Search

Concentration – discharge (C – Q) relationships in streamflow can serve a variety of purposes, including elucidating catchment water sources, quantifying chemical weathering, and estimating solute fluxes. Four main C – Q relationships have been identified: dilution (decreasing C with increasing Q), flushing (increasing C with increasing Q), chemostatic (little or no change in C with increasing Q) and chemostochastic (great variation in C relative to that of Q) behaviour. We used a 40‐year data record for 10 headwater forested catchments in central Ontario, Canada, to examine C – Q relationships for a range of geogenic, exogenic and bioactive solutes. The thin overburden cover of this landscape and general absence of deep groundwater contributions to streamflow suggest that streamflow solute concentrations and their relationship with discharge would be sensitive to pronounced changes in climate and atmospheric deposition chemistry over the monitoring period. We explored the temporal and spatial stability of C – Q relationships in response to these changes at annual and seasonal timescales for relatively wet and dry conditions and for periods with relatively high and low atmospheric deposition. Chemostasis dominated C – Q relationships at the annual and seasonal scales for geogenic (e.g., SiO2) and exogenic (e.g., Cl−) solutes, although bioactive solutes (e.g., NO3−, NH4+) exhibited non‐chemostatic behaviour for some catchments, time periods and wetness conditions. C – Q relationships derived at the annual timescale often masked pronounced seasonal shifts in bioactive solute concentration response to changes in streamflow and provide only partial insight into the production and delivery of such solutes in this forest landscape. Relatively subtle changes in overburden thickness across this landscape appeared to explain some of the deviations from widespread chemostasis. Nevertheless, this general chemostatic behaviour was largely temporally stable across catchments and solutes, highlighting its resilience in the face of such non‐stationary influences as climate conditions and atmospheric deposition. [ABSTRACT FROM AUTHOR]

Abstract: Buffer zones are an important component of forest-management strategies and are thought to reduce the impact of nutrients released after harvesting on water quality. Conceptually, steep slopes have shorter [...]

Soil water recharge (R) below 1 m depth was estimated via a 1-d water balance for grasslands, hardwood stands and red pine plantations on the Oak Ridges Moraine (ORM) in southern Ontario, Canada. Annual R values (431-696 mm) were in the order of previous estimates for outcropping sands and gravels on the ORM (∼400 mm); however, they only partially supported hypothesized differences in R between land covers. Annual R was similar for grasslands and hardwood stands and exceeded that for red pine plantations. However, there were no consistent differences in R between land covers for growing or dormant seasons, due to relatively large uncertainties for R estimates as well as inter-site differences in the soil's ability to store and transmit inputs below 1 m. Nevertheless, shifts in annual R appear to have accompanied historical land cover changes from hardwood-conifer stands→agricultural fields→red pine plantations→regenerating hardwoods. Growing season R in hardwoods makes a larger contribution to total R than for other land covers, partly due to spatially focused throughfall and stemflow contributions to R. Results highlight the role of land cover differences when assessing spatial variations in R along the ORM. [ABSTRACT FROM AUTHOR]

