Graduate Theses & Dissertations

Phosphorus delivery in the Rainy-River Lake of the Woods Watershed
Lake of the Woods (LOW) is a large international waterbody which suffers from frequent and widespread algae blooms. Previous studies have highlighted the importance of the lake's largest tributary, the Rainy River (RR) and its significance in total phosphorus (TP) delivery to the LOW. Unfortunately, little is known about TP contributions from the RR and its tributaries within the Canadian portion of the watershed. This thesis examines patterns and sources of TP from four tributaries on the Canadian side of the lower RR region, two of which are predominantly natural, and two that are predominantly agricultural. Relationships between water quality parameters, land use and geologic characteristics were observed over a complete hydrologic year (Oct 1, 2018 - Sept 31, 2019), and through an intensive sampling campaign using a nested watershed approach during the spring high flow and summer low flow periods. Results revealed that TP and total suspended sediment (TSS) concentrations (>100 µg/L and >20 mg/L respectively), and loads (>20 kg/km2 and >3500 kg/km2, respectively), were greater at agricultural sites compared with natural sites (<65 µg/L TP and <15 mg/L TSS concentration, and <20 kg/km2 TP and <4000 kg/km2 TSS export). Total P, TSS, Fe, and Al were significantly positively correlated (R2= 0.26-0.59; p<0.05) and intensive sampling revealed that these relationships were strongest during the spring and at the agricultural sites (R2= 0.73-0.98; p<0.05). In contrast, the summer intensive sampling revealed that TP and redox sensitive Fe were significantly correlated (R2= 0.72; p<0.005), whereas redox insensitive Al and TSS were not, suggesting TP may be sourced via redox processes in the summer due to favourable hydrologic conditions. This was observed not only at sites with high wetland influence, but also at sites with more agricultural presence suggesting that redox sourced TP may also originate from mineral stream bed sediment during low flow periods. This research suggested two primary TP sources in the lower RR region: erosion in the spring, and redox processes (internal release) in the summer. It is recommended that intensive monitoring continue in Canada, and further research be conducted to fully understand the significance of internal P release in the tributaries. Author Keywords: erosion, land use, nutrients, particulates, redox, water quality
Hydrochemistry and critical loads of acidity for lakes and ponds in the Canadian Arctic
Threats such as climate change and increased anthropogenic activity such as shipping, are expected to negatively affect the Arctic. Lack of data on Arctic systems restricts our current understanding of these sensitive systems and limits our ability to predict future impacts. Lakes and ponds are a major feature of the Arctic landscape and are recognized as ‘sentinels of change’, as they integrate processes at a landscape scale. A total of 1300 aquatic sites were assessed for common chemical and physical characteristics. Geology type was found to be the greatest driver of water chemistry for Arctic lakes and ponds. Acid-sensitivity was assessed using the Steady State Water Chemistry model and a subset of 1138 sites from across the Canadian Arctic. A large portion of sites (40.0%, n = 455) were classified as highly sensitive to acidic deposition, which resulted in a median value of 35.8 meq·m―2·yr―1 for the Canadian Arctic. Under modelled sulphur deposition scenarios for the year 2010, exceedances associated with shipping is 12.5% (n = 142) and 12.0% (n = 136) for without shipping, suggesting that impacts of shipping are relatively small. Author Keywords: Acidic deposition, Arctic lakes, Critical loads, Shipping emissions, Steady-State Water Chemistry Model, Water chemistry
Discontinuities in stream networks
The network composition hypothesis (NCH) suggests that i) large confluence symmetry ratios (drainage area of the tributary relative to the mainstem) and ii) landscape differences (differences in landscape characteristics between the mainstem and tributary drainages) lead to greater ecological changes below confluences. As a test of the NCH, 34 confluences were sampled in southern Ontario to examine the effects of these two factors on benthic invertebrate communities to infer the degree of ecological change at confluences. Given the typology of streams surveyed, there was subtle evidence that benthic invertebrate communities below confluences changed as a function of confluence symmetry ratio and landscape differences. This indicates that abrupt changes in stream networks are not as common as theory may suggest. Further support for the network composition hypothesis may be found by examining a wider range of stream types and examining single-species responses. Author Keywords: benthic invertebrates, community similarity, landscape characteristics, stream networks, tributary
Calcium in the Muskoka River Watershed- Patterns, trends, the potential impact of forest harvesting and steps toward an ecosystem approach to mitigation
Decreasing lake calcium (Ca) concentration, in lakes located in base poor catchments of the Muskoka River Watershed (MRW) in south-central Ontario, is a well- established acid-rain driven legacy effect threatening the health and integrity of aquatic ecosystems that can be compounded by additional Ca removals through forest harvesting. The objectives of this thesis were to assess patterns and temporal trends in key water chemistry parameters for a set of lakes in forested catchments in the MRW in south- central Ontario, to predict the pre-industrial steady state lake Ca concentration and the potential impact of harvesting on lake Ca levels in lakes located in managed MRW Crown forests, and to assess potential effects of various mitigation strategies in Ca depleted managed forests. Mean lake Ca (mg L-1) in 104 lakes across the MRW have decreased by 30% since the 1980's with the rate of decrease slowing over time. Mean Lake SO4 (mg L-1), and Mg (mg L-1) concentration also decreased significantly with time (37% and 29%, respectively) again with a declining rate of decrease, while mean lake pH and DOC increased significantly between the 1980's and the 1990's (16% and 12%, respectively) but exhibited no significant pattern after that. Principal components and GIS spatial analyses of 75 lakes with data from 2011 or 2012 water seasons suggested that smaller lakes, at higher elevation in smaller catchments with higher runoff and minimally impacted by the influence of roads and agriculture are associated with lower Ca concentrations and thus are the lakes at risk of amplified Ca depletion from forest harvesting. Spatial analyses of harvested catchments indicated that, under the proposed 10 year land forest management cut volumes, 38% of 364 lakes in the MRW will fall below the critical 1 mg L-1 Ca threshold compared with 8% in the absence of future harvesting. With respect to potential mitigation measures, soil pH and foliar Ca were indicated by meta-analysis to be more responsive to lime addition studies while soil base saturation and tree growth appeared more responsive to wood-ash addition. Future research should address the spatial extent of lakes at risk and identify when critical levels will be reached under harvesting regimes. Further investigation into the use of Ca-addition as a tool for managing the cumulative effects of past, present and future stressors is recommended. Author Keywords: calcium, harvesting, lakes, lime, Muskoka River Watershed, wood-ash

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