Trend analysis of nutrient loadings in a large prairie catchment

Nutrient loadings in many river catchments continue to increase due to rapid expansion of agriculture, urban and industrial development, and population growth. Nutrient enrichment of water bodies has intensified eutrophication which degrades water quality and ecosystem health. In this study, we carried out a trend analysis of total phosphorus and total nitrogen loads in the South Saskatchewan River (SSR) catchment using a novel approach to analyse nutrient time series. Seasonal analysis of trends at each of the water quality stations was performed to determine the relationships between annual flow regimes and nutrient loads in the catchment, in particular, the influence of the high spring runoff on nutrient export. Decadal analysis was also performed to determine the long-term relationships of nutrients with anthropogenic changes in the catchment. Although it was found that seasonal and historical variability of nutrient load trends is mainly determined by streamflow regime changes, there is evidence that increases in nitrogen concentration can also be attributed to anthropogenic changes.     

Micro-environmental controls on biomineralization: superficial processes of apatite and calcite precipitation in Quaternary soils, Roussillon, France

Calcium hydroxyapatite and calcite precipitates around bacteria were observed in 2-week-old alluvial topsoil (Roussillon area, SE France). This observation prompted a laboratory study of Ca²⁺ and PO₄³⁻ incorporation into hydroxyapatite and Ca²⁺ into calcite mediated by bacteria using similar topsoil material, but free from apatite and calcite. Subsamples were prepared using three different grain sizes, and experiments were undertaken using sucrose and different contents of Ca²⁺ and PO₄³⁻. Mineralization experiments proceeded over 5 days. Calcium and PO₄³⁻ sorption onto clay influenced the Ca/P ratio in the solutions. Hydroxyapatite and calcite precipitation only occurred in unsterilized samples. The presence of clay minerals promoted biomineralization.     

Ice‐jam flood risk assessment and mapping

In northern regions, river ice‐ jam flooding can be more severe than open‐water flooding causing property and infrastructure damages, loss of human life and adverse impacts on aquatic ecosystems. Very little has been performed to assess the risk induced by ice‐related floods because most risk assessments are limited to open‐water floods. The specific objective of this study is to incorporate ice‐jam numerical modelling tools (e.g. RIVICE, Monte‐Carlo simulation) into flood hazard and risk assessment along the Peace River at the Town of Peace River (TPR) in Alberta, Canada. Adequate historical data for different ice‐jam and open‐water flooding events were available for this study site and were useful in developing ice‐affected stage‐frequency curves. These curves were then applied to calibrate a numerical hydraulic model, which simulated different ice jams and flood scenarios along the Peace River at the TPR. A Monte‐Carlo analysis was then carried out to acquire an ensemble of water level profiles to determine the 1 : 100‐year and 1 : 200‐year annual exceedance probability flood stages for the TPR. These flood stages were then used to map flood hazard and vulnerability of the TPR. Finally, the flood risk for a 200‐year return period was calculated to be an average of $32/m²/a ($/m²/a corresponds to a unit of annual expected damages or risk). Copyright © 2016 John Wiley & Sons, Ltd.     

Climatic effects on ice phenology and ice-jam flooding of the Athabasca River in western Canada

ABSTRACT

In cold region environments, any alteration in the hydro-climatic regime can have profound impacts on river ice processes. This paper studies the implications of hydro-climatic trends on river ice processes, particularly on the freeze-up and ice-cover breakup along the Athabasca River in Fort McMurray in western Canada, which is an area very prone to ice-jam flooding. Using a stochastic approach in a one-dimensional hydrodynamic river ice model, a relationship between overbank flow and breakup discharge is established. Furthermore, the likelihood of ice-jam flooding in the future (2041–2070 period) is assessed by forcing a hydrological model with meteorological inputs from the Canadian regional climate model driven by two atmospheric–ocean general circulation climate models. Our results show that the probability of ice-jam flooding for the town of Fort McMurray in the future will be lower, but extreme ice-jam flood events are still probable.     

Assessing vertical diffusion in a stratified lake using a three-dimensional hydrodynamic model

Vertical turbulent diffusivity (K_z), which can be estimated from water temperature, is a key factor in the evolution of water quality in lentic waters. In this study, we analysed the capability of a three-dimensional hydrodynamic model (EFDC) to capture water temperature and vertical diffusivity in Lake Arendsee in the Northern German plain. Of particular interest to us is to evaluate the model performance for capturing the diffusion minimum within the metalimnion and analyse the response of the metalimnetic K_z to meteorological forcing, namely changing wind speed and warming. The comparison confirmed that the calibrated model could reproduce both stratification dynamics and vertical diffusion profiles in the lake. The model was also shown to be able to capture the duration and vertical extent of the metalimnetic diffusion minimum. The scenario results illustrate that, compared to air temperature, wind velocity appeared to be the more influential meteorological variable on the vertical exchange within the metalimnion. While increasing wind velocities mostly affected the minimum values of K_z in the metalimnion and thus led to intensified vertical exchange, the reduction of wind velocity mostly affected the depth of minimal K_z, but not its absolute value.     

