Soil Solution Samples Research Articles

Catchments as heterogeneous and multi-species reactors: An integral approach for identifying biogeochemical hot-spots at the catchment scale

Summary From a biogeochemical perspective, catchments can be regarded as reactors that transform the input of various substances via precipitation or deposition as they pass through soils and aquifers towards draining streams. Understanding and modeling the variability of solute concentrations in catchment waters require the identification of the prevailing processes, determining their respective contribution to the observed transformation of substances, and the localization of “hot spots”, that is, the most reactive areas of catchments. For this study, we applied a non-linear variant of the Principle Component Analysis, the Isometric Feature Mapping (Isomap), to a data set composed of 1686 soil solution, groundwater and stream water samples and 16 variables (Al, Ca, Cl, Fe, K, Mg, Mn, Na, NH4, NO3, SO4, total S, Si, DOC, electric conductivity and pH values) from the Lehstenbach catchment in Germany. The aim was (i) to assess the contribution of the prevailing biogeochemical processes to the variability of solute concentrations in water samples taken from soils, in groundwater and in stream water in a catchment and (ii) to identify hot spots at the catchment scale with respect to 16 solutes along different flow paths. The first three dimensions of the Isomap analysis explained 48%, 30% and 11%, respectively, i.e. 89% of the variance in the data set. Scores of the first three dimensions could be ascribed to three predominating bundles of biogeochemical processes: (i) redox processes, (ii) acid-induced podzolization, and (iii) weathering processes. In general, the upper 1 m topsoil layer could be considered as hot spots along flow paths from upslope soils and in the wetland, although with varying extents for the different prevailing biogeochemical processes. Nearly 67% and 97% of the variance with respect to redox processes and acid induced podzolization could be traced back to hot spots, respectively, representing less than 2% of the total spatial volume of the catchment. In contrast, biogeochemical processes in deep groundwater had only minor effects on the biogeochemical turnover in catchment waters. Hot spots with respect to weathering processes along upslope and wetland flow paths could not be quantified due to effects of preferential sampling in soil solution samples. Predominating flow paths and biogeochemical processes crucial for the variability of stream water chemistry differed substantially for three streams but were consistent with presumed mixing ratios.

Evaluation of sampling and sample preparation procedures for the determination of aromatic acids and their distribution in a podzol soil using liquid chromatography–tandem mass spectrometry

In this work the distribution of free and weekly adsorbed aromatic acids (phthalic acid and ten phenolic acids; gallic, p-hydroxybenzoic, salicylic, vanillic, protocatechuic, p-coumaric, syringic, sinapic, ferulic and caffeic acid), which could participate in weathering and soil formation processes, were studied for O, E and B horizons in a podzol soil in central Sweden. For the analysis a simple and rapid quantitative and qualitative liquid chromatography–tandem mass spectrometry method (using gradient elution) was developed with LODs ranging from 5 to 25nM. Different soil solution sampling techniques (tension-lysimeter and soil centrifugation) and soil extraction with either 10mM phosphate buffer (pH7.2) or 50:50 (v/v) 10mM phosphate buffer:MeOH were compared. All eleven acids were found in detectable or trace concentrations. The most abundant aromatic acids were vanillic and phthalic acid with concentrations around 1μM for O and E horizon respectively. Lysimeter samples resulted in the lowest concentrations followed by centrifugation samples. In general, buffer:MeOH extraction resulted in the highest concentrations for the O horizon, likely due to MeOH's ability to compete for hydrophobic sites on soil organic matter (SOM). Then again, pure buffer with its higher ion strength, interfering with the acids electrostatic interactions with clay particles, leads to higher extracted concentrations for the E and B horizons. Since the efficiency of the extraction solutions, to a large extent, depends on the sample properties, a general approach is hard to appoint. However, the extraction of substituted cinnamic acids is in general facilitated by adding MeOH to the extraction solution. The use of statistical methods for the evaluation of the results showed a large and significant difference in aromatic acid concentrations received using different sampling techniques and sample preparations. In fact, sampling methods resulted in higher variations in aromatic acid concentrations than sampled horizon.

