Nitrate sources and mixing in the Danube watershed: implications for transboundary river basin monitoring and management.

Dispersed and unknown pollution sources complicate water management in large transboundary watersheds. We applied stable isotopes of water and nitrate together with contaminants of emerging concern (CECs: carbamazepine, caffeine, sulfamethoxazole, perfluorooctanoic acid and 2,4-dinitrophenol) to evaluate mixing and inputs of water and contaminants from tributaries into the mainstem of the transboundary Danube River. Stable isotope (δ18O, δ2H) variations from low values (- 13.3 ‰, - 95.1 ‰) in the Upper Danube after the Inn River confluence to high values (- 9.9 ‰, - 69.7 ‰) at the Danube River mouth revealed snowmelt dominated tributary mixing (~ 70%) in the mainstem. Stable isotopes of nitrate (δ15N-NO3) in the Danube River varied from lower values (+ 6.7 ‰) in the Upper Danube to higher values after the mixing with Morava River (+ 10.5 ‰) and showed that cold snowmelt can reduce biological activity and controls nitrate biotransformation processes in the mainstem up to 1000 km downstream. Data on emerging contaminants affirmed the low biodegradation potential of organic compounds transferred into the mainstem by tributaries. We found pollutant source tracing in large rivers is complicated by mixing of multiple sources with overlapping isotopic signatures, but additional tracers such as CECs improve the interpretation of hydrological processes (e.g., water transit time) and support tracing of nitrate pollution sources, and biogeochemical processes. Our approach can be applied to other watersheds to improve the understanding of dilution and mixing processes. Moreover, it provides directions for improving national and transboundary water quality monitoring networks.

Temperature and precipitation effects on the isotopic composition of global precipitation reveal long-term climate dynamics.

Earth's climate history is traced through the long-term covariance between the isotopic (δ 18O) composition of archived meteoric waters (groundwater, ice cores) with air temperature (T) and amount of precipitation (P). To assess recent multi-decadal climatic changes, we analysed δ18O, T and P, and the relationships between these parameters at 20 stations having 60 years of continuous monthly isotopic records. Using nonparametric regressions and time series modelling we found significant linear and non-linear relationships for δ18O with T and P and showed that the δ18O dependency on these two parameters varied over decadal scales, thereby revealing complex relationships related to recycled moisture, large-scale convective processes and atmospheric-oceanic oscillations. Due to multiple factors controlling the δ 18O composition of precipitation including P and T effects, we found that time-varying relationships between δ18O in precipitation P and T were better explained using the non-linear regressions. Our results affirmed that δ18O distributions in global precipitation are integrative indicators of climate dynamics whose patterns can be applied to better understand region-specific climatic changes in the present, past, and future.

Seeking excellence: An evaluation of 235 international laboratories conducting water isotope analyses by isotope-ratio and laser-absorption spectrometry.

RATIONALE: Water stable isotope ratios (δ2 H and δ18 O values) are widely used tracers in environmental studies; hence, accurate and precise assays are required for providing sound scientific information. We tested the analytical performance of 235 international laboratories conducting water isotope analyses using dual-inlet and continuous-flow isotope ratio mass spectrometers and laser spectrometers through a water isotope inter-comparison test. METHODS: Eight test water samples were distributed by the IAEA to international stable isotope laboratories. These consisted of a core set of five samples spanning the common δ-range of natural waters, and three optional samples (highly depleted, enriched, and saline). The fifth core sample contained unrevealed trace methanol to assess analyst vigilance to the impact of organic contamination on water isotopic measurements made by all instrument technologies. RESULTS: For the core and optional samples ~73 % of laboratories gave acceptable results within 0.2 ‰ and 1.5 ‰ of the reference values for δ18 O and δ2 H, respectively; ~27 % produced unacceptable results. Top performance for δ18 O values was dominated by dual-inlet IRMS laboratories; top performance for δ2 H values was led by laser spectrometer laboratories. Continuous-flow instruments yielded comparatively intermediate results. Trace methanol contamination of water resulted in extreme outlier δ-values for laser instruments, but also affected reactor-based continuous-flow IRMS systems; however, dual-inlet IRMS δ-values were unaffected. CONCLUSIONS: Analysis of the laboratory results and their metadata suggested inaccurate or imprecise performance stemmed mainly from skill- and knowledge-based errors including: calculation mistakes, inappropriate or compromised laboratory calibration standards, poorly performing instrumentation, lack of vigilance to contamination, or inattention to unreasonable isotopic outcomes. To counteract common errors, we recommend that laboratories include 1-2 'known' control standards in all autoruns; laser laboratories should screen each autorun for spectral contamination; and all laboratories should evaluate whether derived d-excess values are realistic when both isotope ratios are measured. Combined, these data evaluation strategies should immediately inform the laboratory about fundamental mistakes or compromised samples.

