Dean Jeffries | Environment Canada (original) (raw)

Papers by Dean Jeffries

The International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers a... more The International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes (ICP Waters) is designed to assess the degree and geographical extent of acidification of surface waters. During the last ten years international emission reduction measures in Europe and Northe America have resulted in a decrease in atmospheric sulphur deposition of up to 50%. Nitrogen deposition has stayed almost constant. Trends in surface water chemistry at the ICP Waters sites were calculated by applying the Nonparametric Seasonal Kendal Test and, on a regional scale, by Trend Meta-Analyses. Empirical relationships between nitrogen deposition and stages of nitrogen saturation were used to assess the importance of nitrogen leaching at the sites. To show effects of acidification on aquatic fauna (geographic extent and long-term trends) presence/absence studies, acidification indexes and correlation analysis were used. Trends in water chemistry indicate that sulphate concentrations are decreasing at almost all ICP Waters sites, and in almost all cases the decreases in the 1990s are larger than in the 1980s. This is partly also reflected in a recovery of the invertebrate fauna at many sites. Decreasing sulphate concentrations emphasize the importance of nitrate as the second important acidifying anion. Besides nitrogen deposition, the overall nitrogen status of ecosystems, changes in climate extremes and hydrology can have strong influences on leaching of excess nitrate (and ammonium) from a watershed.Norwegian Pollution Control Authority-SF

Revue des sciences de l'eau, 1998

Cet article représente une évaluation de l'état actuel et des tendances observées dans les éc... more Cet article représente une évaluation de l'état actuel et des tendances observées dans les écosystèmes lacustres, ainsi que de leur état futur probable lorsque les réductions d'émissions requises dans le cadre de l'Entente Canada-États-Unis sur la qualité de l'air auront été effectives. Outre une synthèse des faits saillants de ce dossier pour l'ensemble du Canada, le présent article s'appuie aussi sur l'ensemble des données physico-chimiques récentes (8874 échantillons) observées sur 2779 lacs de l'est canadien, ainsi que celles recueillies (1012 échantillons) sur 252 lacs de l'ouest canadien depuis 1985. Des données biologiques (poissons, benthos, zooplancton et oiseaux aquatiques) ont également été inventoriées pour identifier l'ampleur des dommages biologiques. Les nombreux lacs ayant subi une acidification anthropique récente sont situés pour la plupart dans l'est du Canada où les dépôts de SO- sont élevés. La sensibilité des sols inf...

Water Resources Research, 1996

During the past decade, significant spatial and temporal variability in the release of nitrate-ni... more During the past decade, significant spatial and temporal variability in the release of nitrate-nitrogen (N) from catchments in a sugar maple forest in central Ontario was observed. To explain this variability, we tested the flushing hypothesis , where, when the soil saturation deficit is high, N accumulates in the upper layers of the soil and, as the soil saturation deficit decreases, the formation of a saturated subsurface layer flushes N from the upper layers of the soil into the stream. We used the Regional Hydro-Ecological Simulation System to simulate water, carbon, and N dynamics. A N flushing index was modeled as S/S 30 , the ratio of the current day saturation deficit to the previous 30-day average saturation deficit. A N source index was modeled as the ratio of N supply/demand. The relationship between the simulated N indices and the observed release of N indicated two mechanisms for the release of N from catchments: (1) a N flushing mechanism, where the N-enriched upper layer of the soil is flushed, after a period of low demand for N by the forest (e.g., during spring snowmelt and autumn stormflow, the water table rising into previously unsaturated parts of a N-enriched soil profile) or after a period of high demand for N by the forest (e.g., during summer droughts, the water table rising into previously saturated parts of a N-impoverished soil profile following a period of enhanced rates of nitrification); and (2) a N draining mechanism, where spring snowmelt recharge of the groundwater translocates N from the upper layer of the soil into deeper hydrological flow pathways that are released slowly over the year.

