Tracking and quantifying hydrologic change in urbanizing watersheds is a complex problem which can vary spatially and temporally throughout the effective catchment area as change occurs. Hydromodification due to urbanization usually results in a larger peak event stream discharge, a change in typical event volume, a reduced lag time between rainfall and stream discharge events, and a more complex falling hydrograph. Recently extracted Environment Canada data have allowed the creation of a high resolution instantaneous stream flow dataset dating to the late 1960s for many Ontario gauge stations. Hydrometric data were obtained for fifteen urban and semi-urban catchments within Southern Ontario ranging in size from ~50km² to 300 km² with urbanized land use assemblages varying from <5% to 80%. Utilizing automated methods, each individual runoff event from the hydrographic record was identified and characterized. Temporal changes to urban land area, land use, and road length were quantified for each watershed from aerial photography spanning the period of record at approximately 8 year intervals allowing identified trends in event hydrograph parameters to be correlated quantitatively with the alteration of the catchment over time. <br> Increasing trends in event peak discharge were identified in all but one study catchment. Event volume was found to be consistently increasing in most of the urban watershed, while trends in event duration were observed but with no clear increasing or decreasing trend. The lack of consistent trends in the timing and distribution of flow during runoff events suggest that build-out, drainage network design, and stormwater management systems play differing roles in the neighbouring urban catchments. Changes to flood recurrence intervals through the period of urbanization were also investigated; peak magnitude of high frequency events is affected to a greater extent than low frequency or flood events. The relative change in return frequency distribution is not consistent between catchments, also the degree of alteration can differ between various recurrence intervals at a gauge. Peak discharge of some return periods appeared to decrease with urban development suggesting that the increased detention brought with urban stormwater management systems have effectively offset the increased runoff due to additional impervious area and improved drainage efficiency. A consistent relationship defining the change in geomorphically significant return periods (i.e. channel forming flow) with urbanization was identified in neighbouring urban catchments.

Anthropogenic disruptions in the form of hydrological alterations, such as dam construction and the associated water diversions are a cause of much upheaval to local and regional ecosystems. Lake 626 within the Experimental Lakes Area of north-west Ontario, along with its downstream wetlands, 626A and 626B are one such system. Construction of a dam at the L626 inflow has completely restricted water flow, reducing and reshaping the watershed, increasing water retention time, and decreasing outflow into the wetlands. This study investigates the state of each wetland through physical and geochemical characterization during the first year following the diversion. Previous studies have found that hydrological diversions in wetlands can lower water table levels, altering soil chemistry and producing a shift in floral and faunal communities. Ultimate consequences involve significant loss of wetland area through conversion to upland habitat. This provides a model for climatic warming scenarios, wherein sustained drought conditions can produce the same result. Boreal wetlands are surprising fragile ecosystems that store massive quantities of carbon and are at risk of releasing it in such situations. One study showed that an extended summer drought in an otherwise average year with above average precipitation produced losses of 90 g C/m2 over the course of the year. Maintenance of reduced-flow in wetlands 626A and 626B is expected to convert the system into a carbon source and reduce overall wetland area. Radiocarbon dating has revealed that following deglaciation, both 626A and 626B basins were open water wetlands, depositing limnic peat for about 3200 and 1300 years respectively. Each site then transitioned into open sedge dominated fen – 626B to the present and 626A until about 2.5 ka BP when Sphagnum began to develop. Wetland 626B is decidedly an open shrub/sedge fen, supporting Myrica gale, Chamaedaphne calyculata and Carex rostrata / lasiocarpa communities. Wetland 626A is a bog/fen complex, sharing similar communities in the fen areas, but housing a large, centrally located bog of shrub species overlying Sphagnum hummocks. Tritium values in 626A were similar to cosmic background levels, indicating that recharge of basal pore water has not occurred in at least 60 years. Tritium in 626B was much higher, suggesting a substantial difference in hydrology or peat hydraulic conductivity between the basins. Measurement of DOC profiles showed high concentrations in near-surface water, reaching over 80 mg/L, and dropping to about 20 mg/L at maximum depths. An opposite trend was seen for DIC and CH4 profiles which increased concentration with depth (25 – 70 mg/L DIC; 75 – 700 μmol/L CH4). Isotopically however, 13C signatures from basal DIC were more positive while signatures from CH4 were typically more negative (-6 ‰ to +4 ‰ DIC; -57 ‰ to -73 ‰ CH4). Breakdown of DOC by LC-OCD showed high concentrations of humic substances and low molecular weight neutrals. The origin of humic substances in surface water became more pedogenic with increasing distance from the L626 outflow, indicating the influence of decaying wetland vegetation on the DOC of adjacent water. A comparison between contemporary and future characterization of boreal peatlands under drought-like conditions will provide a better understanding of the impacts suffered by wetlands during hydrological alterations. The high sensitivity of wetlands to changing hydrology should also provide a measure for gauging the effects of long term climate warming. This will assist in the development of environmental policies to better govern both the establishment of water diversions and the multitude of other practices leading to climate change.