A compact tritium enrichment unit for large sample volumes with automated re-filling and higher enrichment factor.

Tritium (3H) in natural waters is a powerful tracer of hydrological processes, but its low concentrations require electrolytic enrichment before precise measurements can be made with a liquid scintillation counter. Here, we describe a newly developed, compact tritium enrichment unit which can be used to enrich up to 2L of a water sample. This allows a high enrichment factor (>100) for measuring low 3H contents of <0.05TU. The TEU uses a small cell (250mL) with automated re-filling and a CO2 bubbling technique to neutralize the high alkalinity of enriched samples. The enriched residual sample is retrieved from the cell under vacuum by cryogenic distillation at -20°C and the tritium enrichment factor for each sample is accurately determined by measuring pre- and post- enrichment 2H concentrations with laser spectrometry.

Measurement of extremely (2) H-enriched water samples by laser spectrometry: application to batch electrolytic concentration of environmental tritium samples.

RATIONALE: Natural water samples artificially or experimentally enriched in deuterium ((2) H) at concentrations up to 10,000 ppm are required for various medical, environmental and hydrological tracer applications, but are difficult to measure using conventional stable isotope ratio mass spectrometry. METHODS: Here we demonstrate that off-axis integrated cavity output (OA-ICOS) laser spectrometry, along with (2) H-enriched laboratory calibration standards and appropriate analysis templates, allows for low-cost, fast, and accurate determinations of water samples having δ(2) HVSMOW-SLAP values up to at least 57,000 ‰ (~9000 ppm) at a processing rate of 60 samples per day. RESULTS: As one practical application, extremely (2) H-enriched samples were measured by laser spectrometry and compared to the traditional (3) H Spike-Proxy method in order to determine tritium enrichment factors in the batch electrolysis of environmental waters. Highly (2) H-enriched samples were taken from different sets of electrolytically concentrated standards and low-level (<10 TU) IAEA inter-comparison tritium samples, and all cases returned accurate and precise initial low-level (3) H results. CONCLUSIONS: The ability to quickly and accurately measure extremely (2) H-enriched waters by laser spectrometry will facilitate the use of deuterium as a tracer in numerous environmental and other applications. For low-level tritium operations, this new analytical ability facilitated a 10-20 % increase in sample productivity through the elimination of spike standards and gravimetrics, and provides immediate feedback on electrolytic enrichment cell performance. Copyright © 2016 John Wiley & Sons, Ltd.

Comparison of manual and semi-automatic measuring techniques in MSCT scans of patients with lymphoma: a multicentre study.