Producing Isotopically Enriched Plant, Soil Solution, and Rhizosphere Soil Materials over a Few Hours

There are scientific benefits for using an automated closed steady-state flow 13C (carbon; C) plant–soil labeling system (PSLS) for online recording and adjustment of 13CO2 (carbon dioxide) concentration equivalents to those used by photosynthesis, as compared to widely used uncontrolled open pulse labeling systems. Wheat plants were labeled at four growth stages (four leaves, tillering, late boot, and early dough) with 13CO2 for 2 and 6 h continuously. Analyses of the 13C/12C isotope using isotope ratio mass spectrometry of plant, soil solution, and rhizosphere soil samples showed that the injected 13CO2 was closely correlated with the 13C pools. The labeled 13C root exudates at tillering stage to rhizosphere soil increased from 0.4 ± 0.1 mg 13C pot−1 (four plants) after 2 h to 2.5 ± 1.0 mg 13C pot−1 after 6 h of labeling. The steady-state PSLS permits rapid control and maintenance of 13C by 13CO2 injection, enabling detailed examination of the C budget over short labeling periods.

Concentração de nitrato no perfil do solo fertigado com diferentes concentrações de fontes nitrogenadas

Objetivou-se, neste trabalho, avaliar o efeito da concentração de nitrato de potássio e ureia da água de irrigação no teor de nitrato da solução do solo e do extrato de saturação, em duas profundidades do sistema radicular da bananeira tipo Plátano, cultivar Terra Maranhão fertigada. O experimento conduzido entre janeiro e dezembro de 2008 seguiu um delineamento em blocos casualizados com três repetições em esquema fatorial 2 x 4, em que os tratamentos consistiram no uso de duas fontes de nitrogênio (ureia e nitrato de potássio) sob quatro concentrações (2,7; 4,0; 6,5 e 7,2 g L-1), aplicadas via gotejamento, com três emissores de 4 L h-1 por planta. Amostras de solo e de solução do solo foram colhidas mensalmente em todos os tratamentos nas profundidades de 0,30 e 0,60 m, com determinação em laboratório da concentração de nitrato na solução do solo e no extrato de saturação. Os resultados permitiram concluir que o aumento da concentração do fertilizante nitrogenado da água na fertigação implicou em aumento da concentração do íon nitrato na solução do solo e no extrato de saturação para as duas fontes de nitrogênio aplicadas.

Eficiência do fosfato natural para o arroz irrigado em solo do sul do Brasil

Com o objetivo de avaliar a eficiência do fosfato natural na cultura do arroz irrigado, foi desenvolvido um experimento onde testou-se: a) fontes de fósforo(P) : 1- Superfosfato triplo (SFT); 2- Fosfato natural (FN); e b) Doses de P: 0, 10, 20, 40 e 80 mg kg-1. Arroz da cultivar EMBRAPA 7 "TAIM", foram cultivadas em vasos durante trinta dias. O pH na solução do solo não diferiu entre as doses na mesma fonte. O P na solução aumentou com o acréscimo das doses de P, porém na primeira coleta não diferiu entre as fontes. Na segunda coleta os teores de P foram similares nas diferentes doses para a mesma fonte, diferindo apenas no SFT na dose de 80 mg kg-1. A produção de matéria seca aumentou conforme a dose de P sendo que a dose de 80 mg kg-1 foi superior nas duas fontes. Os teores de P na solução do solo e na planta, a quantidade acumulada de P e a produção de matéria seca do arroz, aumentaram com o acréscimo das doses de P aplicadas ao solo; o fosfato natural apresentou alta eficiência agronômica a partir de doses equivalentes à 40 mg kg-1 de P.

Regulated deficit irrigation, soil salinization and soil sodification in a table grape vineyard drip-irrigated with moderately saline waters

