Use of stable tracer studies to evaluate pesticide photolysis at elevated temperatures

New methods were developed to determine photolysis rates of medium-weight pesticides in the gas phase using elevated air temperatures and solid-phase microextraction (SPME). A 57-L glass chamber was constructed that utilized collimated xenon arc irradiation that could heat chamber air to increase the amount of pesticide in the gas phase. Gas-phase photolysis rates were determined at various air temperatures by comparing the rate of loss of each of the tested pesticides to a photochemically stable tracer, hexachlorobenzene. Interval sampling of gas-phase constituents was performed using SPME immediately followed by GC-ECD or GC-MSD analysis. The two pesticides under examination were the dinitroaniline herbicide trifluralin and the organophosphorus insecticide chlorpyrifos. The gas-phase photolysis for trifluralin was found to be rapid with half-lives of 22-24 min corrected for sunlight. These results were comparable to photochemical lifetime estimates from other investigators under sunlight conditions. Elevating temperatures from 60 to 80 degrees C did not affect photolysis rates, and these rates could be extrapolated to environmental temperatures. From 60 to 80 degrees C, gas-phase chlorpyrifos photolysis lifetimes were observed to range from 1.4 to 2.2 h corrected for sunlight and will thus be important together with hydroxyl radical reactions for removing this substance from the atmosphere. At these elevated temperatures, pesticides and tracer compounds were found to be substantially in the gas phase, and possible effects on reaction rates from wall interactions were minimized.     

Use of respirometry to evaluate sulphur oxidation in soils

Conventional Warburg respirometric techniques were used to evaluate sulphur-oxidizing activity in soils derived from sediments deposited in brackish environments. Experiments were carried at 30° C on fresh samples dried under vacuum or a warm draught, and enriched either with thiosulphate or with elemental S. By difference from the respiration of the non-enriched sample, a rate of S oxidation was calculated. This rate was higher when the soil was moistened by a 1% solution (v/v) of Tween 80 than when water alone was used. Sublimed elemental S was a better substrate than thiosulphate for the measurement of S oxidizing activity. In all samples, the rate of S oxidation was correlated with counts of autotrophic S oxidizing microorganisms. (Thiobacillus sp) on selective agar.     

Use of models to evaluate carbon sequestration in agricultural soils

ABSTRACT

The Rothamsted Carbon (RothC) model, which is one of widely used soil carbon (C) models, was validated against long-term experimental datasets in Japan and modified to suit Andosols and paddy soils reflecting unique soil C turnover mechanisms in these soils. Nationwide soil C calculation system was developed by combining these modified models and spatial model input data such as weather, soil type, land use, and agricultural activities. The model was validated in China and Thailand by using long-term field experimental datasets, too. Further studies especially in tropical Asia will be needed. Matching conceptual model C pools with measurable fractions have been big challenges. Using various plant materials, two conceptual pools of plant litter, decomposable plant material (DPM) and resistant plant material (RPM), in the RothC were successfully identified. It was achieved by comparing the default proportions of DPM and RPM pools in the RothC and proportions in plant material fractions determined by two-step acid hydrolysis with H₂SO₄. The trial to match all of five C pools in the model, however, remains unachieved though a study was conducted comparing not only the size of C pools but mean residence time of the pools. A web-based decision support tool called ‘Visualization of CO₂ absorption by soils’ was developed. This allows users to easily calculate changes in soil C, CH₄ and N₂O emissions, and fossil fuel consumption. With this tool, farmers can see how to improve the environmental sustainability of their products and this tool may help spread mitigation options widely. Soil C sequestration can help achieve climate change mitigation and sustainable agricultural production. Importance of long-term field observations should be more highlighted because long-term experiments have supported the development of modeling approaches. I hope models will be more widely used by decision makers. Collaboration between modeling and monitoring studies is important.     