OBJECTIVES: Multicentre evaluation of the precision of semi-automatic 2D/3D measurements in comparison to manual, linear measurements of lymph nodes regarding their inter-observer variability in multi-slice CT (MSCT) of patients with lymphoma. METHODS: MSCT data of 63 patients were interpreted before and after chemotherapy by one/two radiologists in five university hospitals. In 307 lymph nodes, short (SAD)/long (LAD) axis diameter and WHO area were determined manually and semi-automatically. Volume was solely calculated semi-automatically. To determine the precision of the individual parameters, a mean was calculated for every lymph node/parameter. Deviation of the measured parameters from this mean was evaluated separately. Statistical analysis entailed intraclass correlation coefficients (ICC) and Kruskal-Wallis tests. RESULTS: Median relative deviations of semi-automatic parameters were smaller than deviations of manually assessed parameters, e.g. semi-automatic SAD 5.3 vs. manual 6.5 %. Median variations among different study sites were smaller if the measurement was conducted semi-automatically, e. g. manual LAD 5.7/4.2 % vs. semi-automatic 3.4/3.4 %. Semi-automatic volumetry was superior to the other parameters (2.8 %). CONCLUSIONS: Semi-automatic determination of different lymph node parameters is (compared to manually assessed parameters) associated with a slightly greater precision and a marginally lower inter-observer variability. These results are with regard to the increasing mobility of patients among different medical centres and in relation to the quality management of multicentre trials of importance. KEY POINTS: • In a multicentre setting, semi-automatic measurements are more accurate than manual assessments. • Lymph node volumetry outperforms all other semi-automatically and manually performed measurements. • Use of semi-automatic lymph node analyses can reduce the inter-observer variability.

Therapy response evaluation of malignant lymphoma in a multicenter study: comparison of manual and semiautomatic measurements in CT.

PURPOSE: Comparison of manual one-/bi-dimensional measurements versus semi-automatically derived one-/bi-dimensional and volumetric measurements for therapy response evaluation of malignant lymphoma during CT follow-up examinations in a multicenter setting. MATERIALS AND METHODS: MSCT data sets of patients with malignant lymphoma were evaluated before (baseline) and after two cycles of chemotherapy (follow-up) at radiological centers of five university hospitals. The long axis diameter (LAD), the short axis diameter (SAD) and the bi-dimensional WHO of 307 target lymph nodes were measured manually and semi-automatically using dedicated software. Lymph node volumetry was performed semi-automatically only. The therapeutic response was evaluated according to lymphoma-adapted RECIST. RESULTS: Based on a single lymph node, semi-automatically derived multidimensional parameters allowed for significantly more accurate therapy response classification than the manual or the semi-automatic unidimensional parameters. Incorrect classifications were reduced by up to 9.6%. Compared to the manual approach, the influence of the study center on correct therapy classification is significantly less relevant when using semi-automatic measurements. CONCLUSION: Semi-automatic volumetry and bi-dimensional WHO significantly reduce the number of incorrectly classified lymphoma patients by approximately 9.6% in the multicenter setting in comparison to linear parameters. Semi-automatic quantitative software tools may help to significantly reduce wrong classifications that are associated with the manual assessment approach. KEY POINTS: ► Semi-automatic volumetry and bi-dimensional WHO significantly reduce the number of incorrectly classified lymphoma patients ► Manual lymph node evaluation with uni-dimensional parameters is inferior to semi-automatic analysis in a multicenter setting ► Semi-automatic quantitative software tools should be introduced in clinical study evaluation.

Worldwide proficiency test for routine analysis of δ2H and δ18O in water by isotope-ratio mass spectrometry and laser absorption spectroscopy.

RATIONALE: The interpretation of stable hydrogen and oxygen isotope data in isotope hydrology relies on accurate, high-precision analytical measurements of the (2)H:(1)H and (18)O:(16)O ratios in liquid H(2)O samples. METHODS: A synthesis of the International Atomic Energy Agency (IAEA) worldwide proficiency test for analytical laboratories conducting routine analysis of δ(2)H and δ(18)O values in water (WICO2011) by isotope-ratio mass spectrometry (IRMS) and laser absorption spectroscopy (LAS) technology has been carried out. RESULTS: This test revealed that >96% of the 160 laboratory submissions provided acceptable results within ±2‰ for δ(2) H values and ±0.2‰ for δ(18)O values of the established reference values for four test waters, and no difference in outcomes based on IRMS vs. LAS technology was found for good performing laboratories. CONCLUSIONS: The leading cause of outliers appeared to be improper calibration or compromised storage of laboratory standard and primary reference waters; hence the importance of judicious storage of lab standards cannot be understated. The deprecated practice of single standard normalization was identified as a problem for some laboratories. We further recommend that laboratories strive to report parsimonious long-term precisions based upon control standards, and to improve quantification and correction for LAS instrumental drift and inter-sample carryover effects.