Irrigation with moderately saline waters may provoke soil salinization and sodification. The objectives of this three-year study were (1) to quantify these processes in two seedless table grapevines (Vitis vinifera cvs. Autumn Royal and Crimson) subject to a full irrigation and two regulated deficit irrigations (RDI, irrigated at 80% and 60% of net irrigation requirements from post-veraison till harvest) with 1.7dSm−1 electrical conductivity irrigation waters, and (2) to assess the impact of soil salinization on grapevine's response. Soil samples were taken three times along each irrigation season and soil solution samples were extracted weekly by suction cups. Soil saturation extract electrical conductivity (ECe) and sodium adsorption ratio (SARe) were high in Autumn Royal (4.4dSm−1 and 6.1 (mmoll−1)0.5) and very high in Crimson (7.0dSm−1 and 8.6 (mmoll−1)0.5) due to relatively low leaching fractions (LF) (0.20 in Autumn Royal and 0.13 in Crimson). Soil solution salinity and sodicity were generally higher in the more severe RDI than in the full irrigation treatment. Soil salinity and sodicity generally increased along the irrigation seasons and decreased along the non-irrigation seasons. Salt accumulation or leaching and LF were significantly correlated, so that LF estimates could anticipate the required irrigation depths for soil salinity control. Grapevine yield declined with increases in soil salinity. Leaf Na concentrations were very low (<0.1%), but leaf Cl concentrations were higher and the maximum value of 0.61% measured in the more severe Crimson RDI treatment was within the interval reported as toxic in grapevine. Despite the water saving benefits of drip irrigation in combination with deficit irrigation strategies, its implementation in low-precipitation semiarid areas must be cautiously assessed and monitored because soil salinization and sodification may threaten the sustainability and profitability of these grapevine orchards irrigated with moderately saline waters.

Soil and soil-solution chemistry after burning a clear-felled area in boreal Sweden

In Scandinavian forestry, prescribed burning is carried out to promote biodiversity. This study was initiated to examine how burning of a clear-felled area affected the soil and soil-solution chemistry in a nitrogen-limited coniferous forest in boreal Sweden. The stand was clear-felled and the logging residues were left on site. The harvested area was divided into two parts: one part was burnt within three months after clear-felling while the other part was left as a control. Soil and soil-solution samples were collected before and after felling and burning. In the FH layer, pH and the concentration of K and P tended to increase immediately after burning. Six years later, only small effects on soil chemistry were indicated, but the N concentration in the FH layer appeared lower in the burnt area even after 11 years. In the deep soil solution, the total organic carbon concentration was lower in the burnt area than in the unburnt area. The -N concentration in the burnt area peaked at 0.50 mg l−1 and the mean concentration during the first seven seasons was 0.13 mg l−1. In the unburnt area, the -N concentration peaked at 3.1 mg l−1 and the corresponding mean concentration was 1.0 mg l−1. Although the general level of -N was low in this study, burning largely counteracted the increase in -N concentration that usually follows final felling.

Development of a capillary electrophoresis–mass spectrometry method for small peptides in the soil solution

Small peptides are being investigated for their role in ecosystem cycling and plant uptake of organic N, but little is known of molecular forms in the soil solution. The aim of this study was to develop a capillary electrophoresis–tandem mass spectrometry procedure for profiling small peptides in the soil solution. Capillary electrophoresis–mass spectrometry was capable of separating and detecting a range of small peptide standards. Adequate recovery (>90%) of standard peptides spiked into samples of soil solution indicated that separation and detection were robust and not significantly affected by the sample matrix. The method was applied to samples of soil solution from grassland mesocosms filled with clay-loam soil from an abruptic lixisol. Soil solution (ultrafiltered <3 kDa) contained at least 298 putatively identified peptides with most being smaller than 600 Da. Less than 5% of small peptides contained basic amino acids, which may reflect their preferential adsorption to the soil stationary phase versus peptides comprised of acid or neutral amino acids. Capillary electrophoresis–mass spectrometry of small peptides is robust and has already yielded novel findings with its first proof of concept measurements on the soil solution.

Effects of previous nitrogen fertilization on soil-solution chemistry after final felling and soil scarification at two nitrogen-limited forest sites

