Tracer Methods Research Articles

Multi-scale characterization of a complex karst and alluvial aquifer system in southern Germany using a combination of different tracer methods

Water suppliers face major challenges such as climate change and population growth. To prepare for the future, detailed knowledge of water resources is needed. In southern Germany, the state water supplier Zweckverband Landeswasserversorgung provides 3 million people with drinking water obtained from a complex karst and alluvial aquifer system and the river Danube. In this study, a combination of different tracing techniques was used with the goal of a multi-scale characterization of the aquifer system and to gain additional knowledge about groundwater flow toward the extraction wells in the Danube Valley. For the small-scale characterization, selected groundwater monitoring wells were examined using single-borehole dilution tests. With these tests, a wide range of flow behavior could be documented, including fast outflow within just a few hours in wells with good connection to the aquifer, but also durations of many weeks in low-permeability formations. Vertical flow, caused by multiple flow horizons or uprising groundwater, was detected in 40% of the tested wells. A regional multi-tracer test with three injections was used to investigate the aquifer on a large scale. For the highly karstified connection between a swallow hole and a spring group, high flow velocities of around 80 m/h could be documented. Exceptionally delayed arrivals, 250 and 307 days after the injection, respectively showing maximum velocities of 0.44 and 0.39 m/h, were observed in an area where low-permeability sediments overlay the karst conduits. With the chosen methods, a distinct heterogeneity caused by the geological setting could be documented on both scales.

A review of the technology and applications of methods for evaluating the transport of air pollutants

A variety of methods based on air quality models, including tracer methods, the brute-force method (BFM), decoupled direct method (DDM), high-order decoupled direct method (HDDM), response surface models (RSMs) and so on forth, have been widely used to study the transport of air pollutants. These methods have good applicability for the transport of air pollutants with simple formation mechanisms. However, differences in research conclusions on secondary pollutants with obvious nonlinear characteristics have been reported. For example, the tracer method is suitable for the study of simplified scenarios, while HDDM and RSMs are more suitable for the study for nonlinear pollutants. Multiple observation techniques, including conventional air pollutant observation, lidar observation, air sounding balloons, vehicle-mounted and ship-borne technology, aerial surveys, and remote sensing observations, have been utilized to investigate air pollutant transport characteristics with time resolution as high as 1 sec. In addition, based on a multi-regional input-output model combined with emission inventories, the transfer of air pollutant emissions can be evaluated and applied to study the air pollutant transport characteristics. Observational technologies have advantages in temporal resolution and accuracy, while modeling technologies are more flexible in spatial resolution and research plan setting. In order to accurately quantify the transport characteristics of pollutants, it is necessary to develop a research method for interactive verification of observation and simulation. Quantitative evaluation of the transport of air pollutants from different angles can provide a scientific basis for regional joint prevention and control.

Comparison of methods to estimate air-water interfacial areas for evaluating PFAS transport in the vadose zone

When performing calculations or numerical simulations for the fate and transport of PFAS and other surface-active solutes in the vadose zone, accurately representing the relationship between the area of the air-water interfaces (Aaw) as a function of water saturation (Sw), and changes in that relationship resulting from changes in soil texture, are equally important as accurately characterizing interfacial adsorption coefficients and the concentration dependence for PFAS solutes. This is true because the magnitude of the Aaw directly governs the degree of air-water interfacial adsorption, which contributes to the transport retardation of these solutes within unsaturated porous media. Herein, a well-known thermodynamic-based model for predicting the Aaw-Sw relationship is evaluated through comparisons to literature data collected using various measurement techniques for model sands and a limited number of soils using data collected from the current published literature. This predictive model, herein termed the Leverett thermodynamic model (LTM), relies on the characterization of the soil-water retention curve (SWRC) for a given soil, using the van Genuchten (VG) equation for the pressure head-vs-Sw relationship. Therefore, methods to estimate the VG equation parameters are also compared as to the Aaw-Sw relationships predicted. Comparisons suggest that the LTM provides the best estimate of the actual Aaw-Sw relationships for water containing non-surface-active solutes. Because PFAS solutes are also surface-active, Aaw measurement methods utilizing surface-active tracers are considered to provide the most accurate representation of the Aaw-Sw relationship for these solutes. Differences between Aaw-Sw relationships derived from tracer methods and the LTM are described in relation to media surface roughness effects. Based on the available literature data, a practical empirical model is proposed to adjust the LTM prediction to account for the effects of surface roughness on the magnitude of the Aaw for surface-active solutes. Finally, example retention calculations are performed to demonstrate the sensitivity of the predicted Aaw-Sw relationship on the vadose zone transport of of a representative PFAS, perfluorooctane sulfonate.