Correcting for methane interferences on δ2H and δ18O measurements in pore water using H2Oliquid-H2Ovapor equilibration laser spectroscopy.

Cavity ring-down spectroscopy (CRDS) is a new and evolving technology that shows great promise for isotopic δ(18)O and δ(2)H analyses of pore water from equilibrated headspace H(2)O vapor from environmental and geologic cores. We show that naturally occurring levels of CH(4) can seriously interfere with CRDS spectra, leading to erroneous δ(18)O and δ(2)H results for water. We created a new CRDS correction algorithm to account for CH(4) concentrations typically observed in subsurface and anaerobic environments, such as ground waters or lake bottom sediments. We subsequently applied the correction method to a series of geologic cores that contain CH(4). The correction overcomes the spectral interference and provides accurate pore water δ(18)O and δ(2)H values with acceptable precision levels as well as accurate concentrations of CH(4).

Inferring heterogeneity in aquitards using high-resolution deltaD and delta18O profiles.

Vertical depth profiles of pore water isotopes (deltaD and delta18O) in clay-rich aquitards have been used to show that solute transport is dominated by molecular diffusion, to define the timing of geologic events, and to estimate vertical hydraulic conductivity. The interpretation of the isotopic profiles in these studies was based on pore water samples collected from piezometers installed in nests (typically 4 to 15 piezometers) over depths of 10 to 80 m. Data from piezometer nests generally have poor vertical resolution (meters), raising questions about their capacity to reveal the impact of finer scale heterogeneities such as permeable sand bodies or fractured till zones on solute transport. Here, we used high-resolution (30-cm) depth profiles of deltaD and delta18O from two continuously cored boreholes in a till aquitard to provide new insights into the effects of sand bodies on solute transport. High-resolution core-derived profiles indicate that such heterogeneities can cause major deviations from one-dimensional diffusion profiles. Further, comparison of piezometer-measured values with best-fit diffusion trends shows subtle deviations, suggesting the presence of heterogeneities that should not be ignored. High-resolution profiles also more clearly defined the contact between the highly fractured oxidized zone and the underlying unoxidized zone than the piezometers.

Comparative microscale analysis of the effects of triclosan and triclocarban on the structure and function of river biofilm communities.

The broad spectrum antimicrobials triclosan (TCS) and triclocarban (TCC) are commonly detected in the environment. However, there is very limited understanding of the aquatic ecological implications of these agents. During this study, river biofilms were cultivated using 10 microg l(-1) of TCS or TCC and the equivalent in nutrients (carbon, nitrogen) over a developmental period of 8 weeks. Confocal laser microscopy showed that the biofilm communities developing under the influence of TCS and TCC had community architecture and composition different from either control or nutrient exposed communities. Microscale analyses of biofilm community structure indicated a significant reduction in algal biomass (p<0.05) as a result of exposure to either TCS or TCC. Thymidine incorporation did not detect significant differences between control and treated communities. The use of carbon utilization assays based on growth indicated that, in general, TCS and TCC suppressed utilization. The community was altered from one dominated by autotrophic processes to one dominated by heterotrophic processes. Both TCS and TCC treatments resulted in significant (p<0.05) alterations in the composition of the EPS matrix of the communities, suggesting significant changes in community composition. Denaturing gradient gel electrophoresis and PCA-ANOSIM analyses indicated a significant change occurred in the bacterial community as a consequence of TCS treatments. Enumeration of micrometazoa and protozoa revealed an increase in micrometazoan numbers over control values, whereas no clear impact on protozoa was detected in any treatment. This study indicated significant effects of 10 microg l(-1) TCS and TCC on microbial community composition, algal biomass, architecture and activity.

