Comparison of field techniques for sampling soil solution in an upland peatland

Abstract. Results from recent studies of peatland biogeochemistry suggest that appropriate soil water sampling techniques are required in order to advance our understanding of peatland soil systems. In a comparative field experiment, concentrations of inorganic solutes and dissolved organic carbon (DOC) were measured in soil water extracted at a depth of 10 cm beneath the surface of deep peat by three techniques: zero-tension (z-t) lysimeters, PTFE suction samplers, and polysulfone suction samplers. The majority of solute concentrations were broadly similar, but mean concentrations of silicon, DOC, iron and aluminium in water extracted by z-t lysimeters and PTFE samplers were in ratios of 1:5; 1:2; 1:5 and 1:3 respectively. Mean conductivity and concentrations of chloride and hydrogen ion were significantly larger in the z-t lysimeter samples, which had sodium, potassium and magnesium to chloride ratios that were very similar to local rainfall. The z-t lysimeters appeared to sample macropores preferentially, while the suction samplers collected micropore water.     

Soil-solution chemistry in a low-elevation spruce-fir ecosystem,Howland, Maine

Soil solutions were collected monthly by tension and zero-tension lysimeters in a low-elevation red spruce stand in east-central Maine from May 1987 through December 1992. Soil solutions collected by Oa tension lysimeters had higher concentrations of most constituents than the Oa zero-tension lysimeters. In Oa horizon soil solutions growing season concentrations for SO₄, Ca, and Mg averaged 57, 43, and 30 μmol L^?1 in tension lysimeters, and 43, 28, and 19 μmol L^?1 in zero-tension lysimeters, respectively. Because tension lysimeters remove water held by the soil at tensions up to 10 kPa, solutions are assumed to have more time to react with the soil compared to freely draining solutions collected by zero-tension lysimeters. Solutions collected in the Bs horizon by both types of collectors were similar which was attributed to the frequency of time periods when the water table was above the Bs lysimeters. Concentrations of SO₄ and NO₃ at this site were lower than concentrations reported for most other eastern U.S. spruce-fir sites, but base cation concentrations fell in the same range. Aluminum concentrations in this study were also lower than reported for other sites in the eastern U.S. and Ca/Al ratios did not suggest inhibition of Ca uptake by roots. Concentrations of SO₄, Ca, K, and Cl decreased significantly in both the Oa and Bs horizons over the 56-month sampling period, which could reflect decreasing deposition rates for sulfur and base cations, climatic influences, or natural variation. A longer record of measured fluxes will be needed to adequately define temporal trends in solution chemistry and their causes.     

Comparison of soil water chemistry and sample size requirements for pan vs tension lysimeters

A study was conducted to compare soil leachate chemistry and determine sample size requirements for tension vs pan (zero-tension) lysimeters. Analyses were performed on an annual and seasonal basis for one year of data collected at Pea Vine Hill, a forested site in southwestern Pennsylvania. On an annual basis, SO₄ ^?2, Ca⁺², Mg⁺², Mn⁺², K⁺ and specific conductance were significantly higher in tension lysimeter samples but no chemical species were significantly higher in pan lysimeters. Seasonal comparisons indicated chemical differences between lysimeter types were variable with more significant deviations present during wet periods. Nearly all significant seasonal differences were comprised of higher concentrations in tension compared to pan lysimeters. Disparities in leachate chemistry between lysimeter types were ascribed to different sources of water collected by the instruments especially during wet periods. Sample size requirements were calculated for two biweekly periods for each lysimeter type at three confidence levels. Based upon calculated sample demands, pan lysimeter soil leachate chemistry could be characterized with fewer samples than tension lysimeters. Less than .30 samples were generally necessary for pan B-horizon lysimeters at the 70% confidence level. Sample requirements were usually unreasonable at higher confidence levels.     

