Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Geography

Supervisor

Yates, Adam G.

Abstract

Small tributary streams are conduits between the landscape and larger waterbodies and provide important ecosystem services including assimilation of nutrients from human activities which may be protective of downstream waterbodies. In the Red River Valley (RRV), Manitoba, numerous nutrient sources including agricultural runoff, livestock manure, and municipal wastewater effluent, have been attributed to the eutrophication of Lake Winnipeg and thus require targeted management to prevent loss of nutrients from land to lake. However, linkages between land-based nutrient-producing human activities in the RRV and the ecological status of the tributaries remain poorly understood. Furthermore, the proportional contribution of each source of nutrients to the tributaries is not known and the capacity of streams to take up these nutrients thereby preventing downstream losses is also unknown. My doctoral research improved understanding of the interaction between human activities in the RRV and the streams that serve to assimilate nutrients through the following three projects: 1) an evidence-weighting assessment identifying nutrient-producing human activities in the RRV with evidence of stream ecological effects; 2) an assessment determining the sources and seasonal variation of nitrogen to 14 RRV tributaries using established (stable isotope ratios) and novel (artificial sweeteners) tracers; and, 3) an examination of the fate of nutrients from municipal wastewater lagoon effluent releases into an RRV stream by measuring nutrient transformation, uptake, and retention. Together, these three projects identified human and livestock wastes as important drivers of current ecological condition of RRV tributaries, while underlining the need for better biomonitoring strategies in the region. Furthermore, my research highlighted the key role of livestock manure as a contributor to snowmelt nutrient runoff and improved knowledge about seasonal differences in the transfer of nutrient sources from RRV catchments to streams. Finally, I showed that the large pulsed delivery of nutrients during wastewater lagoon discharge may overwhelm stream capacity for uptake; a finding that has important implications for the protection of downstream waterbodies. The outcomes of my thesis research will enable managers to more effectively target nutrient mitigation efforts and improve management of stream ecosystem services that reduce transport of nutrients to Lake Winnipeg.

Summary for Lay Audience

Nutrients are required by aquatic organisms; however, when nutrients are present in excess, they are detrimental to aquatic life. Humans release nutrients to the environment through activities such as agriculture and wastewater treatment. Streams receive nutrients from human activities via landscape runoff or through direct release to waterways. Within streams nutrients are transformed, retained, or removed through chemical and biological reactions facilitated by stream organisms. However, when the amount of nutrients is high and/or conditions are not favorable for stream organisms, nutrients are lost downstream to larger lakes and rivers where they may cause harm to aquatic life. Streams in the Red River Valley (RRV), Manitoba are at risk due to the detrimental effects of human activities related to agriculture and growing communities. Furthermore, RRV streams flow downstream to Lake Winnipeg, which is already vulnerable due to the high amount of nutrients entering the lake over the past three decades. The objectives of the projects presented in this thesis were to 1) identify which human activities are most likely having an effect on RRV streams; 2) identify when specific sources of nutrients are most likely to enter streams; and, 3) examine what happens to the nutrients once they enter a stream via release from a wastewater treatment lagoon. I identified human wastewater as the source of nutrients most likely to impact streams. Nutrients from livestock manure entered streams in the early spring when cold weather likely slows chemical and biological reactions and prevents transformation and retention. In contrast, wastewater from lagoons entered streams in later spring and summer when stream organisms were more active. I found that stream organisms do transform and retain some of the nutrients from wastewater treatment lagoons, but the large amount of nutrients released is likely more than organisms need; therefore, the excess is transported downstream. The outcomes of these projects will help managers to effectively plan nutrient reduction strategies in the RRV and provide insight about the amount of work a stream can do to prevent nutrient loss downstream. Overall, these outcomes will aid in the protection of RRV streams and downstream Lake Winnipeg.

Available for download on Saturday, January 01, 2022

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