Date of Award:

12-2022

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Janice Brahney

Committee

Janice Brahney

Committee

James Elser

Committee

Zachary Aanderud

Abstract

Increasing quantities of dust emitted from semi-arid soils, agricultural soils, and urban regions are blown to remote mountain lakes in the American West. Remote mountain lakes lacking local nutrient inputs and presenting simple food webs that are easily affected by climate changes. Dust can carry nutrients (e.g., nitrogen and phosphorus) to mountain lakes and potentially enhance algae growth and change algal communities. However, experimental tests of this hypothesis are lacking. Using in situ experiments, we investigated the effects of dust enrichment on the production, biomass, and primary algal species in three mountain lakes in the American West. We found that dust additions increased algal biomass at all three lakes, but the magnitude differed, ranging from 32% to 226%. This variation may be associated with the initial algal biomass before the experiments and nutrient limitation of lakes (limited by nitrogen, phosphorus, or both). Surprisingly, bioassays with increased dust additions showed decreased 14C primary productivity (the ability to fix carbon). The first reason could be that dust inputs stimulated bacteria that could fix carbon under dark conditions while suppressing algal production that can fix carbon during the day. The second reason could be that nutrient-limited algae allocated energy to uptake dust nutrients instead of fixing carbon after the dust was added. The relative abundance of algal species changed in dust treatments compared to the controls. Mixotrophs (algal species that both photosynthesize and take up organic matter or eat other plankton) increased at Castle Lake but decreased at the other lakes compared to phototrophs (species that only photosynthesize). Our study presented experimental evidence on how dust deposition influences remote mountain lakes. We proposed the hypothesis that the pre-existing status of the lake may affect the responses of dust inputs. This hypothesis needs to be tested in the future.

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