A Cycle of Inflammatory Adipocyte Death and Regeneration in Murine Adipose Tissue.

Adipose tissue (AT) expands by a combination of two fundamental cellular mechanisms: hypertrophic growth of existing adipocytes or through generation of new adipocytes, also known as hyperplastic growth. Multiple lines of evidence suggest a limited capacity for hyperplastic growth of AT in adulthood and that adipocyte number is relatively stable, even with fluctuations in AT mass. If the adipocyte number is stable in adulthood, despite well-documented birth and death of adipocytes, then this would suggest that birth may be coupled to death in a regenerative cycle. To test this hypothesis, we examined the dynamics of birth of new fat cells in relationship to adipocyte death by using high-fidelity stable isotope tracer methods in C57Bl6 mice. We discovered birth of new adipocytes at higher frequency in histological proximity to dead adipocytes. In diet-induced obesity, adipogenesis surged after an adipocyte death peak beyond 8 weeks of high-fat feeding. Through transcriptional analyses of AT and fractionated adipocytes, we found that the dominant cell death signals were inflammasome related. Proinflammatory signals were particularly evident in hypertrophied adipocytes or with deletion of a constitutive oxygen sensor and inhibitor of hypoxia-inducible factor, Egln1. We leveraged the potential role for the inflammasome in adipocyte death to test the adipocyte death-birth hypothesis, finding that caspase 1 loss of function attenuated adipocyte death and birth in murine visceral AT. These data collectively point to a regenerative cycle of adipocyte death and birth as a driver of adipogenesis in adult murine AT.

Application of oil and dye flow visualization in incompressible turbomachinery flows

Flow visualization is one of many available tools in experimental fluid mechanics and is used from the primary stages of fluid mechanics research in order to identify the physical sizes and locations of the flow features under consideration. Most of the fluids used in engineering applications are transparent (water, air, etc) and flow visualization techniques are used in order to make their flow patterns visible. Simple flow visualization experiments are relatively inexpensive and they can be easily implemented providing with a first feeling of the characteristics of the flow domain. Subsequently, flow visualization techniques are of great applicability in complex flow fields and especially in turbomachinery applications where the flow is characterized by three dimensional and secondary flow patterns. In general, fluid motion can be visualized by surface flow visualization, by particle tracer methods or by optical methods. The former flow visualization technique reveals the streamlines of fluid flows around a solid surface. In this paper flow visualization techniques applied in two different cases of experimental testing (fans in crossflow and cascade experiment) are presented. In both cases, the mixture of paint was prepared using a highly volatile light mineral or heavy machine oil of viscosities of approximately100cPand200cP, respectively, together with very fine pigments of Titanium Dioxide (TiO2) or fluorescein sodium in various colors. After the preparation of the mixture, a homogenous thin film was applied onto the whole plate surface by painting it with a soft brush. The air stream which flows over the surface of the plate, modifies the concentration and the homogeneity of the oil film, according to the flow conditions very close to the wall. The film was dried by the airflow and photographed for further consideration while the time taken for drying depended on the wind tunnel velocity as well as, on the pigmentation of the mixture. Successful and un-successful flow visualization tests are herein presented while each case is respectively commented as far as the mixtures, the proportions used and the application onto the rigs are concerned.