Simulation of water flow and solute transport in free-drainage lysimeters and field soils with heterogeneous structures

Lysimeters are valuable for studying the fate and transport of chemicals in soil. Large‐scale field lysimeters are used to assess pesticide behaviour and radionuclide transport, and are assumed to represent natural field conditions better than laboratory columns. Field lysimeters are usually characterized by a free‐draining lower boundary. As a result, the hydraulic gradient is disrupted, and leachate cannot be collected until the bottom of the lysimeter becomes saturated. We compared heterogeneously structured, free‐drainage lysimeters and field soils with respect to water flow and solute transport. Numerical simulations were carried out in a two‐dimensional heterogeneous sandy soil under unsaturated water flow conditions with the CHAIN_2D code. Three different soil structures (isotropic, horizontal, and vertical) were generated, and Miller–Miller similitude was used to scale the hydraulic properties of the soil. The results showed that ponding occurs at the bottom of the lysimeter for the three soil structures and that it occurred faster and was more pronounced with the vertical structure (preferential flow effect). Breakthrough curves of a conservative solute (bromide) showed that solutes are moving faster in the field than in the lysimeters. Fewer differences between lysimeters and field soils were found with the horizontal soil structure than with the isotropic and vertical structures.     

The solubility of aluminium in two Swedish acidified forest soils: An evaluation of lysimeter measurements using batch titration data

This paper presents aluminium (Al)-solubility data for two acid forest soils (Inceptisol and Spodosol), obtained in connection with lysimeter measurements (tension-cup and zero-tension lysimeters) and batch equilibrium experiments. The solubility of Al obtained in the batch experiments was used as a reference to test whether Al³⁺in soil solutions collected by the lysimeters was in equilibrium with secondary forms of solid-phase Al (Al(OH)₃or organically bound Al). The relation between pH and Al³⁺activity found for the zero-tension lysimeter solutions collected from the Inceptisol agreed well with that obtained in the batch experiment. This suggests that Al³⁺in the lysimeter solutions were in, or close to, equilibrium with the solid phase, whether this was organically bound Al (A horizon) or an Al(OH)₃phase (B horizon). For the tension-cup lysimeters, solutions obtained from the Inceptisol B and Spodosol Bs1 horizons were generally close to equilibrium with respect to secondary solid-phase Al (apparently Al(OH)₃; average ion activity product was 10^9.3and 10^8.8, respectively), whereas the Inceptisol A and Spodosol Bh solutions were not. The Al solubility in Inceptisol A and Spodosol Bh horizons was consistently higher than that obtained in the batch equilibrium experiment, indicating that the sampled solution partly originated from the underlying horizons. Thus, tension-cup lysimeters should be used with care in soils (or in parts of soil profiles) having steep solute concentration gradients because the soil volume from which the sample is drawn with this lysimeter type seems to be poorly defined.     

Apparent Cation – Exchange Equilibria and Aluminium Solubility in Solutions Obtained from Two Acidic Forest Soils by Centrifuge Drainage Method and Suction Lysimeters

Apparent cation–exchange equilibria and solubility of aluminium were analysed in two acidic forest soils: a Cambisol and a Cambic Podzol. Soil solution was obtained by a centrifuge drainage method from fresh soil samples and with suction lysimeters. The total positive charge of the measured cations as well as the concentrations of the cations were generally much larger in the centrifugates than in the lysimeter solutions, which implies that total charge of soil solution is larger in small pores than in large pores. Hydrogen ion in particular was concentrated in some of the centrifugates, the ratio centrifugate:lysimeter solution being over 10. The total positive charge of the measured cationsdecreased with increasing depth with both methods. Theapparent cation–exchange coefficients K _H-Ca, K _Al-Ca, and K _K-Ca had different values in the methods, and the variation in the cation exchange coefficients was larger in the lysimeter method than in the centrifuging method. The coefficient K _Mg-Ca had similar values in both methods. The results imply that mobile solution could not have cation–exchange equilibria with bulk exchangeable cations in the soils, although solution in small pores seemed to have equilibria. Solubility of Al did not follow the solubility of an Al(OH)₃ phase in the centrifugates, and the centrifugates with a H⁺ activity larger than 60 μmol were undersaturated with respect to the gibbsite. Solubility of Al was between gibbsite and amorphousAl(OH)₃ in the lysimeter solutions. Differencesbetween the centrifugates and the lysimeter solutionsin the ion concentrations and in the apparent chemicalequilibria were similar for both soils studied.     

