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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. |
