Potential of Tamarix africana and other halophyte species for phytostabilisation of contaminated salt marsh soils

Purpose

Salt marsh plants are colonising wastes from a steel plant deposited on the Coina River Banks posing a potential contamination risk to the Tagus estuary ecosystem. The objectives of this study were to assess the uptake, accumulation and translocation of hazardous elements/nutrients in three spontaneous halophytic species, to evaluate the capacity of Tamarix africana to stabilise a contaminated salt marsh soil, and to evaluate the ecotoxicity of the pore water and elutriates from phytostabilised soils.

Materials and methods

The work comprises the following: fieldwork collection of soil samples from Coina River (an affluent of Tagus River) bank landfill, estuarine water and spontaneous plants (Aster tripolium, Halimione portulacoides and Sarcocornia sp.), and greenhouse studies (microcosm assay) with T. africana growing in one landfill salt marsh soil, for 97 days, and watered with estuarine water. Soils were analysed for pH, EC, C_organic, NPK, iron and manganese oxides. Soils total (acid digestion) elemental concentrations were determined by ICP/INAA. Estuarine waters, plants roots and shoots (acid digestion), soils available fraction (diluted organic acids extraction-RHIZO or pore water), and salts collected from the T. africana leaves surface were analysed for metals/metalloids (ICP-MS). Ecotoxicity assays were performed in T. africana soil elutriates and pore waters using Artemia franciscana and Brachionus plicatillis.

Results and discussion

Soils were contaminated, containing high total concentrations of arsenic, cadmium, chromium, copper, lead and zinc. However, their concentrations in the available fraction were <4 % of the total. The estuarine waters were contaminated with cadmium, but negligible ecotoxicological effect was observed. The spontaneous plants had significant uptake of the above elements, being mostly stored in the roots. Elemental concentrations in the shoots were within the normal range for plants. These species are not hazardous elements accumulators. Tamarix africana was well adapted to the contaminated saline soils, stored the contaminants in the roots, and had small concentrations of hazardous elements in the shoots. Excretion of hazardous elements by the salt glands was also observed. Elutriates from soils with and without plant did not show ecotoxicity.

Conclusions

The salt marsh species play an important role in the stabilisation of the soils in natural conditions. Tamarix africana showed potential for phytostabilisation of saline-contaminated soils. The low translocation of the elements from roots to shoots and/or active excretion of the elements by the salt glands was a tolerance mechanism in T. africana.

     

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.     

Long-term observations of the vertical distributions of mineral elements and phosphorus dynamics in sediments in a shallow eutrophic lake in Japan

Purpose

To explore the mechanisms in the deposition and release of phosphorus (P) in the sediment of a shallow eutrophic lake using preserved samples, we investigated the vertical and temporal changes in P, manganese (Mn), sulfur (S), iron (Fe), aluminum (Al), calcium (Ca), and magnesium (Mg) in the sediment samples and the phosphate in the sediment pore water samples over a period of 6 years.

Materials and methods

The upper 15 cm of sediment from Lake Kasumigaura in Japan was collected monthly from 2003 to 2008 from the center of the lake. Sediment cores were divided into seven depth segments and were acid-digested for an elemental analysis via inductively coupled plasma atomic emission spectroscopy. Phosphate concentrations of the sediment pore water were determined using the molybdenum blue method. A multiple regression analysis was conducted by setting the P content as the response variable and Mn, S, Fe, Al, Ca, and Mg as explanatory variables.

Results and discussion

The results of the multiple regression analysis demonstrated that P co-precipitates with Fe and Al oxides and accumulates on the sediment surface. The vertical distributions of Mn and S suggest that Mn reduction occurs within the 0–1-cm-depth layer of the sediment and that iron sulfide is actively formed in the 6–10-cm-depth layer of the sediment. These findings imply that the layer in which ferric oxides are reduced to ferrous ions is present near the 1–6-cm-depth layer of the sediment. This layer corresponds to the layer in which the maximum phosphate concentration of the sediment pore water often occurred (the 2–6-cm-depth layer). These results indicate that vertical distributions of mineral elements are useful for assessing P dynamics in sediments.