Partitioning of Hg Between Solid and Dissolved Organic Matter in the Humus Layer of Boreal Forests

The mobility of mercury (Hg) deposited on soils controls the concentration and toxicity of Hg within soils and in nearby streams and lakes, but has rarely been quantified under field conditions. We studied the in situ partitioning of Hg in the organic top layer (mor) of podsols at two boreal forest sites differing in Hg deposition and climatic regime (S. and N. Sweden, with pollution declining to the north). Soil solution leaching from the mor layer was repeatedly sampled using zero-tension lysimeters over 2 years, partly in parallel with tension lysimeters. Concentrations of Hg and dissolved organic carbon (DOC) were higher while pH was lower at the southern site (means ± SD: Hg?=?44?±?15 ng L^?1, DOC?=?63.0?±?31.3 mg L^?1, pH?=?4.05?±?0.53) than at the northern site (Hg?=?22?±?6 ng L^?1, DOC?=?41.8?±?12.1 mg L^?1, pH?=?4.28?±?0.43). There was a positive correlation over time between dissolved Hg and DOC at both sites, even though the DOC concentration peaked during autumn at both sites, while the Hg concentration remained more constant. This correlation is consistent with the expected strong association of Hg with organic matter and supports the use of Hg/C ratios in assessments of Hg mobility. In the solid phase of the overlying O_f layer, both Hg concentrations and Hg/C ratios were higher at the southern site (means ± SD: 0.34?±?0.06 μg g^?1 dw and 0.76?±?0.14 μg g^?1 C, respectively) than at the northern site (0.31?±?0.05 μg g^?1 dw and 0.70?±?0.12 μg g^?1 C, respectively). However, concentrations in the solid phase differed less than might be expected from the difference in current atmospheric input, suggesting that the fraction of natural Hg is still substantial. At both sites, Hg/C ratios in the upper half of the mor layer were only about two thirds of those in the lower half, suggesting that the recent decrease in anthropogenic Hg deposition onto the soil is offset by a natural downward enrichment of Hg due to soil decomposition or other processes. Most interestingly, comparison with soil leachate showed that the average Hg/C ratios in the dissolved phase of the mor layers at both sites did not differ from the average Hg/C ratios in the overlying solid organic matter. These results indicate a simple mobilisation with negligible fractionation, despite differences in Hg deposition patterns, soil chemistry and climatic regimes. Such a straight-forward linkage between Hg and organic matter greatly facilitates the parameterisation of watershed models for assessing the biogeochemical fate, toxic effect and critical level of atmospheric Hg input to forest soils.     

An experimental and numerical study on flow and transport in a field soil using zero-tension lysimeters and suction plates

Zero-tension lysimeters are widely applied to study the fate of chemicals in the subsurface environment. However, conditions in lysimeters differ from the field situation, because local saturation is required at the lower boundary to collect leachate. The objective was to characterize the influence of the lower boundary on the flow and transport behaviour of bromide observed in six 1.2-m-long lysimeters and in the field by 30 suction plates installed at 1.2-m depth, which were operated with a time-variable suction equal to the ambient soil water potential. A bromide pulse was applied at the bare surface of a silty soil in autumn 1997 and monitored for 2.5 years. The mean leachate flux was 0.98 mm day⁻¹ for the lysimeters versus 0.66 mm day⁻¹ for the suction plates. The lysimeters had a slightly slower effective mean pore-water velocity, expressed as transport distance per unit of leaching depth, and exhibited more solute spreading than the suction plates. Numerical simulations revealed that the amount of water collected with the suction plates was sensitive to the hydraulic conductivity of the plates. The spatial variability in hydraulic properties in the model explained the observed variability in cumulative leachate, at least qualitatively. The arrival time and spreading of the breakthrough curves (BTCs) were well described by the simulations in the lysimeters, but were underestimated in the suction plates. Preferential flow through macropores, which is not an effective carrier for bromide, might be the reason for this discrepancy. Molecular diffusion contributed significantly to solute spreading and enhanced lateral mixing. Both the experiments and the simulations revealed that the dispersivity derived from BTCs is significantly influenced by the observation method and experimental conditions.     

