Published Laboratory Studies Research Articles

Fatiguing effect of multiple take-offs and landings in regional airline operations

Fatigue is a risk factor for flight performance and safety in commercial aviation. In US commercial aviation, to help to curb fatigue, the maximum duration of flight duty periods is regulated based on the scheduled start time and the number of flight segments to be flown. There is scientific support for regulating maximum duty duration based on scheduled start time; fatigue is well established to be modulated by circadian rhythms. However, it has not been established scientifically whether the number of flight segments, per se, affects fatigue.To address this science gap, we conducted a randomized, counterbalanced, cross-over study with 24 active-duty regional airline pilots. Objective and subjective fatigue was compared between a 9-hour duty day with multiple take-offs and landings versus a duty day of equal duration with a single take-off and landing. To standardize experimental conditions and isolate the fatiguing effect of the number of segments flown, the entire duty schedules were carried out in a high-fidelity, moving-base, full-flight, regional jet flight simulator. Steps were taken to maintain operational realism, including simulated airplane inspections and acceptance checks, use of realistic dispatch releases and airport charts, real-world air traffic control interactions, etc. During each of the two duty days, 10 fatigue test bouts were administered, which included a 10-minute Psychomotor Vigilance Test (PVT) assessment of objective fatigue and Samn–Perelli (SP) and Karolinska Sleepiness Scale (KSS) assessments of subjective sleepiness/fatigue.Results showed a greater build-up of objective and subjective fatigue in the multi-segment duty day than in the single-segment duty day. With duty start time and duration and other variables that could impact fatigue levels held constant, the greater build-up of fatigue in the multi-segment duty day was attributable specifically to the difference in the number of flight segments flown. Compared to findings in previously published laboratory studies of simulated night shifts and nighttime sleep deprivation, the magnitude of the fatiguing effect of the multiple take-offs and landings was modest. Ratings of flight performance were not significantly reduced for the simulated multi-segment duty day.The US duty and flight time regulations for commercial aviation shorten the maximum duty duration in multi-segment operations by up to 25% depending on the duty start time. The present results represent an important first step in understanding fatigue in multi-segment operations, and provide support for the number of flight segments as a relevant factor in regulating maximum duty duration. Nonetheless, based on our fatigue results, a more moderate reduction in maximum duty duration as a function of the number of flight segments might be considered. However, further research is needed to include investigation of flight safety, and to extend our findings to nighttime operations.

Modeling Coupled Hydromechanical Behavior of Landfilled Waste in Bioreactor Landfills: Numerical Formulation and Validation

AbstractBioreactor landfills involving leachate recirculation are emerging as the preferred option for managing municipal solid waste (MSW). Effective bioreactor landfill performance can be achieved by ensuring uniform and adequate moisture (leachate) distribution in landfilled MSW. This paper presents a numerical two-phase flow model as a tool to predict hydraulic behavior (moisture distribution and pore fluid pressures) in unsaturated MSW under leachate recirculation, mechanical response (stress-strain behavior), and coupled hydromechanical interactions of MSW in landfills. The selected mathematical model is the Fast Lagrangian Analysis of Continua (FLAC), which assumes leachate and landfill gas as two immiscible phases. The governing equations and numerical implementation are presented along with the general model implementation considerations. The model is validated by simulating the published laboratory studies, field studies, and published modeled studies. Overall, it is shown that the mathematical ...

A unified set of experimental data for cylindrical, natural draft, shielded, single pot, wood-fired cookstoves

This article presents a unified dataset of 63 points compiled from three published laboratory studies for the most common type of improved household cookstove used in the developing world—a cylindrical, natural draft, shielded, wood-fired cookstove. Each data point includes 11 geometric variables, thermal conductivity of the stove body and insulation, lower heating value and moisture content of the fuel, heat release rate, and efficiency. Analysis of the dataset finds that the data are consistent between the studies and consistent with the current rules of thumb for the design of cookstoves. Specifically, it was found that pot shield gap, combustion chamber height, and insulation each have approximately the same impact on stove performance, increasing efficiency from roughly 20% to 40%. In contrast increases in pot shield height above 8cm have limited impact on efficiency. No correlation between stove performance and volumetric or plan area heat release rate was found.

Why are workers lazy?

