Influence of nature preserves on macroinvertebrate assemblages, water quality, and habitat quality along two urban streams

The increase in urbanization as a threat to aquatic ecosystems, particularly stream ecosystems, is of growing concern due to the reliance of the condition of surrounding watersheds. Mitigation techniques, such as riparian re-planting and habitat enhancement, are often met with little improvement in stream biodiversity. The understanding of the ecological effect of nature preserves in urban areas on stream assemblages can lead to more effective stream restoration. Benthic macroinvertebrates and water quality in two streams, Poplar Creek and Spring Creek in the Fox River watershed of northeastern Illinois, were monitored along an urban stream continuum upstream, within, and downstream of two nature preserves. Urban land cover within the riparian zone was considerably low at sites within (0.5%) the preserves compared to those outside (59.3%). Reductions in amount of silt substrates and increases in gravel-dominated substrate were evident within preserve sites in both streams. Taxa richness and a benthic macroinvertebrate index of biological integrity (MIBI) increased within the preserve sites for Poplar Creek, however there was no consistent improvement in biodiversity observed in Spring Creek. Additionally, percentage of Ephemeroptera, Trichoptera, and Plecoptera (%EPT) showed no improvements at sites located further downstream within the preserves compared to those outside or upstream in either stream. Water quality monitoring showed no consistent trends and seemed to be confounded by precipitation events between sampling occasions. Nature preserves in urbanized areas could increase macroinvertebrate biodiversity through local reductions in impervious surfaces and improvements in stream substrate based on responses in MIBI scores at Poplar Creek, despite lack of evidence that they could significantly improve water quality