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Indian Mill Creek (HUC 040500060504) is a third-order tributary to the Grand River in Kent County, Michigan, USA (Fig. 1, Fig. S1). It is 18.5 km long with a 44-km2 watershed. Indian Mill Creek is a coldwater stream with stable to moderate temperature fluxes, conducive to rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), and sculpins (Cottus spp.) in the lower reaches (Wehrly et al. 1999; Sigdel 2017). The amount of groundwater influx to the creek increases along an upstream to downstream continuum (Sigdel 2017). Land use in the watershed is predominately urban (43%) and agricultural (39%) (LGROW 2011). Commercial and residential development is mostly in the lower reaches as it flows through the Grand Rapids metropolitan area, natural and urban lands are in the middle reaches, and farmland and orchards are in the agricultural upper reaches (Fig. 1, Fig. S2) (LGROW 2011). Impervious surfaces cover 12% of the watershed and up to 25% of some lower catchments (AWRI, unpublished data; Sigdel 2017). Indian Mill Creek is designated as a coldwater trout stream by the State of Michigan; however, it is currently listed as impaired by the Michigan Department of Environment, Great Lakes, and Energy (EGLE) due to degraded fish communities (Goodwin et al. 2016).
For river basins following a land use pattern of agricultural headwaters to urban lower reaches, interactions of landscape, geomorphic, and water quality/pollution variables can be influential on the structure of fish and macroinvertebrate communities. For instance, the integrity of stream macroinvertebrate communities, as well as the prevalence of macroinvertebrate scrapers and shredders, was associated with surrounding land use and riparian management. Also, lower fish abundance and community integrity in the lower urban reaches of Indian Mill Creek could be explained by a combination of geomorphology and episodic urban pollution events in addition to flow and temperature regimes. Next, we found that aquatic communities would not always conform to expectations for longitudinal gradients like the unimpacted natural stream from the River Continuum Concept. Deforestation and clearing of the riparian zone in agricultural headwaters caused there to be more scraping macroinvertebrates than we would have expected in a natural stream without these impacts. We also found that impacts would not always increase in a downstream direction through the agricultural and urban developments. This is because the abundance and richness of sensitive EPT macroinvertebrates increased within the urban zone of the Indian Mill Creek watershed, downstream of extensive agriculture, within a forested riparian buffer. This shows that recovery of degraded aquatic communities downstream of urban or agricultural impacts is possible given effective management choices, such as maintaining small patches of forest along the streams. Agricultural and urban land cover changes and their associated impacts to lotic ecosystems are prevalent and increasing worldwide. This study has provided a better understanding of these impacts along streams following an agricultural-to-urban land cover gradient, which may not conform with general expectations of land use patterns. It has also provided guidance for successful mitigation of these stressors. 2b1af7f3a8