Modelling and application of the geomorphic and environmental controls on flash flood flow

The surface water runoff (sheet wash) during simulated heavy rainfall of between 25 and 100 mm/h (rainfall durations of between 1 and 6 hours, on plots of between 2.5 and 3.5 m²) on soils of Pliocene and Quaternary sediments and on cherts from Ordovician sediments in nearly-natural environments was dependent on inclination of slope (32%) and on kinetic energy of rainfall (30%). When using vegetation cover as an additional variable for nearly-natural and human influenced environments, the vegetation cover increases R² from 0.62 to 0.74. The degree of slope controls between 25 and 30% of topsoil characteristics. The results of model simulations were confirmed during natural heavy rainfalls on different field plots. Because simulated rainfalls were based on recorded intensities and durations, results compared with historic records and estimations imply also that specific intensity of between 25 and 100 mm/h and duration of between 1 and 6 hours are not so important, relative to geomorphic-environmental impact, in flash flood generation in a Mediterranean climate area like the Roussillon area (SE-France).On 26 September 1992 the rainfall intensity of a four-hour heavy rainfall event was to a large extent influenced by the topography of the catchment of River Réart/Canterrane (Roussillon, SE-France), increasing with altitude. As an example of the model application: the flash flood of 26/27 September 1992 was simulated. The peak flash-flood flow at the river mouth of River Réart/Canterrane was 1100 m³/s or 7 (m³/km²)/s. Runoff conditions for the natural or nearly natural catchment would have accounted for 43.6% of this, agricultural impact for 9.1% and building areas and construction sites for 5.5%. A further 41.8% was accounted for by the effects of breaching of stored floodwater. In absence of breaching of stored floodwater, the nearly-natural part of the peak flash-flood flow would have been about 480 m³/s (75%) and the part caused by human influence about 160 m³/s (25%).     

A multi-objective calibration approach using in-situ soil moisture data for improved hydrological simulation of the Prairies

ABSTRACT

Traditionally, hydrological models are only calibrated to reproduce streamflow regime without considering other hydrological state variables, such as soil moisture and evapotranspiration. Limited studies have been performed on constraining the model parameters, despite the fact that the presence of a large number of parameters may provide large degree of freedom, resulting in equifinality and poor model performance. In this study, a multi-objective optimization approach is adopted, and both streamflow and soil moisture data are calibrated simultaneously for an experimental study basin in the Saskatchewan Prairies in western Canada. The results of this study show that the multi-objective calibration improves model fidelity compared to the single objective calibration. Moreover, the study demonstrates that single objective calibration performed against only streamflow can fairly mimic the streamflow hydrograph but does not yield realistic estimation of other fluxes such as evapotranspiration and soil moisture (especially in deeper soil layers).     

Impacts of future climate on the hydrology of a northern headwaters basin and its implications for a downstream deltaic ecosystem

Anthropogenic and climatic-induced changes to flow regimes pose significant risks to river systems. Northern rivers and their deltas are particularly vulnerable due to the disproportionate warming of the Northern Hemisphere compared with the Southern Hemisphere. Of special interest is the Peace–Athabasca Delta (PAD) in western Canada, a productive deltaic lake and wetland ecosystem, which has been recognized as a Ramsar site. Both climate- and regulation-induced changes to the hydrological regime of the Peace River have raised concerns over the delta's ecological health. With the damming of the headwaters, the role of downstream unregulated tributaries has become more important in maintaining, to a certain degree, a natural flow regime, particularly during open-water conditions. However, their flow contributions to the mainstem river under future climatic conditions remain largely uncertain. In this study, we first evaluated the ability of a land-surface hydrological model to simulate hydro-ecological relevant indicators, highlighting the model's strengths and weaknesses. Then, we investigated the streamflow conditions in the Smoky River, the largest unregulated tributary of the Peace River, in the 2071–2100 versus the 1981–2010 periods. Our modelling results revealed significant changes in the hydrological regime of the Smoky River, such as increased discharge in winter (+190%) and spring (+130%) but reduced summer flows (−33%) in the 2071–2100 period compared with the baseline period, which will have implications for the sustainability of the downstream PAD. In particular, the projected reductions in 30-day and 90-day maximum flows in the Smoky River will affect open-water flooding, which is important in maintaining lake levels and connectivity to perimeter delta wetlands in the Peace sector of the PAD. The evaluation of breakup and freeze-up flows for the 2071–2100 period showed mixed implications for the ice-jam flooding, which is essential for recharging high-elevation deltaic basins. Thus, despite projected increase in annual and spring runoff in the 2071–2100 period from the Smoky sub-basin, the sustainability of the PAD still remains uncertain.