Stable Isotope Techniques Research Articles

Home for Marine Species: Seagrass Leaves as Vital Spawning Grounds and Food Source

Seagrass beds provide nursery habitats for marine species. Seagrass leaves, in particular, are used as spawning grounds and food source for fishes and invertebrates, but direct evidence of spawning in seagrass leaves is rare. It is also very challenging to identify eggs through morphological analysis, since the eggs of many marine species appear similar. To accurately identify the eggs on the leaves of the dominant seagrass species in the South China Sea, and evaluate seasonal contribution of seagrass leaves as food source, DNA barcoding and stable isotope technique were conducted. Interestingly, Monetaria annulus was found to spawn on the leaf sheath of Thalassia hemprichii in Li'an gang, Hainan Island. This selection of oviposition site might increase embryo survival compared to the other parts of the seagrass leaves. Meanwhile, the eggs of Stethojulis trilineata were deposited on the entire leaf of Halophila ovalis in Liusha Bay, Guangdong Province. The small fingernail-shaped leaves of H. ovalis might be beneficial for S. trilineata to lay eggs as they are closer to the sediment surface than other seagrass leaves. Based on the stable carbon and nitrogen isotope analyses, the primary food source of M. annulus in summer and in winter were particulate organic matter and seagrass, respectively. The results suggest that seagrass leaf is not only important for fish and invertebrates as a spawning site, but also as a food source. The findings of the present study may support the urgent requirement of the conservation of seagrass beds for sustaining the productivity of marine fisheries.

The diet of spotted-necked otters foraging in trout-stocked waters in Mpumalanga, South Africa

Human-wildlife conflict is likely to increase as urbanisation increases. African clawless otters, Aonyx capensis, and spotted-necked otters, Hydrictis maculicollis, are illegally persecuted for their perceived role in reducing trout in artificially stocked habitats in South Africa. The diet of African clawless otters has been investigated, but little is known about the diet of spotted-necked otters in these habitats. Using stable isotope techniques, we investigated the diet of spotted-necked otters occupying habitats artificially stocked with trout. Stable isotope analyses revealed that the diet of spotted-necked otters included equal proportions of crab and trout followed by frog. Diet was found to vary between, as well as within, individuals suggesting individual dietary plasticity. Temporal variation in foraging areas was evident for some otters. These results suggest that individual animals specialise on trout when available. However, this was not consistent between individuals. The resulting conflict with freshwater fisheries may, therefore, be primarily due to individual animals adapting to diets consisting largely of farmed trout. The extent of spotted-necked otter influence on stocked trout, however, needs further investigation.

Diet Survey and Trophic Position of Macrobrachium nipponense in the Food Web of Anzali Wetland

The oriental river shrimp (Macrobrachium nipponense), an exotic species, has been well adapted and dispersed in Iranian freshwater ecosystems. The feeding ecology and trophic level of this species in the Anzali Wetland, southwestern Caspian Sea, was investigated by both a traditional method and the carbon and nitrogen stable isotope technique. The highest feeding index (FI) was seen in mollusca at 35.9%, followed by detritus at 31.3%. While no significant differences were observed in the preference of food items among different seasons. A Bayesian mixing model was used to estimate the contributions of the stomach contents to the isotopic signature of M. nipponense. According to mixing model results, M. nipponense obtain food from gastropod, fish, shrimp (as cannibalism), insecta, other crustacea, aquatic plants, worms, zooplankton, and unrecognizable content (as detritus) with 30.6%, 16.8%, 12.7%, 5.2%, 4.3%, 3.5%, 0.6%, 0.3%, and 25.9%, respectively. M. nipponense showed a high δ15N and its trophic level (TL = 3.38) was at the top of the Anzali Wetland food web, close to commercially important fish species such as pike, Esox Lucius. Being at this trophic level, this shrimp is expected to possess high nutritional quality for human consumption.

