Migratory behavior can be an important factor in determining contaminant exposure in avian populations. Accumulation of organochlorine (OC) pesticides while birds are wintering in tropical regions has been cited often as the reason for high concentrations in migrant populations. To explore this issue, we satellite tracked 16 Ospreys (Pandion haliaetus) over the period 1996-2003 from breeding sites in British Columbia, Canada, and integrated the results into a database on 15 Ospreys that were satellite tracked over the period 1995-1999, from breeding locations in Washington and Oregon, USA. Data on wintering sites of 31 Ospreys in Mexico and Central America were used for spatially targeted sampling of prey fish. Concentrations of the main organochlorine contaminant, p,p'-dichloro-diphenyl-dichloroethylene (DDE), in fish composites from Mexico ranged from 0.005 to 0.115 nicrog/g wet mass. Significant differences existed among fish families in p,p'-DDE, total dichloro-diphenyl-trichloroethane (sigmaDDT), sigmachlordanes, and total polychlorinated biphenyls (sigmaPCBs). Catfish (family Ariidae) generally had significantly higher levels of DDT metabolites and other organochlorine contaminants compared to other fish families collected. Differences in prey contaminant levels were detected among the collection sites around coastal Mexico, with fish from Veracruz State generally having higher levels of DDT metabolites, sigmachlordanes, sigmaPCBs, and hexachlorobenzene. Eggs collected from 16 nests throughout the Pacific Northwest (nine from British Columbia, seven from Oregon and Washington) where Ospreys had been satellite tagged, showed marked variation in levels of DDT metabolites (p,p'-DDE; range 0.02-10.14 microg/g). Wintering site had no significant effect on contaminant concentrations in sample eggs from those specific Ospreys; rather concentrations of p,p'-DDE, were predicted by breeding sites with highest levels in eggs of Ospreys breeding in the lower Columbia River, consistent with published reports of continued high concentrations of DDT and related compounds in that system.

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Six regional recharge and groundwater models have been recently developed of the Chalk and Upper Greensand from Dorset to Kent. Updated Chalk stratigraphy and mapping have improved understanding of geological structure and the development of preferential groundwater flow pathways along hardground horizons. Where shallow dipping folds bring these into the zone of active groundwater flow, extensive ‘underdrainage’ may result in marked differences between surface and groundwater catchments. Hardgrounds and marls are also associated with spring discharges, as are some faults and the clay formations that underlie or confine the aquifer system. Higher specific yield within the Upper Greensand helps support summer baseflow, as do local groundwater discharges from augmentation schemes, watercress and fish farm operations. The aquifer system has been successfully modelled using the ‘variable hydraulic conductivity with depth’ version of MODFLOW. Depths of secondary permeability development have been distributed according to ground and groundwater level data. Interfluve–valley contrasts overlie a base hydraulic conductivity set according to the formation saturated at the water table and enhanced by active hardgrounds. Local parameter overrides may also be needed. The Wessex Basin conceptual and numerical model is described before summarizing similarities and contrasts from the other five regional model areas.

Runoff or water yield is an important input to the Steady-State Water Chemistry (SSWC) model for estimating critical loads of acidity. Herein, we present site-specific water yield estimates for a large number of lakes (779) across three provinces of western Canada (Manitoba, Saskatchewan, and British Columbia) using an isotope mass balance (IMB) approach. We explore the impact of applying site-specific hydrology as compared to use of regional runoff estimates derived from gridded datasets in assessing critical loads of acidity to these lakes. In general, the average water yield derived from IMB is similar to the long-term average runoff; however, IMB results suggest a much larger range in hydrological settings of the lakes, attributed to spatial heterogeneity in watershed characteristics and landcover. The comparison of critical loads estimates from the two methods suggests that use of average regional runoff data in the SSWC model may overestimate critical loads for the majority of lakes due to systematic skewness in the actual runoff distributions. Implications for use of site-specific hydrology in regional critical loads assessments across western Canada are discussed

High-elevation lakes are sensitive to acidification from atmospheric deposition owing to their generally small catchment areas, thin soils and low bedrock weathering rates. The Georgia Basin, southwest British Columbia, Canada, receives atmospheric inputs from emissions originating in Vancouver, Victoria, and from marine traffic in the Strait of Georgia. There is growing concern on the influence of this air pollution on high-elevation systems in the region. Water chemistry and catchment characteristics were used to assess the sensitivity of 72 lakes in the Georgia Basin to acidic deposition. Twenty percent of the study lakes had pH levels less than 6, and acid neutralising capacity (ANC) concentrations below 20 μeq L–1, which are key thresholds for biological sustainability. Base cation and trace metal concentrations were low, typical of the dilute nature of high-elevation lakes (median conductivity = 7.0 μS cm–1). Nonetheless, concentrations of trace metals (such as lead) decreased with distance from major cities. The primary factors influencing the pH and ANC of surface waters were investigated using multiple linear regression; both ANC and pH were related to longitude and the proportion of the catchment dominated by ice and glaciers. Increasing sulphur deposition resulted in decreasing pH. The median critical load of acidity (sulphur) for the study lakes was approximately 70 meq m–2 y–1; 18% of the lakes received sulphur deposition (range: 6-81 meq m–2 y–1 for the period 2005-2006) in excess of their critical load