Comparison of chemical composition of soil solutions collected by zero-tension plate lysimeters with those from ceramic-cup lysimeters in a forest soil

We analysed the chemistry of solutions collected from soil by zero-tension plate lysimeters and cup lysimeters connected to a constant suction (600 hPa) under Douglas fir in the Beaujolais mountains (France). The chemistry of zero-tension lysimeters' (ZTL) and tension lysimeters' (TL) solutions differed enormously: TL solutions were most concentrated in Si, NH₄-N, NO_3--N, Cl^?, Mg²⁺ and A1³⁺ and TOC, whereas Ca²⁺ and K⁺ concentrations were greater in ZTL solutions. Organic matter (OM) greatly influenced the solution chemistry in both ZTL and TL. The chemistry of ZTL solutions was affected mainly by OM mineralization in the forest floor and upper soil horizon, and that of TL solution seemed to be related to destabilization of humified compounds under the new vegetation. Nitrification was important: residual nitrification led to excess protons neutralized in weathering or ion exchange reactions, mobilized cations, mainly A1³⁺. Selectivity coefficients calculated both for ZTL and TL solutions formalized the differences between the two types of solutions. Nevertheless, these coefficients remained most often within the same order of magnitude indicating relations between them. Solutions from the two devices provided different information and should not be used for the same objectives. Solutions from ZTL are suited for ecosystem input-output budgets, whereas TL solutions are more useful when equilibrium between the solution and solid phase or when plant nutrition are considered.     

A comparison of water flux measurements: passive wick‐samplers versus drainage lysimeters

Quantification of soil water flow is a prerequisite to accurate prediction of solute transfer within the unsaturated zone. The monitoring of these fluxes is challenging because the results are required to answer both scientific and practical questions regarding protection of groundwater, sustainable management of agricultural, forestry, mining or set‐aside industrial areas, reducing leachate loss from landfills or explaining the fate of environmentally harmful substances. Both indirect and direct methods exist for estimating water‐flux rates and have been used with varying success. In Europe, the use of direct lysimetry methods for measuring water and solute fluxes in soils has increased in recent years. This technique ensures reliable drainage data, but requires relatively large investment and maintenance expenses. Other research groups, especially in the USA, have developed alternative techniques. In this paper we compare the functioning of a passive‐wick sampler, especially the deep‐drainage meter type (DDM), with two different types of drainage lysimeters (weighing and non‐weighing) under field conditions in Germany for the measurement period from May 2004 until April 2009. The study showed that under sandy soil conditions no significant differences occurred between the measurements from DDM and both drainage lysimeter types. Only in periods with increased precipitation was there a tendency of drainage over‐estimation by the DDM in comparison with the lysimeters tested. For longer periods, no significant differences in the amount of drainage or the pattern of drainage formation were found between weighing and non‐weighing gravitation lysimeters. The practical use of DDMs is restricted because the groundwater level must be >2 m from the soil surface. Suggestions are made for the technical improvement of the DDM as well as the testing of the device with more cohesive soils.     