Impact of vegetation restoration on soil properties in near-surface fissures located in karst rocky desertification regions

Karst rocky desertification and vegetation restoration have become major environmental and social problems throughout the world. In regions facing rocky karst desertification, any form of residual soil is pivotal to vegetation growth and the restoration of rocky desertification. The goals of this study were to discover the impact of vegetation restoration on soil properties in near-surface fissures of karst rocky desertification regions, and analyses of the physical and chemical properties of soil and stable isotope techniques were used to achieve these goals. We found that the morphological structures of karst near-surface fissures are diverse. Fissures with grass and shrubs exhibit improved soil bulk density and more fine soil particles than those with other vegetation. Fissures with shrubs have higher soil field capacity, an increased capillary water content and a greater field capacity, whereas fissures with grass display greater fertility, particularly with respect to hydrolysable nitrogen, and greater available phosphorus and potassium contents, which create conditions that are superior to those found in areas with other crops, shrubs and even trees. Karst near-surface fissures are the optimal locations for vegetation restoration in areas of karst rocky desertification. Fissures with grass have a better soil structure, a higher water content and improved fertility compared with other fissure with growing crops, shrub grasses and forests with certain soil degradation. The use of grasses should be prioritized to improve soil conditions and to advance sustainable land use during the implementation of vegetation restoration projects in karst rocky desertification regions, particularly in highly fissured areas.

Application of isotope techniques to study groundwater resources in the unconsolidated aquifers along the Ping River (Thailand)

ABSTRACTSevere droughts during the dry season and floodings during the rainy season are among the major problems encountered in the valleys along the Ping River in Thailand. Improving our understanding of the groundwater resources in this agricultural area is an important issue for the sustainable development of the region. Hence, in order to gain understanding on the groundwater flow dynamics in the unconsolidated shallow aquifers along the Ping River, stable (13C, 18O, 2H, noble gases) and radioactive (3H, 14C) isotope techniques were combined with hydrogeochemical tools. The comprehensive interpretation of the chemical and isotope data consistently showed different origins for groundwater in the northern and southern areas of the investigated aquifers. Groundwaters in the northern part have younger 3H/3He ages, are less mineralized, and have suffered a stronger evaporation than groundwaters in the southern part of the aquifer. Overall, our results are consistent with the hydrogeological situation of the investigated area, namely shallow groundwaters and a spatially extended recharge. 3H/3He apparent ages indicated that young groundwater (<50 years) is present in all the investigated wells. Elevated concentrations of some pollutants (nitrate and phosphate) in parts of the aquifer evidenced a relatively high vulnerability of the aquifer to surface pollution.

VLDL (Very-Low-Density Lipoprotein)-Apo E (Apolipoprotein E) May Influence Lp(a) (Lipoprotein [a]) Synthesis or Assembly.

To clarify the association between PCSK9 (proprotein convertase subtilisin/kexin type 9) and Lp(a) (lipoprotein [a]), we studied Lp(a) kinetics in patients with loss-of-function and gain-of-function PCSK9 mutations and in patients in whom extended-release niacin reduced Lp(a) and PCSK9 concentrations. Approach and Results: Six healthy controls, 9 heterozygous patients with familial hypercholesterolemia (5 with low-density lipoprotein receptor [LDLR] mutations and 4 with PCSK9 gain-of-function mutations) and 3 patients with heterozygous dominant-negative PCSK9 loss-of-function mutations were included in the preliminary study. Eight patients were enrolled in a second study assessing the effects of 2 g/day extended-release niacin. Apolipoprotein kinetics in VLDL (very-low-density lipoprotein), LDL (low-density lipoprotein), and Lp(a) were studied using stable isotope techniques. Plasma Lp(a) concentrations were increased in PCSK9-gain-of-function and familial hypercholesterolemia-LDLR groups compared with controls and PCSK9-loss-of-function groups (14±12 versus 5±4 mg/dL; P=0.04), but no change was observed in Lp(a) fractional catabolic rate. Subjects with PCSK9-loss-of-function mutations displayed reduced apoE (apolipoprotein E) concentrations associated with a VLDL-apoE absolute production rate reduction. Lp(a) and VLDL-apoE absolute production rates were correlated (r=0.50; P<0.05). ApoE-to-apolipoprotein (a) molar ratios in Lp(a) increased with plasma Lp(a) (r=0.96; P<0.001) but not with PCSK9 levels. Extended-release niacin-induced reductions in Lp(a) and VLDL-apoE absolute production rate were correlated (r=0.83; P=0.015). In contrast, PCSK9 reduction (-35%; P=0.008) was only correlated with that of VLDL-apoE absolute production rate (r=0.79; P=0.028). VLDL-apoE production could determine Lp(a) production and/or assembly. As PCSK9 inhibitors reduce plasma apoE and Lp(a) concentrations, apoE could be the link between PCSK9 and Lp(a).