Does the highly touted efficiency of social insect colonies stem from a dedicated work force? Are all animals in the society engaged at the highest possible level in their work? Intuition and fairy tales, such as Aesop’s fable of the ant and the grasshopper, tell us this is exactly the case. But even casual observation of a social insect colony reveals the puzzling truth: many workers are inactive at any given moment and rarely, if ever, does the entire colony stir into concerted action. This observation of lazy workers or helpers extends to vertebrate societies including the eusocial naked mole rat [6]. An animal society, including a social insect colony, can appear to be the exact opposite of the paragon of efficiency. A number of hypotheses attempt to explain this observation. The first invokes workers held in reserve for rare but essential tasks [4]. This has also been expressed as the concept that workers or helpers may be in a holding pattern waiting to fill in as needed [1]. Second, worker ineffectiveness is possible due to genetic variation in worker response thresholds not matching the distribution of tasks at hand [2]. Third, Mattila et al. [5] put forward the intriguing idea that workers in colonies monogamous queens focus more on reproductive competition and less on work than workers in polygynous colonies, meaning that workers’ activities in monogamous colonies are more biased to reproduction rather than labor. In an interesting article in this issue, Charbonneau and colleagues [3] note that most of the observations of lazy workers in eusocial insect colonies have been obtained from laboratory colonies. This brings into question the validity of the lazy worker concept as differences in the demand for work in the laboratory, as compared to field settings, may create behavioral artifacts in division of labor among workers. Charbonneau and colleagues compare the behavior of workers in laboratory and field colonies of Temnothorax rugulatus, a species of ant commonly used for laboratory studies. Their key finding is that division of labor in the laboratory colonies closely matches that of field colonies. While this could seem like a simple confirmation of the soundness of previously published laboratory studies, the significance of this work has far reaching implications for our understanding of division of labor. Even rate of foraging behavior, for which labor demands could be quite different between laboratory and field colonies, showed no significant differences in time budget between the two settings. The reason for the presence of lazy workers remains to be discovered. Of particular interest will be the determination of whether a single underlying explanation covers all cases. If so, this could reflect fundamental algorithms that govern division of labor. On the other hand, the widespread presence of lazy workers may reflect convergence on a behavioral phenotype with many possible roots. The reserve force/holding pattern explanation seems most generally plausible based on the slender evidence available. Future studies on how task performance is replaced when workers are removed should help to sort this out. In the meantime, we can be sure that social insect workers are not governed by the moral drive to work asserted in Aesop’s fable. Michael Breed Editor-in-Chief M. Breed (&) Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309-0334, USA e-mail: michael.breed@colorado.edu Insect. Soc. (2015) 62:7–8 DOI 10.1007/s00040-014-0388-9 Insectes Sociaux

The relationship between craving and tobacco use behavior in laboratory studies: a meta-analysis.

Published laboratory studies from the last 50 years that included measures of craving and tobacco-consumption or tobacco-seeking measures were included in a meta-analysis in order to assess the relationship between craving and tobacco use. Seeking measures were further subdivided into those that reflected control by nonautomatic and automatic cognitive processes. Of 2,498 articles identified by the initial literature review, 204 analyses from 50 studies were deemed eligible. Overall, the relationship between craving and outcome behaviors was modest (r = .20, p < .001). Studies that imposed abstinence during data collection showed a stronger relationship between craving and outcome (r = .24, p < .001) than studies that did not (r = .18, p < .001). Further, of those studies that reported dependence, the overall association between craving and outcome was stronger for smokers who were less dependent. Separate meta-analyses revealed that the type of outcome measure moderated the omnibus effect, with the relationship between craving and nonautomatic seeking measures (r = .34, p < .001) being stronger than the relationship between craving and automatic seeking/consumption measures (both rs = 0.15, p < .001). These findings suggest that craving may play a role in, but does not fully account for, tobacco-use behaviors; furthermore, the extent to which craving predicts behavior may be increased when the behavior is under nonautomatic cognitive control.