Barley growth in coal liquid and diesel liquid fuels from coal and oil: A comparison of potential toxic effects on Barley

The production of new liquid fuels from coal creates the potential for environmental releases of new products and waste materials via spills or leaching of material from waste storage areas. The chemical composition of these products and waste materials suggests possible toxic effects upon exposed plants and animals. In this study, barley was grown in field lysimeters containing three concentrations (0.07, 0.74, 7.421 m^?2 equivalent to 80, 800, and 8000 gal/acre, respectively) of a sample product blend of Solvent Refined Coal (SRC) heavy and middle distillates. Three methods of soil amendment simulated possible spill clean-up alternatives: adding the coal liquid as a surface layer, as a subsurface layer covered by uncontaminated soil, or intermixed with the top 1 dm of soil. To permit comparison of the coal liquid with familiar commercial material, the study protocol was followed simultaneously in lysimeters amended with # 2 diesel fuel. Statistically significant reductions in grain yield were observed for both the SRC and diesel materials for all methods of soil amendment at concentrations equivalent to 0.74 and 7.421 m^?2, and for the SRC material only when mixed with soil at a concentration equivalent to 0.071 m^?2. Where differences between fuel types were observed, the coal liquid was consistently more toxic.     

Bioavailability of DOC in leachates, soil matrix solutions and soil water extracts from beech forest floors

The biodegradability of dissolved organic carbon (DOC) in different fractions from the forest floor was studied. Soil leachate (SL, the soil solution in macropores which is freely drained from forest floor after rainfall), the soil matrix solution (SMS, the soil solution in meso-/micropores of the soil matrix), and soil water extracts (SWE) from two different beech forest floors were compared. Zero-tension and tension lysimeters were used to collect SL and SMS, respectively. Loss of DOC (during 21 days) and respiration of CO₂-C (during 7 days) were used as conventional measures of the availability of DOC. Bacterial production, measured using the leucine incorporation technique, and bacterial growth efficiency were also estimated. All methods were used to study differences in biodegradability between plots with and without ground flora (Deschampsia flexuosa or Anemone nemorosa) and different type of forest floor (with an organic (O) horizon or a mull (A) horizon). There were no differences in bioavailability of DOC from soil solutions extracted from plots with and without ground flora. The bioavailability of DOC in the different collected soil solutions varied, however. DOC in SWE was the most available, with a mean of 39% of DOC-loss in 21 days, and 18% of DOC being respired in 7 days. DOC in soil matrix solution was the least available of the soil solutions (7% respired), significantly less than DOC in soil leachate (11% respired). The methods measuring biodegradation of DOC, DOC-loss and CO₂-C respiration gave similar results and were comparable to bacterial production and bacterial growth efficiency, with the exception of SWE from the O-horizon at the D. flexuosa site, which had low bacterial production and bacterial growth efficiency, indicating a limitation of the bacterial growth. This study is one of the first to use bacterial production and bacterial growth efficiency for measuring bioavailability in terrestrial environments, giving an extra dimension for the process of biodegradation of DOC.     

Comparisons of methods for measuring the leaching of mineral nitrogen from arable land

Comparisons were made between 1988 and 1991 to evaluate three methods of estimating the leaching of mineral nitrogen (N) from unstructured freely draining sandy loam and loamy sand soils. The studies compared the drainage patterns and quantities of N (almost exclusively nitrate) leached from monolith lysimeters with those estimated from ceramic suction cups and soil core extracts. The latter two methods gave direct measurements of the mineral N concentrations in drainage, but required an estimate of the drainage volume calculated from meteorological observations and evapotranspiration equations to give total N leached. A bromide tracer was also used to confirm conclusions from nitrate leaching studies. There was a delay in the onset of drainage from free draining lysimeters because they lack the subsoil matric potential of field soils. However, total annual drainage measured by lysimeters or calculated from meteorological observations was similar, providing that return to field capacity was correctly identified in the field soil. During the first year there were discrepancies between methods which were attributed to soil disturbance during lysimeter and/or ceramic cup installation. In the second and third years of the experiment, estimates of N leaching losses using the lysimeters and ceramic cups were in good agreement. Nitrate concentrations in soil solution at a depth of 130 cm measured from soil core extracts were smaller than found by the other methods during the second year and the peak concentrations were significantly different (P<0.05). However, total overwinter N leached was not significantly different. Thus, while lysimeters and cups can be used to quantify leaching losses on unstructured, free draining soils if used correctly, the use of soil core extracts is questionable.     