Isotopic Study of Springs Near Haditha Dam Western Iraq

Stable isotopic technique and hydrochemistry was used in studying the water resources interaction of near Haditha Reservoir area, western Iraq. Throughout the study area, 14 groundwater samples (Bashina, Zwachi springs and Wells), 8 surface water samples from the study area, and 7 spring samples were analyzed for 2H and 18O stable isotopes and hydrochemical analysis. In this study, the temperature, altitude and continental effects on the isotopic composition of rain water in Iraq were studied. The climate of the study area is classified as semi-arid to arid region. The results show a variation in the isotopic values of Haditha reservoir and Euphrates river. This variation is due to the effect of the low surface area and the low velocity of water of Haditha Reservoir on the amount of evaporation, compared with the high velocity and the large surface area of Euphrates river. There was a variation in the isotopic values between Bishina and Zwachi springs, due to two factors that appear to modify the isotopic signatures of the springs, namely the lack of hydraulic connection between the springs of Bishina and Zwachi, meaning that they recharge from different sources. The changes in oxygen isotope composition of the groundwater between a deep reservoir and the springs (Bishina) may be caused by the dilution with near surface waters (Haditha reservoir) with different oxygen isotope compositions. The variation in the isotopic content in the studied area indicated that there are various origins of springs recharge and a different interactions of the multiple sources of springs with the mutli-depths of springs water.

Exploring the hydrogeochemical evolution of cold and thermal waters in the Sarein-Nir area, Iran using stable isotopes (δ18O and δD), geothermometry and multivariate statistical approaches

In recent years, water management in Iran has mostly focused on monitoring, understanding and mitigating issues of water quality. To understand the processes that can affect water quality, this study carried out a geochemical study on cold (5 well water samples and 6 cold springs) and thermal (9 hot springs) waters in the Sarein-Nir area in Iran. A total of 20 water samples were collected in July 2016, and physicochemical variables such as pH, electrical conductivity (EC) and major, minor and trace element concentrations were determined. Using multivariate statistics, the main geochemical processes and possible origin of selected trace elements were investigated. The maturity and mixing processes of the waters were investigated using stable isotope (δ18O and δD) and geothermometry techniques. It was found that water-rock interaction was the predominant process, and that denitrification and ion exchange processes also took place in the groundwater system of the area. Thermal waters had an elevated EC, whereas cold waters showed elevated pH and NO3 values, indicating the impact of anthropogenic activities on water quality. Alkalinity and temperature were recognized as the most important variables that control the release of trace elements into the groundwater. Most thermal water samples were immature and belonged to peripheral water types, indicating that these samples came in part from deep circulation. Geothermometry of the thermal waters showed that the springs of the Sarein region had high temperatures compared to the springs of the Nir region. Considering that the Sarein spring waters had lower deuterium ratios than spring waters in the Nir region, it was concluded that the recharge elevation of the Sarein springs was higher than that of the Nir springs.

The stable isotopic composition variation characteristics of desert plants and water sources in an artificial revegetation ecosystem in Northwest China

Characterizing the dynamics of plant water availability and the mechanisms through which plants access available water sources are key challenges in ecohydrology, especially in arid and semi-arid regions. The establishment of artificial revegetation of different ages has formed vegetation landscapes with different chronological sequences in the southeast margin of the Tengger Desert. As an important regulatory factor of the Soil Plant Atmosphere Continuum (SPAC) system, changes in vegetation characteristics will affect the water uptake of the entire ecosystem. In this study, the δ2H and δ18O isotope ratios in precipitation, plant water, soil moisture, and underground water, and the δ13C isotope ratio of plant leaves were measured using the stable isotope technique for artificial revegetation used to fix the sand dunes in the Tengger Desert. The purpose of this study was to establish the isotope content and characteristics of potential water sources for plants and leaf carbon isotopes, to clarify whether the soil moisture condition and duration of sand-fixing influenced the isotopic signal, and to identify the main water source for desert plants. The results indicated that air temperature and amounts of precipitation were two important influencing factors in precipitation isotope ratio change. Soil water isotopic ratios were different under different water conditions, and under the same water conditions, the vertical variation in soil water isotopes in a single area and spatial variation at any depth for different revegetation areas were all significant (p < 0.01). Shallow soil waters were enriched in isotope ratios and the value increased with an increase of the sand-fixing duration (as found in older revegetation areas). The δ2H and δ18O values in Caragana korshinskii leaves were higher than they were in Artemisia ordosica leaves because the former has a higher transpiration rate. The higher δ13C value of Artemisia ordosica plant leaves indicated high water use efficiency, which is a result of better adapting to the arid environment compared to Caragana korshinskii. Overall, water uptake of these two shrubs was mainly (>70%) concentrated at a soil depth of 20–150 cm. For Caragana korshinskii plants, the 60–150 cm soil layer was the main water supply layer, while the water contribution layer of Artemisia ordosica plants focused on the 20–100 cm soil layer and the contribution rate of shallow soil water increased with the increase of sand fixation time in older revegetation areas, regardless of the species used for revegetation.

