Aquatic macroinvertebrate diversity within an urbanized gradient

In urban areas, the amount of impervious surface and storm water infrastructure has altered natural streams and riparian areas, ultimately degrading their functionality.Urban development decreases water quality, which in turn, changes the aquatic insect community. Macroinvertebrates within urban streams are susceptible to habitat change, some being more tolerant than others to pollutants. Low levels of development (upstream percent impervious surface levels of 5-10% at watershed level), can eliminate or reduce many pollution intolerant native macroinvertebrate families. However, there is very little, if any, understanding of how 59 increment levels of urbanization above these thresholds influences the remaining macroinvertebrate communities. In this a study, we assessed the integrity of the macroinvertebrate community using the Family Biotic Index (FBI) within an urbanization gradient (25-60% upstream impervious surface) in Rock Island and Moline, IL. The study area consisted of 30 sampling sites located in 12 urban watersheds characterized by at least some remnant natural riparian stretches. A pilot study was conducted in 2013 during which a total of 5 pool and 5 riffle stretches were sampled using dip nets; however no effort was made to standardize the total sampling effort. Samples were collected approximately once per month from May-September. Continuing the study in 2014, a standardized unit effort was established,consisting of 10 pool/10 ripple dip net samples and a 30 minute limit effort. 2014 data was also collected in one sampling event in April. The results are reported separately due to the incomparability of sampling methods. In 2013, the FBI ranged from 4.40 (good)-8.46 (verypoor). Similarly, in 2014 it ranged from 4.00-8.00. Across both years of sampling, there were 30% (10 out of 30) of the sampling sites where only between 0-3 individuals were found despiteintensive sampling effort. Water quality parameters at each site varied significantly, which should help explain macroinvertebrate diversity across watersheds. We found almost no reliable predictors of FBI, with the exception of a weak negative relationship between dissolved oxygen levels and FBI in 2014 (regression, p-value = .035; R2 = 0.298). Our findings provide important insights into the integrity of the macroinvertebrate community within an urbanization gradientand are consistent with the findings of other studies showing that high levels of urbanization can homogenize communities. Future research will focus on increasing the intensity of sampling effort over an expanded range sample sites in order to capture the maximum urbanization gradient. We also intend to focus on collecting data on more promising predictors such as finescale patterns in the amount, shape, and connectivity between patches dominated by different urban land uses (manicured lawns, urban forest, unmaincured vegetation, buildings, sidewalks,roads, etc.