Search

This study was conducted to identify temporal changes in nutrient and sediment concentrations and loads (total phosphorus, particulate phosphorus, total dissolved phosphorus, total nitrogen, and total suspended solids) in Swan River and Woody River of the Swan Lake watershed, Manitoba. Temporal changes in physical hydrology (river discharge and precipitation) were also investigated to determine if these parameters influenced the changes in water quality concentrations and loads across the Swan Lake watershed. Annual and seasonal totals of water quality variables, river discharge, and average watershed total precipitation were examined for change over 30 years. The results showed a statistically significant increase in nutrients and total suspended solids (TSS), and river discharge, particularly in Swan River. Both rivers experienced statistically significant increases during the spring season with changes in median values as high as 450% in TSS between 1989 – 2000 and 2010 – 2018. Annual river discharge in Swan River and Woody River increased by 182% and 103%, respectively, with Swan River experiencing a statistically significant increase over the 30-year period. Seasonally, both rivers increased statistically significantly in the spring season with an 80% increase. Total precipitation across the watershed increased 3% annually, including a 6% increase in the spring, and summer and fall seasons, and 8% decrease in the winter season between 1995 – 2001 and 2009 – 2015. There were correlations between water quality variables and river discharge, and between river discharge and precipitation. Precipitation in this area influences river discharge and since nutrients and sediments are strongly correlated with river discharge, precipitation indirectly influences nutrient and sediment exports.

Water-eroded channels are focal points for water, wind, and tillage erosion processes as they can function as pathways for sediment transport, sources or traps of sediments and topography features that alter the nature of soil redistribution by tillage. The linkages and interactions of different erosion processes around the channel area are complex and dynamic, not only during the period when the channel is created but also after it is created. The effects of channels on subsequent water and tillage erosion and their contribution to total soil erosion have not been examined. To fill this knowledge gap, we carried out three studies, focusing on the role of channels in water and tillage erosion processes and the assessment of total soil erosion. In the first study, we examined the effects of a channel on tillage translocation. For downslope tillage, channels reduced total translocation, whereas, for upslope tillage, channels increased total translocation. For contour tillage, channels increased total translocation as well. The patterns of tillage translocation can be well explained by the balance of the trapping effect versus the energy-intensity-increase effect. Soil movement decreases when the trapping effect dominates and increases when other effect dominates. Additionally, a plot experiment examined the effects of an existing channel and tillage on water erosion. With an existing channel, runoff discharge and sediment export increased, whereas, with tillage, runoff discharge and sediment export decreased. When an existing channel was tilled, the effects of tillage dominated, while the existing channel only demonstrated some minor impacts. In the third study, a modeling procedure was developed to integrate the Raster-RUSLE2, Ephemeral Gully Erosion Estimator and Modified Directional Tillage Erosion Model for simulating water and tillage erosion. This integrated approach incorporated insights gained from previous studies on interaction effects. The individual models

Maintaining the future sustainability of agriculture and ensuring soil security is of primary concern across Canada. Understanding the state of soil erosion and determining the vulnerable areas are essential measures in combatting future soil erosion and avoiding soil degradation. Therefore, the general goal of this thesis was to quantify soil erosion rates and develop an improved understanding of erosion processes within the Canadian Prairies. To fulfill the aim of the research project, typical agricultural and native prairie landscapes of the region were studied within three watersheds including the Red River Valley and the Broughton’s Creek watershed in Manitoba, and the Bigstone Creek watershed in Alberta. Initially, passive uni-directional wind erosion sediment samplers were employed to assess wind-eroded soil movement in agricultural lands of the Red River Valley. Cesium-137 (137Cs) measurements were conducted to quantify total soil loss and deposition rates within the wetland landscapes in the Broughton’s Creek and Bigstone Creek watersheds. In addition, soil and sediment properties were characterized to understand tillage-, water- and wind-induced sediment transport dynamics and distinguish between eroded and depositional zones. Landform classification maps of the studied wetland catchments were also created to assist developing sediment budgets of soil loss and accumulation, and quantify sediment flux rates from agricultural fields to wetland environments. Furthermore, soil erosion models were used to characterize spatial patterns of soil loss by tillage, water, and wind erosion and assess relative contribution of these processes towards total soil erosion. This study found that: i) Measured soil loss and sedimentation caused by wind erosion are very small in the Red River Valley. Moreover, abrasion of crops by wind-transported sediment was not observed in this study; ii) Using the measurements of 137Cs, average annual soil losses in cultivated fields were

Soil erosion accelerated by agriculture reduces agricultural productivity and compromises the function of drainage infrastructure and downstream water quality. In Manitoba, the relationship between soil erosion and water quality is of particular concern, following measurable declines in Lake Winnipeg’s water quality since the 1990s. Understanding the state of soil erosion, transportation, and deposition in the Red River Valley is of interest, due to the extensive cultivation of the river’s watershed and its contribution to total flow (and by extension, sediment flux) into the lake. Sediment budgets were drafted for two sub-watersheds of the well-studied Boyne-Morris and La Salle River watersheds, located in the Red River Valley, and coded 05OF024 and 05OG008 by the Water Survey of Canada (WSC), respectively. To characterize soil erosion, the sediment budgets used published National Agri-Environmental Health Analysis and Reporting Program (NAHARP) soil erosion risk estimates calculated with the SoilERI model. Sediment transportation was quantified using flow and total suspended solids (TSS) measurements made by the WSC and other organizations. Deposition within the sub-watersheds was quantified through measurements made in road-side ditches (a common sediment sink in the Red River watershed) and inferred through imbalances in the sediment budgets. Rates of soil erosion, deposition within, and transportation out of the 05OF024 sub-watershed were an order of magnitude greater than in the 05OG008 sub-watershed due to differences in basin scale, but relative differences in their rates in each basin were the same. Rates of erosion were 1 order of magnitude greater than rates of deposition in road-side ditches and 3 orders of magnitude greater than transportation past the sub-watershed outlets. Differences between rates of soil erosion and deposition in road-side ditches were noted and attributed to unmeasured deposition in cultivated fields. Rates of deposition in such se

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

Hudson Bay is a large Arctic/sub-Arctic shelf sea that covers an area of approximately 841,000 km2, and is estuarine in character, with a large watershed and more than 40 rivers discharging into the bay. Sediment core data for 18 new cores in Hudson Bay was used to understand the processes effecting sedimentation in the bay. This data was interpreted together with sedimentation rates and inventories of 210Pb and 137Cs from previously published articles, archived cores, and geophysical data from the past four decades. Geophysical data shows that the bulk of sedimentation occurs offshore, between 100 and 150 m depth, on the east and northwest coasts of the bay, localized depressions along the southern coast between 50 and 100 m depth, and basins in the center of the bay. Inventories of 210Pb and 137Cs are variable but overall show a trend of lower inventories in the northwest to higher inventories in the southeast. Both geophysical and geochemical data show that sedimentation in the bay is largely transient with sediment deposits at the base of slopes, in localized depressions, and near the mouths of rivers.