Organic Matter Sources, Composition, and Quality in Rivers and Experimental Streams

Organic matter (OM) is often considered the “currency” for ecosystem processes, such as respiration and primary production. OM in aquatic ecosystems is derived from multiple sources, and is a complex mixture of thousands of different chemical constituents. Therefore, it is difficult to identify all the sources of OM that enter and exit aquatic ecosystems. As humans develop undisturbed land, the rate at which terrestrial OM (e.g.soil and plants) and associated nutrients (e.g.nitrogen) enters rivers has increased. Increased nutrients may lead to increased primary production from aquatic plants and algae, potentially causing eutrophication and harmful algal blooms. In this study, I identified and characterized different sources of OM in four watersheds of Northeastern Utah with multiple land covers such as cities, forests, and crops. I expected OM in watersheds with human-altered land cover would have more OM produced instream by algae and other primary producers, than OM in less disturbed watersheds, which typically have OM from terrestrial sources. I found that OM at river sites with high human impact had high amounts of OM from instream primary production, but there was also OM produced in-steam at sites with low human impact. The greatest differences in OM across watersheds was due to wastewater treatment effluent. I also measured microbial consumption rates of algal derived and terrestrially derived DOM in experimental streams to quantify how much faster algal derived OM was consumed than terrestrial OM. I found algal derived OM was consumed extremely fast, so fast that realistic measurements of its consumption in some river ecosystems may not be possible. It is important to identify and characterize sources of OM to rivers, so watershed manager scan devise effective OM reduction plans appropriate for the constituent of concern unique to that watershed or region. Constituents of concern associated with OM include pathogens affiliated with manure, toxins in harmful algal blooms, metals, and pharmaceuticals from wastewater treatment effluent. Each pollutant requires a unique mitigation strategy and therefore the first step to pollution mitigation is source identification.