Stable Isotope Content Research Articles

Spatial subsidies in spider diets vary with shoreline structure: Complementary evidence from molecular diet analysis and stable isotopes.

Inflow of matter and organisms may strongly affect the local density and diversity of organisms. This effect is particularly evident on shores where organisms with aquatic larval stages enter the terrestrial food web. The identities of such trophic links are not easily estimated as spiders, a dominant group of shoreline predator, have external digestion. We compared trophic links and the prey diversity of spiders on different shore types along the Baltic Sea: on open shores and on shores with a reed belt bordering the water. A priori, we hypothesized that the physical structure of the shoreline reduces the flow between ecosystem and the subsidies across the sea–land interface. To circumvent the lack of morphologically detectable remains of spider prey, we used a combination of stable isotope and molecular gut content analyses. The two tools used for diet analysis revealed complementary information on spider diets. The stable isotope analysis indicated that spiders on open shores had a marine signal of carbon isotopes, while spiders on reedy shores had a terrestrial signal. The molecular analysis revealed a diverse array of dipteran and lepidopteran prey, where spiders on open and reedy shores shared a similar diet with a comparable proportion of chironomids, the larvae of which live in the marine system. Comparing the methods suggests that differences in isotope composition of the two spider groups occurred because of differences in the chironomid diets: as larvae, chironomids of reedy shores likely fed on terrestrial detritus and acquired a terrestrial isotope signature, while chironomids of open shores utilized an algal diet and acquired a marine isotope signature. Our results illustrate how different methods of diet reconstruction may shed light on complementary aspects of nutrient transfer. Overall, they reveal that reed belts can reduce connectivity between habitats, but also function as a source of food for predators.

Adapting the diffusive exchange method for stable isotope analysis of pore water to brine-saturated rocks

The isotope diffusive exchange technique was originally developed to indirectly measure the hydrogen and oxygen stable isotope composition (δ2H and δ18O values) and content of pore water (WC) in low permeability rocks. This study aims to benchmark developments of the technique adapted for high salinity (low water activity) pore waters by: 1) investigating the factors that might influence the results of the isotope diffusive exchange technique for saline solutions through solution-solution experiments; and 2) apply the adapted diffusive exchange method to rock samples previously equilibrated with synthetic solutions of known chemical and isotopic composition. Two different rocks were used in the benchmarking tests: Queenston Formation red shale from Ontario, Canada; and Opalinus Clay from the Mont Terri Underground Research Laboratory (URL), Switzerland.Solution-solution experiments showed that the main sources of error included a mismatch between the water activities (aw), a major chemical mismatch, and/or a significant weight difference between the test and sample solution. Samples with aw spanning from 1 to 0.5 can be matched with adequate precision using a set of test waters with an aw of 0.99, 0.805, and 0.5. The aw of the test water must be equal or lower than the sample because equilibration is faster at low aw (i.e. higher salinities). Experiments with contrasting chemistry between test and sample solutions (NaCl vs CaCl2), induced a deviation in the δ2H and δ18O values (<5‰ and <2‰, respectively) calculated for the sample water. This deviation can be minimized by matching the aw of the test solution with salts that correspond to the dominant dissolved species in the sample pore water. The mass of test water must be no <0.5 times the mass of the sample water to maintain acceptable errors. This means the technique is adapted for rocks having a WC >0.5wt%. The WCs are generally estimated with errors of about 10% for all solution-solution experiments.To prepare rock samples containing pore waters of known composition, rocks were equilibrated with 0.3 and 5m NaCl, and 2.5 and 5m CaCl2 synthetic solutions. Based on time series chemical analyses of the solutions, equilibrium was attained in about 1 and 4days for the Opalinus Clay and Queenston shale samples, respectively. Benchmarking experiments were then conducted by applying the diffusive exchange method to determine the pore water isotopic compositions of these equilibrated rock samples and comparing to the known values of the equilibrated solution. The water stable isotope compositions are identical within 2σ error and do not depend on salinity or type of salt (NaCl, CaCl2). The adapted diffusive exchange method allows reliable stable isotope analysis of pore waters at all salinities when aw and chemistries of the pore and test waters are similar.

