Traditionally, macrophyte density has been considered the primary factor affecting the large dissolved oxygen fluctuations in the Bow River. After a major flood event scoured macrophytes in 2005, and subsequently changed river dynamics, the City of Calgary needed to update their predictive computer model for water quality to reflect the new conditions, which led to this study. A 2006 aquatic vegetation survey was also completed to assess post-flood conditions. The survey found that the average macrophyte dry weight was much lower (28 g/m 2 ± 100 (p = 0.05)) than the historic average of 241 g/m 2 ± 29, while the average periphyton chlorophyll-a concentration was higher (343 mg/m 2 ± 71) than the historic average (158 mg/m 2 ± 17)). Dissolved oxygen (DO) fluctuations were similar to pre-flood levels despite changes in the dominant vegetation. Using the results of this survey, the significant and previously unrecognized effects of periphyton diurnal processes on DO concentrations in the Bow River were identified and the Bow River water quality model (BRWQM) was recalibrated to reflect these findings. Adjustments were made to the BRWQM's periphyton submodel to account for the more dominant role played by these organisms in river processes, and a competitive shading factor between macrophytes and periphyton was also introduced to more accurately model the species' competition for available sunlight. This newly calibrated and validated version of BRWQM was tested and found capable of predicting the occurrence of low DO concentrations in the Bow River and can provide a useful tool for forecasting the water quality effects of the city's planned wastewater infrastructure expansion.Résumé : Traditionnellement, la densité en macrophytes a été considérée comme étant le principal facteur relié à de fortes fluctuations en oxygène dissous dans la rivière Bow. Après le lessivage des macrophytes par une inondation majeure en 2005 et le changement subséquent dans la dynamique de la rivière, la Ville de Calgary a demandé la mise à niveau de son modèle informatique prédictif sur la qualité de l'eau pour les nouvelles conditions déterminées lors d'un relevé de la végé-tation aquatique en 2006. Le relevé a permis de découvrir que le poids sec moyen de macrophytes (28 g/m 2 ± 100 (p = 0.05)) beaucoup plus bas que la moyenne historique de 241 g/m 2 ± 29 alors que la moyenne de la concentration en chlorophylle-a du périphyton était plus élevée (343 mg/m 2 ± 71) que la moyenne historique de 158 mg/m 2 ± 17. Les fluctuations de la teneur en oxygène dissous étaient similaires aux teneurs avant l'inondation malgré les changements dans la végéta-tion dominante. Les effets importants, et antérieurement inconnus, des processus diurnes du périphyton sur les concentrations en oxygène dissous ont été identifiés et le modèle de la qualité de l'eau de la rivière Bow (« BRWQM ») a été étalonné de nouveau pour refléter ces conclusions. Le sous-modèle de périphyton du « BRWQM » a été ajusté afin de tenir compte du rôle plus dominant joué par ces organi...

The potential effect of manure management from livestock production on groundwater quality is an issue of concern. Groundwater sampling from a regional transect in southern Alberta, Canada, was conducted to determine changes in groundwater quality with time. The study area has extensive irrigation and a high density of confined feeding operations. Nitrate-N (NO3−-N) and chloride (Cl−) concentration data from 23 groundwater-study wells were evaluated from 1994 to 2014. Twelve of these wells were water-table wells and 11 were piezometers. Of the 23 wells, 14 had significant temporal trends (increasing or decreasing) for NO3−-N and/or Cl− concentrations. On a regional basis, NO3−-N increased slightly with time while Cl− changed very little, suggesting that the effects of agricultural activities on regional groundwater quality have generally remained constant. However, concentration changes occurred on a smaller scale. Shallow groundwater in coarse-textured soils is at a relatively higher risk of contamination than groundwater in fine-textured soils, especially in locations where intensive agricultural activities occur.

Leaching of nitrate (NO − 3 ) from animal waste or fertilisers at agricultural operations can result in NO − 3 contamination of groundwater, lakes, and streams. Understanding the sources and fate of nitrate in groundwater systems in glacial sediments, which underlie many agricultural operations, is critical for managing impacts of human food production on the environment. Elevated NO − 3 concentrations in groundwater can be naturally attenuated through mixing or denitrification. Here we use isotopic enrichment of the stable isotope values of NO − 3 to quantify the amount of denitrification in groundwater at two confined feeding operations overlying glacial sediments in Alberta, Canada. Uncertainty in δ 15 N NO 3 and δ 18 O NO 3 values of the NO − 3 source and denitrification enrichment factors are accounted for using a Monte Carlo approach. When denitrification could be quantified, we used these values to constrain a mixing model based on NO − 3 and Cl − concentrations. Using this novel approach we were able to reconstruct the initial NO 3 −N concentration and NO 3 −N/Cl − ratio at the point of entry to the groundwater system. Manure filtrate had total nitrogen (TN) of up to 1820 mg L −1 , which was predominantly organic N and NH 3 . Groundwater had up to 85 mg L −1 TN, which was predominantly NO − 3 . The addition of NO − 3 to the local groundwater system from temporary manure piles and pens equalled or exceeded NO − 3 additions from earthen manure storages at these sites. On-farm management of manure waste should therefore increasingly focus on limiting manure piles in direct contact with the soil and encourage storage in lined lagoons. Nitrate attenuation at both sites is attributed to a spatially variable combination of mixing and denitrification, but is dominated by denitrification. Where identified, denitrification reduced agriculturally derived NO − 3 concentrations by at least half and, in some wells, completely. Infiltration to groundwater systems in glacial sediments where NO − 3 can be naturally attenuated is likely preferable to off-farm export via runoff or drainage networks, especially if local groundwater is not used for potable water supply.

No abstract

for using a Monte Carlo approach. When denitrification could be quantified, we reconstructed the initial NO3-N concentration and NO3-N/Cl -ratio at the point of entry to the groundwater system. The addition of NO3 -to the local groundwater system from temporary manure piles and pens equalled or exceeded NO3 -additions due to leaching from earthen manure storages at these sites. Nitrate attenuation at both sites is attributed to a spatially 20 variable combination of mixing and denitrification, but is dominated by denitrification. On-site denitrification reduced agriculturally derived NO3 -concentrations by at least half and, in some wells, completely. These results indicate that infiltration to groundwater systems in glacial sediments where NO3 -can be naturally attenuated is likely preferable to off-farm export via runoff or drainage networks. The application of isotopes of nitrate to constrain a mixing model based on concentrations of Cl -and NO3 -, which can be routinely monitored in 25 groundwater, provides a relatively simple method to assess the sources and fate of agriculturally derived NO3 -in these settings.