High Spatiotemporal Dynamics of Methane Production and Emission in Oxic Surface Water.

The discovery of methane (CH4) accumulation in oxic marine and limnic waters has redefined the role of aquatic environments in the regional CH4 cycle. Although CH4 accumulation in oxic surface waters became apparent in recent years, the sources are still subject to controversial discussions. We present high-resolution in situ measurements of CH4 concentration and its stable isotope composition in a stratified mesotrophic lake. We show that CH4 accumulation in surface waters originates from a highly dynamic interplay between (oxic) CH4 production and emission to the atmosphere. Laboratory incubations of different phytoplankton types and application of stable isotope techniques provide a first unambiguous evidence that major phytoplankton classes in Lake Stechlin per se produce CH4 under oxic conditions. Combined field and lab results show that the photoautotroph community is an important driver for CH4 production and its highly dynamic accumulation in oxic surface waters.

Spatio-temporal variation of sediment properties reveals missing trophic links for deposit-feeding crabs in sandy shore food webs

Quantifying trophic relationships among basal food sources and primary consumers is essential to our understanding of food web structure and dynamics, but is challenging in soft shore systems where the variety of potential food sources often masks the actual pathways of energy flow. To elucidate trophic relationships among basal food sources and primary consumers, we assessed the diet composition of a deposit-feeding crab,Scopimera intermedia, an abundant primary consumer inhabiting tropical shores, using direct enumeration and stable isotope techniques. Stable isotope analyses revealed that meiofauna accounted for the majority of the crab’s diet (nematodes reaching 43% in median proportion) compared to, at most, 11% contributed by microphytobenthos (MPB). Although the abundances of MPB and meiofauna varied, meiofauna dominated over MPB in the crab’s diet at different sites and seasons. Such an important role of meiofauna in consumer diets contrasts with previous studies on sediment food webs, where MPB has often been proposed as the most plausible primary food source. The relative roles of meiofauna and MPB as food sources are, however, likely to be mediated by local physical environments. Sediment particle size, for example, is more coarse higher on the shore, where the larger interstitial spaces enable colonization of meiofauna but will limit large, motile MPB due to increased photostress. The trophic importance of commonly assumed primary food sources may thus be modified by environmental physical stress and, as a result, the role of intermediate trophic links in modulating food web dynamics should not be neglected.

Editorial introductions

Editorial introductions

Applications of nitrogen stable isotope techniques in the study of nitrogen cycling in terrestrial ecosystems

Applications of nitrogen stable isotope techniques in the study of nitrogen cycling in terrestrial ecosystems

The influences of eutrophication for the carbon and nitrogen sources for aquatic consumer communities—A case study in Lake Baiyangdian