The Effects of Dairy Management on Milk Quality Characteristics

The article focuses on the impact of different dairy management types on quality characteristics of organic and conventional milk. The study was conducted during 9 months (spring-autumn), raw milk samples were collected from organic and conventional dairy farms from two Ukrainian regions. The milk samples were analyzed for dry matter, total protein and non-protein nitrogen, ammonia content and values of stable isotopes 13С/12С were measured in fat and milk protein fractions. The values of dry matter, total protein, true protein and non-protein nitrogen content do not represent a statistically significant effect of farming type. The values of ammonia content, ammonia/non-protein nitrogen and ammonia/total protein ratios were statistically significant and reflected the impact of farming type which is, probably, linked with different protein content in cows’ diet. Conversion of some parameters on the dry matter allows more precise differentiation among types of milk, including statistically significant differences (e.g. total protein and ammonia content). The values of δ13C in fat fraction (-26.00‰) and protein fraction (-22.89‰) of organic milk were statistically significant differed in comparison with conventional milk (-23.14 ‰ and -19.15‰ respectively), due to the high amount of maize in the diet on conventional farm. The values of Δδ13C also were statistically significant: 3.99‰ in conventional milk and 3.11‰ in organic. It was established that conventional milk has a greater range of the different parameter seasonal variations than organic milk.

High-throughput method for simultaneous quantification of N, C and S stable isotopes and contents in organics and soils.

Information about the sulfur stable isotope composition (δ(34) S value) of organic materials and sediments, in addition to their nitrogen (δ(15) N value) and carbon (δ(13) C value) stable isotope compositions, can provide insights into mechanisms and processes in different areas of biological and geological research. The quantification of δ(34) S values has traditionally required an additional and often more difficult analytical procedure than NC dual analysis. Here, we report on the development of a high-throughput method that simultaneously measures the elemental and isotopic compositions of N, C and S in a single sample, and over a wide range of sample sizes and C/N and C/S ratios. We tested a commercially available CHNOS elemental analyzer in line with an isotope ratio mass spectrometer for the simultaneous quantification of N, C and S stable isotope ratios and contents, and modified the elemental analyzer in order to overcome the interference of (18) O in δ(34) S values, to minimize any water condensation that could also influence S memory, and to achieve the complete reduction of nitrogen oxides to N2 gas for accurate measurement of δ(15) N values. A selection of organic materials and soils was analyzed with a ratio of 1:1.4 standards to unknowns per run. The modifications allowed high quality measurements for N, C and S isotope ratios simultaneously (1 SD of ±0.13‰ for δ(15) N value, ±0.12‰ for δ(13) C value, and ±0.4‰ for δ(34) S value), with high throughput (>75 unknowns per run) and over a wide range of element amount per capsule (25 to 500μgN, 200-4000μg C, and 8-120μgS). This method is suitable for widespread use and can significantly enhance the application of δ(34) S measurements in a broad range of soils and organic samples in ecological and biogeochemical research. Copyright © 2016 John Wiley & Sons, Ltd.

The effects of water use on Tothian flow systems in the Mexico City conurbation determined from the geochemical and isotopic characteristics of groundwater

Groundwater flow systems have been differentiated in the metropolitan zone of Mexico City based on their chemical composition and stable isotope contents. The existing hydrogeological framework for the region provided a reference for such differentiation. Local flows (Flow-system I) represent the youngest and shallowest groundwater flow identified in boreholes on the hills. Intermediate flows (Flow-system II) in boreholes on the plain represent a mixture of inflows travelling horizontally, and vertically upwards (Flow-system IV) and downwards (overlaying aquitard leakage) to extraction boreholes. Flow-system III identified in boreholes on the plain is an intermediate flow system which extends deeper than Flow-system II. Flow-system IV, which is classified as a regional system, is related to a former thermal spring site. Groundwater travelling times, and their regional distribution and the thickness of related rock formations suggest extensive inflow supporting Flow-system IV. Future climate condition evolution (i.e. drought) will only have a limited impact on Flow-system IV as compared to Flow-system I which have relatively rapid and short flow paths. The identification of the hierarchy of the flow systems is of paramount importance in achieving adequate groundwater management in any region where the aquifer units are several thousand metres thick.

