Small settlements structure the taxonomic and functional organisation of stream-dwelling chironomid assemblages in a rural landscape

Studies examining the effect of populated areas on streams are mainly focusing on densely populated towns and cities, while that of small settlements is less understood. This study evaluated the influence of small rural settlements on the taxonomic and functional organisation of chironomid assemblages in low-order streams of the Lake Balaton region (Hungary). Environmental variables and chironomid assemblage attributes were compared between unaffected upstream, settlement, and downstream sections in eight streams. Both stream habitat properties and chironomid assemblages changed between upstream and settlement sections, and partially recovered downstream. Settlement sections showed an increased occurrence of regulated and artificial channel structures and a decreased proportion of arboraceous riparian vegetation. Sample level taxon richness was the same in the three sections, while section level total taxon richness increased downstream. The functional approach provided stronger explanatory power in the majority of analyses than the traditional taxonomic approach, and indicated ecosystem wide shifts in functioning within the settlements, especially in the source and processing of organic matter. The negative effect of settlements on the stream biota could be compensated by a more natural-like channel design and by a reforested riparian zone. The high environmental and biotic heterogeneity necessitates regional thinking in conservation planning.