Geoff Koehler

Stable Isotope Laboratory, National Hydrology Research Centre · Environment and Climate Change Canada

We investigated the influence of land cover on nutrient concentrations (295 samples) in headwater streams over a 2‐year period in 10 agriculture‐dominated subcatchments (163–8373 ha) in southern Ontario Canada. In this region, monitoring and research on nutrient dynamics in headwater wetlands is sparse. Our results indicated a significant positive...

All African felids are listed as vulnerable or endangered according to the IUCN (International Union for Conservation of Nature) Red List of Threatened Species. Cheetahs (Acinonyx jubatus) in particular have declined rapidly as a result of human impacts so that development of effective strategies and tools for conservation of this highly vulnerable...

Nutrient concentrations in riparian groundwater are variable from site to site, making it challenging to use these data to quantify nutrient fluxes contributed by groundwater discharge to headwater streams. Instead, we define event‐excluded baseflow (BFEE), and use stream discharge data and stream samples collected during BFEE to estimate groundwat...

Ecohydrological investigations commonly use the stable isotopes of water (hydrogen and oxygen) as conservative ecosystem tracers. This approach requires accessing and analyzing water from plant and soil matrices. Generally, there are six steps involved to retrieve hydrogen and oxygen isotope values from these matrices: (1) sampling, (2) sample stor...

Ecohydrological investigations commonly use the stable isotopes of water (hydrogen and oxygen) as a conservative ecosystem tracer. This approach requires accessing and analyzing water constrained within plant and soil matrices. Generally, there are six steps that researchers must pass through to retrieve hydrogen and oxygen isotope values from thes...

Freshwater fish production depends on the production and use of polyunsaturated fatty acids (n-3 and n-6 PUFA) from lower trophic levels. Here, we aimed to identify the main trophic pathways that support PUFA content in different fish species (mean 39.7 mg/g dry weight) used in the subsistence fishery of the Inuit community in Greiner Lake near Cam...

Concepts and terms used in previous multidisciplinary studies of tile-drained aquitard-dominated catchments (TDADC) are inconsistent and confusing. We provide a well-defined, comprehensive conceptual model of the subsurface hydrology of TDADC by selecting seven mutually compatible and consistent concepts. These concepts are: (1) groundwater as the...

Rationale: Hydrogen and oxygen stable isotope ratios (δ2 H, δ17 O, and δ18 O values) are commonly used tracers of water. These ratios can be measured by isotope ratio infrared spectroscopy (IRIS). However, IRIS approaches are prone to errors induced by organic compounds present in plant, soil, and natural water samples. A novel approach using 17 O...

Lake Winnipeg is the 10th largest freshwater lake in the world and, like many of the world’s great lakes, it is increasingly being affected by anthropogenic pressures, such as high nutrient loads and invasive species. The consequences of these on the hydrology and ecology of the lake are the focus of continuing research, funded by the renewed inves...

The Arctic biome is currently undergoing major modifications with climate change. Arctic freshwater ecosystems, as sentinel ecosystems, can record major climate changes before they affect the entire region. However, to fully evaluate the amplitude of changes in Arctic freshwaters, we need to be able to compare future measurements to baseline data....

Municipal wastewater lagoons are common across North America and, unlike larger mechanical wastewater treatment plants, typically release nutrient-rich effluent directly to rivers in intermittent pulses. However, little is known about the fate of nutrients from these episodic events, which may happen under varying hydrologic or thermal conditions....

Intensive agriculture and growing human populations are important nitrogen (N) sources thought to be associated with eutrophication. However, the contribution and seasonality of N delivery to streams from human activities is poorly understood and knowledge of the role of stream communities in the assimilation of N from human activities is limited....

The relationship between hydrogen and oxygen stable isotopic compositions in environmental water and hair was investigated for both domestic cats (Felis catus) and dogs (Canis lupus familiaris). A strong, but different, covariance was measured between the hydrogen and oxygen stable isotopic compositions of local precipitation and hair keratin from...

Wide-ranging apex predators are among the most challenging of all fauna to conserve and manage. This is especially true of the polar bear (Ursus maritimus), an iconic predator that is hunted in Canada and threatened by global climate change. We used combinations of stable isotopes (13C,15N,2H,18O) in polar bear hair from > 1000 individuals, sampled...

The measurement of naturally occurring stable hydrogen (δ2H) and carbon (δ13C) isotopes in wings of the eastern North American monarch butterflies (Danaus plexippus) have proven useful to infer natal origins of individuals overwintering in Mexico. This approach has provided a breakthrough for monarch conservation because it is the only viable means...

We investigated the influence of post-collection changes and snow gauge undercatch on the stable isotopic compositions of winter precipitation. Post-collection changes by evaporation or sublimation can be severe, and may be minimized, but not eliminated, by emptying collection gauges immediately after snowfall. Snow gauge undercatch caused two main...

We investigated the effect of tanning on the stable isotopic compositions (CNHOS) of hair keratin. Samples of hair from polar bear (Ursus maritimus) hides were collected before and after the tanning process from a commercial tannery. With the exception of sulphur isotopes, tanning did not alter the stable isotopic compositions of hair. δ34S values...

Blooms of filamentous benthic algae that plagued Lake Erie in the 1950s through 1970s were largely reduced through reductions of phosphorus (P) loading from point sources. Since the mid-1990s, these blooms have returned despite a period of relatively stable external P inputs. While increased loadings of dissolved P have been causally linked to cyan...

Rationale: Determination of non-exchangeable hydrogen isotopic compositions (δ(2) H values) of bulk complex organic materials is difficult due to uncontrolled H isotope exchange between the organic material and ambient water vapor. A number of calibration keratinous materials with carefully measured hydrogen isotopic compositions of the non-exchan...