“等标污染法”在山东省水环境农业非点源污染源评价中的应用

综合评价不同污染源对水环境的影响是进行污染物总量控制的前提,也是农业非点源污染源头预防的重要依据。采用"等标污染法"计算了2007年山东省化肥、畜禽粪便、生活排污3种污染源中总氮、总磷2种污染物的流失量,以及全省17个地市3种污染源中2种污染物的等标污染负荷与等标污染指数。结果表明:全省总氮流失量以化肥贡献率最高,而总磷流失量以畜禽粪便所占比例最大,畜禽粪便、化肥、生活排污3种污染源中营养元素流失量分别占总流失量的49.3%、42.6%、8.1%;山东省总氮等标污染负荷略高于总磷,不同地市间差异较大,化肥与畜禽粪便以潍坊市最高,而临沂市生活排污等标污染负荷最大,2种污染物等标污染负荷均以潍坊市最高;3种污染源中以畜禽粪便对山东省水环境的影响强度最大,生活排污、化肥、畜禽粪便的等标污染负荷比例为1:4:7;受等标污染负荷与水环境总量的共同影响,山东省不同地市间等标污染指数差异明显,等标污染指数以德州市最高,农业非点源污染潜在威胁最大,其次为聊城、菏泽、滨州、泰安。应针对各区域不同的重点污染源进行农业非点源污染防控技术研究,降低其对水资源污染的威胁。     

Use of plants to evaluate the difference in available cadmium between soils

Abstract

A new method was proposed for assessing the difference in the capacity of soils to supply Cd to plants. The relation of tissue (tc) to soil (sc) Cd concentrations can be expressed as; log(tc) = α+βlog(sc), where α and β are the regression coefficients. When the same plant is grown on another soil, the equation will change to; log(tc) = α'+β'log(sc’). Based on both equations, the relationship between sc‘and sc becomes; log(sc’) = (α‐α')/β’ + (β/β') log(sc). Set p = (α‐α')/β’ and q = β/β’, then the difference of Cd availability between two soils can be evaluated according to the values of p and q. The p and q values were determined among four treatments in which radish was grown on a sand soil and a silty loam soil at two pH levels. The values showed that the Cd present in the sand soil (pH 5.6) and the metal in the silty loam soil (pH 7.5) were the most and least available, respectively. It was therefore considered that the parameters p and q could be used as criteria for selecting an ideal extractant capable of removing the actually available Cd from soils.     

Use of sequential extraction to evaluate the heavy metals in mining wastes

Lead-zinc mine tailings from the ‘old lead-belt’ in Missouri were chemically characterized using total chemical analysis and sequential extraction. These tailings have been considered as an inert and safe material for years. However, the levels of heavy metals in these tailings were found elevated with Pb values as high as 5000 ppm. The sequential extraction results indicated that the Pb was primarily found in the residual fraction and probably is in the PbS form. Some Pb was found in the oxide fraction. Cu, Zn, and Cd were found in several different fractions, but primarily in the residual fraction. Some Cu was found in the organic fraction. The Zn showed a wide variation between samples with high levels in the carbonate, oxide and residual fractions. Very little Pb, Cd, Cu, and Zn was leached by water. The heavy metals in these tailings do appear to be in the more inert forms and should not be readily available to the environment unless there is an interaction of the tailings with acids, microorganisms or chelating materials. The breathing and ingestion of this material may provide such an environment for such interactions and these materials should still be considered dangerous and managed properly.     

Subcritical water extraction to evaluate desorption behavior of organic pesticides in soil

We evaluated the feasibility of extracting organic pesticides in soil using a hot-water percolation apparatus at 105 degrees C and 120 kPa pressure. Efficiency of the method was assessed by extracting six selected pesticides (acetochlor, atrazine, diazinon, carbendazim, imidacloprid, and isoproturon) from previously equilibrated soil at 13.6-65.8 mg/kg concentration range. Studies were performed on brown forest soil with clay alluviation (Luvisol). The method developed was compared to the traditional batch equilibrium method in terms of desorbed amount of pesticides from soil and extraction time. Pesticides in the liquid phase from the batch sorption experiment and in the effluent from the hot-water percolation were quantified by high-performance liquid chromatography with UV detection. The results of the percolation experiment are in close correlation with those of the conventional soil testing method. Desorbed quantities by hot-water percolation were 85% acetochlor, 62% atrazine, 65% carbendazim, 44% diazinon, 95% imidacloprid, and 84% isoproturon, whereas using batch equilibrium method 101, 66, 64, 37, 81, and 90% were desorbed, expressed as the percentage of the adsorbed amount of pesticide on soil following equilibration. The average time for hot-water extraction was 3.45 min, in contrast to the 16 h time consumption of the traditional batch method. The effect of temperature on stability of selected compounds was also evaluated using pesticide-spiked sand without soil. Recoveries of analytes ranged between 84.6 and 91.1% with reproducibility of 7.9-10.2%, except for diazinon, for which recovery was 59.4% with 14.4% relative standard deviation since decomposition occurred at elevated temperature. The percolation process has been described by a first-order kinetic equation. The parameters calculated from the equation provide an opportunity to estimate the amount of compound available for desorption, the rate of desorption processes in the studied soil-pesticide-water system, and modeling the leaching process to obtain additional information on the environmental behavior of the examined pesticide.     