Nitrogen (N) fertilization and soil scarification are common measures used in commercial forestry in the boreal zone. This study was performed to investigate how previous N fertilization in two N-limited Scots pine (Pinus sylvestris L.) stands affected the soil-solution chemistry after final felling and also to determine the effect of subsequent soil scarification. Nitrogen had been applied to study plots at different intervals, resulting in total applications of 0, 450, 900, or 1800 kg N·ha−1. Soil-solution samples were collected before and after whole-tree harvesting of the P. sylvestris stand, from undisturbed soil and also after harvesting from soil below furrows, tilts, and areas between furrows created by disc trenching. After harvesting, the K+ concentration was lower at higher N fertilization intensities. No overall effect on the N concentrations was detected. Electrical conductivity and the concentrations of Na+, K+, Mg2+, Ca2+, Cl−, NO3−–N, total N, and total C were all affected by soil scarification. The highest concentrations of these variables were found below tilts and the lowest concentrations below furrows. The experiment was repeated, at a lower monitoring intensity, at a site where the previous total N application amounted to 0 and 450 kg N·ha−1. Here the NO3−–N concentration responded to disc trenching in a similar way to that observed in the main experiment. The study shows that previous N fertilization of N-limited forest does not necessarily affect the soil-solution chemistry significantly after whole-tree harvesting.

Trace element uptake dynamics for maize (Zea mays L.) grown under field conditions

Background and aims The trace element uptake process of plants is a key factor in assessing the risks of trace element build-up in agricultural soils. Scarce information exists on the trace element dynamic uptake of plants grown in the field, especially on those potentially hazardous. In this study, the uptake process of As, Cd, Cu, and Zn in maize plants was quantified and characterized throughout the entire season. Methods Along two seasons, the uptake dynamics of field-grown maize plants in absorbing the soil borne trace elements was examined. Biomass production and the concentration of the elements in plant and soil solution samples were determined. A kinetic model was employed to characterize the uptake by plants. Results The kinetic parameters of the uptake process, maximum cumulative uptake rate, Umax, time to reach 50 % of Umax, tU50, and reciprocal of the uptake rate, bU when followed throughout the season in terms of the plant’s growing degree days remained constant between seasons and were element specific. In spite of the large amount biomass produced, maize plants extracted minute quantities of Cd and As. Increasing cumulative uptake rates of As, Cd, Cu, and Zn from the soil took place primarily in the early half of the growing season when the biomass accumulation was still less than 50 % of the maximum harvested biomass. The element-specific plant uptake factor (PUF), which denote the partition of trace elements between the soil solution and plant phases, decreased following

Dissolution of phosphorus into pore-water flowing through an organic soil

Understanding dissolution and transport of phosphorus (P) from organic soils in agricultural fields and restored wetlands is critical for devising management strategies to mitigate P losses. The objective of this study was to evaluate the dissolution of P in water flowing through the vadose zone-shallow ground water continuum of an organic soil. Three 90cm×50cm×8cm flow cells were uniformly packed with organic soil material from a Ponzer muck (Terric Haplosaprists) collected from an area that had been in agricultural production for at least 30years. The packed flow cells were instrumented with soil solution samplers and platinum-tipped redox electrodes at approximately 5cm below a simulated water table (WT), and in the capillary fringe (CF) at approximately 5 and 20cm above the WT to collect soil solution and monitor the reduction potential (Eh), respectively. Distilled water was continuously supplied at constant rates of 1.2, 2.4, and 3.6Ld−1 to one end, and drained at the other end of the flow cells while maintaining a WT at 12cm above the bottom of the midpoint of each flow cell. Phosphorus concentration in the outflow solution was consistently above the USEPA water quality criteria of 0.1mgL−1. Changes in pore-water velocity did not alter the amounts of P leached within the time frame of the experiment. Dissolved phosphorus concentrations at both 5cm below and 5cm above the WT were significantly higher than at 20cm above the WT. This observation indicated that P that leached out of the flow cells was not only from the saturated zone but also from the lower part of the CF. These results suggest that controlling the height of the WT to limit saturation of P enriched surficial soils, while considering the contribution of the CF, may be an effective management tool for limiting P export from restored wetland sited on former agricultural fields.