Conclusions

The lake sediments record the dynamics of P in the sediment. Our analytical approach using long-term observation data demonstrated that the accumulation and release of P associated with a change in the redox state can be assessed based on the vertical distributions of mineral elements in the lake sediments.

     

Evaluating the Influence of Storage Time,Sample‐handling Method,and Filter Paper on the Measurement of Water‐Extractable Phosphorus in Animal Manures

Abstract

Surface‐applied manures create a potential phosphorus (P) runoff hazard, especially when unincorporated. In such cases, the concentration of water‐extractable P in the manure has been correlated to soluble P concentrations in runoff. This study evaluated the influence of holding time, sample‐handling procedure, and filtration method on measurement of the water‐extractable P content of manures in a 3×3×2 factorial arrangement of treatments. A two‐way interaction between holding time and sample‐handling procedure occurred for most samples. Six samples had water‐extractable P concentrations that were less than or equal to dried and dried/ground treatments. Only one sample had higher water‐extractable P concentrations for fresh than for dried and dried/ground treatments. When significant differences occurred as a result of the filtration method, results for Whatman No. 40 filters, with a larger pore size than 0.45 µm nitrocellulose membranes, were usually higher. There was no significant difference in the coefficient of variation across sample‐handling procedures, suggesting that efforts to dry and/or grind samples were not needed. These results support the adoption of a standardized protocol for measuring water‐extractable P in manures that represents the appropriate balance between the ease of implementation and the strength of the correlation to P runoff concentrations.     

Comparison of Two Digestion Methods for Determining Total Phosphorus in Farm Canal Water

Abstract

Rapid and accurate determination of low‐level (0.01 to 1.0 mg L^?1) phosphorus (P) concentrations in farm canal water is important in evaluating water quality in the Everglades Agricultural Area (EAA) canals in south Florida. Two U.S. Environmental Protection Agency methods, persulfate digestion (365.1) and Kjeldahl digestion with mercury oxide (365.4), were used to analyze total P (TP) and total dissolved P (TDP) in two sets of representative canal water samples collected at low‐flow conditions in 2003 and high‐flow conditions in 2004. Quality assurance samples (blanks, duplicates, and spikes) were included to evaluate differences between the two digestion methods. Precision analysis had a mean of less than 5% for both TP and TDP using both methods. The high coefficient of correlations (r>0.98) indicated that the two methods were significantly correlated in determining TP and TDP of the samples. Low detection limits (0.004 mg L^?1) were achieved by the persulfate method. This method offers many other advantages over the mercury digestion: it produces no toxic mercury waste, uses less time, and uses a lower temperature. High suspended solids in canal water samples were not proven to be a problem when using the persulfate digestion, though lower spike recoveries were observed than those when using the mercury digestion. We conclude that persulfate digestion is a more sensitive and environmentally responsible alternative to and is, as precise as, the mercury method for routine determination of TP and TDP in water samples. This information is useful to environmental laboratories in monitoring P concentrations in surface and groundwater.     

Applicability of cavity-throat connecting model for estimating the hydraulic conductivity of fine-grained soils: a geometrical and mathematical approach

Purpose

Determining the hydraulic conductivity of low permeable fine-grained soils is difficult and time-consuming. This work develops a new method with an eye to the pore morphology to correlate hydraulic conductivity with pore-size distribution (PSD) parameters obtained from mercury porosimeter data. In order to realize this method, calculating percolation loss along the flow paths in pore channels and quantifying the spatial morphology of pore channels by proposing a cavity-throat connecting model is necessary.

Materials and methods

In order to establish the standard process of the new method, a kind of sedimentary mucky clay with regular dual-structural PSD has been collected. The samples are divided into three series: (a) vibrated with variable frequencies; (b) frozen at variable temperatures and unfrozen, making the freezing-thawing effect as the variable; and (c) remolded with different water contents. The PSD of freeze-dried samples at the end of each process is obtained by mercury intrusion porosimetry. After that, the method is demonstrated with application to 12 series of fine-grained soils.