Fundamental to effective management of migratory waterbird populations is an understanding of their flyway delineation. Taiga Bean Geese Anser fabalis fabalis wintering in NW Denmark, Scotland and England are considered to originate from northern and central Sweden, southern and central Norway (‘Western flyway’), those wintering in southern Sweden,...

We present a novel approach for nitrogen (δ(15)N) and oxygen (δ(18)O) isotopic analysis of nitrate in water based on the isotopic analysis of N2O produced from the conversion of NO3(-) by cultured denitrifying bacteria and off-axis integrated cavity output spectroscopy (OA-ICOS). The headspace N2O was manually injected into an OA-ICOS isotopic N2O...

Tracking migratory animals has benefitted using measurements of naturally occurring stable isotopes of hydrogen (δ2H) in keratinous tissues such as hair and feathers to link animal origins to continental patterns or isoscapes of δ2H in precipitation. However, for most taxa, much less information exists on the use of stable oxygen isotope ratios (δ1...

The requirement to measure the stable isotopic compositions of saline pore fluids by optical methods has prompted a re-evaluation of the isotopic salt effect for common salts. Hydrogen and oxygen isotopic salt effects were measured at room temperature (21°C) by optical methods. For hydrogen isotopes, our results agree well with those of previous st...

Hydrogen isotopic compositions of hydrous minerals and organic materials were measured by combustion to water, followed by optical isotopic analysis of the water vapor by off-axis integrated cavity output spectroscopy. Hydrogen and oxygen isotopic compositions were calculated by numerical integration of the individual isotopologue concentrations me...

A parallel-flow H(2)O(liquid)-H(2)O(vapor) equilibration and laser spectroscopy method provides a new way to monitor the hydrogen and oxygen stable isotopic composition of water from rivers or lakes or in hydrologic tracer tests in real time. Two custom-built equilibrator devices and one commercial membrane device were tested to determine if they c...

The spatial footprint over which municipal wastewater effluents cause changes to aquatic community structure and metabolism is key information required for the management of discharges into rivers. Longitudinal studies were undertaken on the Bow and South Saskatchewan rivers, Canada, to assess a new isotopic and modelling approach that combined O2...

The spatial footprint over which municipal wastewater effluents cause changes to aquatic community structure and metabolism is key information required for the management of discharges into rivers. Longitudinal studies were undertaken on the Bow and South Saskatchewan rivers, Canada, to assess a new isotopic and modelling approach that combined O-2...

The stable isotopic composition of dissolved Cl- in rainwater was measured from a coastal and an interior location in eastern Canada. At the interior Bonner Lake, Ontario, site the δ37Cl values of dissolved Cl- in precipitation ranged from −3.5‰ to −1.2‰ (SMOC) with an amount-weighted annual average of −2.3‰. At the coastal site, Bay D’Espoir, Newf...

The cumulative effect of multiple agricultural and urban impacts on river ecology is examined using two Canadian prairie rivers with various upstream nutrient loadings and metabolic histories. While diel changes in O2 concentrations have traditionally been used to estimate biological rates, this approach suffers from a lack of information on re-aer...

The Mackenzie River, draining an area of 1.7 million km 2 , incorporates a diverse range of geographic source regions, including 8 of the 15 distinct ecoclimatic regions identified in Canada [1]. The basin is mountainous in the west and relatively flat-lying in the east with strong north-south climatic gradients, and generally cold, dry climate con...

The stable-oxygen and -hydrogen isotopic values (deltaD, delta18O) of porewater in geologic media are commonly determined on water obtained by extraction techniques such as centrifugation, mechanical squeezing, vacuum heating and cryogenic microdistillation, and azeotropic distillation. Each of these techniques may cause isotopic fractionation as p...

The stable-oxygen and -hydrogen isotopic values (δD, δ18O) of porewater in geologic media are commonly determined on water obtained by extraction techniques such as centrifugation, mechanical squeezing, vacuum heating and cryogenic microdistillation, and azeotropic distillation. Each of these techniques may cause isotopic fractionation as part the...

Few studies have used the stable isotopic composition of O(2) as a tracer of gas transport or biogeochemical processes in environmental research. Here we demonstrate field sampling techniques for gaseous and dissolved O(2) and describe an analytical method for measuring δ(18)O and δ(17)O values of O(2) in air, soil gas, and water samples using cont...

In the Paleozoic Elk Point Basin, Saskatchewan, Canada, hematite in evaporite rocks of the Middle Devonian Prairie Formation records two magnetizations that are very different from those expected when the evaporites were originally deposited. The first (X magnetization) corresponds to Cretaceous or Cenozoic paleofield directions and contains both n...

The Prairie Formation in Saskatchewan represents the largest of several evaporite cycles preserved in the rocks of the Paleozoic Elk Point Basin. Solutions of 1-5 molal NaCl, KCl, CaCl2, and MgCl2, and synthetic brines were analyzed for hydrogen and oxygen isotopic compositions by vacuum distillation-microequilibration techniques. No effect on the...

Fractionation of hydrogen and oxygen isotopes between the hydration water of carnallite (KMgCl3 . 6H(2)O) and brines are evaluated by exchange and synthesis of carnallite in the laboratory at temperatures between 22 and 45 degrees C, and by analyses of carnallites from natural environments. Hydration water in carnallite is depleted in D relative to...

Solutions of 1-5 m NaCl, KCl, CaCl2 and MgCl2, and synthetic brines were analyzed for hydrogen and oxygen isotopic compositions by vacuum distillation-microequilibration techniques. No effect on the hydrogen isotopic composition was observed for any of the solutions within the precision of the technique of +/- 5 parts per thousand determined from a...