Variability and relationships between Pb,Cu, and Zn concentrations in soil solutions and forest floor leachates at heavily polluted sites

Seasonal variability of Cu, Pb, and Zn concentrations in litter leachates and soil solutions was examined in an afforested zone surrounding a copper smelter in SW Poland. Litter leachates (with zero‐tension lysimeters) and soil solutions (with MacroRhizon suction‐cup samplers, installed at a depth of 25–30 cm) were collected monthly at three sites differing in contamination levels in the years 2009 and 2010 (total Cu: 2380, 439, and 200 mg kg^–1, respectively). Concentrations of Cu in the litter leachate were correlated with dissolved organic C (DOC), whereas Zn and Pb were mainly related to leachate pH. Metal concentrations in the soil solution were weakly influenced by their total content in soils and the monthly fluctuations reached 300, 600, and 700% for Cu, Pb, and Zn, respectively. Metal concentrations in soil solutions (Cu 110–460 μg L^–1; Zn 20–1190 μg L^–1; Pb 0.5–36 μg L^–1) were correlated with their contents in the litter leachates. Chemical speciation, using Visual Minteq 3.0, proved organically‐complexed forms even though the correlations between metal concentrations and soil solution pH and DOC were statistically insignificant. The flux of organically‐complexed metals from contaminated forest floors is believed to be a direct and crucial factor affecting the actual heavy metal concentrations and their forms in the soil solutions of the upper mineral soil horizons.     

Effects of Chronic Nitrogen Amendments on Production of Dissolved Organic Carbon and Nitrogen in Forest Soils

Chronic N deposition has been hypothesized to affect DOC production in forest soils due to the carbon demand exerted by microbial immobilization of inorganic N. We tested this hypothesis in field experiments at the Harvard Forest, Petersham, Massachusetts, USA. During four years of sampling soil solution collected beneath the forest floor in zero-tension lysimeters, we observed little change in DOC concentrations (10-30% increase, not statistically significant) associated with elevated N inputs, but did observe significant increases in DON concentrations. Both DOC and DON varied seasonally with highest concentrations in summer and autumn. Mean DON concentrations increased 200-300 % with the highest rate of inorganic N fertilization, and concentrations of DON were highest in samples with high inorganic N concentrations. We conclude that the organic chemistry of soil solution undergoes qualitative changes as a result of long-term N amendment at this site, with small changes in DOC, large increases in DON, and a decline in the C:N ratio of dissolved organic matter.     

土壤深度对土磷素淋失的影响

利用渗漏池设施,研究了冬小麦-夏玉米轮作条件下不同土壤深度对土磷素淋失的影响。种植8季作物结果表明,对深度小于80 cm 的渗漏池,淋出土体的累积渗滤液量和累积全磷量随化学磷肥施用量的增加而减少; 随土层深度的增加,淋出土体的渗滤液和磷量均减少,且二者的减少率都很接近,表明磷素淋失主要受通过土体的土壤水分控制。相对于深度小于80 cm的土层,供试土壤的粘化层有效地减少了土壤渗滤液和磷素淋失。各深度渗漏池渗滤液中的磷以可溶态为主,约占全磷的70%左右,颗粒磷约占30%。合理施肥并加强水分管理是土区减少磷素向土壤深层迁移的有效手段。     

The phosphorus composition of soil solutions and soil leachates: Influence of soil:solution ratio