Soil Biology and Biochemistry, 2003

In central Ontario, elevated SO 4 concentrations and export have been measured in both upland and... more In central Ontario, elevated SO 4 concentrations and export have been measured in both upland and wetland-draining catchments following summer droughts, although the source of excess SO 4 is unclear. The objective of this study was to determine the effects of drying and rewetting and temperature, respectively, on the release of SO 4 from the primary S pools in wetlands (Sphagnum and peat) and uplands (forest floor and mineral soil), using material collected from the PC1 catchment in Haliburton County, and from catchment S50 in the Turkey Lakes Watershed. Peat exhibited the most marked response to drying of the four materials considered, and within 24 h of re-wetting dried peat from both catchments released 3-4 times more SO 4 (50 -67 mg kg 21 S-SO 4 ) than continuously moist peat (16 mg kg 21 S-SO 4 ), although temperature had only a marginal effect on SO 4 concentrations. There was no immediate response of Sphagnum to either drying or temperature, although S-SO 4 concentrations in Sphagnum tended to increase over the 30-day (d) incubation. There was a small but immediate increase in S-SO 4 concentrations in forest floor material (LFH) from both catchments within the first 24 h of incubation, which was greatest in treatments that were dried and/or incubated at a higher temperature. In contrast, neither temperature nor drying appeared to affect SO 4 release from mineral soil collected from either site. Results of laboratory incubations suggest that increases in SO 4 concentration that have been reported in wetland-draining streams immediately following summer dry periods may be quantitatively explained by drying and rewetting of peat rather than increased mineralization in Sphagnum. Similarly, the higher SO 4 concentrations that have been measured in upland streams following summer droughts may in part be due to enhanced SO 4 release from the forest floor following drying and re-wetting. In contrast, while the mineral soil constitutes a large pool of total S, it does not appear to be responsive to changes in moisture or temperature in the short-term (, 30 d) and therefore likely does not contribute to reported climate-related temporal variations in stream SO 4 .

Limnology and Oceanography, 2010

We analyzed the 21-yr dynamics of dissolved organic carbon (DOC) in 55 lakes during ice-free peri... more We analyzed the 21-yr dynamics of dissolved organic carbon (DOC) in 55 lakes during ice-free periods in five regions across eastern Canada in relation to total solar radiation (TSR), precipitation, air temperature, sulfate deposition (SO 4 ), Southern Oscillation Index (SOI), North Atlantic Oscillation, and Pacific Decadal Oscillation (PDO). A synchronous pattern in DOC was found among lakes within each region; however, a synchronous pattern in DOC was not found among regions, except for Kejimkujik and Yarmouth. Long-term trends of increasing or decreasing DOC concentration were not evident except at the Experimental Lakes Area (ELA), where an increase in DOC correlated with a decrease in summer TSR and an increase in summer precipitation. Annual mean temperature increased at the Nova Scotia and Turkey Lakes Watershed regions (TLW) over the study period, but there was no corresponding change in DOC. TSR and precipitation were important explanatory variables across all regions, except for the TLW. Summer TSR, or annual TSR, had a negative relationship, while summer precipitation had a positive relationship with the temporal DOC pattern in all regions except TLW. TSR and precipitation explained 78%, 49%, and 84% of the variation in the long-term DOC patterns at Dorset, ELA, and Nova Scotia (NS) regions, respectively. In contrast, the long-term pattern in DOC at TLW was only weakly related to SOI and PDO.

Limnology and Oceanography, 1996

A distributed data and simulation system for forested watersheds was used to investigate the pote... more A distributed data and simulation system for forested watersheds was used to investigate the potential changes in watershed hydrological and ecological processes under hypothesized climate change scenarios. RHESSys (Regional HydroEcological Simulation System) incorporates a spatial representation of nested catchment and lake systems in a GIS, along with a set of process submodels to compute local flux and storage of energy, water, carbon, and nutrients. A hierarchy of potential climate change shifts in weather, forest canopy physiological processes, and forest cover were used to operate RHESSys for comparison with control simulations for present-day conditions. Use of projected temperature and precipitation changes alone led to qualitatively different forecasts of watershed climate change impact when compared to simulations that also incorporated adjustment of canopy physiology to elevated concentrations of atmospheric CO*. In addition, ecosystem processes may be more resilient to climate change due to the existence of a series of offsetting effects. Annual net effects on specific processes such as watershed outflow and forest productivity may qualitatively vary from year to year rather than showing consistent increases or decreases relative to current conditions. The model results illustrate the significance of incorporating a reasonable description of terrestrial ecosystem processes within the contributing watershed when assessing the impact of climate change.

