INTRODUCTION Winter snow and ice can have a significant impact on our mobility, whether on foot or by car. Alongside plowing, arguably the greatest tool in combating snow and ice is salt. The most commonly used salt for winter maintenance is Sodium Chloride (NaCl), the same salt used in food and water softeners, is applied to roads, sidewalks, and parking lots as it is an effective deicer when temperatures are between 0°C and −12°C. Studies have shown that deicing with salt reduces accidents by 88% and injuries by 85% (Salt Institute 2017). The effectiveness of road salt, as well as its relative affordability, means that as much as four million tonnes may be applied annually in Canada for deicing (Environment Canada 2012). However, while salt is relatively inexpensive to purchase, there are a number of external costs that are becoming increasingly apparent. These include corrosion of vehicles and infrastructure like concrete, bridges, and water mains; damage and staining to the interior and exterior of buildings; impacts to roadside vegetation and soils; and the contamination of fresh water. In fact, the environmental impacts are such that it prompted Environment Canada to propose that winter salt be considered a toxic substance primarily due to the quantity that is applied annually (Environment Canada 2001). The Lake Simcoe watershed, approximately 3,400km2 in size, is situated just 20km north of Toronto, Ontario, with the southern portion of the watershed being considered part of the Greater Toronto Area (GTA), the most populous metropolitan area in Canada. As part of the GTA, the Lake Simcoe watershed has experienced and continues to experience considerable growth, and with this growth comes an increase in the amount of impervious surfaces requiring winter salting. Indeed, chloride has been showing a strong increasing trend in the urban creeks and in Lake Simcoe itself over the last 30 years. Even rural creeks are showing an increasing trend, albeit not as severe, nor are the concentrations of chloride reaching the same levels (LSRCA 2015). The highest chloride level recorded in a Lake Simcoe tributary was 6,120mg/l in the winter of 2013. Chloride guidelines for the protection of aquatic ecosystems utilize a guideline of 120mg/L for chronic exposure and 640mg/L for acute exposure (CCME 2011). While the high value recorded in the Lake Simcoe tributary greatly exceeds these guidelines, it is still drastically lower than values being recorded in larger, intensively urbanized catchments such as Cooksville Creek in Mississauga, Ontario, which sees concentrations in excess of 20,000 mg/L, the concentration of sea water, nearly every winter (Credit Valley Conservation personal comm). Similarly, in July of 2011 a small population of Atlantic blue crabs, a marine species, was found surviving in Mimico Creek in Toronto (Toronto Star: May 26, 2012). That a marine species was able to survive in this fresh water creek in summer demonstrates that the impacts of winter salt are not just limited to winter but are impacting shallow groundwater and thus summer baseflow, maintaining high chloride concentrations year round. The same is being seen in some urban creeks in the Lake Simcoe watershed, with summer baseflow concentrations exceeding the chronic guideline and trending upwards (LSRCA unpublished). While not yet as extreme as rivers in the more densely urbanized parts of the GTA, these examples foreshadow what is in store for Lake Simcoe rivers if current winter salt practices continue along with the projected urban growth. During the winter of 2012 an estimated 99,300 tonnes of salt was applied in the Lake Simcoe watershed, an amount that equals nearly 250kg of salt per capita, or ~3 times the average person's body weight in salt. This estimate was generated through a survey of local road agencies along with the total area of commercial/institutional parking lots within the watershed. The exercise served to highlight a knowledge gap around application practices and rates in commercial/institutional parking lots. The majority of road agencies were found to record annual volumes, application dates and rates whereas literature values range from 10–40% of the salt applied in a catchment come from commercial/institutional parking lots (Perera et al, 2009; Trowbridge et al, 2010; Lake Simcoe Region Conservation Authority, 2015), and a survey of winter maintenance contractors cite an average value of approximately 58g/m2/application (Fu et al, 2013) ( Figure 1 ). [Figure: see text] While these values were used in the estimation as they were the best available, observational data suggested these may be on the conservative side ( Figure 2 ). [Figure: see text] Therefore, monitoring of a 14 ha commercial lot was undertaken for the winters of 2014/15, 2015/16, and 2016/17 to better quantify the amount of salt coming from this type of land use. The winters of 2014/15 and 2016/17 saw similar applications of 1,067 and 1,010 tonnes applied respectively, while the mild winter of 2015/16 saw 556 tonnes applied. While the amounts varied somewhat each winter, the impacts downstream were consistent. Maximum concentrations recorded in the melt water reached 3.5 to 4 times the salt concentration of sea water every winter, equating to chloride concentrations of 70,000mg/L to 85,000mg/L; two orders of magnitude above the water quality guideline. As with most parking lots constructed in the last two decades, the runoff from this parking lot is captured in a stormwater pond prior to entering the receiving watercourse. Interestingly, the winter salt also caused persistent chemical stratification in the permanent pool of the pond. The pond was monitored with continuous monitors for the ice free period of 2015 and 2016 (April to December) during which the bottom water chloride concentration remained distinct from the surface chloride concentration, indicating stratification ( Figure 3 ). This has two significant implications; first of which is that this pond, and therefore many other ponds like it, may not be functioning as designed which is leading to diminished performance (McEnroe 2012, Marsalek 2003). Second is that ponds are acting as salt reservoirs, slowly releasing salt year round and contributing to river chloride concentrations that continually exceed the chronic exposure guideline and thereby exposing aquatic life to harmful concentrations during sensitive life cycle stages. [Figure: see text] To determine the extent to which the catchment land use type impacts stormwater ponds, chemical profiles were measured on three ponds in February 2017. The catchments included the 24.6 ha commercial catchment with 14 ha of salt application surface, an institutional catchment (14.3 ha) with 6 ha of salt application area that includes parking lots and roads, and a 16.4 ha residential catchment with 3 ha of salt application area comprised of tertiary municipal roads. Interestingly, all three ponds showed chemical stratification, with the severity of the stratification and highest chloride concentrations relating to the amount of salt application area in the catchment. The residential pond yielded a maximum chloride concentration of 3,115mg/L in the bottom waters, the institutional yielded 16,144mg/L, and the commercial yielded 25,530 mg/L with chloride concentrations in the bottom 0.5m of the pond exceeding that of sea water. The maximum chloride concentration recorded in the receiving watercourse downstream of the commercial lot was measured at 5,406 mg/L, well in excess of the acute guideline of 640 mg/L. These results highlight that commercial parking lots are not only receiving a significant volume of salt but are also having the most dramatic impacts on receiving stormwater infrastructure and watercourses.
