Rivers are important systems for the delivery of nutrients and materials into receiving bodies and provide important ecosystem services. The Kalamazoo River is an ideal system for researching basic river ecosystem processes as well as to understand past contamination, restoration potential, and future risks. In this study, I examined the impacts of a run-of-river reservoir, which alters hydrologic retention time but does not change discharge. The increased water residence time from the reservoir led to an increase of algae downstream. Nutrients upstream were in a bioavailable form but were converted into particulate forms, likely mainly as algal biomass, immediately downstream of the reservoir. Phosphorus appeared to follow suspended chlorophyll-a patterns closely. However, the fate of suspended chlorophyll-a and nutrients from the reservoir was complex. The suspended chlorophyll-a produced in the reservoir provided a subsidy that was evidently consumed by benthic macroinvertebrates. Using natural abundance stable carbon isotopes to indicate longitudinal patterns in macroinvertebrate diets and artificial substrata to quantify macroinvertebrate densities, I was able to trace which taxa responded to the algal food subsidy. Filter feeding caddisflies from the family Hydropsychidae appeared to respond to the subsidy most clearly, although they were also abundant above the reservoir. More work is needed to understand food web dynamics in rivers the size of the Kalamazoo River. Lastly, a major oil sands spill occurred on July 25th, 2010. This work quantified the responses of river macroinvertebrates to the oil and its cleanup. In addition, an in-situ bioassay using Hyalella azteca was conducted, and I collected Orconectes spp. crayfish to measure metal bioaccumulation, to understand the impacts of submerged oil. This study found that macroinvertebrates were severely reduced in two sections of river, but showed recovery one year later. Hydropsychidae caddisflies seemed particularly impacted by the oil spill. The in-situ bioassay showed the possibility of sub-lethal impacts. This study from the Kalamazoo River oil spill will be useful for understanding the risks to other rivers, and in particular the impacts of diluted bitumen spills on benthic macroinvertebrates. More work is needed to understand if bitumen is more or less toxic than conventional crude, and the risk of submerged oil in freshwater ecosystems.
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