Lake and Reservoir Management, 1994

Page 1. Lakeshore Capacity Study: Part I—Test of Effects of , Shoreline Development on the Trophi... more Page 1. Lakeshore Capacity Study: Part I—Test of Effects of , Shoreline Development on the Trophic Status of Lakes 1 P. Dillon Ontario Ministry of Environment and Energy, Dorset Research Centre, Bellwood Acres Road, PO Box 39, Dorset, Ontario POA 1 E0, Canada. ...

Journal of Limnology, 2010

Based on minimal information, lakes in the western Canadian provinces of Manitoba (MB) and Saskat... more Based on minimal information, lakes in the western Canadian provinces of Manitoba (MB) and Saskatchewan (SK) have long been considered unaffected by acid rain. However, emissions of acidifying pollutants from MB smelters and oil sand processing in Alberta (AB) may pose a developing threat. Surveys of 347 lakes located on geologically sensitive terrain in northern MB and SK were conducted to assess their acidification sensitivity and status. The survey domain (~193,000 km 2 ) contained 81,494 lakes ≥1 ha in area. Small lakes dominated the inventory in terms of numbers, and large lakes dominated in terms of area. Survey lakes were selected using a stratified-random sampling design in 10 sampling blocks within the overall survey domain. Few lakes had pH <6, and only three (all in SK) were acidic, i.e., Gran Alkalinity (Alk) <0 μeq L -1 . A broad range in lake sensitivity was apparent, and very sensitive lakes (low specific conductance, base cations and Alk) were present in all sampling blocks. Dissolved organic carbon (DOC) was an important constituent of many lakes. Critical loads (CL) of acidity calculated using the Steady-State Water Chemistry model (SSWC) revealed extremely low 5th percentile values for every block (range 1.9 to 52.7 eq ha -1 y -1 ). Block CL exceedances calculated using estimated S and N deposition for 2002 ranged from 54.5 to 909 eq ha -1 y -1 . The largest exceedances were for sampling blocks located near smelter sources or downwind of the oil sands. Lake chemistry revealed by our surveys was compared to others conducted both nearby and outside Canada.

Hydrological Processes, 1997

The hydrological sensitivities to long-term climate change of a watershed in Eastern Canada were ... more The hydrological sensitivities to long-term climate change of a watershed in Eastern Canada were analysed using a deterministic watershed runo model developed to simulate watershed acidi®cation. This model was modi®ed to study atmospheric change eects in the watershed. Water balance modelling techniques, modi®ed for assessing climate eects, were developed and tested for a watershed using atmospheric change scenarios from both state of the art general circulation models and a series of hypothetical scenarios. The model computed daily surface, inter-and groundwater ows from the watershed. The moisture, in®ltration and recharge rate are also computed in the soil reservoirs. The thirty years of simulated data can be used to evaluate the eects of climatic change on soil moisture, recharge rate and surface and subsurface¯ow systems. The interaction between surface and subsurface water is discussed in relation to climate change. These hydrological results raise the possibility of major environmental and socioeconomic diculties and have signi®cant implications for future water resource planning and management.

Hydrological Processes, 2001

Consistent relationships between groundwater conditions and topographic properties in small drain... more Consistent relationships between groundwater conditions and topographic properties in small drainage basins would assist the study and modelling of basin hydrology and hydrochemistry. Hydrochemical simulation using topographically based models would benefit in particular from the linkage of groundwater residence times to topographic indices, such as the ln(a/ tanˇ) index of Beven and Kirkby. Hypothesized associations between this index and groundwater characteristics were tested during the spring 2000 snowmelt in two sub-basins in the Turkey Lakes Watershed near Sault Ste Marie, ON. One sub-basin is in mature hardwood forest, and the other was clearcut in the fall of 1997. Piezometric surface elevations were monitored in each sub-basin throughout the melt, and the topographic index value for each piezometer was determined. The υ 18 O signatures of input water and groundwater were also measured. Mean groundwater residence times were obtained using the exponential system response function, which generally produced good fits to the observed groundwater υ 18 O time series in both sub-basins. There were significant contrasts in groundwater conditions between the sub-basins. The forested sub-basin exhibited higher and more temporally variable piezometric surface elevations and a greater contrast between υ 18 O signatures and water residence times in shallow versus deeper groundwater relative to the harvested sub-basin. Patterns of groundwater residence times in the subbasins were supported by pre-harvest groundwater chemistry; however, data from the two sub-basins largely failed to support the hypothesized relationships between groundwater conditions and topographic index values. Methodological limitations that may have precluded a more rigorous test of the hypotheses are reviewed, and the potential for using groundwater residence times to evaluate the impacts of forest harvesting on basin hydrochemistry is briefly discussed.