基于局部离群指数的土壤重金属污染评价方法

为评价土壤重金属污染,该文提出了一种局部离群指数方法。局部离群指数方法计算监测样点的局部离群指数,监测样点的局部离群指数越大,则该样点是污染样点的趋势越大。为确保算法的准确性,定义了深度离群点以及广度离群点;为减少算法处理海量数据的计算复杂性,开发了基于密度取样的数据过滤方法,以过滤数据分布致密的数据点而保留稀疏区域的数据点。以京郊农田重金属监测数据为实例,比较局部离群指数方法与内梅罗污染指数方法的评价结果的准确性,结果显示局部离群指数方法的评价结果与内梅罗污染指数方法的结果吻合,表明局部离群指数方法可作为一种有效的重金属污染评价方法。     

Peatland water chemistry in Central Ontario in relation to acid deposition

Thirty-one peatlands from two areas of central Ontario were sampled to assess the influence of acid deposition on peatland water chemistry. Factor analysis differentiated peatland water chemistry along three major axes of chemical variation, interpreted as axes of organic concentration, mineral concentration, and deposition influence. Water from the surface mats had a higher organic concentration than water from open pools. Mineral influence in peatland waters was reflected by higher concentrations of Ca, Mg, Na, and silica in fen pools compared to bog pools. The influence of high acid deposition in the Wanapitei study area was indicated by high concentrations of sulphate, Ni, Mn, and Cu, and lower pH compared to an area that has received less acidic deposition (Ranger). Regression analyses indicated that H⁺ variation in bogs could be largely explained by organic C concentration, but that sulphate concentration was also positively associated with acidity, while Ca was negatively associated with acidity.     

Sample size calculations for studies designed to evaluate diagnostic test accuracy

We developed a Bayesian approach to sample size calculations for cross-sectional studies designed to estimate sensitivity and specificity of one or more diagnostic tests. Sample size calculations can be made for common study designs such as one test in one population, two conditionally independent or dependent tests in ≤2 populations, and three tests in ≤2 populations. We determine a sample size combination that yields high predictive probability, with respect to the future study data, of accurate and precise estimates of sensitivity and specificity. We also consider hypothesis testing for demonstrating the superiority or equivalence of one diagnostic test relative to another. The predictive probability can also be computed when the sample size combination is fixed in advance, thereby providing a “power-like” measure for the future study. The method is straightforward to implement using the S-Plus/R library emBedBUGS together with WinBUGS.     

Use of a three-compartment model to evaluate the dynamics of cover crop residues

Cover crop (CC) residues protect the soil from erosion and their permanence on the surface is largely influenced by their biochemical constituents. In this study, the dynamics of CC residue decomposition by applying mathematical models was described. The kinetics of decomposition of residues was obtained from a laboratory incubation experiment. Three CC shoot residues were applied on the soil surface and incubated for 362 days (with eight sampling times). Oats and vetch residues decomposed the most than clover, where k values were 3.6 × 10^?3, 3.7 × 10^?3 and 5.3 × 10^?3 day^?1, respectively. The three-compartment model (nonstructural carbohydrates, cellulose–hemicellulose and lignin) to simulate residue decomposition presented a close fit between simulated and measured data. The decomposition rate constant (k) of CC can be used to estimate how long residues will remain in the field and how they could affect soil organic carbon.     