富营养化对湖泊生态系统能流和物流的影响具有不确定性，多数研究仅关注富营养化对浅水湖泊食物网结构和功能的影响，而富营养化对消费者群落碳源和氮源的影响及其时空分异特征较少关注.鉴于此，本研究选取华北平原最大的浅水富营养化湖泊——白洋淀为研究区，依据生境理化参数将白洋淀划分为3类生境（生境1（Ⅰ和Ⅱ区）主要遭受上游府河废水排放影响；生境2（Ⅴ、Ⅶ和Ⅷ区）主要遭受水产养殖和生活污水的影响；生境3（Ⅲ、Ⅳ和Ⅵ区）遭受人为干扰较小）.在2018年4月和8月分别收集了浮游生物、底栖生物和鱼类样品，运用碳、氮稳定同位素技术定量估算3类生境中底栖和浮游生物对消费者群落碳源和氮源贡献百分比的时空分异特征；同时收集水体和沉积物样品进行常规理化参数分析，明晰富营养化对白洋淀消费者群落碳源和氮源贡献百分比的影响.结果表明：1）就水体和沉积物理化参数季节变化而言，除pH相对稳定外，化学需氧量（COD）、沉积物氨氮（NH₃-Ns）、总氮（TN）和沉积物总磷（TPs）4月高于8月，而其他理化参数则8月高于4月；就空间分布而言，温度（T）、水深（WD）、溶解氧（DO）和沉积物总碳（TCs）值在生境3中最高，而其他理化参数的值则在生境1中最高；2）就δ¹³C和δ¹⁵N空间分布而言，对于同一群落，δ¹³C和δ¹⁵N在3类生境中富集程度呈现显著差异；就时间分布而言，不同季节消费者群落的δ¹³C值存在显著差异，而δ¹⁵N值未呈现显著差异，且消费者群落的δ¹³C和δ¹⁵N呈显著负相关；3）就消费者营养级的空间分布而言，3类生境存在显著差异，同一消费者营养级在生境1中最高，在生境3中最低；就时间分布而言，消费者营养级未呈现显著差异；4）浮游生物对消费者群落碳源和氮源贡献百分比4月高于8月，生境1高于其他生境；而底栖生物对消费者群落碳源和氮源贡献百分比则8月高于4月，生境3高于其他生境；5）通过相关分析，结果表明白洋淀消费者群落的δ¹³C与总磷（TP）、TCs、沉积物总氮（TNs）、总有机碳（TOCs）、TPs呈现负相关关系；δ¹⁵N值与TP、TCs、TNs、TOCs、TPs呈正相关关系.因此，湖泊富营养化会影响消费者群落的碳源和氮源，进而改变湖泊生态系统的能流和物流.;The effects of eutrophication on the energy flow and material flow for lake ecosystems need to be studied. Most of previous studies showed the impacts of eutrophication on the structure and function of lake food web, while the influences of eutrophication on the nitrogen and carbon sources for consumer communities were limited. In view of this, the largest shallow eutrophic lake in North China Plain—Lake Baiyangdian was selected as the study area. According to the physical-chemical parameters in water and sediment, the Lake Baiyangdian was subdivided into three habitats(Habitat 1 strongly influenced by wastewater discharge(Sites Ⅰ and Ⅱ), Habitat 2 influenced by aquaculture and densely populated villages(Sites Ⅴ, Ⅶ and Ⅷ), and Habitat 3 influenced the least by human disturbances (Sites Ⅲ, Ⅳ and Ⅵ)). In April and August 2018, the samples for pelagic organisms, benthic organisms and fish were collected, respectively. Carbon and nitrogen stable isotope techniques were used to quantitatively calculate the contribution percentage of benthic and pelagic organism for the carbon and nitrogen sources of consumer communities. The results showed that: 1) according to the seasonal variation of water and sediment parameters, except pH, the values of chemical oxygen demand (COD), Ammonia nitrogen in sediments (NH₃-Ns), total nitrogen (TN), and total phosphorus in sediment (TPs) in April were higher than that in August, while the other parameters were existed higher values in August; in terms of spatial distribution, temperature (T), water depth (WD), dissolved oxygen (DO), total carbon in sediments (TCs) were showed the highest values in Habitat 3, while the other parameters were showed the highest values in Habitat 1; 2) According to the spatial distribution of δ¹³C and δ¹⁵N, for the same populations, the degree of enrichment were appeared significantly different at three habitats; while for the seasonal variation, the values of δ¹³C for the consumer communities showed significant difference, while the values of δ¹⁵N without significant difference; furthermore, the δ¹³C and δ¹⁵N of the consumer communities were existed the negatively correlated; 3) According to the spatial distribution of consumer trophic level (TL), the TL was appeared significantly different at three habitats; for the same consumer community, the highest values were appeared in Habitat 1, while the lowest values were appeared in Habitat 3; in terms of the temporal variation, the TL was not existed the significantly difference; 4) For the pelagic organisms, the contribution percentage for the carbon and nitrogen sources of consumer communities were appeared higher values in April, and the highest values were existed in Habitat 1; while for the benthic organisms, the contribution percentage for the carbon and nitrogen sources of consumer communities were appeared higher values in August, and the highest values were existed in Habitat 3; 5) Through correlation analysis, the results showed that the δ¹³C of consumer communities were appeared the negatively correlated with TP, TCs, TN in sediment (TNs), total organic carbon in sediment (TOCs), TPs; while the δ¹⁵N were existed the positive correlation with TP, TCs, TNs, TOCs, TPs. Therefore, the eutrophication can influence the carbon and nitrogen sources for consumer communities, and change the energy flow and material flow for the lake ecosystem.