Environmental Science & Technology, 2004

In this study we have analyzed the hydrochemical effect of drought conditions during 311 hydrolog... more In this study we have analyzed the hydrochemical effect of drought conditions during 311 hydrological episodes in nine headwater streams in central Ontario over the past 20 years. Acid Neutralization Capacity (ANC) was logarithmically correlated (p<0.05) to antecedent discharge in eight of the nine streams, with the largest decline in ANC occurring after low antecedent flow. In eight of the nine streams SO 4 2was the most important driving mechanism of ANC decline, but dilution as well as organic acidity was important in several streams. No decrease in the SO 4 2driven ANC decline was observed over the 20 year study period despite a ∼40% reduction in SO 4 2deposition. The strong correlation between ANC decline and low antecedent discharge demonstrates that episodic acidification during rain events is strongly associated with preceding drought conditions, especially in wetland-dominated catchments. The results have important implications for recovery from acidification, especially in northern ecosystems where climate scenarios forecast that warmer and drier conditions will be more common.

Environmental Pollution, 1992

Fifty-six headwater Canadian Shield lakes were repetitively sampled from 1979 to 88 to determine ... more Fifty-six headwater Canadian Shield lakes were repetitively sampled from 1979 to 88 to determine their response to changes in acidic deposition of the period. Annual wet sulphate loadings varied between 38 and 83 meq m(-2), with highest deposition in the late 1970s followed by somewhat lower but variable deposition in the 1980s. Median pH of the lakes increased 0.42 pH units from 1979 to 1985 and decreased by 0.15 units between 1985 and 1988. Short water renewal times (x=1.1 y) promoted rapid equilibration. Since lake were so responsive to changes in SO4(2-) inputs, they were at or near steady state at all times. Comparison of predicted original pH and ANC with 1979 data indicate a median decline of 0.45 pH units and a loss of 34 microeq litre(-1). ANC. Four of 9 lakes were found to be historically fishless, based on the continued presence of Chaoborus americanus in sediment cores. The remaining five lakes historically had fish populations, but fish were not collected in 1979 when pH ranged betwen 4.6 and 5.3. By 1987, fish species were found in five of these lakes where pH had increased on average by 0.9 pH units. Our data indicate that water quality improvements could allow for the reinvasion or resumption of recruitment for a significant number of Ontario lakes.

Environmental Monitoring and Assessment, 2005

The New England Governors and Eastern Canadian Premiers (NEG/ECP) adopted the Acid Rain Action Pl... more The New England Governors and Eastern Canadian Premiers (NEG/ECP) adopted the Acid Rain Action Plan in June 1998, and issued a series of action items to support its work toward a reduction of sulfur dioxide (SO 2 ) and nitrogen oxide (NO x ) emissions in northeastern North America. One of these action items was the preparation of an updated critical load map using data from lakes in the NEG/ECP area. Critical load maps provide a more complete index of the surface water sensitivity to acidification. Combined sulfur and nitrogen critical loads and deposition exceedances were computed using Henriksen's Steady-State Water Chemistry (SSWC) model. Results show that 28% of all 2053 lakes studied have a critical load of 20 kg/ha/year or less, making them vulnerable to acid deposition. Emission reductions, and more specifically SO 2 emission reductions have proven beneficial because critical loads were exceeded in 2002 for 12.3% of all studied lakes. Those lakes are located in the more sensitive areas where geology is carbonate-poor. Of these lakes, 2.9% will never recover even with a complete removal of SO 4 deposition. Recovery from acidification for the remaining 9.4% of the lakes will require additional emission SO 2 reductions.

Drugs & Therapy Perspectives, 2014

Canadian Journal of Fisheries and Aquatic Sciences, 1988

Canadian Journal of Fisheries and Aquatic Sciences, 1988

ABSTRACT

Canadian Journal of Fisheries and Aquatic Sciences, 1988

Page 1. Chemica ogical Charaderistics of the Turkey Lakes Watershed, Central Ontario, Canada Dean... more Page 1. Chemica ogical Charaderistics of the Turkey Lakes Watershed, Central Ontario, Canada Dean S. Jeffries /Vationat Water Research Institute, Canada Centre for Inland Waters, Bur%ington, One. L7W 4A6 John RM Kelso ...