Enhancing Understanding of the Hydrological Cycle via Pairing of Process‐Oriented and Isotope Ratio Tracers

AbstractThe hydrologic cycle couples the Earth's energy and carbon budgets through evaporation, moisture transport, and precipitation. Despite a wealth of observations and models, fundamental limitations remain in our capacity to deduce even the most basic properties of the hydrological cycle, including the spatial pattern of the residence time (RT) of water in the atmosphere and the mean distance traveled from evaporation sources to precipitation sinks. Meanwhile, geochemical tracers such as stable water isotope ratios provide a tool to probe hydrological processes, yet their interpretation remains equivocal despite several decades of use. As a result, there is a need for new mechanistic tools that link variations in water isotope ratios to underlying hydrological processes. Here we present a new suite of “process‐oriented tags,” which we use to explicitly trace hydrological processes within the isotopically enabled Community Atmosphere Model, version 6 (iCAM6). Using these tags, we test the hypotheses that precipitation isotope ratios respond to parcel rainout, variations in atmospheric RT, and preserve information regarding meteorological conditions during evaporation. We present results for a historical simulation from 1980 to 2004, forced with winds from the ERA5 reanalysis. We find strong evidence that precipitation isotope ratios record information about atmospheric rainout and meteorological conditions during evaporation, but little evidence that precipitation isotope ratios vary with water vapor RT. These new tracer methods will enable more robust linkages between observations of isotope ratios in the modern hydrologic cycle or proxies of past terrestrial environments and the environmental processes underlying these observations.

Editorial introductions.

Editorial introductions.

Contribution of industrial and traffic emissions to ultrafine, fine, coarse particles in the vicinity of industrial areas in Japan

Atmospheric particulate matter (PM) in industrial areas is typically enriched with potentially toxic trace metals. However, measurements of ultrafine particles (PM0.1) in industrial areas, and the source apportionment of PM0.1 based on these results, are limited. Robust source apportionment studies are therefore necessary in order to identify the source of toxic emissions and to develop measures for reducing such emissions. The present study sought to clarify the contributions to PM mass of ultrafine, fine (PM2.5), and coarse particles (PM10 – PM2.5) in an urban–industrial area with multiple emission sources. We performed both online measurements of PM at a high temporal resolution and size-resolved offline measurements. Source apportionments were then performed for each particle size range by combining a positive matrix factorization method applied to organic aerosol data measured using an aerosol mass spectrometer, a twin-site study, and elemental tracer methods, and then assigning PM mass concentrations to 13 emission sources. The major contributing emission sources for PM0.1 were automobile exhaust (30%) and coal combustion, possibly related to integrated steelworks (24%), in winter, and fuel combustion (39%) and automobile exhaust (11%) in summer. Despite conducting measurements at one of the most heavily polluted traffic intersections in Japan, more than half of the anthropogenic primary emissions of PM0.1 and PM2.5 measured at the intersection were derived from sources other than automobile exhaust emissions. Since PM emissions from stationary-source flue gas has historically been less well regulated than automobile exhaust emissions, further mitigation measures need to be implemented in order to reduce atmospheric PM levels.

Cryptic Constituents: The Paradox of High Flux–Low Concentration Components of Aquatic Ecosystems

The interface between terrestrial ecosystems and inland waters is an important link in the global carbon cycle. However, the extent to which allochthonous organic matter entering freshwater systems plays a major role in microbial and higher-trophic-level processes is under debate. Human perturbations can alter fluxes of terrestrial carbon to aquatic environments in complex ways. The biomass and production of aquatic microbes are traditionally thought to be resource limited via stoichiometric constraints such as nutrient ratios or the carbon standing stock at a given timepoint. Low concentrations of a particular constituent, however, can be strong evidence of its importance in food webs. High fluxes of a constituent are often associated with low concentrations due to high uptake rates, particularly in aquatic food webs. A focus on biomass rather than turnover can lead investigators to misconstrue dissolved organic carbon use by bacteria. By combining tracer methods with mass balance calculations, we reveal hidden patterns in aquatic ecosystems that emphasize fluxes, turnover rates, and molecular interactions. We suggest that this approach will improve forecasts of aquatic ecosystem responses to warming or altered nitrogen usage.