Fast photolysis of carbonyl nitrates from isoprene

Abstract. Photolysis is shown to be a major sink for isoprene-derived carbonyl nitrates, which constitute an important component of the total organic nitrate pool over vegetated areas. Empirical evidence from published laboratory studies on the absorption cross sections and photolysis rates of α-nitrooxy ketones suggests that the presence of the nitrate group (i) greatly enhances the absorption cross sections and (ii) facilitates dissociation to a point that the photolysis quantum yield is close to unity, with O–NO2 dissociation as a likely major channel. On this basis, we provide new recommendations for estimating the cross sections and photolysis rates of carbonyl nitrates. The newly estimated photo rates are validated using a chemical box model against measured temporal profiles of carbonyl nitrates in an isoprene oxidation experiment by Paulot et al. (2009). The comparisons for ethanal nitrate and for the sum of methacrolein- and methyl vinyl ketone nitrates strongly supports our assumptions of large cross-section enhancements and a near-unit quantum yield for these compounds. These findings have significant atmospheric implications: the photorates of key carbonyl nitrates from isoprene are estimated to be typically between ~ 3 and 20 times higher than their sink due to reaction with OH in relevant atmospheric conditions. Moreover, since the reaction is expected to release NO2, photolysis is especially effective in depleting the total organic nitrate pool.

Slope stability of bioreactor landfills during leachate injection: Effects of unsaturated hydraulic properties of municipal solid waste

In bioreactor landfill, the leachate flow and moisture distribution depend upon saturated and unsaturated hydraulic properties of municipal solid waste (MSW). The effects of unsaturated parameters have not been studied because of scarcity of the data and variation in unsaturated parameters due to MSW heterogeneity, degree of decomposition, and pore structure. In this study, a numerical two-phase flow model was used to examine the effects of unsaturated hydraulic properties on the moisture distribution, pore fluid pressures, and the stability of a bioreactor landfill slope with horizontal trench as leachate recirculation system. Unsaturated hydraulic parameters were based on the van Genuchten model and obtained from previously published laboratory studies. The unsaturated hydraulic properties of MSW are found to significantly influence the leachate distribution, pore water and capillary pressures, and landfill slope stability during the operations of leachate injection and subsequent gravity drainage. Further research is needed for better understanding and accurate measurement of hydraulic properties and shear strength parameters of unsaturated MSW.

Lab tests on the biodegradation of chemically dispersed oil should consider the rapid dilution that occurs at sea

Most crude oils spread on open water to an average thickness as low as 0.1mm. The application of dispersants enhances the transport of oil as small droplets into the water column, and when combined with the turbulence of 1m waves will quickly entrain oil into the top 1m of the water column, where it rapidly dilutes to concentrations less than 100ppm. In less than 24h, the dispersed oil is expected to mix into the top 10m of the water column and be diluted to concentrations well below 10ppm, with dilution continuing as time proceeds. Over the multiple weeks that biodegradation takes place, dispersed oil concentrations are expected to be below 1ppm. Measurements from spills and wave basin studies support these calculations. Published laboratory studies focused on the quantification of contaminant biodegradation rates have used concentrations orders of magnitude greater than this, as it was necessary to ensure the concentrations of hydrocarbons and other chemicals were higher than the detection limits of chemical analysis. However, current analytical methods can quantify individual alkanes and PAHs (and their alkyl homologues) at ppb and ppm levels. To simulate marine biodegradation of dispersed oil at dilute concentrations commonly encountered in the field, laboratory studies should be conducted at similarly low hydrocarbon concentrations.

Numerical modelling of methyl iodide in the eastern tropical Atlantic

Abstract. Methyl iodide (CH3I) is a volatile organic halogen compound that contributes significantly to the transport of iodine from the ocean to the atmosphere, where it plays an important role in tropospheric chemistry. CH3I is naturally produced and occurs in the global ocean. The processes involved in the formation of CH3I, however, are not fully understood. In fact, there is an ongoing debate whether production by phytoplankton or photochemical degradation of organic matter is the main source term. Here, both the biological and photochemical production mechanisms are considered in a biogeochemical module that is coupled to a one-dimensional water column model for the eastern tropical Atlantic. The model is able to reproduce observed subsurface maxima of CH3I concentrations. But, the dominating source process cannot be clearly identified as subsurface maxima can occur due to both direct biological and photochemical production. However, good agreement between the observed and simulated difference between surface and subsurface methyl iodide concentrations is achieved only when direct biological production is taken into account. Production rates for the biological CH3I source that were derived from published laboratory studies are shown to be inappropriate for explaining CH3I concentrations in the eastern tropical Atlantic.

IDENTIFYING SOCIAL NORMS USING COORDINATION GAMES: WHY DOES DICTATOR GAME SHARING VARY?