Investigation of discharge-area groundwaters for recharge source characterization on different scales: the case of Jinan in northern China

Discharge-area groundwater in Jinan, a typical karst region in northern China, was investigated by studying both the hydrological and chemical processes evolving from the recharge in mountainous terrains to the karst-spring outflows in the metropolitan area. Large-scale exploitation of karst groundwater has led to a disturbing trend in the ever-decreasing spring outflow rates and groundwater level. There is insufficient information about the Jinan karst aquifers, which provide the main water sources to meet human demand and to sustain spring outflow. The coupling of hydrological and chemical processes quantifies the flow system through aqueous chemistry characterization of the water sources. This approach is used to study the groundwater flow discharges in different locations and geological settings. The potentiometric data indicated limited vertical connectivity between distinct hydrogeological units and alteration of the recharge regime by the faults and by artificial exploitation. Shallow groundwater primarily belongs to the local flow system, with high nitrate concentration and enriched stable isotopic contents. Thermal groundwater has high concentrations of chloride and total dissolved solids, derived from a regional flow system with the highest recharge altitudes and long residence time. Non-thermal karst water may be attributed to the intermediate flow system, with uniform HCO3–Ca(Mg) facies and low nitrate concentration. This work highlighted discharge as a fingerprint of groundwater flow conditions and provides a better insight into the hydrogeological system.

Subsurface Flow and Surface Water Interactions Quantification in Gunung Kidul Karst Area Using Hydro- Chemical and Stable Isotopes Data Variations

Subsurface flow is one of the available water sources in the Karsts area such as in GunungKidul. The study of the pattern of the variations of stable isotopes content as a function oftime and its interaction with other water sources such as rain waters, groundwater, riverwater will be a very good tool to assess the potential of the subsurface flow as a water source.For this purpose, the variations of stable isotopes content of subsurface flow around GunungKidul Karsts area and its interactions with other local water sources have been studied for thelast two years. From the comparison of stable isotopes variations pattern of the subsurfaceflow with monthly rain water, the interaction of the subsurface flow with other water sourcesin the area has been quantified. Based on hydro-chemical data, it was found that the rechargearea of subsurface flow were relatively further than other samples and it was also found thatSeropan and Bribin subsurface flow systems originate from different geologic structures.Based on stable isotopes relative contents, it was found Ngobaran and Baron Caves have beenmixed with domestic sewerage water or other surface water.Keywords : Karsts area, stable isotopes, subsurface flow

Origin and characteristics of brackish groundwater in Abu Madi coastal area, Northern Nile Delta, Egypt

Hydrogeochemical and geoelectrical resistivity investigations were carried out to assess the origin and characteristics of a brackish groundwater in Abu Madi coastal area. Twenty six surface water, shallow and deep groundwater samples were collected and analyzed for various ionic concentrations as well as oxygen and hydrogen stable isotopic contents. In addition, a total of 20 vertical electrical sounding sites were conducted to investigate layers’ thicknesses, resistivities, and to detect the water-bearing layers. Then, 2-D Electrical Resistivity Tomography (ERT) along two profiles in the study area was conducted to get information about the surface water effect on recharge. The stable isotopic composition and the chloride concentrations strongly suggest that the deep groundwater in Abu Madi area is dominated by inland freshwater with a minor seawater component. This groundwater was recharged during the first and the third Holocene humid climatic cycles where the sea surface was about 125 and 25 m below the current sea level, respectively. The brackish nature and higher piezometric surface of the groundwater, as well as the occurrence of vertical low-salinity seawater zone in front of the study area, support the possibility of submarine groundwater discharge. The geoelectrical resistivity surveying, on the other hand, revealed a number of geoelectrical groundwater-bearing layers. The main water-bearing layer in the study area is represented by the sixth geoelectrical layer, which has relatively high resistivity and a considerable thickness being consistent with the hydrogeochemical observations. ERT results point to the presence of shallow water-bearing layers recharged from the surface water drains with low resistivity and surface rain water of moderate resistivity. Results from the hydrogeochemical analyses and the different hydrogeological data are consistent with the high resistivity values of this geoelectrical layer. However, the overall high specific conductance and high sodium hazards indicate that the groundwater in the study area should be carefully treated before irrigation and domestic uses through mixing it with surface irrigation water.