Recent advances in measuring and understanding the regulation of exercise-mediated protein degradation in skeletal muscle.

Skeletal muscle protein turnover plays a crucial role in controlling muscle mass and protein quality control, including sarcomeric (structural and contractile) proteins. Protein turnover is a dynamic and continual process of protein synthesis and degradation. The ubiquitin proteasome system (UPS) is a key degradative system for protein degradation and protein quality control in skeletal muscle. UPS-mediated protein quality control is known to be impaired in aging and diseases. Exercise is a well-recognized, nonpharmacological approach to promote muscle protein turnover rates. Over the past decades, we have acquired substantial knowledge of molecular mechanisms of muscle protein synthesis after exercise. However, there have been considerable gaps in the mechanisms of how muscle protein degradation is regulated at the molecular level. The main challenge to understand muscle protein degradation is due in part to the lack of solid stable isotope tracer methodology to measure muscle protein degradation rate. Understanding the mechanisms of UPS with the concomitant measurement of protein degradation rate in skeletal muscle will help identify novel therapeutic strategies to ameliorate impaired protein turnover and protein quality control in aging and diseases. Thus, the goal of this present review was to highlight how recent advances in the field may help improve our understanding of exercise-mediated protein degradation. We discuss 1) the emerging roles of protein phosphorylation and ubiquitylation modifications in regulating proteasome-mediated protein degradation after exercise and 2) methodological advances to measure in vivo myofibrillar protein degradation rate using stable isotope tracer methods.

Comparison of 1-D analytical solutions and a numerical model for quantifying hyporheic exchange flux using the temperature tracer method

Recently, the use of temperature tracer methods to investigate hyporheic exchange in rivers has attracted widespread attention. The quantification of the hyporheic exchange flux using temperature has been a topic of interest. Based on a summary and elaboration of the one-dimensional (1-D) analytical models for quantifying the hyporheic exchange flux based on the temperature tracer method, a hydrothermal coupling numerical model for the hyporheic zone considering the overall model of a river is further constructed. Combined with the water level and temperature time-series monitoring data collected from relevant rivers in the Walker Lake Basin in the United States, the effectiveness of the constructed numerical model in simulating the temperature and seepage patterns in the hyporheic zone is verified. Based on the verified hydrothermal coupling numerical model, the differences in the quantification of the vertical hyporheic exchange flux between different models are compared and analyzed. In addition, a sensitivity analysis based on the orthogonal test method is carried out to investigate the uncertainty of the 1-D analytical solution model. Finally, the advantages and disadvantages of the 1-D analytical model and the numerical model are discussed from the perspective of theoretical analysis. The results show that the constructed numerical model can be used to effectively characterize the heat transfer and fluid flow patterns in the hyporheic zone. When the result from the numerical model is not considered, the l-D analytical model based on the Hatch amplitude method is an ideal model for quantifying the vertical hyporheic exchange flux using temperature. The sensitivity analysis results reveal that the volumetric heat capacity of the soil (Cs) and the porosity (n) are relatively sensitive parameters for the Hatch solution.

A comparison of radon, heat tracer and head gradient methods to quantify surface water - groundwater exchange in a tidal wetland (Kooragang Island, Newcastle, Australia)

Subsurface flow plays an important role in the functioning of wetlands and in the maintenance of their ecosystem services. Specifically, the transport and exchange of dissolved matter between sediments and surface waters is regulated by subsurface flow, which can strongly affect ecological zonation and productivity. Having a quantitative understanding of this subsurface flow is therefore important. Field techniques based on Darcy’s equation or natural tracers are often used separately to assess flows. Here, radon and heat (both natural groundwater tracers) and Darcy’s equation are used simultaneously to quantify the subsurface flow in a tidal wetland (Kooragang Island, Newcastle, Australia) and the results of the independent methods are compared. A steady-state radon mass balance model indicated an overall net subsurface exfiltration of 10.2 ± 4.2 cm/d while a 1D, vertical fluid heat transport model indicated a net exfiltration of 4.3 ± 2.9 cm/d. Flow estimated from analysis of hydraulic heads indicated an exfiltration rate of 3.2 ± 1.8 cm/d. The difference in flow rates is likely due to the localised measurement of the heat and head methods relative to radon, and therefore, these methods are less likely to capture zones of preferential subsurface flow. The main advantage of radon is that it provides the total subsurface flow regardless of the driving force. While head gradient or heat tracer method have the advantage of temporally quantify infiltration and exfiltration, we highlight that these methods may underestimate subsurface flows in highly dynamic coastal systems, such as tidal wetlands where a large portion of the subsurface flow is recirculated seawater. This could potentially lead to errors in solute flux estimates. This study highlights the importance of employing a multi-tracer approach and has implications towards quantifying the hydrological export of dissolved constituents (e.g., carbon and nitrogen) in coastal wetlands.

