Linkages among land cover, in-stream physicochemical features, and macroinvertebrate community attributes in urban and agricultural landscapes of central lowa

Relationships among land cover and in-stream physicochemical and macroinvertebrate community attributes were quantified within agricultural and urban landscapes of central Iowa.  Multiple regression analyses revealed that coarse substrate, organic matter, and dissolved oxygen concentration were positively related to important macroinvertebrate-based attributes, including total biomass and taxa richness, and EPT taxa richness (p<0.01).  Invertebrate attributes also varied significantly with measures of land cover, even when all significant in-stream factors were held constant.  Stream sites characterized by high urban land cover had lower taxa richness, EPT density, EPT richness, and scraper richness than sites with low urban (i.e., high agricultural) land cover (p<0.05).  Land cover was measured at multiple landscape scales, including 1) local riparian area (100-m buffer extending 100 m upstream), 2) 200-m buffer extending 1 km upstream, 3) 200-m buffer extending to headwaters, and 4) subwatershed.  Regression analyses revealed that land cover at subwatershed or local scales was most strongly related to those macroinvertebrate attributes listed above.  Results suggest that, in these streams, negative impacts of urbanization on invertebrate communities exceed adverse effects of intensive agriculture, and land cover at local and subwatershed scales appears to have the most influence on invertebrate assemblages.