Results and discussion

Deduced from mercury porosimeter data, the volume-based PSD curves of fine-grained soils are bimodal, due to the presence of inter-aggregate and intra-aggregate pores. Two important hypotheses have been proposed: (i) one is that in the smaller pore scales, the experimental extrusion curve controlled by the hysteresis loop has a really approximate part compared to the theoretical overall retraction curve, making the experimental extrusion curve characterize the pore cavity size approximately, and (ii) the pore system consists of a series of multistage cavity-throat connections. Accumulating the effects of single connection on the percolation can be used to measure the overall effects of pore system on the percolation. Based on fluid-driven path analysis of percolation, the pore system is quantified by a series of cavity-throat connections and the percolation loss has been derived to estimate the hydraulic conductivity.

Conclusions

The permeable parameter (κ) representing the overall effects of pore connections on the hydraulic conductivity (K) is suited to correlate the microstructure and hydraulic conductivity by the linear relationship with the fixed slope in semilogarithmic coordinate for the fine-grained soils. It is the destruction and recombination of cavity-throat connections that are dominant during the treatments like freezing, remolding, and reinforcing.

     

Squeezed soil-pore solutes — A comparison to lysimeter samples and percolation experiments

This paper presents data on the chemical composition of soil pore fluids that have been obtained by a high-pressure squeezing technique and lysimeter sampling. Cation-exchange capacity has been calculated from cations extracted by a simple percolation method. All pore water concentrations are greatly influenced by the pH in solution. Most pore water concentrations do not simply parallel the corresponding mineralogical and chemical composition of the solids. The depth of the acidification front, as determined by analysis of samples obtained by percolation, is much better reflected in the chemical composition of the squeezed soil pore fluids than in the lysimeter samples. Distinct gradients are seen in Al concentration. In the B-horizons, concentrations of Al are close to the solubility of gibbsite. The pore water concentration profiles of Si and K apparently indicate dissolution of K-silicates, in particular K-feldspar. Contrary to the squeezed pore solutions the sulphate maximum concentration in the soil profile is not recorded by lysimeter samples. Mineral saturation indices show that pore solutions by squeezing are close to the saturation concentrations for K-jarosite and K-alunite. Sulphur-rich phases from the soil are compatible with mixtures of alunite jarosite, zaherite, basaluminite, and hydrobasaluminite. In the upper soil horizons the liquid/solid ratios [calculated as: concentration in solution (µg/ml) * solution fraction in solids (ml/g)/concentration in solids (µg/g)] increase in the order Ph < OC ≈ Zn < Cd and range from 10^?6 to 10^?3, indicating that Ph is most strongly held and still accumulates in the organic top soil. In the underlying deeper mineral horizons the ratios for Pb, Zn, and Cd decrease by one order of magnitude.     

A disposable system for soil pore‐water extraction by centrifugation

Abstract

Evaluation of the partitioning of contaminant and nutrient elements between soil particles and their surrounding solution requires separation of the pore‐water from the solids. Disposable soil‐sample holders are described that can be used in low‐ and ultra‐speed centrifuges. The pore‐water sample is filtered of paniculate during centrifugation, thus eliminating the tedious step of separating the centrifugate from the soil using pipettes. The system is inexpensive, works for both fine mineral and peat soils, requires little preparation time and provides enough pore‐water of sufficient quality for chemical analysis.     

Measurement of the size distribution of water-filled pores at different matric potentials by stray field nuclear magnetic resonance

The water retention characteristic provides the traditional data set for the derivation of a soil's pore‐size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI‐NMR) to probe the water‐filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water‐occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T₁ proton relaxation time of water. The T₁ values are linearly related to pore size and consequently measured T₁ distributions provide a measure of the pore‐size distribution. For both the sands and the glass beads at saturation the T₁ distributions are unimodal, and the samples with small particle sizes show a shift to small T₁ values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water‐occupied pore‐size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel‐capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T₁ distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water‐filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T₁ distributions are bimodal or asymmetrical, indicative of inter‐aggregate and intra‐aggregate pore spaces. We conclude that the NMR method provides a characterization of the water‐filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage.     