Identification of the production system of beef cattle by the stable isotope analysis

Abstract: The objective of this work was to evaluate the potential of the stable isotope technique to characterize beef cattle production systems in tropical conditions. For this, carbon and nitrogen stable isotopes were identified in non-defatted and defatted bovine muscles. A total of 45 cattle were evaluated in three production systems: pasture, conventional feedlot, and young beef bull feedlot (n = 15 per system). Samples from the Trapezius cervicis, Longissimus dorsi, and Semitendinosus muscles were collected to determine the isotopic composition of δ13C and δ15N. The isotopic data of the δ13C and δ15N of non-defatted and defatted muscles were subjected to the principal component analysis (PCA) and to the discriminant analysis (DA). The PCA allowed separating the three production systems based on the results obtained for the non-defatted and defatted muscles. A correct global classification rate of 100% and a cross-validation rate of 100% were obtained with the DA. The carbon and nitrogen isotopic ratio of non-defatted and defatted muscles allows for the precise identification of beef cattle production systems in tropical conditions.

Transference of Robinia pseudoacacia water-use patterns from deep to shallow soil layers during the transition period between the dry and rainy seasons in a water-limited region

Soil water plays a critical role in determining plant survival and growth globally, especially in water-limited regions. This study explores water-use characteristics of Robinia pseudoacacia during the transition period between the dry and rainy seasons in the Chinese Loess Plateau (CLP). A stable isotope technique (δ18O and δD) and two complementary approaches (i.e., the direct inference method and the MixSIAR model) were used to distinguish water source changes during this transition period. Based on δ18O and δD distribution patterns, we subdivided a 500 cm soil profile into four potential water sources: shallow (0–40 cm), intermediate-shallow (40–120 cm), intermediate (120–200 cm) and deep (200–500 cm). During the transition period, R. pseudoacacia exhibited different water uptake patterns. In April 26.2% and 48.4% of water uptake derived from the 40 to 120 and 200 to 500 cm soil profile layers; in May, 21.5%, 24.5% and 37.4% of water was absorbed from the 0 to 40, 40 to 120 and 200 to 500 cm soil profile layers. In June and July, 51.6% and 53.6% of the water mainly derived from the 0 to 120 cm soil profile layer, respectively. During the dry season (April), the trend in water uptake shifted to the deep soil layer, potentially a key period for the onset of soil desiccation in this soil layer. As precipitation increased, the proportion of water uptake from the shallow and intermediate-shallow soil layers increased. Because water-use pattern characteristics could provide important information on the development of the dried soil layer (DSL), the stable isotope technique could help reveal the water sources used by trees while also offering insight into water movement mechanisms of local ecosystems. Given its usefulness, the application of the stable isotope technique should be expanded in analyzing practical ecohydrological issues that occur in deep soils in the future.

Investigating ammonia emissions in a coastal urban airshed using stable isotope techniques

Increases in reactive nitrogen (N) production and consumption have caused ammonia (NH3) emissions to the atmosphere to increase up to five times since the industrial revolution, resulting in negative impacts on the environment and human health. Understanding regional NH3 emissions and atmospheric dynamics is essential for creating realistic mitigation strategies. This study utilized stable isotope techniques to quantify and characterize NH3 emissions in a coastal urban air shed (i.e., Corpus Christi, TX, U.S.A.). NH3 was then passively collected at eight sites from September 2016 through August 2017 and analyzed for isotopic composition. The average atmospheric NH3 concentration for the region was 1.24 ± 0.98 μg/m3 with mean and concentration-weighted mean δ15N-NH3 values of −19.1 ± 12.7‰ and −17.1‰ respectively. The mixing model IsoError was used for source attribution, indicating that ambient NH3 was equally influenced by non-agricultural (55 ± 6%) and agricultural (45 ± 6%) emission sources with some seasonal variation. Sites adjacent to large water bodies exhibited low [NH3] coupled with a significant influence from non-agriculture emissions indicating a possible influence from marine-sourced NH3 which was further investigated using a three endmember SIAR bayesian mixing model. This work also examined the effects that varying degrees of kinetic and equilibrium fractionation via PM2.5 formation may have had on the δ15N-NH3(g) values observed in this study. A practical scenario assuming competing equilibrium and kinetic effects was used to calculate the δ15N-NH3(g) value of the original NH3 gas before fractionation occurred and calculated mean and concentration-weighted mean δ15N-NH3 for the region were −21.5 ± 12.4‰ and –22.3‰ respectively with no significant changes in source attribution. This work has shown that agricultural and non-agricultural sources of NH3 can equally contribute to ambient NH3 in urban environments and that marine NH3 must be taken into consideration when performing emission inventories in coastal regions.

