The quantification of groundwater NO loading associated with a specific field or set of management practices so that groundwater quality improvements can be objectively assessed is a major challenge. The magnitude and timing of NO export from a single agricultural field under raspberry ( L.) production were investigated by combining high-resolution groundwater NO concentration profiles (sampled using passive diffusion samplers) with Darcy's flux estimation at the field's down-gradient edge (based on field-measured hydraulic gradients and laboratory-estimated hydraulic conductivity). Annual recharge estimated using Darcy's law (1002 mm) was similar to that obtained using two other approaches. The similarity in the rate of Cl applied to the field and the estimated export flux over the 1-yr monitoring period (51 vs. 56 kg Cl ha) suggested the mass flux estimation approach was robust. An estimated 80 kg NO-N ha was exported from the agricultural field over the 1-yr monitoring period. The greatest monthly groundwater mass flux exported was observed in February and March (∼11 kg NO-N ha), and was associated with NO leached from the soil zone during the onset of precipitation in the previous autumn. Provided the groundwater recharged from the field of interest can be isolated within a vertical profile, this approach is an effective method for obtaining spatially integrated estimates of the magnitude and timing of NO loading to groundwater.

A detailed geochemical study of surface waters, spring waters, and groundwaters was undertaken to examine the geochemical evolution of groundwater on Saturna Island, British Columbia. The purpose of the study was to characterize the nature and occurrence of saline waters and to provide insight on chemical processes that lead to salinization in the fractured sedimentary bedrock aquifers of this small island. Major ion chemistry shows that groundwater is recharged locally but mixes with saline waters that occur at depth or near the coast. Simple mixing is complicated by cation exchange (between calcium-rich waters and sodium-rich exchange sites offered by mudstone beds) and results in a spatially variable hydrochemical composition that is dependent on the island topography and geological framework (structural, sedimentological, and glacial), in combination with groundwater use patterns. Sodium, present at exchange sites, is speculated to be a remnant of ocean water intrusion during the Pleistocene, when the island was submerged. As a result of its high mobility and conservative nature, chloride (and sulphate) has been flushed from the shallow bedrock during a process of natural desalinization but may remain trapped in the pores and fractures at depth. Modern salt-water intrusion, brought about by increased development on the island, is now competing with natural desalinization along the coast and has left many drinking-water supplies contaminated.Résumé : Une étude géochimique détaillée des eaux de surface, des eaux de sources et des eaux souterraines a été entreprise pour examiner l'évolution géochimique de l'eau souterraine sur l'île de Saturna, en Colombie Britannique. Le but de l'étude était de caractériser la nature et l'occurrence d'eau saline et de comprendre les processus chimiques qui conduisent à la salinisation des aquifères situés dans la roche mère sédimentaire fracturée de cette petite île. La chimie des ions majeurs montre que l'eau souterraine est rechargée localement, mais qu'elle se mélange aux eaux salines qui se trouvent en profondeur ou près de la côte. Le simple mélange se complique par l'échange de cations (entre les eaux riches en calcium et les sites d'échanges riches en sodium des lits de mudstone); il en résulte une composition hydrochimique à variation spatiale qui dépend de la topographie de l'île et de son cadre géologique (structural, sédimentologique et glacial) combinés aux patrons d'utilisation de l'eau souterraine. Nous proposons que le sodium, présent aux sites d'échanges, est un restant d'intrusion d'eau océanique au cours du Pléistocène, lorsque l'île était submergée. En raison de sa grande mobilité et de sa nature conservatrice, le chlorure a été retiré de la roche-mère à faible profondeur durant un processus de dessalement mais, en profondeur, il peut demeurer emprisonné dans les pores et les fractures (idem pour le sulfate). L'intrusion d'eau saline moderne, amenée par la croissance du développement sur l'île, est maintenant en compétition avec le dessalement naturel le long...

Abstract. Poultry manure is the primary cause of nitrate (NO3-) exceedances in the transboundary Abbotsford–Sumas aquifer (ASA; Canada–USA) based on synoptic surveys two decades apart, but questions remained about seasonal and spatial aspects of agricultural nitrate fluxes to the aquifer to help better focus remediation efforts. We conducted over 700 monthly δ15N and δ18O of nitrate assays, focusing on shallow groundwater (< 5 years old) over a 5-year period to gain new insight on spatio-temporal sources and controls of groundwater nitrate contamination. NO3- concentrations in these wells ranged from 1.3 to 99 mg N L−1 (n=1041) with a mean of 16.2±0.4 mg N L−1. The high-frequency 15N and 18O isotope data allowed us to identify three distinctive NO3- source patterns: (i) primarily from synthetic fertilizer, (ii) dynamic changes in nitrate due to changes in land use, and (iii) from a mix of poultry manure and fertilizer. A key finding was that the source(s) of nitrate in recharge could be quickly influenced by short-term near-field management practices and stochastic precipitation events, which ultimately impact long-term nitrate contamination trends. Overall, the isotope data affirmed a subtle decadal-scale shift in agricultural practices from manure increasingly towards fertilizer nitrate sources; nevertheless, poultry-derived N remains a predominant source of nitrate contamination. Because the aquifer does not generally support denitrification, remediation of the Abbotsford–Sumas aquifer is possible only if agricultural N sources are seriously curtailed, a difficult proposition due to longstanding high-value intensive poultry and raspberry and blueberry operations over the aquifer.