The International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers a... more The International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes (ICP Waters) is designed to assess the degree and geographical extent of acidification of surface waters. During the last ten years international emission reduction measures in Europe and Northe America have resulted in a decrease in atmospheric sulphur deposition of up to 50%. Nitrogen deposition has stayed almost constant. Trends in surface water chemistry at the ICP Waters sites were calculated by applying the Nonparametric Seasonal Kendal Test and, on a regional scale, by Trend Meta-Analyses. Empirical relationships between nitrogen deposition and stages of nitrogen saturation were used to assess the importance of nitrogen leaching at the sites. To show effects of acidification on aquatic fauna (geographic extent and long-term trends) presence/absence studies, acidification indexes and correlation analysis were used. Trends in water chemistry indicate that sulphate concentrations are decreasing at almost all ICP Waters sites, and in almost all cases the decreases in the 1990s are larger than in the 1980s. This is partly also reflected in a recovery of the invertebrate fauna at many sites. Decreasing sulphate concentrations emphasize the importance of nitrate as the second important acidifying anion. Besides nitrogen deposition, the overall nitrogen status of ecosystems, changes in climate extremes and hydrology can have strong influences on leaching of excess nitrate (and ammonium) from a watershed.Norwegian Pollution Control Authority-SF

Revue des sciences de l'eau, 1998

Cet article représente une évaluation de l'état actuel et des tendances observées dans les éc... more Cet article représente une évaluation de l'état actuel et des tendances observées dans les écosystèmes lacustres, ainsi que de leur état futur probable lorsque les réductions d'émissions requises dans le cadre de l'Entente Canada-États-Unis sur la qualité de l'air auront été effectives. Outre une synthèse des faits saillants de ce dossier pour l'ensemble du Canada, le présent article s'appuie aussi sur l'ensemble des données physico-chimiques récentes (8874 échantillons) observées sur 2779 lacs de l'est canadien, ainsi que celles recueillies (1012 échantillons) sur 252 lacs de l'ouest canadien depuis 1985. Des données biologiques (poissons, benthos, zooplancton et oiseaux aquatiques) ont également été inventoriées pour identifier l'ampleur des dommages biologiques. Les nombreux lacs ayant subi une acidification anthropique récente sont situés pour la plupart dans l'est du Canada où les dépôts de SO- sont élevés. La sensibilité des sols inf...

Water Resources Research, 1996

During the past decade, significant spatial and temporal variability in the release of nitrate-ni... more During the past decade, significant spatial and temporal variability in the release of nitrate-nitrogen (N) from catchments in a sugar maple forest in central Ontario was observed. To explain this variability, we tested the flushing hypothesis , where, when the soil saturation deficit is high, N accumulates in the upper layers of the soil and, as the soil saturation deficit decreases, the formation of a saturated subsurface layer flushes N from the upper layers of the soil into the stream. We used the Regional Hydro-Ecological Simulation System to simulate water, carbon, and N dynamics. A N flushing index was modeled as S/S 30 , the ratio of the current day saturation deficit to the previous 30-day average saturation deficit. A N source index was modeled as the ratio of N supply/demand. The relationship between the simulated N indices and the observed release of N indicated two mechanisms for the release of N from catchments: (1) a N flushing mechanism, where the N-enriched upper layer of the soil is flushed, after a period of low demand for N by the forest (e.g., during spring snowmelt and autumn stormflow, the water table rising into previously unsaturated parts of a N-enriched soil profile) or after a period of high demand for N by the forest (e.g., during summer droughts, the water table rising into previously saturated parts of a N-impoverished soil profile following a period of enhanced rates of nitrification); and (2) a N draining mechanism, where spring snowmelt recharge of the groundwater translocates N from the upper layer of the soil into deeper hydrological flow pathways that are released slowly over the year.