Trees whose branches slope towards or away from the bole differ in the spatial pattern of water delivery to the soil surface beneath their canopies. This study examines the implications of these differences for soil water recharge below 1 m depth in a managed forest on the Oak Ridges Moraine in southern Ontario. Throughfall and vertical profiles of soil water content at varying distances from the boles of a sugar maple and two red pines of differing ages (36 and 57 years old) were measured during rainfall inputs in the summer of 2009 and in the spring/early summer of 2010. Stemflow fluxes were estimated using measurements on nearby trees with similar morphologies. A water balance approach was used to estimate recharge at each distance from the bole, as well as for the entire sampled area beneath each tree's canopy. Throughfall was more than 1.3 times above-canopy rainfall within 0.5 m of the bole of the sugar maple, and stemflow volumes were at least an order-of-magnitude greater than those for the pines in both 2009 and 2010. These focused inputs resulted in greater near-bole soil water contents and soil water recharge in excess of above-canopy rainfall within 0.3 m of the sugar maple bole. In contrast, both young and old pines showed no significant trends in throughfall with distance from the bole, and minor stemflow volumes made insignificant contributions to recharge near the pine boles. Recharge was significantly greater than 0 beneath the canopy of all three trees in both years and was generally similar between trees. The exception was recharge beneath the sugar maple in 2010, which exceeded that of the young red pine as a result of the former's large stemflow fluxes. Results suggest the transition from red pine plantations to mixed hardwood-conifer stands will not alter total soil water recharge during spring and summer rainfall inputs; nevertheless, it will generate marked changes in the spatial pattern of sub-canopy recharge in this forest landscape on the Oak Ridges Moraine. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hydrologic classification is useful for data organization, transfer of model parameters and estimation of hydrologic sensitivity to disturbance and climatic change. Stream-flow regime has frequently been used as a basis for classification, typically by mapping regimes defined by stream-flow data from a gauging network. As an alternative, we hypothesized that ecological classification systems can predict stream-flow regime because they are based on the same characteristics that control run-off generation (soils, climate and topography). A multivariate regression tree (MRT) was used to relate stream-flow regime to the fractional coverages of the Biogeoclimatic Ecological Classification (BEC) zones within the catchment for gauged streams in British Columbia, Canada. Although the MRT identified a realistic set of regimes, only a small number of BEC zones were used as predictors, reflecting bias in the gauging network. To avoid this bias, we used a water balance model to compute mean monthly stream flow for 932 ungauged basins in British Columbia that were generated with areas between 10 and 1000 km2; these monthly stream flows were used to train an MRT model based on BEC zone coverages. This model predicted the regime at gauged basins nearly as accurately as the water balance model for pluvial, nival and glacier-supported nival regimes. Difficulties occurred in smaller basins and in specific regions where the local BEC zones were not included as predictors. Coastal hybrid nivo-pluvial regimes were poorly predicted. With further development, ecological classification systems could have great value as a tool for hydrologic classification for both research and operational applications. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article examines the implications of changes in the annual water balance and seasonal streamflow distribution for water quality and in-stream ecology in northern regions. An overview of how hydrological processes in northern catchments will be affected by changes in magnitude, timing and phase of precipitation, along with changing temperatures is presented. It describes the role of vegetation in the dynamics of change in water balance in catchments using the Budyko model.

Copyright of Canadian Water Resources Journal / Revue Canadienne des Ressources Hydriques is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Increased attention is being paid to the role of reforestation in strategies for sustainable forest management, landscape restoration and carbon sequestration. Reforestation of drainage basins is generally assumed to reduce annual streamflow as well as peak and low flows. However, most studies of reforestation effects on streamflow have been conducted on small experimental basins, and the applicability of their results to larger basins is unclear. This study revisits an earlier examination of streamflow response to headwater reforestation in a 267 km2 basin (Ganaraska River) in southern Ontario, Canada for 1945-2007. Forest cover in the basin headwaters increased from 13 km2 in 1945 to 31 km2 by 1990, with most of this change between 1950 and 1965. Streamflow metrics from the reforested basin and two headwater sub-basins were compared to those from a nearby basin and sub-basin of similar size and physiography to the Ganaraska basins but without extensive headwater reforestation. No temporal trends were found for inter-basin differences in annual runoff or runoff ratios for the entire Ganaraska basin or its largest sub-basin; however, reforestation appears to have reduced several metrics of peak streamflow at the basin and sub-basin scale. Relationships between high flows classified according to generating event type and the associated precipitation depth suggest that expansion of forest cover in the Ganaraska River basin (GRB) and associated changes in microclimatic conditions have reduced the potential for frozen soil to generate surface runoff and high flows in response to rain-on-snow during spring snowmelt. This was accompanied by increased low flows from the GRB and its sub-basins from 1960 to 2007 relative to the control basin, suggesting that the expanded forest cover has enhanced groundwater recharge by prolonging spring snowmelt and promoting infiltration of rainfall and snowmelt inputs relative to non-forested areas. Some discrepancies between these results and those of other studies of streamflow response to reforestation may be attributed to the relatively large size of the GRB and the limited extent of reforestation. Nevertheless, the results highlight the importance of considering how reforestation may affect key hydrologic processes in a given landscape when predicting the resulting streamflow response. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents a study which focuses on the significance of rain-on-snow (ROS) events regarding nitrate (NO3-3) exports on the 18 forested catchments in Ontario. It mentions that to determine the minimum daily flow of the catchments in winter, the daily streamflow data was utilized wherein the winter export from 1928-1987 was also calculated. The study reveals that the different magnitudes and frequencies of ROS has been experienced by the catchments due to rainfall variation.