A Comparison of 18Oδ Composition of Water Extracted from Suction Lysimeters, Centrifugation, and Azeotropic Distillation

The representativeness of soil pore water extracted by suction lysimeters in ground-water monitoring studies is a problem that often confounds interpretation of measured data. Current soil water sampling techniques cannot delineate from which soil volume a pore water sample is extracted, neither macroscopic, microscopic, or preferential flowpath. This research was undertaken to compare δ¹⁸O and Br^? values of extracted suction lysimeters samples from intact soil cores with samples obtained by the direct extraction methods of centrifugation and azeotropic distillation. Also, the study was concerned with determining what portion of soil pore water is sampled by each method and explaining differences in concentrations of the extracted water from each method to allow a determination of the accuracy and viability of the three methods of extraction. Intact soil cores (30 cm diameter by 40 cm height) were extracted from two different sites. Site 1 was rapid infiltration basin number 50, near Altamonte Springs in Seminole County, Florida. Site 2 was the Missouri Management System Evaluation Area (MSEA) near Centralia in Boone County, Missouri. Isotopically (¹⁸Oδ) labeled water and bromide concentrations within water samples taken by suction lysimeters was compared with samples obtained by methods of centrifugation and azeotropic distillation. The ¹⁸Oδ water was analyzed by mass spectrometry while bromide concentration, applied in the form of KBr was measured using standard IC procedures. Water collected by centrifugation and azeotropic distillation data were about 0.25‰ more negative than that collected by suction lysimeter values from a sandy soil and about 2–7‰ more negative from a well structured soil. Results indicate that the majority of soil water in well-structured soil is strongly bound to soil grain surfaces and is not easily sampled by suction lysimeters. In cases where a sufficient volume of water has passed through the soil profile and displaced previous pore water, suction lysimeters will collect a representative sample of soil pore water from the sampled depth interval. It is suggested that for stable isotope studies monitoring precipitation and soil water, suction lysimeter be installed at shallow depths (10 cm). Samples should also be coordinated with precipitation events. The data also suggest that each extraction method samples a separate component of soil-pore water. Centrifugation can be used with success, particularly for efficient sampling of large areas. Azeotropic distillation is more appropriate when strict qualitative and quantitative data on sorption desorption, and various types of kinetic studies may be needed.     

Effects of soil compaction and water‐filled pore space on soil microbial activity and N losses

Abstract

Soil compaction is a significant production problem for agriculture because of its negative impact on plant growth, which in many cases has been attributed to changes in soil N transformations. A laboratory experiment was conducted to study the effect of soil compaction and water‐filled pore space on soil microbial activity and N losses. A hydraulic soil compaction device was used to evenly compress a Norfolk loamy sand (fine‐loamy, siliceous, thermic Typic Kandiudults) soil into 50 mm diameter by 127 mm long cores. A factorial arrangement of three bulk density levels (1.4, 1.6, and 1.8 Mg/m³) and four water‐filled pore space levels (60, 65, 70, 75%) was used. Fertilizer application of 168 kg N/ha was made as 1.0 atom % ¹⁵N as NH₄NO₃. Soil cores were incubated at 25°C for 21 d. Microbial activity decreased with both increasing water‐filled pore space and soil bulk density as measured by CO₂‐C entrapment. Nitrogen loss increased with increasing bulk density from 92.8 to 334.4 g N/m³ soil at 60% water‐filled pore space, for 1.4 and 1.8 Mg/m³, respectively. These data indicate that N loss and soil microbial activity depends not only on the pore space occupied by water, but also on structure and size of soil pores which are altered by compaction.     

Spatial variability of organic matter degradability in tidal Elbe sediments

Purpose

The microbial turnover of sediment organic matter (OM) in ports and waterways impacts water quality, sonic depth finding and presumably also rheological properties as well as greenhouse gas emissions, especially if organic carbon is released as methane. As a consequence, sediment management practices as a whole are affected. This study aimed to discern spatial OM degradability patterns in the Port of Hamburg and investigated correlations with standard analytical properties as a basis for future predictive modelling.