Soil Biology and Biochemistry, 2003

In central Ontario, elevated SO 4 concentrations and export have been measured in both upland and... more In central Ontario, elevated SO 4 concentrations and export have been measured in both upland and wetland-draining catchments following summer droughts, although the source of excess SO 4 is unclear. The objective of this study was to determine the effects of drying and rewetting and temperature, respectively, on the release of SO 4 from the primary S pools in wetlands (Sphagnum and peat) and uplands (forest floor and mineral soil), using material collected from the PC1 catchment in Haliburton County, and from catchment S50 in the Turkey Lakes Watershed. Peat exhibited the most marked response to drying of the four materials considered, and within 24 h of re-wetting dried peat from both catchments released 3-4 times more SO 4 (50 -67 mg kg 21 S-SO 4 ) than continuously moist peat (16 mg kg 21 S-SO 4 ), although temperature had only a marginal effect on SO 4 concentrations. There was no immediate response of Sphagnum to either drying or temperature, although S-SO 4 concentrations in Sphagnum tended to increase over the 30-day (d) incubation. There was a small but immediate increase in S-SO 4 concentrations in forest floor material (LFH) from both catchments within the first 24 h of incubation, which was greatest in treatments that were dried and/or incubated at a higher temperature. In contrast, neither temperature nor drying appeared to affect SO 4 release from mineral soil collected from either site. Results of laboratory incubations suggest that increases in SO 4 concentration that have been reported in wetland-draining streams immediately following summer dry periods may be quantitatively explained by drying and rewetting of peat rather than increased mineralization in Sphagnum. Similarly, the higher SO 4 concentrations that have been measured in upland streams following summer droughts may in part be due to enhanced SO 4 release from the forest floor following drying and re-wetting. In contrast, while the mineral soil constitutes a large pool of total S, it does not appear to be responsive to changes in moisture or temperature in the short-term (, 30 d) and therefore likely does not contribute to reported climate-related temporal variations in stream SO 4 .

Limnology and Oceanography, 2010

We analyzed the 21-yr dynamics of dissolved organic carbon (DOC) in 55 lakes during ice-free peri... more We analyzed the 21-yr dynamics of dissolved organic carbon (DOC) in 55 lakes during ice-free periods in five regions across eastern Canada in relation to total solar radiation (TSR), precipitation, air temperature, sulfate deposition (SO 4 ), Southern Oscillation Index (SOI), North Atlantic Oscillation, and Pacific Decadal Oscillation (PDO). A synchronous pattern in DOC was found among lakes within each region; however, a synchronous pattern in DOC was not found among regions, except for Kejimkujik and Yarmouth. Long-term trends of increasing or decreasing DOC concentration were not evident except at the Experimental Lakes Area (ELA), where an increase in DOC correlated with a decrease in summer TSR and an increase in summer precipitation. Annual mean temperature increased at the Nova Scotia and Turkey Lakes Watershed regions (TLW) over the study period, but there was no corresponding change in DOC. TSR and precipitation were important explanatory variables across all regions, except for the TLW. Summer TSR, or annual TSR, had a negative relationship, while summer precipitation had a positive relationship with the temporal DOC pattern in all regions except TLW. TSR and precipitation explained 78%, 49%, and 84% of the variation in the long-term DOC patterns at Dorset, ELA, and Nova Scotia (NS) regions, respectively. In contrast, the long-term pattern in DOC at TLW was only weakly related to SOI and PDO.

Limnology and Oceanography, 1996

A distributed data and simulation system for forested watersheds was used to investigate the pote... more A distributed data and simulation system for forested watersheds was used to investigate the potential changes in watershed hydrological and ecological processes under hypothesized climate change scenarios. RHESSys (Regional HydroEcological Simulation System) incorporates a spatial representation of nested catchment and lake systems in a GIS, along with a set of process submodels to compute local flux and storage of energy, water, carbon, and nutrients. A hierarchy of potential climate change shifts in weather, forest canopy physiological processes, and forest cover were used to operate RHESSys for comparison with control simulations for present-day conditions. Use of projected temperature and precipitation changes alone led to qualitatively different forecasts of watershed climate change impact when compared to simulations that also incorporated adjustment of canopy physiology to elevated concentrations of atmospheric CO*. In addition, ecosystem processes may be more resilient to climate change due to the existence of a series of offsetting effects. Annual net effects on specific processes such as watershed outflow and forest productivity may qualitatively vary from year to year rather than showing consistent increases or decreases relative to current conditions. The model results illustrate the significance of incorporating a reasonable description of terrestrial ecosystem processes within the contributing watershed when assessing the impact of climate change.

Lake and Reservoir Management, 1994

Page 1. Lakeshore Capacity Study: Part I—Test of Effects of , Shoreline Development on the Trophi... more Page 1. Lakeshore Capacity Study: Part I—Test of Effects of , Shoreline Development on the Trophic Status of Lakes 1 P. Dillon Ontario Ministry of Environment and Energy, Dorset Research Centre, Bellwood Acres Road, PO Box 39, Dorset, Ontario POA 1 E0, Canada. ...