The ecological integrity of riverine ecosystems is dependent upon the natural flow regime of the river system. Maintaining natural variability in the flow regime is critical for conserving the structure and function of riverine ecosystems. This research seeks to determine relations between natural variability in the flow regime and basin scale. A distributed hydrologic model was used to characterize the natural flow regime of basins from first to fifth order within tributaries of the Batchawana River in the Algoma Highlands of central Ontario using the range of variability approach (RVA). A 30-year simulated flow record was used to calculate natural variability in the flow regime, defined by the S80 [(90th percentile - 10th percentile)/median]. Flow variability under wetter conditions was similar across all basins, regardless of scale. Conversely, flow variability under drier conditions was scale-dependent, with smaller basins (<600 ha) showing a large range in variability and larger basins (>600 ha) showing a smaller range in variability that converged toward a constant with increasing area. The effect of basin area on flow variability suggested the existence of a representative elementary area (REA). Within the REA, morphometric sources of natural variability were determined through multivariate regression analyses. A combination of indices describing the near-stream riparian area within a basin, median basin residence time, and basin curvature was significantly related to flow variability under drier conditions. These findings present a potential management template for establishing reference conditions against which impacts of disturbance on flows throughout a regional drainage basin may be measured. [ABSTRACT FROM AUTHOR]

Impacts of forest harvesting on groundwater properties, water flowpaths and streamflow response were examined 4 years after the harvest using a paired-basin approach during the 2001 snowmelt in a northern hardwood landscape in central Ontario. The ability of two metrics of basin topography (Beven and Kirkby's ln( a/tan β) topographic index (TI) and distance to stream channel) to explain intra-basin variations in groundwater dynamics was also evaluated. Significant relationships between TI and depth to potentiometric surface for shallow groundwater emerged, although the occurrence of these relationships during the melt differed between harvested and control basins, possibly as a result of interbasin differences in upslope area contributing to piezometers used to monitor groundwater behaviour. Transmissivity feedback (rapid streamflow increases as the water table approaches the soil surface) governed streamflow generation in both basins, and the mean threshold depths at which rapid streamflow increases corresponded to small rises in water level were similar for harvested (0·41 ± 0·05 m) and forested (0·38 ± 0·04 m) basins. However, topographic properties provided inconsistent explanations of spatial variations in the relationship between streamflow and depth to water at a given piezometer for both basins. Streamflow from the harvested basin exceeded that from the forested basin during the 2001 melt, and hydrometric and geochemical tracer results indicated greater runoff from the harvested basin via surface and near-surface pathways. These differences are not solely attributable to harvesting, since the difference in spring runoff from the harvested basin relative to the forested control was not consistently larger than under pre-harvest conditions. Nevertheless, greater melt rates following harvesting appear to have increased the proportion of water delivery to the stream channel via surface and near-surface pathways. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Hydrological Processes is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Coupling of vertical and lateral preferential flow paths was examined on a forested slope with thin soil cover during artificial irrigations. Point-scale infiltration was measured at sites with differing soil macroporosities using vertical profiles of time domain reflectometry probes and suction samplers. Lateral fluxes of water and solutes from the slope were determined at a through flow trench. Sites with greater macroporosities tended to exhibit vertical preferential flow, while infiltration at sites with relatively small macroporosities was largely by vertical propagation of a well defined wetting front through the soil profile. Generation of vertical preferential flow at sites with relatively large macroporosities increased with input intensity. Lateral macropores made a minor contribution to slope runoff. Instead, runoff largely occurred in a thin saturated layer at the soil-bedrock interface, both in a highly conductive zone at the bedrock surface and in the overlying saturated soil matrix. Some assumptions underlying the use of isotopic and geochemical tracers to study runoff generation are called into question by complex mixing of event and pre-event water in this saturated layer. Soil depth, bedrock topography, and antecedent soil wetness determine the thickness, connectivity, and upslope extent of the pre-event saturated layer above the bedrock surface. These, in turn, control whether vertical preferential and matrix flow reaching the bedrock surface participate in slope runoff. [ABSTRACT FROM AUTHOR]

Approximately 42% of Canada is covered by forests, which in turn canbe subdivided into nine distinct forest ecozones. Many forested ecozones are located in northern Canada, where cold winters and cool summers provide forest environments that are less well-understood than those in more temperate locations. A number of major developments in recent years have stressed the need for enhanced understanding of hydrological processes in these forest landscapes. These include an increased emphasis on sustainable forest management in Canada as well as major scientific initiatives (e.g. BOREAS) examining water, carbon and energy fluxes in forest ecosystems, with a particular focus on borealand subarctic forests. Recent progress in our understanding of forest hydrology across Canada is reviewed. Studies of hydrological processes across the spectrum of forest ecozones are highlighted, as well as work on hydrological responses to forest disturbance and recovery. Links between studies of hydrological processes in Canada's forests and other fields of research are examined, with particular attention paid to ongoing efforts to model hydrological impacts and interactionswith the climate, biogeochemistry, geomorphology and ecology of forested landscapes. [ABSTRACT FROM AUTHOR]