Fish species distribution in relation to water chemistry in selected Maine lakes

We examined the possible effects of acidity on the number of fish species in 22 lakes in Maine, ranging in pH from 4.4 to 7.0 (mean values). We caught no fish in three lakes with pH <5.0, but collected 1 to 9 species in the remaining 19 lakes (pH 5.4 to 7.0). Brook trout (Salvelinus fontinalis), golden shiners (Notemigonus crysoleucas), and white suckers (Catostomus commersoni) were ubiquitous, but no common shiners (Notropis cornutus) or creek chubs (Semotilus atromaculatus) were collected from lakes with pH below 6.0 and 5.9, respectively. The fishless lakes differed from the others primarily in water chemistry variables related to acidity, i.e., pH, Al, and concentration of divalent cations. Among lakes that contained fish, the factors related to the number of species collected were lake surface area and maximum depth, which may be related to habitat quantity and diversity. Cluster analysis identified two distinct fish species groups — depauperate and cyprinid-sucker — but multiple comparison analysis failed to relate any measured chemical or physical variable to these two groups, probably because water chemistry was suitable for reproduction by these species.     

Use of chrome azurol S reagents to evaluate siderophore production by rhizosphere bacteria

Summary Siderophores produced by rhizosphere bacteria may enhance plant growth by increasing the availability of Fe near the root or by inhibiting the colonization of roots by plant pathogens or other harmful bacteria. To examine the populations of siderophore-producing bacteria colonizing the roots of two grass species that differed in their susceptibility to Fe deficiency, we inoculated serial dilutions of root samples onto chrome azurol S (CAS) agar and several other selective and non-selective culture meida. CAS agar effectively differentiated bacteria that were capable of excreting large amounts of siderophore, but the composition of the medium limited its usefulness for ecological studies. A large proportion (71–79%) of the bacterial population that grew on a non-selective medium (tryptic soy agar) failed to grow on CAS agar, and several isolates that showed no sign of siderophore production on CAS agar produced siderophore in liquid culture. Similar populations of siderophore-producing bacteria were observed on roots of St. Augustine grass, which frequently exhibits Fe chlorosis, and bermuda grass, which does not. Roots of both grasses were colonized by bacteria that produced siderophore in vitro at concentrations ranging from 100 to 230 M. The CAS assay solution was also used to compare siderophore production by Pseudomonas fluorescens Q6, an isolate from bermuda grass, and by P. putida B 10, a plant growth-promoting pseudomonad. P. fluorescens Q6 produced 2.4 times more siderophore in vitro than P. putida B 10.     

Use of ammonium bicarbonate DTPA soil test to evaluate elemental availability and toxicity

Abstract

The literature published on the use of the Soltanpour and Schwab Ammonium Bicarbonate‐DTPA (AB‐DTPA) soil test shows that it can be used to determine availability and toxicity indices for many elements. It has been shown to be an effective test for measuring the availability indices of P, K, Zn, Fe, Mn, Mo, Pb, Ni, Cd and Se. Theoretically, it can also be used to determine the availability indices for S, Cu and As. The AB‐DTPA test can predict toxicity of B as well as the standard hot water rest, although within the non‐toxic range of B, it is not as effective as the hot water test. The hot water test alone predicts B availability well, but the AB‐DTPA B test result requires inclusion of soil water pH, organic matter and clay contents in a regression equation for predicting B availability. This test is not suitable for determination of exchangeable plus soluble Ca and Mg (high levels), as these precipitate as carbonates during extraction. The AB‐DTPA test procedure with analysis by an inductively‐coupled plasma spectrometer for simultaneous determination of elements, makes soil and overburden testing very efficient.     

Impacts of forests on water chemistry

Forest canopies and soil organic horizons have been identified as two major components of forest ecosystems interacting with and altering the chemistry of rainwater. Data, collected over a 13-yr period from different softwood and hardwood stands located in central New Brunswick, are presented to demonstrate differences among stands in their ability to alter the chemistry of rainwater. In both the canopies and the soil organic horizons, retention and exchange processes are effective in altering the chemistry of rainwater. Significant species effects are recognized in the partitioning of rainwater into throughfall, stemflow, and interception, and in altering of its chemistry. Stemflow components generally contribute to acidity, while throughfall reduces acidity of rainwater. Some of the chemical characteristics of rainwater reaching the forest floor are shown to be similar to those of streams associated with the forest stands. The data show significant species effects on the moisture retention characteristics of the organic materials accumulated under each stand, which in turn affect the residence time of the acid components of rain. Admittedly, before entering streams and lakes associated the composition of the liquid leaving the organic horizons is further altered by mineral soils.     