A high-altitude peatland record of environmental changes in the NW Argentine Andes (24 ° S) over the last 2100 years

Abstract. High-altitude cushion peatlands are versatile archives for high-resolution palaeoenvironmental studies, due to their high accumulation rates, range of proxies, and sensitivity to climatic and/or human-induced changes. Especially within the Central Andes, the knowledge about climate conditions during the Holocene is limited. In this study, we present the environmental and climatic history for the last 2100 years of Cerro Tuzgle peatland (CTP), located in the dry Puna of NW Argentina, based on a multi-proxy approach. X-ray fluorescence (XRF), stable isotope and element content analyses (δ13C, δ15N, TN and TOC) were conducted to analyse the inorganic geochemistry throughout the sequence, revealing changes in the peatlands' past redox conditions. Pollen assemblages give an insight into substantial environmental changes on a regional scale. The palaeoclimate varied significantly during the last 2100 years. The results reflect prominent late Holocene climate anomalies and provide evidence that in situ moisture changes were coupled to the migration of the Intertropical Convergence Zone (ITCZ). A period of sustained dry conditions prevailed from around 150 BC to around AD 150. A more humid phase dominated between AD 200 and AD 550. Afterwards, the climate was characterised by changes between drier and wetter conditions, with droughts at around AD 650–800 and AD 1000–1100. Volcanic forcing at the beginning of the 19th century (1815 Tambora eruption) seems to have had an impact on climatic settings in the Central Andes. In the past, the peatland recovered from climatic perturbations. Today, CTP is heavily degraded by human interventions, and the peat deposit is becoming increasingly susceptible to erosion and incision.

Investigation of uranium geochemistry along groundwater flow path in the Continental Intercalaire aquifer (Southern Tunisia)

Environmental tracers (2H, 18O, isotopes of Uranium) and geochemical processes occurring within groundwaters from the Continental Intercalaire (CI) in Southern Tunisia were used to understand the hydrodynamics and the recharge conditions of this aquifer. This study investigates the chemical and isotopic compositions of the CI groundwater. The water types are dominated by Na+, SO42−, Cl− throughout most of the basin with a general increase in total dissolved solids from the Saharan Platform margins towards the Chotts region. Large scale groundwater flow paths are toward the Chotts region. The stable isotopes composition of the analyzed groundwater ranges from −8.8 to −6‰ vs V-SMOW for δ18O and from −67 to −40‰ vs V-SMOW for δ2H. The relatively enriched stable isotopes contents suggest the contribution of the Dahar sandstones outcrops in the current recharge of the CI aquifer in an arid context. However, the most depleted values in heavy isotopes indicate a paleorecharge of the aquifer under wetter conditions revealing a long residence time of groundwaters. The results from water samples using alpha spectrometry method indicate a range in 238U concentrations and 234U/238U activity ratios (AR) of 0.044–1.285 μg kg−1 and 1.2 to 8.84 respectively. The geochemistry of uranium isotopes in groundwater is controlled by many factors, essentially, the influence of water rock interactions, the preferential dissolution of 234U relative to 238U due to alpha recoil and the mixing processes between different waters with distinct AR as well as 238U concentrations.

Use of hydrochemistry and isotopes for improving the knowledge of groundwater flow in a semiconfined aquifer system of the Eastern Slavonia (Croatia)

Knowledge of groundwater flow, and accordingly, groundwater residence time is immensely important for the sustainable management of groundwater resources. This requires a good conceptual model of the aquifer system. In this paper, a conceptual model based on the interpretations of hydrogeological and hydrochemical data, as well as measurements of environmental tracers (18O, 2H, 3H) was formulated for a semiconfined aquifer system in Eastern Slavonia in Croatia. The aquifer system is composed of Quaternary gravel and sand and silty–clayey interlayers and is covered with low permeability deposits. Measurements of water levels and environmental tracers in the study area clarified the groundwater flow evolution from the recharge area to the discharge area. The content of stable isotopes confirmed that the groundwater originates from precipitation. The tritium content and geochemical processes (such as cation exchange, silicate weathering) suggested a relatively long residence time of groundwater in the part of the aquifer system that is further from the Sava River. The same is confirmed by the results of calculated particle tracking pathlines.

