Abstract
Headwater streams are important lotic systems that represent more than 80% of the total stream lengths in watersheds. The dynamic coupling of hydrological and biogeochemical processes in headwaters is responsible for regulating the chemical form, residence time and longitudinal transport of nutrients. Over time, stream modification (e.g. to enhance drainage in agricultural watershed) has altered natural stream flow-paths and thus, stream functionality. Such alteration has resulted in degradation of habitat and water quality, both in upland and downstream waters. Currently, nutrients exported from the Grand River (Ontario) watershed are contributing to eutrophication and Harmful Algal Blooms in Lake Erie. With respect to the Grand River watershed, this thesis examined (1) the impact of agriculture on the existing stream network, (2) the utility of the Soil and Water Assessment Tool to simulate hydrology, sediment and nutrient export that closely correlate with measured data, and (3) the application of Best Management Practices in the watershed with the intent of meeting provincial and transnational nutrient targets. The results showed that compared to the actual ground-truthed stream network, the predicted stream network based on topography underpredicted a total of 2,535 km of actual channel present in the watershed. Channels not anticipated by topography were mostly first-order, with low sinuosity, and were most common in areas with high agricultural land use, and are likely excavated extensions to headwater streams to facilitate drainage. Then, the sediment and nutrient loading at Dunnville, discharging to entering Lake Erie, was predicted to be 2.3[superscript⁻1] 105 t yr[superscript-1] of total suspended sediment, 7.9 [superscript⁻1] 103 t yr-1 of total nitrogen, and 2.5 ⁻1 102 t yr-1 of total phosphorus. Finally, implementing wide buffer strips, stabilizing channel banks and grassed waterways were found to be the most effective practices for reducing sediment and phosphorus loading into Lake Erie.
Highlights
1.1 Perspective on Streams and Land Use Modifications1.1.1 The Role of Headwater StreamsStrahler (1952) described headwater streams as those streams which are first order, or that can be viewed on a 1:100,000 scale
The quality of predicted stream networks, based on DEMS at 10-m and 25-m resolution, was assessed by comparing the total channel length predicted by these models versus the actual channel length in the Grand River Basin (GRB) network, and by determining how well the predicted stream channels spatially coincided with actual stream channels
The 10-m resolution Digital Elevation Model (DEM) provided a better correspondence to the actual network, as 95% of the total predicted channel length fell within 17 m of actual channel positions, while 95% of predicted channel length fell within 40 m of actual channel positions for the network derived using the 25-m resolution DEM
Summary
1.1 Perspective on Streams and Land Use Modifications1.1.1 The Role of Headwater StreamsStrahler (1952) described headwater streams as those streams which are first order, or that can be viewed on a 1:100,000 scale. With over 80% of total stream length being headwaters, detailed research on their functions and importance is much needed since they play a major role in determining water quality downstream. Due to their dendritic patterns and their large width to depth ratio, these streams are critical in controlling the amount of nutrients that are exported downstream (Peterson et al 2001). Headwater streams play a major role in processing and retaining phosphorus, regulating downstream delivery to receiving waterbodies (Withers and Jarvie 2008). Water quality (based on dissolved oxygen, total phosphorus and suspended solids) has been consistently rated as poor when measured at the Dunnville Dam monitoring site prior to the Grand River entering Lake Erie (Cooke 2006)
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