Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Dr. Adam Yates


Pulsed increases in flow within streams alter abiotic conditions such as nutrient concentrations and velocity which can influence the function of stream ecology, including biofilms. A 31-day artificial stream experiment at Thames River Experimental Stream Sciences (TRESS) Centre, London, Ontario, assessed the response of stream biofilm function (decomposition, primary production, community respiration) to individual and combined increases in velocity and phosphorus associated with a 48-hour hydrological pulse event. There was some evidence of an interactive subsidy effect of increased phosphorus and velocity on algal productivity. Decomposition increased as a result of increased phosphorus but there was no synergistic interaction of phosphorus and velocity. Ecosystem respiration did not show a substantive response to velocity or phosphorus increases. This study contributes to furthering ecological knowledge of the effect of hydrological pulses on biofilm function and to progressing understanding of the potential ecological implications of alterations to nutrient loading and stream hydrology.

Summary for Lay Audience

Flow is an ecologically important variable within streams. Increases in flow (e.g. following rainfall) can change several ecologically important variables within streams. For example, increases in flow can reduce light availability, increase the physical stress experienced by organism due to higher water velocities and alter resource availability such as nutrients. Two of the most ecologically influential changes during high flow events are increases in water velocity and increased nutrient availability, as nutrients can be transported into streams following rainfall. Changes to water velocity and nutrient concentrations influence stream biofilms. Biofilms are communities of algae, bacteria and fungi that grow on surfaces like rocks within most streams. Biofilms influence key ecological processes in streams such as energy availability and nutrient cycling. For example, algae in biofilms use nutrients, such as phosphorus, and energy from light to photosynthesize and grow (primary production). Bacteria and fungi in biofilms break down organic matter like dead leaves (decomposition). Such ecological processes are called ‘functions’. Primary production and decomposition are important functions, providing a pathway for energy into stream food webs.

This study assessed the response of biofilm function, including primary production and decomposition, to increases in velocity and nutrients (phosphorus) during a 48-hour high flow event. The study was conducted in nine outdoor artificial streams in London, Ontario, which provided a controlled environment to assess and compare the effect of individual and combined pulsed increases in phosphorus and velocity.

Primary production in biofilms was greatest when velocity and phosphorus were increased simultaneously. The individual increase in phosphorus had a greater effect on primary productivity compared to the velocity increase. Increased phosphorus, both individually and in combination with velocity, appeared to increase decomposition compared with the individual increases in velocity.

This study, and further related research, is important to understand the effect of high flow events on biofilm function, which influences processes like the energy supply to stream food webs. Understanding the ecological effects of high flow events may allow for assessment of human impacts on streams, such as the effects of alterations to flow and nutrient delivery to streams caused by certain land use changes.