We introduce an incentivized elicitation method for identifying social norms that uses simple coordination games. We demonstrate that concern for the norms we elicit and for money predict changes in behavior across several variants of the dictator game, including data from a novel experiment and from prior published laboratory studies, that are unaccounted for by most current theories of social preferences. Moreover, we find that the importance of social norm compliance and of monetary considerations is fairly constant across different experiments. This consistency allows prediction of treatment effects across experiments, and implies that subjects have a generally stable willingness to sacrifice money to take behaviors that are socially appropriate.

Antimony biomethylation in culture media revisited in the light of solubility and chemical speciation considerations

Laboratory culture experiments have shown that antimony biomethylation can result from bacterial and fungal activity under both aerobic and anaerobic conditions. However, in the light of our current knowledge of antimony solubility and equilibria, critical analysis of the conditions used in published laboratory studies reveals that solution chemistry was generally overlooked and oversaturated solutions were used. As a result, it is very difficult, if not impossible, to establish reliable observed effect-concentration relationships in the experiments published.

Physiological welfare of commercially reared cod and effects of crowding for harvesting

A greater understanding of the effects of pre-slaughter practices on farmed fish is needed, particularly for more recently farmed marine fish species such as the Atlantic cod, Gadus morhua. In the present studies, in order to understand the impacts of crowding prior to harvesting on the physiological well-being of farmed Atlantic cod, we measured blood haematocrit, plasma osmolality, and plasma concentrations of cortisol, glucose, lactate, chloride and sodium of cod held in two commercial sea cages. To investigate any effects of our presence alongside the cages, cod were captured from two non-manipulated cages by rod and line, with a minimal time on the line. Measurements of blood parameters were comparable with those from published laboratory studies, and showed minimal change over the 3 h maximum sampling period. By comparison, a small number of cod that were caught easily in a hand net showed severe osmoregulatory, metabolic and endocrine disturbances. These cod were predominantly mature females, from one cage in which female cod had a low muscle mass (i.e. K based on body mass after removal of viscera), which suggests that maturation and spawning of farmed cod, particularly females, may have welfare implications. Plasma cortisol (ng ml − 1 ) for net-caught cod ( n = 9) was 88.5 ± 20.6 (mean ± SE) compared to 8.13 ± 3.43 for rod–line-caught cod ( n = 54), and plasma osmolality (mOsm kg − 1 ) was 383.27 ± 13.03 compared to 338.55 ± 0.73. Two commercial cages, suspended at 15 m depth, were used to investigate the physiological effects of crowding of cod in a sweep net, comparing initial values in line-caught cod to values observed during crowding. The effects of crowding time, gender and cage were examined. In both cages, crowding caused a rapid and sustained elevation of blood haematocrit and plasma lactate concentrations, probably due to increased physical exertion. Plasma lactate peaked at mean concentrations of 4.17 mM and 3.02 mM in the two cages, compared to initial concentrations of 0.29 mM and 0.17 mM respectively. Disturbed osmoregulation during crowding was not accompanied by parallel changes in plasma concentrations of sodium or chloride. Plasma cortisol during crowding reached peak concentrations of approximately 60 ng ml − 1 in both male and female cod but female cod showed a more rapid and prolonged response. Interpretation of our results suggests that cod crowded for harvesting will benefit from (i) reduced cage depth to minimise swim bladder inflation during the sweep and unnecessary exertion, (ii) limiting crowd density as far as practical to reduce bursts of activity, and (iii) minimising the crowding period.

The Effect of Capture, Handling, and Tagging on Hematological Variables in Wild Adult Lake Sturgeon

AbstractWe measured hematocrit and plasma osmolality, cortisol, lactate, glucose, and chloride in wild lake sturgeon Acipenser fulvescens after gill‐net capture (24‐h sets) and multiple bouts of brief (2–3‐min) air exposure during removal from nets and again during measurement and tagging procedures. Our objective was to evaluate the physiological consequences associated with capture, handling, and tagging activities commonly employed during mark–recapture studies and to determine whether blood chemistry values moved toward a resting state after a 3‐d recovery period. Lake sturgeon that were caught during spring tagging activities showed plasma cortisol, glucose, lactate, osmolality, and chloride levels similar to those exhibited by maximally stressed lake sturgeon in published laboratory studies. After the 3‐d recovery period, all physiological stress indicators had approached a nonstressed state and the values were similar to those previously reported for resting lake sturgeon. It appears that capture–mark–recapture programs that subject lake sturgeon to stressors similar to those applied here do not pose a significant threat to this often legislatively protected species.

