Sedimentary processes in large, regulated river systems in the Canadian subarctic

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Goharrokhi, Masoud
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The goal of this thesis is to develop an improved understanding of sedimentary processes along the Nelson River system in the subarctic region of Canada. Sediment sources and transport dynamics in Lake Winnipeg, the Upper Nelson River (UNR) – between Lake Winnipeg and Split Lake – as well as the Burntwood River (BR) – the major tributary of the Nelson River in the subarctic region – were investigated. The properties of Lake Winnipeg’s bottom sediment and the lake’s total sediment budget were used to provide a better understanding of: a) the sedimentation dynamics in Lake Winnipeg; and b) its role in sediment transport in the Nelson River system. The sediment source fingerprinting technique and long-term record of sediment load data on the BR and the UNR were used for separating the importance of climate change from human-induced environmental changes on these two regulated rivers. Moreover, the influence of Split Lake on the downstream delivery of sediment to the Lower Nelson River and Hudson Bay was investigated by developing the sediment budget for this riverine lake. In addition, the collection of a representative sample of ambient suspended sediment using a well-established time-integrated sampler and two adapted discrete samplers was investigated. The performance of these samplers was examined in a controlled laboratory and under field conditions. Assessing these samplers was conducted to determine the most suitable device to collect representative bulk samples from the Nelson River system. The results show that the sediment load derived from the prairies area is sequestered in Lake Winnipeg, along with nutrients and contaminants bound to them. Another key finding was that sediment derived from bluff erosion on the northern shore of the lake is the major source for sediment being exported in the lake’s outflow. This thesis also found that the UNR is characterized by increases in sediment loading as a result of climate change. However, in the BR, cross-watershed water diversion caused a seven-fold increase in sediment discharge and since diversion flow regulation near the licenced limit has muted the response to variability in local precipitation and runoff. This thesis also provides several recommendations for further research.
Climate change, Human-induced environmental changes, Sediment budget, Sedimentation dynamics, Sediment disconnectivity, Sediment fingerprinting, Lake Winnipeg, Nelson River, Split Lake