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•Riverine NO3 and B concentrations and δ15NNO3, δ18ONO3, and δ11B values were analysed.•Isotope ratios of major nutrient sources assisted in NO3 source apportionment.•WWTP effluent ...was the key nutrient source in the Bow River downstream of Calgary.•Manure-derived nutrients affect the Bow and Oldman Rivers in agricultural regions.•B was proven to be an effective co-tracer of urban and agricultural NO3 sources.
Rapid population growth and land-use intensification over the last century have resulted in a substantial increase in nutrient loads degrading marine and freshwater ecosystems worldwide. In mixed-use watersheds, elevated nitrogen loads from wastewater treatment plant (WWTP) effluent or agricultural runoff often drive the eutrophication of waterways. Accordingly, the objective of this research was to identify sources of riverine nitrate (NO3), a deleterious dissolved species of nitrogen, with a combined isotopic tracing technique in the Bow River and the Oldman River in Alberta, Canada. Riverine NO3 and boron (B) concentrations, mean daily flux and δ15NNO3, δ18ONO3, and δ11B values were determined at 17 mainstem sites during high and low discharge periods in 2014 and 2015. The data for mainstem sites were then compared to results for effluent from seven WWTPs, eight synthetic fertilizers, cow manure, and three predominantly agricultural tributary sites to estimate point and non-point NO3 sources. The NO3 flux, δ15NNO3 and δ18ONO3 values indicated the city of Calgary’s Bonnybrook WWTP effluent accounts for the majority of the NO3 flux in the Bow River downstream of Calgary. δ15NNO3 and δ11B values in the Bow River highlighted an increase in agricultural NO3 loading downstream of irrigation return-flows. A three-fold decrease in the NO3:B flux ratio indicated NO3-removal processes are active in the lower reaches of the Bow River. For the Oldman River, δ11B values revealed elevated nutrient loading from the Lethbridge WWTP effluent (10% of downstream B flux). Furthermore, the agricultural tributaries contributed 25% of the local B flux to the Oldman River. Overall, δ11B was proven to be an effective co-tracer for discriminating between urban and agricultural sources of NO3 in these large mixed-use watersheds. This combined isotope tracing approach has significant potential to identify point and non-point NO3 sources driving eutrophication around the world.
Multiple anthropogenic activities are driving the salinization of freshwater environments threatening water resources worldwide. Accordingly, this research will first examine the spatial and temporal ...variability of major ions (i.e. Ca2+, Mg2+, Na+, K+, SO42−, CO32−, and HCO3−) upstream and downstream of the northernmost major city in North America (Edmonton, Canada). Second, this research will estimate the relative contributions of the major sources of chloride (Cl), the main constituent of road deicers, to the sub-basin around Edmonton. Monthly water quality data was for three sites on the North Saskatchewan River (NSR): Rocky Mountain House (RMH - downstream of the Rocky Mountain headwaters), Devon Bridge (upstream of Edmonton) and Pakan Bridge (downstream of Edmonton). Change ratios investigate the downstream alterations of major ions at Pakan and Devon, relative to RMH. Seasonal Kendall tests examine temporal trends (1987–2017). A mass-balance approach then quantifies the major sources of Cl in the sub-basin of the NSR between Devon and Pakan. Progressing from the Rocky Mountain headwaters (at RMH) to downstream of Edmonton (at Pakan), Cl− increased by >5.5 times, Na+ by 4.8 times and K by 2.7 times. No significant temporal trends for Cl−, Na+ and K+ were evident at Devon (upstream of Edmonton), whereas all three significantly increased at Pakan (downstream of Edmonton). Deicers (54%), agriculture (20%), along with waste water treatment plant and industrial effluent (15%) were the largest Cl sources in the NSR Devon-Pakan sub-basin. In total, 77 Gg yr−1 of Cl (or 6 t km2 yr−1) is added to the Devon-Pakan sub-basin, of which, 43 Gg yr−1 is retained. Understanding and managing the major drivers of freshwater salinization will be of increasing importance in the 21st century owing to the potential salinization of freshwater resources in the context of a changing climate.
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•Deicers often drive freshwater salinization in northern regions of the world.•Less is known in areas where temperatures may be too cold for NaCl to be effective.•Cl is increasing downstream of North America's northernmost major city (Edmonton).•Deicers (54%) and agriculture (20%) are main sources of chloride.•Important to identify and manage all potential drivers of freshwater salinization
Purpose
Evaluating sediment fingerprinting source apportionments with artificial mixtures is crucial for supporting decision-making and advancing modeling approaches. However, artificial mixtures are ...rarely incorporated into fingerprinting research and guidelines for model testing are currently lacking. Here, we demonstrate how to test source apportionments using laboratory and virtual mixtures by comparing the results from Bayesian and bootstrapped modeling approaches.