Food‐web structure and mercury dynamics in a large subarctic lake following multiple species introductions

Summary The rate of non‐native fish introductions into freshwater ecosystems has more than doubled during the past three decades, posing a serious threat to native biodiversity. Despite potential benefits for fisheries, little is known about how introduced species interact with native communities at the food‐web level, or impact energy transfer dynamics and accumulation of contaminants in lake ecosystems. Here, we explored the trophic structure of a large, oligotrophic subarctic lake and assessed the trophic niche use and potential ecosystem‐wide consequences of two introduced salmonid species: piscivorous lake trout (Salvelinus namaycush) and zooplanktivorous vendace (Coregonus albula). We used a combination of diet, stable isotope and total mercury concentration data to test the hypotheses that the introduced fishes: (i) show partial niche overlap with the native fish community; (ii) increase total isotopic food‐web size and dietary linkages by increasing the diversity of niches present within the system, in comparison to analyses where only the native species were considered; and (iii) have differing mercury bioaccumulation rates from native species due to differences in trophic ecology and habitat preferences, being higher in pelagic than in littoral species. Trophic interactions between the introduced and native species were extensive, with evidence of reciprocal predation, resource competition and possible competitive exclusion apparent. Despite partial niche overlap with native species, the inclusion of introduced species in our analysis increased both total isotopic niche space and the number of dietary linkages present in the food web. On the basis of these findings, we suggest that introduced vendace may have led to a shift in system‐wide reliance on pelagically derived energy, whereas generalist foraging by piscivorous lake trout may have further integrated littoral and pelagic food‐web compartments. Mercury bioaccumulation rates were highly species‐specific and varied among habitats, but were generally higher in the pelagic food‐web compartment. However, contrary to expectations, vendace had lower mercury levels than native pelagic species, potentially reducing the extent of biomagnification within the lake. Our study demonstrates how introduced fishes may elicit complex and unpredictable responses in food‐web structure and ecosystem function, and thus complicate contaminant bioaccumulation and transfer processes within freshwater ecosystems.

Fish on the roof of the world: densities, habitats and trophic position of stone loaches (Triplophysa) in Tibetan streams

The fast increase in temperature on the Tibetan Plateau, with anticipated future changes in aquatic ecosystems and biodiversity, highlights the urgent need for ecological data on the sparsely studied Tibetan running waters. In the present study we surveyed eight Tibetan streams to obtain data on densities, feeding selectivity and trophic position of the stone loach Triplophysa. Benthic algae, detritus, macroinvertebrates and fish were quantified and collected for stable isotope and stomach content analysis. Triplophysa density (mean 0.70 individuals m–2, maximum 1.6 individuals m–2) decreased with altitude and increased with the percentage cover of fine substratum. Glacier-fed sites tended to have the lowest fish densities, whereas the highest densities were found near lakes. Mean fish length (4.1–9.6cm) was positively related to the percentage cover of coarse substratum. Triplophysa was omnivorous, but the composition of the stomach contents varied greatly between sites and among individuals. Algal matter was ingested at most sites, but macroinvertebrates (Chironomidae, Baetidae and Simuliidae) dominated the ingestion (average 50–100%). The trophic position of Triplophysa, identified from δ15N (‰) of the biota, varied between 2.6 and 4.2 among localities (mean 3.6) and was inversely related to the biomass of benthic algae, but unrelated to quantities of other potential food sources.

Stable isotope and high precision concentration measurements confirm that all humans produce and exhale methane

Mammalian formation of methane (methanogenesis) is widely considered to occur exclusively by anaerobic microbial activity in the gastrointestinal tract. Approximately one third of humans, depending on colonization of the gut by methanogenic archaea, are considered methane producers based on the classification terminology of high and low emitters. In this study laser absorption spectroscopy was used to precisely measure concentrations and stable carbon isotope signatures of exhaled methane in breath samples from 112 volunteers with an age range from 1 to 80 years. Here we provide analytical evidence that volunteers exhaled methane levels were significantly above background (inhaled) air. Furthermore, stable carbon isotope values of the exhaled methane unambiguously confirmed that this gas was produced by all of the human subjects studied.Based on the emission and stable carbon isotope patterns of various age groups we hypothesize that next to microbial sources in the gastrointestinal tracts there might be other, as yet unidentified, processes involved in methane formation supporting the idea that humans might also produce methane endogenously in cells. Finally we suggest that stable isotope measurements of volatile organic compounds such as methane might become a useful tool in future medical research diagnostic programs.