Macaque monkey trigeminal blink reflex circuits targeting orbicularis oculi motoneurons.

The trigeminal blink reflex plays an important role in protecting the corneal surface from damage and preserving visual function in an unpredictable environment. The closing phase of the human reflex, produced by activation of the orbicularis oculi (ObOc) muscles, consists of an initial, small, ipsilateral R1 component, followed by a larger, bilateral R2 component. We investigated the circuitry that underlies this reflex in macaque (Macaca fascicularis and Macaca mulatta) monkeys by the use of single and dual tracer methods. Injection of retrograde tracer into the facial nucleus labeled neurons in the principal trigeminal nucleus, and in the spinal nucleus pars oralis and interpolaris, bilaterally, and in pars caudalis, ipsilaterally. Injection of anterograde tracer into the principal trigeminal nucleus labeled axons that directly terminated on ObOc motoneurons, with an ipsilateral predominance. Injection of anterograde tracer into pars caudalis of the spinal trigeminal nucleus labeled axons that directly terminated on ipsilateral ObOc motoneurons. The observed pattern of labeling indicates that the reticular formation ventromedial to the principal and spinal nuclei also contributes extensive bilateral input to ObOc motoneurons. Thus, much of the trigeminal sensory complex is in a position to supply a monosynaptic drive for lid closure, and the adjacent reticular formation can supply a disynaptic drive. These findings indicate that the assignment of the R1 and R2 components of the blink reflex to different parts of the trigeminal sensory complex cannot be exclusively based on subdivision connectional relationships with facial motoneurons. The characteristics of the R2 component may be due, instead, to other circuit properties.

The effects of hydroxychloroquine on insulin sensitivity, insulin clearance and inflammation in insulin-resistant adults: A randomized trial.

To determine the effect of hydroxychloroquine (HCQ) on skeletal muscle and liver insulin sensitivity, insulin clearance, inflammation and adipokines. Insulin-resistant adults without rheumatic disease were randomized to 13 weeks of HCQ (400 mg/day) versus placebo (double-blinded). Primary outcomes were changes in skeletal muscle and liver insulin sensitivity assessed by hyperinsulinaemic-euglycaemic clamp and stable-isotope tracer methods. Secondary outcomes included insulin clearance, inflammation biomarkers and adipokines. Compared with placebo, HCQ significantly improved skeletal muscle insulin sensitivity by 26% (p = .019) and enhanced systemic glucose clearance (p = .025). By contrast, HCQ had no effect on hepatic insulin sensitivity. HCQ did not affect insulin clearance but decreased circulating IL-6 (p = .01) and increased adiponectin (p = .045). There were no effects on leptin, RBP-4, FGF-21 or C-reactive protein. HCQ selectively enhances insulin sensitivity and glucose disposal in skeletal muscle, without affecting hepatic insulin sensitivity or insulin clearance. These findings offer a mechanistic explanation for the antidiabetic properties of HCQ and suggest that this medication might be useful in conditions linked to insulin resistance such as type 2 diabetes.