Materials and methods
Laboratory and virtual mixtures (
n
= 79) with known source proportions were created with soil samples from two catchments in Fukushima Prefecture, Japan. Soil samples were sieved at 63 µm and analyzed for colorimetric and geochemical parameters. The MixSIAR Bayesian framework and a bootstrapped mixing model (BMM) were used to estimate source contributions to the artificial mixtures. In addition, we proposed and demonstrated the use of multiple evaluation metrics to report on model uncertainty, residual errors, performance, and contingency criteria.
Results and discussion
Overall, there were negligible differences between source apportionments for the laboratory and virtual mixtures, for both models. The comparison between MixSIAR and BMM illustrated a trade-off between accuracy and precision in the model results. The more certain MixSIAR solutions encompassed a lesser proportion of known source values, whereas the BMM apportionments were markedly less precise. Although model performance declined for mixtures with a single source contributing greater than 0.75 of the material, both models represented the general trends in the mixtures and identified their major sources.
Conclusions
Virtual mixtures are as robust as laboratory mixtures for assessing fingerprinting mixing models if analytical errors are negligible. We therefore recommend to always include virtual mixtures as part of the model testing process. Additionally, we highlight the value of using evaluation metrics that consider the accuracy and precision of model results, and the importance of reporting uncertainty when modeling source apportionments.
The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011
resulted in the contamination of Japanese landscapes with radioactive
fallout. Accordingly, the Japanese authorities decided ...to conduct extensive
remediation activities in the impacted region to allow for the relatively
rapid return of the local population. The objective of this review is to
provide an overview of the decontamination strategies and their potential
effectiveness in Japan, focussing on particle-bound radiocesium. In the
Fukushima Prefecture, the decision was taken to decontaminate the
fallout-impacted landscapes in November 2011 for the 11 municipalities
evacuated after the accident (Special Decontamination Zone – SDZ – 1117 km2) and for the 40 non-evacuated municipalities affected by
lower, although still significant, levels of radioactivity (Intensive
Contamination Survey Areas, 7836 km2). Decontamination
activities predominantly targeted agricultural landscapes and residential
areas. No decontamination activities are currently planned for the majority
of forested areas, which cover ∼75 % of the main
fallout-impacted region. Research investigating the effectiveness of
decontamination activities underlined the need to undertake concerted
actions at the catchment scale to avoid renewed contamination
from the catchment headwaters after the completion of remediation
activities. Although the impact of decontamination on the radioactive dose
rates for the local population remains a subject of debate in the literature
and in the local communities, outdoor workers in the SDZ represent a group
of the local population that may exceed the long-term dosimetric target of
1 mSv yr−1. Decontamination activities generated ∼20 million m3 of soil waste by early 2019. The volume of waste generated
by decontamination may be decreased through incineration of combustible
material and recycling of the less contaminated soil for civil engineering
structures. However, most of this material will have to be stored for
∼30 years at interim facilities opened in 2017 in the
vicinity of the FDNPP before being potentially transported to final disposal
sites outside of the Fukushima Prefecture. Further research is required to
investigate the perennial contribution of radiocesium from forest sources.
In addition, the re-cultivation of farmland after decontamination raises
additional questions associated with the fertility of remediated soils and
the potential transfer of residual radiocesium to the plants. Overall, we
believe it is important to synthesise the remediation lessons learnt
following the FDNPP nuclear accident, which could be fundamental if a
similar catastrophe occurs somewhere on Earth in the future.
Purpose
Surveillance monitoring programs can provide fast, relatively low-cost, synoptic information on key water quality drivers and help inform land management decisions. Here, we evaluate ...longitudinal changes in the geochemical composition and metal speciation of deposited sediment over a 967 km reach of a large glacier-fed river and its key tributaries in central Alberta, Canada. In particular, the work provides a basis to understand how a major urban conurbation influences the geochemical composition and trace element properties of deposited sediment.
Methods
The concentrations and spatial distribution of major elements and sediment-associated metals (As, Cd, Cr, Cu, Pb, Hg, Ni, Zn) were determined and compared to consensus-based threshold effect concentrations (TEC). Metal partitioning to geochemical properties of sediment was evaluated by sequential extraction.