Dissolved organic carbon lability and stable isotope shifts during microbial decomposition in a tropical river system

Abstract. A significant amount of carbon is transported to the ocean as dissolved organic carbon (DOC) in rivers. During transport, it can be transformed through microbial consumption and photochemical oxidation. In dark incubation experiments with water from the Tana River, Kenya, we examined the consumption of DOC through microbial decomposition and the associated change in its carbon stable isotope composition (δ13C). In 15 of the 18 incubations, DOC concentrations decreased significantly by 10 to 60 %, with most of the decomposition taking place within the first 24–48 h. After 8 days, the remaining DOC was up to 3 ‰ more depleted in 13C compared with the initial pool, and the change in δ13C correlated strongly with the fraction of DOC remaining. We hypothesize that the shift in δ13C is consistent with greater microbial lability of DOC originating from herbaceous C4 vegetation than DOC derived from woody C3 vegetation in the semi-arid lower Tana. The results complement earlier findings that the stable isotope concentration of riverine DOC does not necessarily reflect the proportion of C3 and C4-derived DOC in the catchment: besides spatial distribution patterns of different vegetation types, processing within the river can further influence the δ13C of riverine OC.

Isotopic modeling of the sub-cloud evaporation effect in precipitation

In dry and warm environments sub-cloud evaporation influences the falling raindrops modifying their final stable isotopic content. During their descent from the cloud base towards the ground surface, through the unsaturated atmosphere, hydrometeors are subjected to evaporation whereas the kinetic fractionation results to less depleted or enriched isotopic signatures compared to the initial isotopic composition of the raindrops at cloud base. Nowadays the development of Generalized Climate Models (GCMs) that include isotopic content calculation modules are of great interest for the isotopic tracing of the global hydrological cycle. Therefore the accurate description of the underlying processes affecting stable isotopic content can improve the performance of iso-GCMs. The aim of this study is to model the sub-cloud evaporation effect using a) mixing and b) numerical isotope evaporation models. The isotope-mixing evaporation model simulates the isotopic enrichment (difference between the ground and the cloud base isotopic composition of raindrops) in terms of raindrop size, ambient temperature and relative humidity (RH) at ground level. The isotopic enrichment (Δδ) varies linearly with the evaporated raindrops mass fraction of the raindrop resulting to higher values at drier atmospheres and for smaller raindrops. The relationship between Δδ and RH is described by a ‘heat capacity’ model providing high correlation coefficients for both isotopes (R2>80%) indicating that RH is an ideal indicator of the sub-cloud evaporation effect. Vertical distribution of stable isotopes in falling raindrops is also investigated using a numerical isotope-evaporation model. Temperature and humidity dependence of the vertical isotopic variation is clearly described by the numerical isotopic model showing an increase in the isotopic values with increasing temperature and decreasing RH. At an almost saturated atmosphere (RH=95%) sub-cloud evaporation is negligible and the isotopic composition hardly changes even at high temperatures while at drier and warm conditions the enrichment of 18Ο reaches up to 20‰, depending on the raindrop size and the initial meteorological conditions.

The Study of Spatial Distribution of Precipitation and Stable Isotope Content in Mountainous Watershed of MidHimalaya,Northern India from Short Term Records of Monsoon Period

Mountain microclimate is governed by the interplay of insolation, wind, air temperature and topographic dispositions. The lack of appropriate scientific baseline data in all across Indian Himalaya is impairing effective planning process as implementation are being carried out at village clusters at a local scale. This study investigates spatial rainfall variability during the four crucial months of monsoon in a microwatershed (<10km2 ) that is part of large watershed in southern slopes of Lesser Himalaya. To understand the altitudinal variability in terms of daily rain and rainfall isotope variability, samples were collected along transect of 5000m within an altitudinal variability of 700m. The isotopic lapse rate (altitude effect) deciphered at a local scale that has immense role in identifying the recharge areas of local water resources. Monthly surface air temperature is also being investigated along the same transect as it has influence on the isotopic lapse rate. The observed topographical lapse rate is within the range of lapse rate reported for monsoon period from Himalayan region. The study also looks into the various climatological aspect of synoptic and local circulation controlled by orography.

