Effects of urbanization-induced local alterations on the diversity and assemblage structure of macroinvertebrates in low-order streams

Urbanization is one of the most serious threats to stream ecosystems worldwide. It is crucial to understand its effects on stream organisms as a prerequisite for the mitigation of urban degradation. Our aim was to investigate the general effects of urbanization in a moderately urbanized landscape and to assess the relationship between local environmental variables and biotic attributes of macroinvertebrate assemblages. Multiple sites at low-order streams flowing from natural forested areas to moderately urbanized landscapes were surveyed. We found that local habitat properties presented degraded conditions at urban sites. Urbanization had a negative effect on the richness and Shannon diversity of macroinvertebrate assemblages, and altered assemblage composition. Biotic assemblage parameters showed negative, neutral or positive relationships with local physical parameters. Concrete cover was one of the most important variables, which explained a decreasing richness and diversity of macroinvertebrates. In natural conditions, microhabitat-level environmental variables significantly impacted community variation, while in degraded conditions microhabitat and site-level environmental variables had a substantial impact together. Individual streams showed considerable variability under natural conditions, as well as in their response to urban effects. Subsequently, the mitigation of the effects of urbanization might also need considerable variability in the type of actions required.