Natural Resources, School of


First Advisor

Jessica R. Corman

Date of this Version

Summer 7-28-2023

Document Type



Farrell, W. R. 2023. Light Alters Leaf Breakdown Rates and Metabolic Activity in Anthropogenically Impacted Nebraska Streams. UNL Digital Commons.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Natural Resource Sciences, Under the Supervision of Professor Jessica R. Corman. Lincoln, Nebraska: July, 2023

Copyright © 2023 W. Reilly Farrell


Algal growth influences carbon breakdown rates in aquatic ecosystems; however, the magnitude and direction of these effects differ based on ecosystem context. To explore algal priming effects on decomposition in anthropogenically impacted ecosystems, I conducted light manipulation experiments in three streams, each surrounded by different land uses (i.e., predominantly urban, row crop, or concentrated animal feeding operation) across Nebraska. I measured leaf breakdown rates, metabolic activity, fungal and algal biomass, and leaf percent carbon (C) and phosphorus (P) to assess the effect of light differences. These streams were impacted by sedimentation and turbidity over the course of the leaf incubation. Still, I observed higher algal biomass as chlorophyll a in light treatments at all sites. Leaf litter-periphyton respiration rates were higher in sunny treatments at agricultural sites but were not significantly different between light treatments at the Urban site. Among sites in which I measured breakdown rates, I observed higher breakdown rates in the sunny treatment at one site, but an insignificant relationship between light and breakdown rate at the other. Leaf C:P was not significantly different between light treatments. Overall, these findings support results from prior studies that light levels can alter breakdown rates of allochthonous C in streams. They shed light on the influence of changing light on carbon processing in streams while highlighting the sensitivity of algal priming relationships to disturbance.

Advisor: Jessica R. Corman