Journal of Limnology, 2010

Based on minimal information, lakes in the western Canadian provinces of Manitoba (MB) and Saskat... more Based on minimal information, lakes in the western Canadian provinces of Manitoba (MB) and Saskatchewan (SK) have long been considered unaffected by acid rain. However, emissions of acidifying pollutants from MB smelters and oil sand processing in Alberta (AB) may pose a developing threat. Surveys of 347 lakes located on geologically sensitive terrain in northern MB and SK were conducted to assess their acidification sensitivity and status. The survey domain (~193,000 km 2 ) contained 81,494 lakes ≥1 ha in area. Small lakes dominated the inventory in terms of numbers, and large lakes dominated in terms of area. Survey lakes were selected using a stratified-random sampling design in 10 sampling blocks within the overall survey domain. Few lakes had pH <6, and only three (all in SK) were acidic, i.e., Gran Alkalinity (Alk) <0 μeq L -1 . A broad range in lake sensitivity was apparent, and very sensitive lakes (low specific conductance, base cations and Alk) were present in all sampling blocks. Dissolved organic carbon (DOC) was an important constituent of many lakes. Critical loads (CL) of acidity calculated using the Steady-State Water Chemistry model (SSWC) revealed extremely low 5th percentile values for every block (range 1.9 to 52.7 eq ha -1 y -1 ). Block CL exceedances calculated using estimated S and N deposition for 2002 ranged from 54.5 to 909 eq ha -1 y -1 . The largest exceedances were for sampling blocks located near smelter sources or downwind of the oil sands. Lake chemistry revealed by our surveys was compared to others conducted both nearby and outside Canada.

Hydrological Processes, 1997

The hydrological sensitivities to long-term climate change of a watershed in Eastern Canada were ... more The hydrological sensitivities to long-term climate change of a watershed in Eastern Canada were analysed using a deterministic watershed runo model developed to simulate watershed acidi®cation. This model was modi®ed to study atmospheric change eects in the watershed. Water balance modelling techniques, modi®ed for assessing climate eects, were developed and tested for a watershed using atmospheric change scenarios from both state of the art general circulation models and a series of hypothetical scenarios. The model computed daily surface, inter-and groundwater ows from the watershed. The moisture, in®ltration and recharge rate are also computed in the soil reservoirs. The thirty years of simulated data can be used to evaluate the eects of climatic change on soil moisture, recharge rate and surface and subsurface¯ow systems. The interaction between surface and subsurface water is discussed in relation to climate change. These hydrological results raise the possibility of major environmental and socioeconomic diculties and have signi®cant implications for future water resource planning and management.

Hydrological Processes, 2001

Consistent relationships between groundwater conditions and topographic properties in small drain... more Consistent relationships between groundwater conditions and topographic properties in small drainage basins would assist the study and modelling of basin hydrology and hydrochemistry. Hydrochemical simulation using topographically based models would benefit in particular from the linkage of groundwater residence times to topographic indices, such as the ln(a/ tanˇ) index of Beven and Kirkby. Hypothesized associations between this index and groundwater characteristics were tested during the spring 2000 snowmelt in two sub-basins in the Turkey Lakes Watershed near Sault Ste Marie, ON. One sub-basin is in mature hardwood forest, and the other was clearcut in the fall of 1997. Piezometric surface elevations were monitored in each sub-basin throughout the melt, and the topographic index value for each piezometer was determined. The υ 18 O signatures of input water and groundwater were also measured. Mean groundwater residence times were obtained using the exponential system response function, which generally produced good fits to the observed groundwater υ 18 O time series in both sub-basins. There were significant contrasts in groundwater conditions between the sub-basins. The forested sub-basin exhibited higher and more temporally variable piezometric surface elevations and a greater contrast between υ 18 O signatures and water residence times in shallow versus deeper groundwater relative to the harvested sub-basin. Patterns of groundwater residence times in the subbasins were supported by pre-harvest groundwater chemistry; however, data from the two sub-basins largely failed to support the hypothesized relationships between groundwater conditions and topographic index values. Methodological limitations that may have precluded a more rigorous test of the hypotheses are reviewed, and the potential for using groundwater residence times to evaluate the impacts of forest harvesting on basin hydrochemistry is briefly discussed.