The impacts of reservoirs on the sources and transport of riverine organic carbon in the karst area: A multi-tracer study

Reservoirs have been constructed as clean energy sources in recent decades with various environmental impacts. Karst rivers typically exhibit high dissolved inorganic carbon (DIC) concentrations, whether and how reservoirs affect carbon cycling, especially organic carbon (OC)-related biogeochemical processes in karst rivers, are unclear. To fill this knowledge gap, multiple tracer methods (including fluorescence excitation-emission matrix (EEM), ultraviolet (UV) absorption, and stable carbon (δ13C) and radiocarbon (Δ14C) isotopes) were utilized to track composition and property changes of both particulate OC (POC) and dissolved OC (DOC) along river-transition-reservoir transects in the Southwest China karst area. The changes in chemical properties indicated that from the river to the reservoir, terrestrial POC is largely replaced by phytoplankton-derived OC, while gradual coloured dissolved organic matter (CDOM) removal and addition of phytoplankton-derived OC to the DOC pool occurred as water flowed to the reservoir. Higher primary production in the transition area than that in the reservoir area was observed, which may be caused by nutrient released from suspended particles. Within the reservoir, the production surpassed degradation in the upper 5 m, resulting in a net DIC transformation into DOC and POC and terrestrial DOM degradation. The primary production was then gradually weakened and microbial degradation became more important down the profile. It is estimated that ~3.1–6.3 mg L−1 (~15.5–31.5 mg-C m−2 (~10–21%)) DIC was integrated into the OC pool through the biological carbon pump (BCP) process in the upper 5 m in the transition and reservoir areas. Our results emphasize the reservoir impact on riverine OC transport, and due to their characteristics, karst areas exhibit a higher BCP potential which is sensitive to human activities (more nutrient are provided) than non-karst areas.

Quantifying Groundwater Recharge Dynamics and Unsaturated Zone Processes in Snow‐Dominated Catchments via On‐Site Dissolved Gas Analysis

AbstractSnowmelt contributes a significant fraction of groundwater recharge in snow‐dominated regions, making its accurate quantification crucial for sustainable water resources management. While several components of the hydrological cycle can be measured directly, catchment‐scale recharge can only be quantified indirectly. Stable water isotopes are often used as tracers to estimate snowmelt recharge, even though estimates based on stable water isotopes are biased due to the large variations of δ2H and δ18O in snow and the difficulty to measure snowmelt directly. To overcome this gap, a new tracer method based on on‐site measurements of dissolved He, 40Ar, 84Kr, N2, O2, and CO2 is presented. The new method was developed alongside classical tracer methods (stable water isotopes, 222Rn, 3H/3He) in a highly instrumented boreal catchment. By revealing (noble gas) recharge temperatures and excess air, dissolved gases allow (i) the contribution of snowmelt to recharge, (ii) the temporal recharge dynamics, and (iii) the primary recharge pathways to be identified. In contrast to stable water isotopes, which produced highly inconsistent snowmelt recharge estimates for the experimental catchment, dissolved gases produced consistent estimates even when the temperature of snowmelt during recharge was not precisely known. As dissolved gases are not controlled by the same processes as stable water isotopes, they are not prone to the same biases and represent a highly complementary tracer method for the quantification of snowmelt recharge dynamics in snow‐dominated regions. Furthermore, an observed systematic depletion of N2 in groundwater provides new evidence for the pathways of biological N‐fixation in boreal forest soils.

Review: Advances in the methodology and application of tracing in karst aquifers

Tracer methods have been widely used in many fields of environmental and natural sciences, and also in human health sciences. In particular, tracers are used in the study of karst hydrogeology, typically focusing on phenomena such as sinkholes, sinking rivers and large karst springs. It is known that tracers have been used since antiquity. The aim of tracer tests has been to investigate underground flow paths, transport processes and water–rock interactions, and to get an insight into the functioning of a karst aquifer. In karst hydrogeology, tracer methods are the most important investigation tools beside conventional hydrological methods. In early times, tracer methods were applied only to investigate underground flow-paths. Later they were also used to elucidate transport processes associated with water flow, and today they are often the basis, together with detailed hydrological information, of groundwater protection investigations and aquifer modelling. Many substances (spores, microspheres, bacteriophages, salt tracers, fluorescent dyes, radioactive substances) have been investigated for their properties and potential usage in environmental investigations, in particular the often unknown and inaccessible underground systems of karst areas. A great number of analytical techniques is available. This includes instrumentation for laboratory applications and direct online, on-site or in-situ field measurements. Modern instruments have a high capability for data acquisition, storage and transmission in short intervals, as a basis for quantitative evaluation and modelling. This enables research on the hydrological and hydrochemical dynamics of aquifers and their response to different natural or anthropogenic impacts.