Results
Levels of Cr exceeded the TEC in 28% and 20% of the samples in the North Saskatchewan River and tributary samples, respectively. One Ni sample (3%) also exceeds the TEC on the main stem of the North Saskatchewan River. No consistent downstream increase in major element or trace metal concentrations was observed. The majority of Cr was bound to the largely non-bioavailable silicate phase thus highlighting the importance of parent geology as a source of metals to receiving streams.
Conclusion
The results of this surveillance monitoring provide preliminary data on the distribution and speciation of sediment-associated metals in the North Saskatchewan River and thereby address an evidence gap common to many large river basins in Canada.
The Fukushima Daiichi nuclear power plant (FDNPP) accident in March 2011 resulted in the fallout of significant quantities of radiocesium over the Fukushima region. After reaching the soil surface, ...radiocesium is quickly bound to fine soil particles. Thereafter, rainfall and snowmelt run-off events transfer particle-bound radiocesium downstream. Characterizing the precipitation regime of the fallout-impacted region is thus important for understanding post-deposition radiocesium dynamics. Accordingly, 10 min (1995–2015) and daily precipitation data (1977–2015) from 42 meteorological stations within a 100 km radius of the FDNPP were analyzed. Monthly rainfall erosivity maps were developed to depict the spatial heterogeneity of rainfall erosivity for catchments entirely contained within this radius. The mean average precipitation in the region surrounding the FDNPP is 1420 mm yr−1 (SD 235) with a mean rainfall erosivity of 3696 MJ mm ha−1 h−1 yr−1 (SD 1327). Tropical cyclones contribute 22 % of the precipitation (422 mm yr−1) and 40 % of the rainfall erosivity (1462 MJ mm ha−1 h−1 yr−1 (SD 637)). The majority of precipitation (60 %) and rainfall erosivity (82 %) occurs between June and October. At a regional scale, rainfall erosivity increases from the north to the south during July and August, the most erosive months. For the remainder of the year, this gradient occurs mostly from northwest to southeast. Relief features strongly influence the spatial distribution of rainfall erosivity at a smaller scale, with the coastal plains and coastal mountain range having greater rainfall erosivity than the inland Abukuma River valley. Understanding these patterns, particularly their spatial and temporal (both inter- and intraannual) variation, is important for contextualizing soil and particle-bound radiocesium transfers in the Fukushima region. Moreover, understanding the impact of tropical cyclones will be important for managing sediment and sediment-bound contaminant transfers in regions impacted by these events.
Artificial radionuclides including radiocesium (134Cs and 137Cs) and
radiosilver (110mAg) were released into the environment following the
Fukushima Dai-ichi nuclear power plant accident in March ...2011. These
particle-bound substances deposited on soils of north-eastern Japan, located
predominantly within a ∼3000 km2 radioactive fallout plume and
drained by several coastal rivers to the Pacific Ocean. The current dataset
(Evrard et al., 2021), which can be accessed at https://doi.org/10.1594/PANGAEA.928594,
compiles gamma-emitting artificial radionuclide activities measured in 782
sediment samples collected from 27 to 71 locations across catchments draining
∼6450 km2 during 16 fieldwork campaigns. These campaigns were conducted in Japan
between November 2011 and November 2020 in river catchments draining the main
radioactive plume. This database may be useful to evaluate and anticipate the
post-accidental redistribution of radionuclides in the environment and for the
spatial validation of models simulating the transfer of radiocesium across
continental landscapes.
After nuclear accidents, such as those experienced in Chernobyl and Fukushima, microorganisms may help purify contaminated soils by changing the mobility of radionuclides and their availability for ...plants by altering the physical and chemical properties of the substrate. Here, using model experiments with quartz sand as a substrate we investigate the influence of microorganisms on (137)Cs transfer from substrate to plants. The highest transition of (137)Cs from substrate to plants (50% increase compared to the control) was observed after Brassica napus L. seeds were inoculated by Azotobacter chroococcum. The best results for reducing the accumulation of (137)Cs radionuclides (30% less) were noted after the inoculation by Burkholderia sp.. Furthermore, Bacillus megaterium demonstrated an increased ability to accumulate (137)Cs. This research improves our prediction of the behavior of radionuclides in soil and may contribute towards new, microbiological countermeasures for soil remediation following nuclear accidents.
•The source dynamics of total and dissolved material were investigated.•Water quality monitoring data was modelled with Deconvolutional-MixSIAR.•A novel approach to select tracers based on quality ...control samples was presented.•Future research should examine source dynamics in reservoirs and lakes.