Environmental Science & Technology, 2004

In this study we have analyzed the hydrochemical effect of drought conditions during 311 hydrolog... more In this study we have analyzed the hydrochemical effect of drought conditions during 311 hydrological episodes in nine headwater streams in central Ontario over the past 20 years. Acid Neutralization Capacity (ANC) was logarithmically correlated (p<0.05) to antecedent discharge in eight of the nine streams, with the largest decline in ANC occurring after low antecedent flow. In eight of the nine streams SO 4 2was the most important driving mechanism of ANC decline, but dilution as well as organic acidity was important in several streams. No decrease in the SO 4 2driven ANC decline was observed over the 20 year study period despite a ∼40% reduction in SO 4 2deposition. The strong correlation between ANC decline and low antecedent discharge demonstrates that episodic acidification during rain events is strongly associated with preceding drought conditions, especially in wetland-dominated catchments. The results have important implications for recovery from acidification, especially in northern ecosystems where climate scenarios forecast that warmer and drier conditions will be more common.

Environmental Pollution, 1992

Fifty-six headwater Canadian Shield lakes were repetitively sampled from 1979 to 88 to determine ... more Fifty-six headwater Canadian Shield lakes were repetitively sampled from 1979 to 88 to determine their response to changes in acidic deposition of the period. Annual wet sulphate loadings varied between 38 and 83 meq m(-2), with highest deposition in the late 1970s followed by somewhat lower but variable deposition in the 1980s. Median pH of the lakes increased 0.42 pH units from 1979 to 1985 and decreased by 0.15 units between 1985 and 1988. Short water renewal times (x=1.1 y) promoted rapid equilibration. Since lake were so responsive to changes in SO4(2-) inputs, they were at or near steady state at all times. Comparison of predicted original pH and ANC with 1979 data indicate a median decline of 0.45 pH units and a loss of 34 microeq litre(-1). ANC. Four of 9 lakes were found to be historically fishless, based on the continued presence of Chaoborus americanus in sediment cores. The remaining five lakes historically had fish populations, but fish were not collected in 1979 when pH ranged betwen 4.6 and 5.3. By 1987, fish species were found in five of these lakes where pH had increased on average by 0.9 pH units. Our data indicate that water quality improvements could allow for the reinvasion or resumption of recruitment for a significant number of Ontario lakes.

Environmental Monitoring and Assessment, 2005

The New England Governors and Eastern Canadian Premiers (NEG/ECP) adopted the Acid Rain Action Pl... more The New England Governors and Eastern Canadian Premiers (NEG/ECP) adopted the Acid Rain Action Plan in June 1998, and issued a series of action items to support its work toward a reduction of sulfur dioxide (SO 2 ) and nitrogen oxide (NO x ) emissions in northeastern North America. One of these action items was the preparation of an updated critical load map using data from lakes in the NEG/ECP area. Critical load maps provide a more complete index of the surface water sensitivity to acidification. Combined sulfur and nitrogen critical loads and deposition exceedances were computed using Henriksen's Steady-State Water Chemistry (SSWC) model. Results show that 28% of all 2053 lakes studied have a critical load of 20 kg/ha/year or less, making them vulnerable to acid deposition. Emission reductions, and more specifically SO 2 emission reductions have proven beneficial because critical loads were exceeded in 2002 for 12.3% of all studied lakes. Those lakes are located in the more sensitive areas where geology is carbonate-poor. Of these lakes, 2.9% will never recover even with a complete removal of SO 4 deposition. Recovery from acidification for the remaining 9.4% of the lakes will require additional emission SO 2 reductions.

Drugs & Therapy Perspectives, 2014

Canadian Journal of Fisheries and Aquatic Sciences, 1988

Canadian Journal of Fisheries and Aquatic Sciences, 1988

ABSTRACT

Canadian Journal of Fisheries and Aquatic Sciences, 1988

Page 1. Chemica ogical Charaderistics of the Turkey Lakes Watershed, Central Ontario, Canada Dean... more Page 1. Chemica ogical Charaderistics of the Turkey Lakes Watershed, Central Ontario, Canada Dean S. Jeffries /Vationat Water Research Institute, Canada Centre for Inland Waters, Bur%ington, One. L7W 4A6 John RM Kelso ...