Community-level assessment of the effects of the broad-spectrum antimicrobial chlorhexidine on the outcome of river microbial biofilm development.

Chlorhexidine is a common-use antibacterial agent found in a range of personal-care products. We used rotating annular reactors to cultivate river biofilms under the influence of chlorhexidine or its molar equivalent in nutrients. Studies of the degradation of [(14)C]chlorhexidine demonstrated that no mineralization of the compound occurred. During studies with 100 microg liter(-1) chlorhexidine, significant changes were observed in the protozoan and micrometazoan populations, the algal and cyanobacterial biomass, the bacterial biomass, and carbon utilization. Denaturing gradient gel electrophoresis (DGGE) in combination with statistical analyses showed that the communities developing under control and 100 microg liter(-1) chlorhexidine were significantly different. At 10 microg liter(-1) chlorhexidine, there was significantly increased algal and cyanobacterial biomass while the bacterial biomass was not significantly affected (P < 0.05). No significant effects on protozoan or metazoan grazing were detected at the 10-microg liter(-1) chlorhexidine level. Fluorescent in situ hybridization indicated a significant reduction in the abundance of betaproteobacteria and gammaproteobacteria (P < 0.05). Archaeal cell counts were significantly reduced by both chlorhexidine and nutrient treatments. DGGE and statistical analyses indicated that 10 microg liter(-1) chlorhexidine and molar equivalent nutrient treatments were significantly different from control communities. In contrast to community level observations, toxicological testing with a panel of cyanobacteria, algae, and protozoa indicated no detectable effects at 10, 50, and 100 microg liter(-1) chlorhexidine. Thus, community level assessment indicated a risk of low levels of chlorhexidine in aquatic habitats while conventional approaches did not.

High resolution pore water delta2H and delta18O measurements by H2O(liquid)-H2O(vapor) equilibration laser spectroscopy.

A new H2O(liquid)-H2O(vapor) pore water equilibration and laser spectroscopy method provides a fast way to obtain accurate high resolution deltaD and delta18O profiles from single core samples from saturated and unsaturated geologic media. The precision and accuracy of the H2O(liquid)-H2O(vapor) equilibration method was comparable to or better than conventional IRMS-based methods, and it can be conducted on geologic cores that contain volumetric water contents as low as 5%. Significant advantages of the H2O(liquid)-H2O(vapor) pore water equilibration method and laser isotopic analysis method include dual hydrogen- and oxygen-isotope assays on single small core samples, low consumable and instrumentation costs, and the potential for field-based hydrogeologic profiling. A single core is sufficient to obtain detailed vertical isotopic depth profiles in geologic, soil, and lacustrine pore water, dramatically reducing the cost of obtaining pore water by conventional wells or physical water extraction methods. In addition, other inherent problems like contamination of wells by leakage and drilling fluids can be eliminated.

High-precision laser spectroscopy D/H and 18O/16O measurements of microliter natural water samples.

Newly available gas analyzers based on off-axis integrated cavity output spectroscopy (OA-ICOS) lasers have been advocated as an alternative to conventional isotope-ratio mass spectrometers (IRMS) for the stable isotopic analysis of water samples. In the case of H2O, OA-ICOS is attractive because it has comparatively low capital and maintenance costs, the instrument is small and field laboratory portable, and provides simultaneous D/H and 16O/18O ratio measurements directly on H2O molecules with no conversion of H2O to H2, CO, or H2/CO2-water equilibration required. Here we present a detailed assessment of the performance of a liquid-water isotope analyzer, including instrument precision, estimates of sample memory and sample mass effects, and instrumental drift. We provide a recommended analysis procedure to achieve optimum results using OA-ICOS. Our results show that, by using a systematic sample analysis and data normalization procedure routine, measurement accuracies of +/-0.8 per thousand for deltaD and +/-0.1 per thousand delta18O are achievable on nanoliter water samples. This is equivalent or better than current IRMS-based methods and at a comparable sample throughput rate.