Nitrogen and phosphorus leaching in a tropical Brazilian soil cropped with sugarcane and irrigated with treated sewage effluent

There are concerns about groundwater contamination with N and P from fertilizers and other anthropogenic wastes. Use of treated sewage effluent (TSE) for crop irrigation can reduce the use of mineral fertilizers; however, it may add more nutrients into the soil than are necessary for crops, increasing the possibility of leaching. Thus, knowledge of nutrient dynamics in TSE irrigated soils is important for the safe use of this resource. However, the reliability of studies regarding ion leaching is limited due the high propagated variance, as these studies involve independent measurements of variables related to soil and soil solution. The objective of this research was to quantify P and N leaching in a TSE-irrigated Brazilian soil and identify the main causes of variance of this quantification. The experiment consisted of a treatment without irrigation and treatments with TSE irrigation to meet 100% and 150% of the crop water demand (CWD). Soil physical properties and soil water potential gradient were used to calculate internal drainage, and nutrient concentration was measured in soil solution samples taken with ceramic suction cups at a depth of 1m. Variance propagation was calculated by linearization, and the contribution of each variable to the total variance was isolated and quantified. Irrigation with TSE increased N leaching; however, when applied in dosages that met 100% of the CWD, it did not threaten the groundwater quality. P leaching was as low as 100gha−1 and was therefore not an environmental concern. N leaching can be estimated considering the total N input and the rainfall; however, long-term data are needed to improve the accuracy of this estimation. The variance propagation of the soil water potential measurements represented up to 70% of the nitrogen leaching variance.

Impacts of Sampling Dissolved Organic Matter with Passive Capillary Wicks Versus Aqueous Soil Extraction

Quantitative characterization of dissolved organic matter (DOM) in soil and vadose zone solution is needed to interpret mechanisms of nutrient and C cycling as well as bio‐weathering processes. Passive capillary wick samplers (PCaps) are useful for soil solution sampling because they can provide measures of water and associated DOM‐constituent flux in the unsaturated zone, however potential impacts of the wick material on DOM chemical properties has not been investigated yet. We therefore conducted experiments where aqueous soil extracts were transported along PCap fiberglass wicks in flow‐through experiments. Results indicated limited dissolved organic carbon (DOC) sorption and DOM fractionation, and related parameters (total dissolved nitrogen [TDN], DOM fluorescence components) also remained largely unaffected. We note that this experiment does not account for the extent to which soil hydrologic processes may be affected by PCap field installations. However, given that the wicks did not fractionate significantly DOM, we compared field‐based PCap DOM solution collected in situ with laboratory‐based aqueous soil extraction (ASE) of DOM from the same soils to assess differences in DOM quality. Spectroscopic analysis of DOM in ASE solutions showed lower O‐H stretch/carboxlyate band intensity ratios, more pronounced aliphatic C‐H stretching (Fourier Transform Infrared analysis), higher specific ultraviolet‐absorbance (SUVA254) values as well as greater abundance of fluorescence components in the region attributed to fulvic acids. We conclude that difference in molecular properties of DOM derived from laboratory ASE vs. PCap field collection of the same soils is attributable to differential disturbance effects of the two methods of soil solution collection.

Bodenversauerung in den Flächen des Interkantonalen Walddauerbeobachtungsprogramms

Soil acidification in permanent observation plots Soil acidification is followed in Swiss forest observation plots differing in soil chemistry. Soil solution samples from suction cups show clearly increasing soil acidification between 1998 and 2011, although the rate has declined in many cases during the last five years. The most rapid decline is currently observed in plots with medium to high base saturation. Nitrogen addition experiments and time series after thinning out forests confirm the important role of nitrogen input and nitrate leaching for the acidification process. It is suggested that the slowdown of acidification since 2003 has several reasons: reaching of the aluminium buffer range in the very acidic plots, decreased nitrate leaching in a series of dry years, reduction of acid deposition.

Soil and hydrologic effects on fate and horizontal transport in the capillary fringe of surface-applied nitrate

