Effects of agricultural land conversion and interstitial sediment on Tasmanian stream macroinvertebrate communities

Context Conversion of upstream catchments to agriculture usually affects macroinvertebrate diversity metrics, but the strength and direction of these effects varies. Aims We assessed the effects of converting native vegetation to agriculture across 18 Tasmanian streams with upstream catchment conversion ranging from 0 to 95%. Methods We compared the effects at both species- and family-level taxonomic resolutions and described how β-diversity is altered by taxonomic resolution. Results Most univariate diversity metrics were higher in forested streams than agricultural streams; however, this relationship was weak and not detected with family-resolution data. Interstitial fine sediment was a more important driver than was agricultural catchment conversion for stream health metrics, likely owing to these metrics being sensitive to specific species. Species-level data indicated that community composition differed in response to both agriculture and fine sediment, although each stressor influenced communities in distinct ways. The same general patterns were evident at the family level, but without strong statistical support. Conclusions Multivariate methods detected effects of agriculture and interstitial sediment much more strongly than did univariate methods, implying that retaining information about taxa identity is important for detecting changes in stream communities. Implications Agricultural land use alters stream macroinvertebrate communities, highlighting the need to manage intensifying agriculture to prevent biodiversity loss.