Compositional differences between soil solutions obtained by different methods have frequently been reported; variations in the soi1: solution ratio may explain these results. In this study we compared the amount and composition of phosphorus (P) in soil leachates and soil solutions from a temperate grassland soil in northeast Scotland and determined the influence of soi1:solution ratio on P fractions in soil water extracts. Leachates were collected from intact soil cores over 6 months, the cores were then destructively sampled, and soil solutions obtained by centrifuging. Molybdate reactive P (MRP) represented 71% of the total dissolved P (TDP) in soil leachates but only 54% in soil solutions. The MRP component in soil water extracts increased from 71% to 92% as the soi1:solution ratio increased from 1:15 to 1:15·4, while the dissolved organic P (DOP) component decreased from 26% to 6%. As the soil:solution ratio increased the amount of MRP extracted increased; by contrast the amount of DOP and dissolved condensed P (DCP) extracted remained constant. While the MRP component is regulated by soil sorption processes, the supply and amount of DOP and DCP is probably related to biological activity. Dissolved organic carbon (DOC) extracted at wide soi1:solution ratios contained a smaller proportion of P than that extracted at narrower ratios. The results indicate differences in the behaviour of P fractions in the soil at various soi1:solution ratios and that these are reflected in the P composition of soil solution and leachate.     

Measuring phosphorus fluxes through the root zone of a layered sandy soil: comparisons between lysimeter and suction cell solution

Chemical and physical processes govern the extent to which phosphorus dissolved from the plough layer is retained by or leached from the subsoil. The adsorption capacity of deeper layers, the velocity of solution flux and the amount of soil volume in contact with the leaching soil solution are important determining factors. Soil solution from 90-cm depth of a layered sandy soil, sampled over a 3-year period with teflon suction cells, was systematically lower in P content than soil solution sampled with free drainage lysimeters from the same depth. On average 4.6 times as much inorganic P and twice as much organic P was found in lysimeter solutions. Determination of apparent equilibrium solution concentrations of phosphate was performed by means of a series of batch experiments with soil and soil solution of varying initial P content. The results indicated that the suction-cell solution was close to equilibrium with soil from the 90-cm layer. Rhodamine dye was applied, and flow paths of soil solution observed. Preferential flow was initiated from layers of finer texture overlying layers of coarser texture. On the basis of these observations it is concluded that suction cells give the best representation of stagnant soil solution, whereas lysimeters give a better representation of mobile soil solution.     

Effect of extraction techniques on soil pore‐water chemistry

Abstract

The retention of contaminants in soil and overburden is often estimated using a solid/liquid partition coefficient, Kd, which lumps all the processes into an empirical value. Determination of this value in unsaturated porous media requires the separation of the pore water from the solid phase. Soil pore‐water recovery and composition were investigated in three chemically and texturally different mineral soils and one organic soil. The removal of pore water was achieved through centrifugation at low (1000 to 2500 rpm) and ultra (10,000 to 20,000 rpm) speeds, ceramic plate extraction and immiscible displacement. Pore‐water recovery was highest using ceramic plate extraction and lowest with displacement. Pore‐water quality was not affected by centrifugation time. However, the pore‐water concentrations of F, Cl, NO₃, Fe, and Na suggest that the effect of centrifuge speed on the element or ion of interest should be determined prior to extraction. Ceramic plates retained both cations and anions, and the immiscible displacent depressed the pH of the soil slurry affecting the pore‐water composition. Comparisons between distilled water extracts, standardized to field capacity moisture, and the centrifugate for a sand and an organic soil indicated that with low solid/liquid ratios, pore‐water concentrations are influenced by dissolution or desorption. Therefore, Kd values based on centrifuged pore water will be lower than those based on extraction/ desorption.     

Potential leaching of elements in three Danish Spruce forest soils

On three localities in Denmark, all with 40 to 50 yr old Norway spruce plantations, but different soil chemistry, ion balance studies have been implemented in 1983. The annual variations in soil water concentrations of cations and anions are described and the potential annual leaching fluxes are determined by means of zero-tension percolation lysimeters at 2 depths (A- and B-horizon). Leaching of A1 and and heavy metals was much more severe on the acidic sites, whereas especially Ca was leached from the nutrient rich site. In parallel with the high concentrations of Al and heavy metals, great needle loss was observed on the two acidic sites. The maximum leaching from the A-horizon was obtained either in the late summer, associated with the effluent of organic material, or in the winter due to large amounts of percolation water. Apart from low Ca and kin levels of one of the sites, the findings from the two acidic localities were comparable to similar studies in Sweden.