Substantial horizontal solute transport has been demonstrated to occur in the capillary fringe (CF) above a flowing ground water, yet the importance of the CF for solute movement has generally been ignored. This study was conducted to evaluate the fate and horizontal transport of surface-applied nitrate (NO3−) in the CF under simulated hydrologic conditions that varied flow rates. Two soils of different organic carbon content were packed in separate 240-cm long, 60-cm high and 25-cm thick flow cells. A simulated water table (WT) was established at 20cm above the bottom of each flow cell and different pore-water velocities across the flow cell were simulated while a solution containing NO3− and bromide (Br−) was continuously applied over a small area on the surface of the soil in the flow cell. Soil solution samples were collected from two depths below the WT and two depths within the CF above the WT at four locations along the flow cell. Subsurface horizontal transport of surface-applied NO3− tended to occur exclusively in the CF as the pore-water velocity was increased. In the flow cell with soil having a small amount of organic carbon (0.3gkg−1), normalized concentration of NO3− and Br− remained very comparable at all monitoring locations above and below the WT. Nitrate loss via denitrification in this case was not observed as conditions were oxidizing. In flow cells with soils having an organic carbon content of 35gkg−1, some Br− was detected below the WT while NO3− was essentially absent. Conditions below the WT favored NO3− loss via denitrification as reflected by very low redox potentials (<250mV). These results suggest that collection of samples from the CF should be considered when monitoring subsurface fate and transport of surface-applied NO3− in locations with laterally moving shallow ground water.

Cadmium Migration and Distribution Process

The significant pollution accidents which not only threaten public health and public property safety, but also bring major disaster, have become the world concerning environmental problems. The migration process and feature of CdCl2 in the vertical and horizontal profiles of soil were studied by the stimulating experiment to present the theory for the treatment of significant pollution accident. The column leaching device was taken to simulate the vertical and horizontal migration of CdCl2 in the soil profile under two-phase rainfall during 16 days. The portable manual control negative pressure pump was taken to extract soil solution sample and the CdCl2concentration was determined by the atomic absorption spectrophotometer. Results showed that during the whole experiment, the obvious horizontal and vertical migration features of CdCl2appeared. The CdCl2covered the whole horizontal profile in 0.5 h and the whole vertical profile in 146 hours. The relative variation rate of CdCl2in the different depth of bulk showed that the rapid passing time differed in the different depths. The simulating device used in this paper could well investigate the vertical and horizontal distribution and migration of contaminant. Under the condition of greater rainfall, the CdCl2gave priority to the horizontal runoff in the surface soil, followed by the vertical migration.

Modeling Cadmium Transport in Neutral and Alkaline Soil Columns at Various Depths

Human health has been potentially threatened by cadmium (Cd) contained in sewage irrigation water. Previous studies of Cd transport in soils were mainly conducted using small soil cores with pH values less than 6. The objectives of this study were to determine the parameters of the convection-dispersion equation (CDE) for Cd transport in relatively larger columns with neutral and alkaline soils, and to investigate the parameters' variability with depth. The soil columns were 50 cm in length and 12.5 cm in diameter. Ceramic suction lysimeters were buried at depths of 2.5, 7.5, 17.5, 27.5, and 37.5 cm to abstract soil solution. Cd concentration in the soil solution samples were subsequently analyzed to obtain breakthrough curves (BTCs). Equilibrium and nonequilibrium models in CXTFIT program were used to estimate parameters of the CDE. The results suggested that both equilibrium and non-equilibrium models performed well in modeling Cd transport. The hydrodynamic dispersion coefficient (D) ranged from 0.18 to 10.70 cm2 h−1, showing large differences among different depths. The retardation factor (Rd) ranged from 25.4 to 54.7 and the standard deviation of Rd value was lower than 30% of the mean value. Precipitation coefficient (Rp) decreased consistently with increasing depth, varying from 1.000 × 10−10 to 0.661 h−1. Sensitivity tests showed that D was less sensitive than Rd. These results would be helpful in understanding the transport and retention of Cd in non-acidic soils.

Improving the precision of estimating nitrate (NO3 −) concentration in seepage water of forests by prestratification with soil samples