Use of phosphorus vectors to monitor changes in soil phosphorus

Abstract

A study was conducted to evaluate the use of P vectors to predict the amount of P required on a yearly basis to maintain a constant solution‐solid phase P relationship in an irrigated calcareous and a dryland acid soil. Irrigated potato‐spring barley and dryland spring pea spring‐barley crop rotations established at the two locations. Mono‐calcium phosphate (0–45–0) was applied annually at five levels, ranging from 0–4 times estimated crop removal. Phosphorus vectors were determined on soil samples by equilibration with standard P solutions. Yields tended to increase with added P on the calcareous soil; however, significant responses were not recorded at either location. Consequently, critical P vectors were not established. A constant solution‐solid phase P relationship was maintained by addition of P equal to that removed by the crop on the calcareous soil. A constant solution‐solid phase P relationship was not maintained on the acid soil.     

Use of a chlorophyll meter to evaluate the nitrogen status of dryland winter wheat

Abstract

Chlorophyll meter leaf readings were compared to grain yield, leaf N concentration and soil NH₄‐N plus NO₃‐N levels from N rate studies for dryland winter wheat Soil N tests and wheat leaf N concentrations have been taken in the spring at the late tillering stage (Feekes 5) to document a crop N deficiency and to make fertilizer N recommendations. The chlorophyll meter offers another possible technique to estimate crop N status and determine the need for additional N fertilizer. Results with the chlorophyll meter indicate a positive association between chlorophyll meter readings and grain yield, leaf N concentration and soil NH₄‐N plus NO₃‐N. Additional tests are needed to evaluate other factors such as differences among locations, cultivars, soil moisture and profile N status.     

Soil geochemistry in relation to water chemistry and sensitivity to acid deposition in Finnish Lapland

Ecosystems in Finnish Lapland are threatened by heavy metal pollution and acid deposition derived from emissions of Cu-Ni smelters in Kola Peninsula and to varying extent to pollution from southern Fennoscandian and Central European sources. Extensive chemical analyses of small lake waters collected in Finnish Lapland have demonstrated that a significant number of lakes are acidified (ANC < 0μcq/l) or their buffering capacity is critical (ANC = 0–50μe/l). The relative abundance of mafic, ultramafic and carbonate rock components in the catchment were the chief factors controlling ANC and the main base cation (Ca²⁺, Mg²⁺) concentrations of lake waters. Both humic and clearwater lakes with low buffering capacity (ANC < 50μeq/l) were mainly located in the catchment areas identified as sensitive to acidification on the basis of low content of base cations (Ca²⁺ +Mg²⁺ +K⁺ < 500 meq/kg) in till. The ratio of the catchment area to the lake area was distinctly smaller for acidic lakes than for the well-buffered lakes, indicating the importance of catchment processes in determining the ANC and main base cations. The high sulphur concentrations (median 60μeq/1) of acidic lakes in northeastern Lapland, near the Finnish-Norwegian border, were strongly correlated with the highest deposition of sulphur derived from smelters of Kola Peninsula. The anomalously high concentrations of sulphur of well-buffered lakes in the western part of Lapland were due to sulphide minerals of soil and bedrock. The acidity of humic lakes in southern Lapland was in large part due to the organic acidity derived from peatlands.     

Soil water behaviour in response to changes in soil structure

Surface horizons of two Australian alfisols which had been cropped for 3 years to wheat by zero, minimum and ploughed tillage were compared for differences in structure. Total porosities and pore size distributions differed between treatments, but values for water and air permeability, sorptivity, diffusivity and evaporation rate were not necessarily ranked in the same order. The stability of soil structure was usefully described by the ratio of water to air permeability (k_w/k_a), which indicated the relatively fragile nature of the ploughed structures, despite their initially greater proportion of coarse porosity. Time of sampling after seeding also influenced hydraulic properties which were found to vary significantly over a 10-week period. Variations in vertical distribution of organic matter between tillage treatments is postulated as influencing the differences in structural stability.