The source dynamics of total and dissolved material in riverine systems are being affected by anthropogenic activities resulting in the degradation of waterways worldwide. Identifying the main sources of total and dissolved material is thus central to the management of increasingly scarce water resources. Here, we utilize data generated from water quality monitoring programs to investigate the sources of total and dissolved material in a large, semi-arid basin in western Canada. Our research focuses on the confluence of two major tributaries in the South Saskatchewan River Basin (SSRB) in the Province of Alberta: the Bow River (25,611 km2) and the Oldman River (28,270 km2). A tributary tracing technique coupled with a Deconvolutional-MixSIAR (D-MIXSIAR) modelling approach is used to estimate the potential source contributions of total and dissolved material from major tributary sites to target node sites on the main stem of the Bow River and Oldman River in addition to target nodes downstream of their confluence. In total, 812 samples were taken from 29 sites across the SSRB. A novel approach to selecting fingerprints for modelling is presented based on the analyses of additional quality control samples (146 duplicate and 172 blank samples). Overall, the Rocky Mountain headwater catchments were found to dominate the supply of material modelled using total recoverable (68%) and dissolved (76%) metals. There were seasonal fluctuations in source dynamics evident where the Bow River dominated the supply of total (69%) and dissolved (57%) material during the ice-covered season (November-March), and the Oldman River dominated the supply of total (73%) and dissolved (59%) material during the open water season (April-October). On the one hand, these seasonal dynamics are potentially the result of the extensive regulation of flow, particularly along the Bow River. On the other hand, the intensification of agriculture in the prairie/plain catchments may also facilitate the excess supply of total relative to dissolved material. For example, the Little Bow River, with ~70% agricultural land cover, contributed ~14 times more total material than anticipated based on discharge and 1.6 times more than anticipated based on unit area during the open water season. Overall, this research has improved our understanding of the source dynamics of total and dissolved material in the SSRB, providing the foundation for focussed studies targeting the main sources of total and dissolved material in this large, semi-arid basin in western Canada. In addition, our research highlights the potential of using existent data generated from water quality monitoring programs along with quality control best practices to help improve our understanding of the source dynamics of total and dissolved material in waterways around the world.
In a context of accelerated soil erosion and sediment supply to water bodies, sediment fingerprinting techniques have received an increasing interest in the last 2 decades. The selection of tracers ...is a particularly critical step for the subsequent accurate prediction of sediment source contributions. To select tracers, the most conventional approach is the three-step method, although, more recently, the consensus method has also been proposed as an alternative. The outputs of these two approaches were compared in terms of identification of conservative properties, tracer selection, modelled contributions and performance on a single dataset. As for the three-step method, several range test criteria were compared, along with the impact of the discriminant function analysis (DFA). The dataset was composed of tracer properties analysed in soil (three potential sources; n = 56) and sediment core samples (n = 32). Soil and sediment samples were sieved to 63 µm and analysed for organic matter, elemental geochemistry and diffuse visible spectrometry. Virtual mixtures (n = 138) with known source proportions were generated to assess model accuracy of each tracer selection method. The Bayesian un-mixing model MixSIAR was then used to predict source contributions on both virtual mixtures and actual sediments. The different methods tested in the current research can be distributed into three groups according to their sensitivity to the conservative behaviour of properties, which was found to be associated with different predicted source contribution tendencies along the sediment core. The methods selecting the largest number of tracers were associated with a dominant and constant contribution of forests to sediment. In contrast, the methods selecting the lowest number of tracers were associated with a dominant and constant contribution of cropland to sediment. Furthermore, the intermediate selection of tracers led to more balanced contributions of both cropland and forest to sediments. The prediction of the virtual mixtures allowed us to compute several evaluation metrics, which are generally used to support the evaluation of model accuracy for each tracer selection method. However, strong differences or the absence of correspondence were observed between the range of predicted contributions obtained for virtual mixtures and those values obtained for actual sediments. These divergences highlight the fact that evaluation metrics obtained for virtual mixtures may not be directly transferable to models run for actual samples and must be interpreted with caution to avoid over-interpretation or misinterpretation. These divergences may likely be attributed to the occurrence of a not (fully) conservative behaviour of potential tracer properties during erosion, transport and deposition processes, which could not be fully reproduced when generating the virtual mixtures with currently available methods. Future research should develop novel metrics to quantify the conservative behaviour of tracer properties during erosion and transport processes. Furthermore, new methods should be designed to generate virtual mixtures closer to reality and to better evaluate model accuracy. These improvements would contribute to the development of more reliable sediment fingerprinting techniques, which are needed to better support the implementation of effective soil and water conservation measures at the catchment scale.
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