The role of unchelated Fe in the iron nutrition of phytoplankton

The important question of iron bioavailability in the sea has become complicated by the discovery that marine phytoplankton can take up Fe bound in very stable chelates via reductive processes, and some particular Fe species through specialized transport mechanisms. As a result there is some question of whether the small fraction of Fe that is "free" or unchelated in seawater is important in the nutrition of natural phytoplankton assemblages. A careful examination of published laboratory studies on Fe uptake by model organisms all support the idea that unchelated Fe(III) is highly available for uptake and that it is an important source of the Fe taken up by phytoplankton under a variety of experimental conditions. Comparing these results with field data on Fe speciation shows that unchelated Fe can be an important source of Fe to the phytoplankton in the sea: it is likely sufficient to contribute the bulk of the Fe supporting primary production in regions that are not limited by Fe and a significant fraction everywhere, including high‐nutrient low‐chlorophyll areas.

Analysis and modelling of the interactive effects of temperature and light on phytoplankton growth and relevance for the spring bloom

Global climate change alters the relationship between temperature and light in aquatic ecosystems, which is expected to affect the success of different phytoplankton species. To examine this, the interactions between temperature, photoperiod and light exposure (LE) (integral daily light supply) on specific growth rates were analysed for Limnothrix redekei, Planktothrix agardhii (cyanobacteria), Nitzschia acicularis and Stephanodiscus minutulus (diatoms). A model of factor interactions was developed based on new (P. agardhii and St. minutulus) and previously published laboratory studies. It describes the measured data with high precision. Temperature and photoperiod affect the parameters of the light-growth response curve differently, but these effects are the same for all species. The link between functions for temperature and photoperiod is more species-specific. Using meteorological data, the model developed here was used to study the interplay of these factors during a spring bloom in Lake Muggelsee (Berlin). It was found that while all three factors influenced phytoplankton growth, temperature and photoperiod were more important than LE. Both the intensities of the factors and the interactions between them influenced each species to a different degree. The results may help improve our understanding and ability to predict shifts in phytoplankton communities caused by weather patterns and climate change.

Field study of glass-fibre-reinforced polymer durability in concrete

The Canadian Highway Bridge Design Code (CHBDC) does not permit the use of glass-fibre-reinforced polymer (GFRP) for primary reinforcement or prestressing tendons in concrete components. The restriction on the use of GFRP in concrete was based on published laboratory studies indicating that GFRP is not stable in the alkaline environment of concrete. In 2004, ISIS Canada sponsored an extensive study of the durability of GFRP in concrete by removing cores from GFRP-reinforced concrete components of five 5- to 8-year-old structures from across Canada. Three teams working independently at several Canadian universities used a variety of analytical methods to (i) investigate whether the GFRP in concrete field structures had been attacked by alkalis and (ii) compare the composition of GFRP removed from in-service structures with the composition of control specimens that were saved from the projects and not exposed to the concrete environment. The analytical results have confirmed that the GFRP in concrete did not suffer any damage during the 5–8 years of exposure. As a result of this study, the CHBDC in its forthcoming (second) edition has permitted the use of GFRP for both primary reinforcement and prestressing tendons in concrete components, provided the maximum stress level in GFRP at the serviceability limit state is kept at or below 25% of its ultimate strength. It was also found that, contrary to some claims, concrete over GFRP bars does not crack even if the depth of cover is as thin as 28 mm.Key words: alkali attack, barrier wall, crack, deck slab, depth of cover, fibre-reinforced polymer (FRP), glass-fibre-reinforced polymer (GFRP).