A one-level primitive equations mesoscale wind model is applied to the area of Petro-Canada's oil explorations in eastern Lancaster Sound and northwestern Baffin Bay. The model includes effects of orographic channelling, land-water roughness contrasts, and thermal circulations such as land-and sea-breezes and anabatic and katabatic winds. The grid sizeislO' latitude by 40' longitude (approximately 19 km by 20 km). The model is verified with ship winds in the 1978 and 1979 seasons and with Seasat satellite winds in September 1978. Two versions of the model have been investigated. In the first, termed model A, the geostrophic wind was set equal to the analysed Canadian Meteorological Centre (CMC) wind ata = p/p s = 0.94. Herep is pressure and p s is surface pressure. In the second version, model B, the geostrophic wind is obtained from sea-level pressures manually abstracted from surface charts. The latter had been reanalysed after Petro-Canada and delayed ship reports had been plotted. The improvement of model B over model A is significant. The mean underestimate in speed has decreased from 12.0 to 7.8 km h-1 for the ship winds and from 22.6 to 11.2 km h-1 for the Seasat winds. Fifty per cent of the angle errors now lie between-31 and 49° for the ship winds and between-11 and 31° for the Seasat winds. The corresponding figures for model A are-54 and 71° for the ship winds and-14 and 47° for the Seasat winds. The model is also run with prognostic CMC input data. In general, errors grow slowly with time from 0 to 36 h. RÉSUMÉ Un modèle de vent à niveau unique et à échelle moyenne utilisant les équations primitives est appliqué à la région d
The introduction (part I) notes the N.Z. Geological Survey's policy and practice on active earth deformation with its emphasis on standardisation and uniformity in the treatment of data and presentation of interpretations. Part II defines the terminology relating to earth deformation, it classifies active faults and folds by strictly adhering to the available evidence of their past geological history of activity. Where evidence of past activity is missing, but the structure can be geologically identified and the absence of evidence can be shown to have been destroyed or obscured, criteria for classification as "Potentially Active" are presented. The periodicity of movement and the risk of future movement are briefly discussed. The need to separate data from interpretation is clearly indicated by the separate treatment in part III - presentation of data in geological maps and reports – and part IV Town Planning and Engineering Implications. The latter part requires the separate presentation of a Data Map and a Interpretative Map, and concise criteria are listed to achieve standardisation of interpretation. The report ends with a brief and general discussion on the engineering implications of active earth deformation.
Eustatic sea level (ESL) rise during the 21st century is perhaps the greatest threat from climate change, but its magnitude is contested. Geological records identify examples of nonlinear ice sheet response to climate forcing, suggesting a strategy for refining estimates of 21st-century sea level change. In August 2008, Past Global Changes ( PAGES), International Marine Past Global Change Study ( IMAGES), and the University of Bern cosponsored a workshop to address this possibility. The workshop highlighted several ways that paleoceanography studies can place limits on future sea level rise, and these are enlarged upon here.The meeting featured presentations discussing the implications of the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4), which predicted 21st-century global warming of 1.1º-6.4°C for a range of emissions scenarios. Paleoclimate Modeling Intercomparison Project ( PMIP) studies concluded that global warming during the last glacial termination (TI, 21,000 years ago to present) was 3.3º-5.1°C. Given the similarity between the magnitude and rate of warming predicted for the 21st century and the TI warming, workshop speakers considered the relevance of the TI ESL response to understanding future change. TI data (see Figure S1 and caveats in the electronic supplement to this Eos issue, http:// www . agu . org/ eos _elec/) support the notion that the ESL response is rapid following a perturbation but then reduces over time as ice sheets reach a new steady state. However, workshop participants noted that the model used for the AR4 prediction of twentieth-century sea level rise does not capture the mode of integrated ice sheet response observed during TI. Attendees concluded that ice sheet models used to predict future ESL rise must be able to capture the dynamics revealed by the paleo sea level record if we are to have confidence in them.Workshop participants also discussed how relative sea level ( RSL) data from sites distant from the high-latitude ice sheets for the last interglacial period ( LIG) suggest that sea level attained a peak 3-6 meters above modern sea level. Greenland ice sheet ( GrIS) modeling for LIG conditions suggests that GrIS reduction may have contributed 3 meters to ESL rise during this period, adequate to account for the lowest estimate of LIG sea level rise but not for estimates above 3 meters. Participants noted that higher estimates of sea level during the LIG likely require additional contributions from ocean thermal expansion and the West Antarctic ice sheets ( WAIS).RSL and modeling results for the LIG suggest GrIS and WAIS are vulnerable to a warming climate. Although there are direct observations of rapid ice sheet responses to global warming, such observations are typically of several decades duration, and workshop attendees stressed that one cannot conclude whether rapid processes will have a larger-scale impact on the ice sheets. Because the rapid changes observed in modern ice sheets are in general agreement with paleo observations of the respo...
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