Dissimilatory nitrate reduction to ammonium increased with rising temperature

Although recent studies have explored dissimilatory nitrate reduction to ammonium (DNRA), little is known about the dependence of this process on temperature. A laboratory experiment was conducted to investigate if temperature regulates nitrate (NO3ˉ) reduction by DNRA and denitrification. Soil samples were incubated at 10 to 40 °C for 28 days, and 15N tracer methods were applied to estimate the reduction of 15NO3ˉ to 15NH4+ by DNRA organisms and to 15N2O or 15N2 by denitrifiers. Raising the temperature from 10 to 40 °C increased DNRA, which contributed to enrichment of the NH4+ pool, particularly at 40 °C. The percentage of 15NO3ˉ reduced by DNRA was from 4 to 30% of that reduced by denitrification, and decreased with increasing temperature. DNRA and denitrification were positively correlated with the abundance of nrfA and nosZ genes, respectively. The accumulation of 15NH4+ slowed in the final 12 h of sampling times, which may be due to a re-conversion of 15NH4+ to 15NO3ˉ by nitrification. High temperatures (30 to 40 °C) enhanced 15N2 production, which suggests that temperature plays an important role in regulating complete denitrification from NO3ˉ to N2.

Development and Evaluation of an Optical Sensing System for Detection of Herbicide Spray Droplets

Real time monitoring of herbicide spray droplet drift is important for crop production management and environmental protection. Existing spray droplet drift detection methods, such as water-sensitive paper and tracers of fluorescence and Rubidium chloride, are time-consuming and laborious, and the accuracies are not high in general. Also, the tracer methods indirectly quantify the spray deposition from the concentration of the tracer and may change the drift characteristics of the sprayed herbicides. In this study, a new optical sensor system was developed to directly detect the spray droplets without the need to add any tracer in the spray liquid. The system was prototyped using a single broadband programmable LED light source and a near infrared sensor containing 6 broadband spectral detectors at 610, 680, 730, 760, 810, and 860 nm to build a detection system for monitoring and analysis of herbicide spray droplet drift. A rotatory structure driven by a stepper motor in the system was created to shift the droplet capture line going under the optical sensor to measure and collect the spectral signals that reflect spray drift droplets along the line. The system prototype was tested for detection of small (Very Fine and Fine), medium (Medium), and large (Coarse) droplets within the droplet classifications of the American Society of Agricultural and Biological Engineers. Laboratory testing results indicated that the system could detect the droplets of different sizes and determine the droplet positions on the droplet capture line with 100% accuracy at the wavelength of 610 nm selected from the 6 bands to detect the droplets.

Groundwater Recharge in the Cerrado Biome, Brazil—A Multi-Method Study at Experimental Watershed Scale

Groundwater recharge is a key hydrological process for integrated water resource management, as it recharges aquifers and maintains the baseflow of perennial rivers. In Brazil, the Cerrado biome is an important continental recharge zone, but information on rates and spatial distribution is still lacking for this country. The objective of this work was to characterize the groundwater recharge process in phreatic aquifers of the Cerrado biome. For this, an experimental watershed representative of the referred biome was established and intensively monitored. The methodology consisted of an inverse numerical modeling approach of the saturated zone and three classic methods of recharge evaluation—hydrological modeling, baseflow separation, and water table elevation. The results indicated average potential recharge around 35% of the annual precipitation, average effective recharge around 21%, and higher rates occurring in flat areas of Ferralsols covered with natural vegetation of the Cerrado biome. As the level of uncertainty inferred from the methods was high, these results were considered a first attempt and will be better evaluated by comparison with other methods not applied in this work, such as the lysimeter and chemical tracer methods.