Dynamics and stable isotope composition of gaseous and dissolved oxygen.

The vadose zone and ground water environments are a sink for atmospheric O(2). The pathways and rates of O(2) consumption are primarily related to the availability and rate of oxidation of key reductants (e.g., organics, sulfides), through a combination of biological or abiotic reactions. The range in delta(18)O of O(2) in the subsurface is large, from +20 per thousand to +39 per thousand (Vienna Standard Mean Ocean Water) in the vadose zone and from +12 per thousand to +46 per thousand in ground water. The aggregated O(2) isotope fractionation by consumption (alpha(k)) was found to range from 0.970 to 1.300 and 0.980 to 1.030 in vadose zones and aquifers, respectively. These data suggest the delta(18)O patterns in both unsaturated zones and aquifers can be attributed to microbially mediated reactions (alpha(k)= range from 0.975 to 1.000), but there are apparently other inverse isotope fractionating processes (alpha(k) > 1.000). Circumstantial evidence suggested O(2) processed during the sulfide oxidation and precipitation of Fe-oxyhydroxides process (or other unidentified processes) could be the cause of the significant (18)O depletions. Overall, delta(18)O data from vadose zones and ground water revealed that isotope fractionation by consumption of gaseous and dissolved O(2) in the subsurface and ground water environments is more complicated than what has classically been attributed solely to geomicrobial respiration. Given the questions and inexplicable data arising from this study, further detailed research on O(2) consuming processes in the Earth's subsurface and ground water is warranted.

Stable isotope and band-encounter analyses delineate migratory patterns and catchment areas of white-throated sparrows at a migration monitoring station.

The Canadian Migration Monitoring Network consists of several fixed migration monitoring stations (MMS) that apply constant-effort protocols to track changes in the abundance of migratory birds. Such monitoring will be important for tracking long-term population trends of songbirds, especially for species breeding in remote areas such as the North American boreal forest. The geographical catchment sampled by individual MMS, however, remains largely unknown. Here, we used hydrogen isotope measurements (deltaD) of feathers of white-throated sparrows (Zonotrichia albicollis) moving through Delta Marsh MMS in Manitoba, Canada, to determine both wintering and breeding ground catchment areas monitored by this station. The deltaD of tail feathers, collected from spring and fall migrants delineated previous breeding or natal latitudes, ranging from the northern to the southern extremes of the western boreal forest. The deltaD values of head feathers grown on the wintering grounds and collected during spring migration revealed that individuals wintered in a broad region of the southeastern United States. The isotope data showed no relationship between estimated breeding/natal and wintering latitudes of white-throated sparrow populations. Stable isotope data provided little information on longitude. Band-encounter analyses, however, indicated a clear east-west segregation of these sparrows across Canada, supporting connectivity among breeding/natal and wintering longitudes over the entire scale of this species' range. Isotope analyses of multiple feather types representing different periods and geographic regions of the annual cycle can provide key information on migratory connectivity for species moving through dedicated MMS.

Comparative equilibration and online technique for determination of non-exchangeable hydrogen of keratins for use in animal migration studies.

Stable hydrogen-isotope ratios (deltaD) of keratin provide a novel means for tracking geographical movements of birds and other species. Here we describe a rapid, low cost, analytical approach to facilitate online continuous-flow isotope-ratio mass spectrometry (CF-IRMS) deltaD analyses of keratins (120-160 samples per day) through the use of calibrated keratin working standards and "comparative equilibration" to correct for the effects of moisture on exchangeable hydrogen. It is anticipated that this analytical approach and CF-IRMS will greatly aid in providing cost effective and directly comparable deltaD results on keratins and feathers among various laboratories and researchers involved in animal migration studies.

