Dissertation research -- The role of mineralization in nutrient spiralling in heterotrophic streams

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Human activity has greatly increased the amount of nutrients, such as nitrogen and phosphorus, applied to the global landscape. Much of this nutrient load is transported to coastal areas by streams and rivers. However, streams are not passive conduits but are sites of significant nutrient transformation. Nutrients may enter streams in dissolved inorganic forms, are transported a certain distance by water flow, and are eventually transformed into organic forms by stream organisms, which need these chemicals for maintenance and growth. This research will focus on the final stage of this cycle where stream organisms, such as bacteria, fungi, and insects, return excess nutrients to the water. Specifically, this research will determine the effect of increased nutrient input on nutrient transformations by stream organisms and their ability to influence the transport of nutrients downstream. The investigators will use a stable isotope of nitrogen to measure several nutrient processing metrics in both field and laboratory settings. This combined approach will allow for the description of broad patterns across time and space as well as the determination of specific mechanisms responsible for the observed patterns. The increased nutrient loading occurring around the globe is causing a suite of environmental problems including declines in biodiversity, contamination of drinking water, and anoxia of coastal waters. The role of streams in transporting these excess nutrients from terrestrial to marine systems makes understanding the fate of nutrients within streams vital to policy makers attempting to mitigate the negative effects of nutrient loading. The temporal and spatial scope of this research will help fill a gap in the understanding of stream nutrient cycling and will add to the body of knowledge available to policy makers. This research also provides opportunities for undergraduate students to participate in the scientific process and contribute to the understanding of a relevant environmental issue.