Date of Award

Fall 12-1-2018

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)


Biological, Environmental, and Earth Sciences

Committee Chair

Kevin Kuehn

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Halvor Halvorson

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Jake Schaefer

Committee Member 3 School

Biological, Environmental, and Earth Sciences


Anthropogenic influences are increasing algal biomass and activity within aquatic ecosystems, stimulating debate regarding interactions between “green” and “brown” food webs. Specifically, in forested streams, the removal of forest canopy or riparian zones increases light exposure and nutrient fluxes to streams affecting primary productivity and carbon (C) flows across aquatic food webs. Further understanding the synergistic effects of light and nutrients on detrital biofilms may explain how aquatic detritivores respond to anthropogenic change. The objective of this study was to employ C and phosphorus (P) isotopic radiolabels to understand how microbial biofilm constituents (i.e heterotroph and autotroph) contribute C and P to detritivore nutrition under raised light and nutrient regimes. I conducted a feeding study using detritivorous caddisflies (i.e. Pycnopsyche sp.) and conditioned leaf litter across a fully-factorial experimental set up and fed radiolabeled litter in the lab. Additionally, I used dual labels of 14C and 33P to trace radiolabeled C and P into caddisfly tissues. I quantified microbial biomass and production rates, caddisfly consumption and egestion rates, and radiolabel assimilation, and incorporation efficiency. The results of my study report that 94-97% of detritivore C was incorporated from fungi and 1-3% from bacteria and algae. My study shows light and nutrients stimulate heterotrophic activity and determine the microbial quality of C and P available to detritivores. Future studies should assess physiological performance (i.e. growth rates) of caddisflies in response to light and nutrient exposed litter to understand how caddisflies are responding to potential elemental ratio imbalance