Anthropogenic disruptions in the form of hydrological alterations, such as dam construction and the associated water diversions are a cause of much upheaval to local and regional ecosystems. Lake 626 within the Experimental Lakes Area of north-west Ontario, along with its downstream wetlands, 626A and 626B are one such system. Construction of a dam at the L626 inflow has completely restricted water flow, reducing and reshaping the watershed, increasing water retention time, and decreasing outflow into the wetlands. This study investigates the state of each wetland through physical and geochemical characterization during the first year following the diversion. Previous studies have found that hydrological diversions in wetlands can lower water table levels, altering soil chemistry and producing a shift in floral and faunal communities. Ultimate consequences involve significant loss of wetland area through conversion to upland habitat. This provides a model for climatic warming scenarios, wherein sustained drought conditions can produce the same result. Boreal wetlands are surprising fragile ecosystems that store massive quantities of carbon and are at risk of releasing it in such situations. One study showed that an extended summer drought in an otherwise average year with above average precipitation produced losses of 90 g C/m2 over the course of the year. Maintenance of reduced-flow in wetlands 626A and 626B is expected to convert the system into a carbon source and reduce overall wetland area. Radiocarbon dating has revealed that following deglaciation, both 626A and 626B basins were open water wetlands, depositing limnic peat for about 3200 and 1300 years respectively. Each site then transitioned into open sedge dominated fen – 626B to the present and 626A until about 2.5 ka BP when Sphagnum began to develop. Wetland 626B is decidedly an open shrub/sedge fen, supporting Myrica gale, Chamaedaphne calyculata and Carex rostrata / lasiocarpa communities. Wetland 626A is a bog/fen complex, sharing similar communities in the fen areas, but housing a large, centrally located bog of shrub species overlying Sphagnum hummocks. Tritium values in 626A were similar to cosmic background levels, indicating that recharge of basal pore water has not occurred in at least 60 years. Tritium in 626B was much higher, suggesting a substantial difference in hydrology or peat hydraulic conductivity between the basins. Measurement of DOC profiles showed high concentrations in near-surface water, reaching over 80 mg/L, and dropping to about 20 mg/L at maximum depths. An opposite trend was seen for DIC and CH4 profiles which increased concentration with depth (25 – 70 mg/L DIC; 75 – 700 μmol/L CH4). Isotopically however, 13C signatures from basal DIC were more positive while signatures from CH4 were typically more negative (-6 ‰ to +4 ‰ DIC; -57 ‰ to -73 ‰ CH4). Breakdown of DOC by LC-OCD showed high concentrations of humic substances and low molecular weight neutrals. The origin of humic substances in surface water became more pedogenic with increasing distance from the L626 outflow, indicating the influence of decaying wetland vegetation on the DOC of adjacent water. A comparison between contemporary and future characterization of boreal peatlands under drought-like conditions will provide a better understanding of the impacts suffered by wetlands during hydrological alterations. The high sensitivity of wetlands to changing hydrology should also provide a measure for gauging the effects of long term climate warming. This will assist in the development of environmental policies to better govern both the establishment of water diversions and the multitude of other practices leading to climate change.

Tracking and quantifying hydrologic change in urbanizing watersheds is a complex problem which can vary spatially and temporally throughout the effective catchment area as change occurs. Hydromodification due to urbanization usually results in a larger peak event stream discharge, a change in typical event volume, a reduced lag time between rainfall and stream discharge events, and a more complex falling hydrograph. Recently extracted Environment Canada data have allowed the creation of a high resolution instantaneous stream flow dataset dating to the late 1960s for many Ontario gauge stations. Hydrometric data were obtained for fifteen urban and semi-urban catchments within Southern Ontario ranging in size from ~50km² to 300 km² with urbanized land use assemblages varying from <5% to 80%. Utilizing automated methods, each individual runoff event from the hydrographic record was identified and characterized. Temporal changes to urban land area, land use, and road length were quantified for each watershed from aerial photography spanning the period of record at approximately 8 year intervals allowing identified trends in event hydrograph parameters to be correlated quantitatively with the alteration of the catchment over time. <br> Increasing trends in event peak discharge were identified in all but one study catchment. Event volume was found to be consistently increasing in most of the urban watershed, while trends in event duration were observed but with no clear increasing or decreasing trend. The lack of consistent trends in the timing and distribution of flow during runoff events suggest that build-out, drainage network design, and stormwater management systems play differing roles in the neighbouring urban catchments. Changes to flood recurrence intervals through the period of urbanization were also investigated; peak magnitude of high frequency events is affected to a greater extent than low frequency or flood events. The relative change in return frequency distribution is not consistent between catchments, also the degree of alteration can differ between various recurrence intervals at a gauge. Peak discharge of some return periods appeared to decrease with urban development suggesting that the increased detention brought with urban stormwater management systems have effectively offset the increased runoff due to additional impervious area and improved drainage efficiency. A consistent relationship defining the change in geomorphically significant return periods (i.e. channel forming flow) with urbanization was identified in neighbouring urban catchments.