Characterizing geochemical reactions in unsaturated mine waste-rock piles using gaseous O2, CO2, 12CO2, and 13CO2.

In situ determinations of geochemical reaction rates in mine waste-rock piles remain a challenge. Depth-profiles of field O2 and CO2 pore-gas concentrations, delta13C(CO2) values, and moisture contents were used to characterize and quantify geochemical reaction rates in two waste-rock piles at the Key Lake Uranium Mine in northern Saskatchewan, Canada. Traditionally, the presence of O2 concentrations less than atmospheric in waste-rock piles has been attributed to mineral oxidation. This study showed that the interpretation of O2 and CO2 concentration profiles alone could not be used to identify the depths of dominant geochemical reactions in the piles and could lead to erroneous estimates of reaction rates. Modeling of the delta13C(CO2) depth profiles clearly showed that the gas concentration profiles present in the piles were the result of the oxidation of organic matter present below the piles, a mechanism not previously reported in the literature. Based on these findings, the rates of reactions in the organic zone were determined. The oxidation of organic matter at the base of waste-rock piles should be considered in future mine-waste pore-gas studies, in addition to sulfide oxidation and carbonate buffering.

Stable nitrogen isotopes in waterfowl feathers reflect agricultural land use in western Canada.

Stable nitrogen and carbon isotope analysis was performed on secondary feathers collected from flightless, mallard ducklings (Anas platyrhynchos) from 17 locations across western Canada. The delta15N values of mallard feathers ranged from +6.1 to +23.7 per thousand (AIR). Mean delta15N feather values from the 17 locations were strongly correlated with the percentage of land under agricultural development. Higher delta15N values in waterfowl feathers collected from agricultural areas possibly reflected the entry of excess fertilizer nitrogen into local water bodies. However, other processes may have also been important. These results provide evidence that nitrogen isotope values in avian feathers may reflect long-term nitrogen additions to surface waters in agricultural areas and may also provide important clues in elucidating the origin of nonpoint source nitrogen inputs.

A stable-isotope approach to delineate geographical catchment areas of avian migration monitoring stations in North America.

Migration monitoring stations (MMSs) were established to provide information on population trends of North American passerines. However, apart from inferring general origins of birds, there has been no way to delineate geographical catchment areas sampled by MMSs. The ability to resolve MMS catchment areas would greatly enhance our ability to link and constrain population declines to specific geographical areas and thereby focus conservation efforts. Here, we utilize stable-hydrogen (delta D) and carbon (delta 13C) isotope values of rectrices of fall hatch-year (HY) and spring adult after-second year (ASY) Swainson's Thrush (Catharus ustulatus) moving through two MMSs in Canada to determine natal and molting catchment areas for those stations. Stable-carbon isotope signatures provided no information on geographical origins of birds. Conversely, delta D signatures provided good latitudinal geographical control, and this was also supported by analysis of feathers from two other species, Gray-cheeked Thrush (Catharus minimus) and Harris' Sparrow (Zonotrichia querula), also known to breed and molt in northern regions. The delta D values of fall HY birds moving through Delta Marsh MMSs in Manitoba were more negative than those moving through Long Point MMSs in southern Ontario, clearly indicating more northwesterly origins. However, based on delta D values alone, both MMSs sampled birds from broad catchment regions of the Canadian Boreal forest. The interpolated catchment area of the Delta MMS encompassed northwest Manitoba to northwestern Alberta. The interpolated catchment area of the Long Point MMS extended from north central Ontario and Quebec and into western Canada. The delta D values of birds moving northward in spring suggested that most ASY Swainson's Thrush molted at more southerly locations than their breeding sites. We show the stable-hydrogen isotope approach may be employed to significantly improve conventional observational techniques for avian population monitoring, and that MMSs provide a reliable means of associating population productivity with regional conservation issues.