Nitrate (NO3−) concentrations in seepage water (\( {\text{SW}}_{{{\text{NO}}_{ 3} }} \)) of N saturated forests regularly show a high spatial variability. As seepage water sampling is expensive, most studies use small numbers of soil solution samplers. This implies high uncertainties of calculated concentration and flux data. At the N saturated Hoglwald site we investigated, whether a preselection of seepage water sampling places by a prior intensive soil sampling can improve the precision of the estimation of \( {\text{SW}}_{{{\text{NO}}_{ 3} }} \). We implemented 121 suction cups and analyzed the soil, removed with the soil auger during installation at the sampling depth of 40 cm, for water extractable NO3−. The NO3− content in soil (\( {\text{Soil}}_{{{\text{NO}}_{ 3} }} \)) was calculated and \( {\text{SW}}_{{{\text{NO}}_{ 3} }} \) was measured. With this data set we tested the correlation between \( {\text{Soil}}_{{{\text{NO}}_{ 3} }} \) and \( {\text{SW}}_{{{\text{NO}}_{ 3} }} \) and simulated a random selection of sampling places (RS) as well as a prestratified sampling based on \( {\text{Soil}}_{{{\text{NO}}_{ 3} }} \) (PS). With bootstrap statistics different numbers of replications (n) were tested and the 95% confidence interval (95% CI) was used to compare RS with PS. Highly significant correlations between \( {\text{Soil}}_{{{\text{NO}}_{ 3} }} \) and \( {\text{SW}}_{{{\text{NO}}_{ 3} }} \) were found (r = 0.99***). It was even possible to calculate \( {\text{SW}}_{{{\text{NO}}_{ 3} }} \) from \( {\text{Soil}}_{{{\text{NO}}_{ 3} }} \). Here best results where achieved when \( {\text{Soil}}_{{{\text{NO}}_{ 3} }} \) was determined from field moist soil samples. With PS the accuracy of the mean value of \( {\text{SW}}_{{{\text{NO}}_{ 3} }} \) improved considerably. To achieve a 95% CI lower than ±10%, 250 suction cups would be needed for RS compared to n = 20 for PS. Even 6 months after implementation, precision of mean \( {\text{SW}}_{{{\text{NO}}_{ 3} }} \) was higher for suction cup places selected with the PS method. A detailed description is given, how these findings may be applied in studies and monitoring programs focusing on NO3− leaching in forest ecosystems.

Solid-solution partitioning of arsenic (As) in the paddy soil profiles in Chengdu Plain, Southwest China

To predict the long-term behavior of arsenic (As) in soil profiles, the solid-solution partitioning of As was studied in four paddy soil profiles obtained from agricultural areas in Chengdu Plain, Southwest China. Paddy soil profile samples were collected and soil solution samples were extracted. Total As contents in soil solution and soil solid were analyzed, along with the soil solid phase properties. The As in soil solution was significantly higher in the upper layer (0–20 cm) and had a definite tendency to decrease towards 40 cm regardless of the sampling locations. When the concentration of arsenic in soil solution decreased, its content in solid phase increased. Field-based partition coefficient (Kd) for As was determined by calculating the ratio of the amount of As in the soil solid phase to the As concentration in the soil solution. Kd values varied widely in vertical samples and correlated well with soil pH, total organic carbon (TOC) and total As. The results of this study would be useful for evaluating the accumulation trends of arsenic in soil profiles and in improving the management of the agricultural soils.

Imidacloprid Movement in Soils and Impacts on Soil Microarthropods in Southern Appalachian Eastern Hemlock Stands

Imidacloprid is a systemic insecticide effective in controlling the exotic pest (hemlock woolly adelgid) in eastern hemlock () trees. Concerns over imidacloprid impacts on nontarget species have limited its application in southern Appalachian ecosystems. We quantified the movement and adsorption of imidacloprid in forest soils after soil injection in two sites at Coweeta Hydrologic Laboratory in western North Carolina. Soils differed in profile depth, total carbon and nitrogen content, and effective cation exchange capacity. We injected imidacloprid 5 cm into mineral soil, 1.5 m from infested trees, using a Kioritz soil injector. We tracked the horizontal and vertical movement of imidacloprid by collecting soil solution and soil samples at 1 m, 2 m, and at the drip line from each tree periodically for 1 yr. Soil solution was collected 20 cm below the surface and just above the saprolite, and acetonitrile-extractable imidacloprid was determined through the profile. Soil solution and extractable imidacloprid concentrations were determined by high-performance liquid chromatography. Soil solution and extractable imidacloprid concentrations were greater in the site with greater soil organic matter. Imidacloprid moved vertically and horizontally in both sites; concentrations generally declined downward in the soil profile, but preferential flow paths allowed rapid vertical movement. Horizontal movement was limited, and imidacloprid did not move to the tree drip line. We found a negative relationship between adsorbed imidacloprid concentrations and soil microarthropod populations largely in the low-organic-matter site; however, population counts were similar to other studies at Coweeta.