Using stable isotope analysis to answer fundamental questions in invasion ecology: Progress and prospects

Abstract What makes some species successful invaders while others fail, and why some invaders have major impacts in invaded ecosystems are pivotal questions that are attracting major research effort. The increasing availability of high resolution, georeferenced stable isotope landscapes (‘isoscapes’), coupled with the commercialization of stable isotope‐enriched tracer molecules and the development of new analytical approaches, is facilitating novel applications of stable isotope techniques in ecology. We can now address ecological questions that were previously intractable. We review and discuss how stable isotope analysis (SIA) can complement fundamental research themes in the study of biological invasions, especially in answering questions relating to the physiological and ecological mechanisms underlying invasion processes and invader impacts. SIA was first used for simply describing the diet of invaders but, more recently, SIA‐informed metrics of population and community trophic structure have been advanced. These approaches now permit the comparison of diets across space and time and provide quantitative tools to compare food webs across different stages of invasion. SIA has also been pivotal in quantifying competition for resources between native and non‐native species (e.g. competition for food, water, or nutrient use). Specific questions related to modes of dispersal (e.g. origin and distance/direction travelled) and mechanisms of establishment can also be addressed using SIA in diverse taxa. An overarching goal is to highlight examples of recent studies that have used SIA in key areas of invasion ecology and use these to synthesize testable predictions where SIA could be applied to future studies. We conclude by highlighting several paths forward and describing how unresolved challenges in quantifying the rates, impacts, and mechanisms underlying invasions could potentially benefit from the use of SIA.

Iron bioavailability of a casein-based iron fortificant compared with that of ferrous sulfate in whole milk: a randomized trial with a crossover design in adult women

ABSTRACTBackgroundA highly soluble iron–casein complex has been developed for food fortification purposes with the aim to provide high iron bioavailability.ObjectiveWe aimed to determine the iron bioavailability of the iron–casein complex relative to that of ferrous sulfate (control) when given with whole milk in healthy young women.MethodsA randomized comparator-controlled trial with a crossover design was conducted using the erythrocyte incorporation dual stable isotope (57Fe, 58Fe) technique. Iron absorption from the iron–casein complex was compared with that from ferrous sulfate in 21 healthy women aged 20–38 y with normal iron status.ResultsFractional iron absorption (geometric mean; −SD, +SD) from the iron–casein complex (3.4%; 1.4%, 5.4%) and from ferrous sulfate (3.9%; 1.7%, 6.1%) were not statistically different (P > 0.05). The relative bioavailability value of the iron–casein complex to ferrous sulfate was determined to be 0.87 (−1 SD, +1 SD: −0.90, +2.64).ConclusionsThe iron–casein complex has iron bioavailability comparable to that of ferrous sulfate in healthy young women. This trial was registered at www.anzctr.org.au as ACTRN12615000690550.

Developing Meteoric Water Lines for Iran Based on Air Masses and Moisture Sources

Iran is a semi-arid to arid country that faces a water shortage crisis. Its weather is also influenced by various air masses and moisture sources. Therefore, applying accurate stable isotope techniques to investigate Iran’s precipitation characteristics and developing Iran meteoric water lines (MWLs) as an initial step for future isotope hydrology studies is vitally important. The aim of this study was to determine the MWLs for Iran by considering air masses and dominant moisture sources. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model backward analysis was used to determine the trajectories of various air masses in 19 weather stations in Iran and the areas covered by them. δ18O and δ2H contents were obtained for precipitation events from 32 stations in Iran and four in Iraq. Stable isotope samples were gathered from different sources and analyzed in various laboratories across the world. Three MWLs for north of Iran, south Zagros, and west Zagros, were determined based on the locations of dominant air masses and moisture sources. The proposed MWLs were validated by comparison with fresh karstic spring isotope data across Iran. In addition, Iran main moisture sources MWLs were used to determine dominant moisture sources role in karstic springs and surface water resources recharge.