Life Sciences Commons^™

Climate-Driven Impacts Of Warming And Grazing On Sub-Arctic Coastal Wetlands In Alaska, Ryan T. Choi

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Climate change is rapidly warming the Arctic, especially at lower latitudes. Warmer temperatures and earlier springs are altering the timing of plants and animals, especially for long-distance migratory herbivores. Changes in the timing of both plants and herbivores have the potential to impact plant productivity and nutrient cycling, while also altering plant community diversity and composition.

In chapter 2, I conducted a field experiment to investigate how earlier growing seasons and differences in arrival times of migratory geese influence physical traits of sedge forage species. I found that both an earlier growing season and late grazing by geese had similar …

The Fate And Cycling Of Nitrogen, Phosphorous, And Trace Heavy Metals In Beaver-Altered Headwater Streams, Desneiges S. Murray

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Human land-use can increase the amount of non-point source (NPS) pollution in a stream, negatively affecting ecosystem health and beneficial services provided by an ecosystem. Unfortunately, NPS pollution remains high in many waterbodies. Beaver dams may be a passive, cost-effective strategy for removing NPS pollution in headwater streams because beaver dams slow stream flow and collect sediments. Impounded sediments can change how nutrients and pollutants are cycled in a stream through multiple pathways. In the first part of our study, we investigated whether beaver activity can reduce nitrogen, phosphorous and heavy metals from otherwise traveling downstream. Results suggest beaver ponds …

Investigations Of Substrate Reduction By Nitrogenase: Light Powered Substrate Reduction By A Cds:Femoco System And Understanding Dinitrogen Inhibition Of Electron Transfer, Hayden Kallas

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Nitrogen fixation is a key step of the nitrogen cycle which makes biologically inert N₂ gas available for organisms to use in the form of ammonia. Nitrogen fixing microorganisms all contain the same enzyme called nitrogenase which catalyzes the six electron transfers to N₂ required for conversion into ammonia. Nitrogenase is a two-component enzyme that contains a cofactor composed of iron and sulfur as well as heavier metals whose identity can be molybdenum, vanadium, or an additional iron atom depending on the variant. The two components of nitrogenase are the MFe protein and the Fe protein. The Fe …