Spatial distribution of soil macroporosity was determined for a forest podzol from tension infiltrometer measurements at the soil surface. Surface-derived macroporosity values were compared with point infiltration characteristics obtained from soil water content and soil water chemistry measurements during an experimental irrigation, and withparameters of a kinematic wave model applied to soil water content data. Macroporosity estimated by the tension infiltrometer ranged from0.00087 to 0.0219% of soil volume, and infiltration at these two sites was dominated by propagation of a well-defined wetting front through the soil profile and bypass flow via soil macropores, respectively. Infiltration at sites with intermediate macroporosities reflected acombination of these two processes, although results were inconclusive at one site owing to lateral flow at the base of the soil profile.There was no agreement between macroporosities estimated by the tension infiltrometer and the kinematic wave model. The maximum soil conductance parameter within the profile at a site, however, was related directly to the surface-derived macroporosity. The partial agreement between surface-derived macroporosity estimates and point infiltration characteristics shown here supports the use of tension infiltrometry as a rapid, non-destructive method of assessing spatial variations in the relative contribution of macropore flow to the infiltration process. [ABSTRACT FROM AUTHOR]

Environmental impacts of road deicing salt are well known, although salt pathways following application have rarely been quantified. Deicing salt (NaCl) fate was determined from retention and loss in snow cover adjacent to a 14-km section of highway in southern Ontario during the 1994--1995 winter. Total salt application was (approx.) 530 mg (29--74 kg m-1 length). Retention in snow cover in the highway right-of-way (ROW) decayed as a power function of distance from the highway, although melting of proximal snowbanks with high salt loads disrupted this pattern. Peak concentrations in snowbanks reached 6506 (Na+) and 9916 (Cl-) mg L-1. Wind transport of salt from the ROW was minor and restricted to relatively exposed sites. Almost all applied NaCl reached the soil surface via (i) direct runoff and infiltration of saline water from the read into the shoulder and ROW, and (ii) transfer of salt to snow cover adjacent to the highway and release during snowmelt. Total salt flux along the two pathways during a 49-d period was similar. Salt transfer via road runoff occurred during or shortly after application, unlike the intermittent fluxes from snow to soil surfaces in the ROW during this period. The latter were relatively uniform along the highway (3--5 kg m-1 length of highway), accounting for 39 to 65% of applied NaCl. However, magnitude and timing of water and salt fluxes from snow to soil varied within the ROW and should he considered when modeling salt transport to groundwater. [ABSTRACT FROM AUTHOR]

Simultaneous monitoring of conservative and non-conservative tracersin streamflow offers a valuable means of obtaining information on the age and flow paths of water reaching the basin outlet. Previous studies of stormflow generation in a small forested basin on the Canadian Shield used isotopic (IHS) and geochemical hydrograph separations (GHS) to infer that some event water during snowmelt reaches the stream via subsurface pathways, and that surface water runoff is generatedby direct precipitation on to saturated areas (DPSA) in the stream valley. These hypotheses were tested for rainfall inputs using simultaneous IHS (18O) and GHS (dissolved silica) of basin stormflow, supplemented by hydrochemical and hydrometric data from throughflow troughs installed on basin slopes. Comparison of pre-event and subsurface water hydrographs did not provide conclusive evidence for subsurface movement of event water to the stream, owing to the appreciable uncertainty associated with the hydrograph separations. However, IHSs of runoff at the soil--bedrock interface on basin slopes indicated that event water comprised 25--50% of total runoff from areas withdeep soil cover, and that these contributions supplied event water flux from the basin in excess of that attributable to DPSA. The surface water component of stormflow estimated from the GHS was also largely the result of DPSA. GHS assumes that dissolved silica is rapidly and uniformly taken up by water infiltrating the soil and that water moving via surface pathways retains the low dissolved silica level of rainfall; however, neither assumption was supported by the hillslope results. Instead, results suggest that the observed depression of silica levels in basin stormflow previously attributed to dilution by DPSA was partly a function of transport of dilute event water to the channel via preferential pathways. Implications of these results for thegeneral use of simultaneous IHS and GHS to infer hydrological processes [ABSTRACT FROM AUTHOR]