The Fukushima-Daiichi nuclear accident (FDNA) released iodine-129 (15.7 million year half-life)and other fission product radionuclides into the environment in the spring and summer of 2011. 129 I is recognized as a useful tracer for the short-lived radiohazard 131 I, which has a mobile geochemical behavior with potential to contaminate water resources. To trace 129 I released by the FDNA reaching Canada, preaccident and post-accident rain samples collected in Vancouver, on Saturna Island and from the National Atmospheric Deposition Program in Washington State were measured. Groundwater from the AbbotsfordSumas Aquifer was sampled to determine the fate of 129 I that infiltrates below the root zone. Modeling of vadose zone transport was performed to constrain the travel time and retardation of 129 I. The mean preaccident 129 I concentration in rain was 31 3 10 6 atoms/L (n 5 4). Immediately following the FDNA, 129 I values increased to 211 3 10 6 atoms/L and quickly returned to near-background levels. However, pulses of elevated 129 I continued for several months. The increases in 129 I concentrations from both Vancouver and Saturna Island were synchronized, and occurred directly after the initial release from the FDNA. The 129 I in shallow ( 3 H/ 3 He age <1.4 years) Wassenaar et al. (2006) groundwater showed measurable variability through March 2013 with an average of 3.2 3 10 6 atoms/L (n 5 32) that was coincident with modeled travel times for Fukushima 129 I. The groundwater response and the modeling results suggest that 129 I was partially attenuated in soil, which is consistent with its geochemical behavior; however, we conclude that the measured variability may be due to Fukushima 129 I entering groundwater.

Abstract. Poultry manure is the primary source of nitrate (NO3−) exceedances in the transboundary Abbotsford-Sumas aquifer (Canada-USA) based on synoptic surveys two decades apart, but serious questions remained about seasonal and spatial aspects of agricultural nitrate fluxes to the aquifer to help better focus remediation efforts. We conducted over 700 monthly δ15N and δ18O of nitrate assays, focusing on newly recharged groundwater (

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The total dissolved gas pressure (PTDG ) probe has been used in groundwater studies for over a decade, but rarely in assessing contaminant degradation, despite the many degradation reactions that produce or consume dissolved gases. Here we present three studies to demonstrate the application of PTDG measurements to groundwater experiencing contaminant degradation, with discussion of its benefits and limitations. The first study is a pilot‐scale laboratory experiment simulating dissolved ethanol contamination of an anaerobic sand aquifer. Continuous monitoring of PTDG showed the rapid onset of microbial hydrocarbon degradation via denitrification and fermentation. The subsequent formation of a gas phase was revealed when PTDG began mimicking the bubbling pressure (PG *; sum of hydrostatic and atmospheric pressure), fluctuating with atmospheric pressure. Some deviations of PTDG above PG * occurred also, which may hold promise for signalling substantial changes in the rate or type of degradation process (here, the onset of methanogenesis). In the second study, synoptic field measurements at a petroleum plume site demonstrated how elevated PTDG could identify wells with evidence of hydrocarbon degradation (denitrification and/or methanogenesis). And finally, combined field measurements of dissolved oxygen (DO) and PTDG in monitoring wells of a nitrate‐contaminated aquifer (Abbottsford‐Sumas) revealed areas where denitrification was likely occurring. Limitations to PTDG use identified in these studies included the masking of degradation processes by the presence of a gas phase, as when trapped following water table fluctuations or formed from rigorous degradation reactions, and confounded assessment of PTDG patterns from other natural or anthropogenic processes that can also influence groundwater PTDG .

The Abbotsford-Sumas Aquifer is a permeable, unconfined aquifer in British Columbia, Canada, where raspberry (Rubus idaeus L.) production is an important source of groundwater NO 3 contamination. Renovation of raspberry fields (i.e., canes chopped, soil tilled and fumigated, and spring manure application prior to replanting), which typically occurs every 6 to 10 yr in response to decreased crop vigor, has been suggested as a possible cause of significant interannual variation in groundwater NO 3 concentrations. This study used high-resolution passive diffusion sampling to quantify the magnitude and timing of NO 3 loading to shallow groundwater from a commercial raspberry field during a 6-yr (2009-2015) monitoring period after crop renovation. After renovation, the annual NO 3 loading increased from ?95 kg N ha −1 in Year 1 to ?245 kg N ha −1 in Year 2 and decreased to ?85 kg N ha −1 in Year 3. The average annual NO 3 loading from Years 4 to 6 (72 kg N ha −1 ) was assumed to reflect annual loading without a renovation effect, and the increased loading during Years 1 to 3 was attributed to renovation. Renovation contributed an estimated 33 to 23% of total groundwater NO 3 from this field for a 6-to 10-yr renovation cycle. Most of the NO 3 loading associated with renovation occurred in Year 2 and was attributed to the manure application. The increased NO 3 loading after renovation likely contributes to the spatial and temporally varying NO 3 patterns observed in the aquifer. Reducing manure applications during renovation and decreasing renovation frequency have the potential to decrease the groundwater NO 3 concentration.