Effects of cyanobacterial toxicity and morphology on the population growth of freshwater zooplankton: Meta‐analyses of laboratory experiments

We synthesized data from 66 published laboratory studies, representing 597 experimental comparisons, examining the effects of cyanobacterial toxicity and morphology on the population growth rate and survivorship of 17 genera (34 species) of freshwater, herbivorous zooplankton. Two meta‐analyses were conducted with these data. The primary analysis compared herbivore population growth rates for grazers fed treatment diets containing cyanobacteria versus control diets comprising phytoplankton that are generally considered to be nutritious for zooplankton (chlorophytes and/or flagellates). This analysis confirmed that cyanobacteria were poor foods relative to small chlorophytes and flagellates. More importantly, filamentous cyanobacteria were found to be significantly better foods for grazers than single‐celled cyanobacteria over all studies. Surprisingly, the presence or absence of commonly‐measured toxic compounds (microcystins in 70% of the cases) in the diet had no overall influence on grazer population growth relative to control diets. A secondary analysis compared survival rates for grazers fed cyanobacteria versus no food. In contrast to the primary analysis, grazer survival was more negatively affected by toxic cyanobacteria than non‐toxic cyanobacteria, relative to starvation. However, this difference was attributable to the effects of a single Microcystis strain, PCC7820. Thus, though some cyanobacterial strains appear to be toxic to some strains of zooplankton, the overall role of commonly‐assayed cyanobacterial toxins as a determinant of food quality may be less than widely assumed. We suggest that more attention be focused on nutritional deficiencies, morphology, and the toxicity of undescribed cyanobacterial compounds as mediators of the poor food quality of cyanobacteria for zooplankton.

Kin distribution of amphibian larvae in the wild

According to kin selection theory, the location of an individual with respect to its relatives can have important ramifications for its fitness. Perhaps more than any other vertebrate group, anuran amphibian larvae have been the subject of many experiments on this topic. Some anuran species have been shown in the laboratory to recognize and associate with their siblings and half-siblings. However, due to the difficulty of identifying sibships, no kinship studies with anuran larvae have been conducted in the wild. Here, we use microsatellite analysis to show that wood frog (Rana sylvatica) tadpoles were nonrandomly distributed in two ponds with respect to their relatives. In one pond, the tadpoles were significantly clumped with their siblings or half-siblings as expected from other published laboratory studies on this species. However, in another pond, the tadpoles were significantly nonrandomly dispersed from their siblings or half-siblings. This is the first example of kin repulsion of nonreproductive animals in the wild and the first time a species has been shown to display both aggregation and repulsion under different circumstances. These results suggest that kin distribution is context dependent and demonstrate the importance of testing kin selection hypotheses under natural conditions.

The Effect of Waste Concentration on Destruction Efficiency During Incineration

Data from industrial incinerators and previously published laboratory studies have shown that destruction and removal efficiency (DRE) of chemical waste is adversely affected by lower inlet waste concentrations. The objective of this research is to use experimental data and theoretical modeling to study the effect of waste concentration on DRE. Original experimental data on methylene chloride (CH2Cl2) destruction and literature data on the destruction of methyl chloride (CH3Cl) and benzene (C6H6), together with detailed mechanistic modeling, are used. It is shown that fragments derived from waste molecules modify the free radical composition in the combustion environment, and induce additional or altered destruction pathways. To evaluate the effect of waste concentration on its DRE quantitatively, the rate function η= e−ΔKτ is derived, where ΔK is the total additional rate of destruction, and τ is the waste residence time. It is shown that the additional rate of waste destruction, ΔK, increases exponentially with waste inlet concentration.

Modelling water and chemical transport in large undisturbed soil cores using HYDRUS-2D

The ability of HYDRUS-2D (HYDRUS) to simulate water and chemical transport in large, undisturbed cores of a Vertosol and a Podosol soil was investigated. Parameters required by HYDRUS for simulating water and chemical transport, and nitrogen transformation, were obtained from previously published laboratory studies. HYDRUS simulated the measured cumulative drainage and cumulative chloride (Cl–) leaching behaviour very closely for both soil types, and also provided a very good description of coupled nitrogen transformation (conversion of ammonium to nitrate) and leaching (coefficient of model efficiency ∼1). There was little correlation between measured and predicted potassium (K+) leaching from the Podosol, suggesting that the mathematical equations governing the transport of reactive chemicals did not adequately reflect K+ behaviour in this coarse-textured soil. The reason for this discrepancy is unclear but may have been related to the use of sorption parameters obtained from batch rather than miscible displacement techniques, or mechanisms controlling K+ sorption were not well represented by the general non-linear sorption equation used by HYDRUS. The ability of HYDRUS to accurately simulate water and non-reactive chemical transport agrees with previous studies; however, more investigation into its suitability for predicting the movement reactive chemicals in soil is warranted.