Chemical and isotopic changes in Williston Basin brines during long-term oil production: An example from the Poplar dome, Montana

Brine samples were collected from 30 conventional oil wells producing mostly from the Charles Formation of the Madison Group in the East and Northwest Poplar oil fields on the Fort Peck Indian Reservation, Montana. Dissolved concentrations of major ions, trace metals, Sr isotopes, and stable isotopes (oxygen and hydrogen) were analyzed to compare with a brine contaminant that affected groundwater northeast of the town of Poplar. Two groups of brine compositions, designated group I and group II, are identified on the basis of chemistry and 87Sr/86Sr ratios. The solute chemistry and Sr isotopic composition of group I brines are consistent with long-term residency in Mississippian carbonate rocks, and brines similar to these contaminated the groundwater. Group II brines probably resided in clastic rocks younger than the Mississippian limestones before moving into the Poplar dome to replenish the long-term fluid extraction from the Charles Formation. Collapse of strata at the crest of the Poplar dome resulting from dissolution of Charles salt in the early Paleogene probably developed pathways for the ingress of group II brines from overlying clastic aquifers into the Charles reservoir. Such changes in brine chemistry associated with long-term oil production may be a widespread phenomenon in the Williston Basin.

Trophic pathways supporting juvenile Chinook and coho salmon in the glacial Susitna River, Alaska: patterns of freshwater, marine, and terrestrial food resource use across a seasonally dynamic habitat mosaic

Contributions of terrestrial-, freshwater-, and marine-derived prey resources to stream fishes vary over time and space, altering the energy pathways that regulate production. In this study, we determined large-scale use of these resources by juvenile Chinook and coho salmon (Oncorhynchus tshawytscha and Oncorhynchus kisutch, respectively) in the glacial Susitna River, Alaska. We resolved spatial and temporal trophic patterns among multiple macrohabitat types along a 97 km segment of the river corridor via stable isotope and stomach content analyses. Juvenile salmon were supported primarily by freshwater-derived resources and secondarily by marine and terrestrial sources. The relative contribution of marine-derived prey to rearing salmon was greatest in the fall within off-channel macrohabitats, whereas the contributions of terrestrial invertebrate prey were generally greatest during midsummer, across all macrohabitats. No longitudinal (upstream–downstream) diet pattern was discernable. These results highlight large-scale spatial and seasonal patterns of energy flow and the dynamic interplay of pulsed marine and terrestrial prey subsidies to juvenile Chinook and coho salmon in a large, complex, and relatively pristine glacial river.

Is fog an important water source for woody plants in an Asian tropical karst forest during the dry season?

AbstractFog is an important supplemental source of water in regions with heavy fog and little rainfall. In the present study, we used the stable isotope content of xylem water to investigate the dry season water source partition between soil and fog water of two evergreen tree species (Cleistanthus sumatranus and Lasiococca comberi), two deciduous tree species (Mayodendron igneum and Lagerstroemia tomentosa), two liana species (Acacia pennata and Combretum latifolium) and understory seedlings of three tree species (C. sumatranus, L. comberi and Celtis philippensis) in a tropical karst forest in southern Yunnan, China. The soil gravimetric water content (GWC) and volumetric water content (VWC), pre‐dawn leaf water potential (Ψpre‐dawn) and leaf water absorbance were also measured. There were no significant differences in both GWC and VWC among 10 to 100 cm depths in the dry season. In the dry season 2009, Ψpre‐dawn of the two evergreen tree species and the understory seedlings down to −4.5 to −6.3 MPa, and which were significantly lower than those of a normal dry season. The proportion that fog contributed to xylem water ranged from 15.8% (understory seedling of C. sumatranus) to 41.3% (liana species C. latifolium). After immersing in water for 3 h, leaves of all the studied species absorbed a significant volume of water. Our results reveal that the woody plants in the tropical karst forest of Xishuangbanna use fog water as an important supplement in the dry season, with more fog water being used by lianas than by trees. Copyright © 2015 John Wiley &amp; Sons, Ltd.