Year of Award

2024

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Ecology and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

Robert O. Hall Jr.

Commitee Members

James J. Elser, Anna Sala, Mary E. Power, Andrew C. Wilcox

Keywords

algae, aquatic plants, benthic cyanobacteria, nutrients, primary production, river metabolism

Abstract

Algae, cyanobacteria, and aquatic plants are essential components of river ecosystems, providing the basis for aquatic food webs, determining water quality, and controlling carbon and nutrient cycling in rivers. Despite their importance to river ecosystems, growth and accumulation of river photoautotrophs beyond historic levels cause ecological and social harm. The drivers of riverine primary production are poorly understood relative to algae blooms in lakes due to a paucity of studies in rivers, challenges with quantifying periphyton, and interacting and co-varying controls associated with river flows. In my dissertation, I quantified photoautotrophs and aquatic primary productivity in a dammed, eutrophic river where high nutrient concentrations, high gross primary production (GPP), and high autotrophic biomass impair water quality. In chapter 1, I documented widespread proliferations of anatoxin-producing benthic cyanobacteria throughout the Klamath River Watershed. I tested techniques to monitor these benthic cyanobacterial mats in large rivers and I compared toxin concentrations in different mediums that presented exposure risks to river users. I also explored physical and chemical drivers of benthic anatoxin production across the Klamath River Watershed to increase understanding of the causes of benthic anatoxins. In chapters 2 and 3, I explored drivers of reach-scale metabolism. Measurements of GPP and ecosystem respiration (ER) help overcome challenges associated with measuring photoautotrophic biomass or growth, which have high spatial and temporal heterogeneity and can be especially challenging to survey in large rivers. In chapter 2, I explored how variation in aquatic primary producer assemblages influenced whole ecosystem metabolism. I snorkeled 11 sites spanning 300 river km to survey the reach-scale biomass of rooted aquatic plants and filamentous algae. I related the biomass of submerged aquatic vegetation to summer reach-scale GPP and ER to explore how ecosystem metabolism time series reflected aquatic vegetation assemblages. In chapter 3, I tested hypotheses of nutrients driving GPP on daily and annual time scales. I used a ∼15 y data set of daily ecosystem metabolism at 3 sites on the Klamath River to test relationships between nutrient concentrations and seasonal and daily GPP. As large dams are being removed from the Klamath River in 2023 and 2024, improving understanding of drivers of photoautotrophic biomass and GPP will inform predictions about how the river ecosystem will respond to dam removal, with implications for water quality and human health on the Klamath River, while also informing expectations of river response to changing conditions more broadly.

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