream width, salinity and NOx-N concentrations because intermittent streams were narrower, more brackish and less enriched than with nitrogen than perennial streams. Riparian vegetation benefited invertebrate assemblages in all stream types, showing that revegetation is as effective a restoration action in intermittent and humic streams as it is in perennial streams.