Graduation Date

Spring 2022

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Catalina Cuellar-Gempeler

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Bob Gearheart

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Mark Wilson

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Paul Bourdeau

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



Microbial communities play a crucial role in ecosystems, yet we know little about how microbial diversity influences ecosystem functioning. An important gap in our understanding is how environmental change affects microbial Biodiversity-Ecosystem Function relationships (BEF). These complex interactions between microbial biodiversity and ecosystem function can influence major biogeochemical processes, such as the nitrogen cycle in wetland ecosystems, which play an important role in managing wastewater. To address the effect of biodiversity on function, my study investigates the BEF relationships between microbial diversity and the function in terms of ammonia removal from wastewater at the Arcata Wastewater Treatment Facility (AWTF) both spatially and temporally. The AWTF uses several natural treatment systems consisting of Oxidation Ponds and constructed wetlands for secondary wastewater treatment. These natural treatment systems provide a unique opportunity to study microbial community BEF relationships because they are interconnected by the flow of nutrients in the wastewater and are exposed to seasonal changes. First, I conducted a field study where I sampled the AWTF natural treatment system from Autumn to Spring. Based on classical BEF studies, I expected a positive relationship between microbial biodiversity and ecosystem function, but also anticipated a potential effect of seasonal and spatial factors in strengthening or weakening the relationship. Instead, I found a significant negative BEF relationship between microbial community richness and ammonia removal. Ammonia concentration significantly decreased through the wastewater purification system, yet microbial diversity was unrelated to the different locations in the wastewater treatment system. In turn, seasonality significantly affected the microbial community diversity where richness was lower during Spring. Following the field study, I conducted a microcosm experiment to determine the direct effect of an environmental change in terms of dissolved oxygen (DO) concentration on biodiversity and ecosystem function. The DO concentration had a positive relationship with evenness and a negative relationship with richness. In addition to the DO relationships, I observed a negative correlation between evenness and nitrification which reflects the BEF relationship findings from the field study. Because the lower evenness values are associated with more ammonia removal, these results further support that ammonia removal capabilities of the AWTF are most efficient when fewer species dominate the microbial communities in the natural treatment system, regardless of oxygen levels and other environmental factors. By expanding our search for more microbial community BEF relationship scenarios we can further unravel how richness and evenness influence ecosystem processes in natural and humanized systems.

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