Materials and methods

Sediments in the Port of Hamburg were repeatedly sampled at nine locations along an east-west transect using a 1-m corer. In a stratified sampling approach, layers of suspended particulate matter (SPM), fluid mud (FM), pre-consolidated sediment (PS) and consolidated sediment (CS) were identified and individually analysed for long-term aerobic and anaerobic degradation of organic matter, DNA concentration, stable carbon isotope signature, density fractions and standard solids and pore water properties.

Results and discussion

The investigation area was characterised by a distinct gradient with a 10-fold higher OM degradability in upstream areas and lower degradability in downstream areas. Concomitantly, upstream locations showed higher DNA concentrations and more negative δ¹³C values. The share of bulk sediment in the heavy density fraction as well as the proportion and absolute amount of organic carbon were significantly larger at downstream locations. A depth and hence age-related gradient was found at individual locations, showing higher degradability of the upper, younger material, concomitant with higher DNA concentration, and lower OM turnover in the deeper, older and more consolidated material. Deeper layers were also characterised by higher concentrations of pore water ammonium, indicative of anaerobic nitrogen mineralisation.

Conclusions

Organic matter lability is inversely linked to its stabilisation in organo-mineral complexes. The observed degradability gradient is likely due to the different OM quality in relation to its origin. Downstream OM enters the system with the tidal flood current from the direction of the North Sea whereas upstream locations receive OM originating from the catchment, containing more autochthonous, plankton-derived and more easily degradable components. At individual sampling points, depth-related degradability gradients reflect an age gradient, with easily degradable material in top layers and increasing stabilisation of OM in organo-mineral compounds with depth.

     

Soluble Phosphorus Released by Poultry Wastes in Acidified Aqueous Extracts

Abstract

Research has shown that measured water‐soluble phosphorus (WSP) from poultry litter might have been less than that released in the field. The effects of acidified extractions on soluble P (SP) concentrations were studied, and a buffer was selected to measure SP at pH 6.0, which is a target value for soil management in Georgia.

Soluble P concentrations were extracted from poultry wastes at three pHs: 1) at natural pH, using deionized water (DI_w); 2) after titrating DI_w suspensions with 0.5N hydrochloric acid (HCl) to pH end‐points 3.0, 4.0, and 6.0; and 3) at pH 6.0 with buffers of sodium (Na) acetate, potassium hydrogen phthalate (KHP), 2‐(N‐morpholino) ethanesulphonic acid (MES), Na cacodylate, imidazole, N‐(2‐acetamido)‐2‐aminoethansulphonic acid (ACES), N‐(carbamoyl‐methyl) iminodiacetic acid (ADA), bis‐(2‐hydroxyethyl) imino]‐tris‐[(hydroxymethyl) methane (Bistris), and 1,4 piperazine‐bis‐(ethane sulphonic acid) (PIPES).

Total SP increased 60% to 140% in suspensions acidified with HCl to pH 6.0 compared to suspensions at pH≥8. Dissolved unreactive P responded more (2× to 30×) than molybdate reactive P (20–100%). Buffers extracted more soluble minerals than suspensions acidified with HCl, probably because of their complexation ability. The most effective buffer was MES, because its effects seemed mainly due to acidification.     

The effect of peatland drainage and rewetting (ditch blocking) on extracellular enzyme activities and water chemistry

Extensive areas of European peatlands have been drained by digging ditches in an attempt to improve the land, resulting in increased carbon dioxide fluxes to the atmosphere and enhanced fluvial dissolved organic carbon (DOC) concentrations. Numerous peatland restoration projects have been initiated which aim to raise water tables by ditch blocking, thus reversing drainage‐induced carbon losses. It has been suggested that extracellular hydrolase and phenol oxidase enzymes are partly responsible for controlling peatland carbon dynamics and that these enzymes are affected by environmental change. The aim of this study was to investigate how drainage and ditch blocking affect enzyme activities and water chemistry in a Welsh blanket bog, and to study the relationship between enzyme activity and water chemistry. A comparison of a drained and undrained site showed that the drained site had higher phenol oxidase and hydrolase activities, and lower concentrations of phenolic compounds which inhibit hydrolase enzymes. Ditch blocking had little impact upon enzyme activities; although hydrolase activities were lowered 4–9 months after restoration, the only significant difference was for arylsulphatase. Finally, we noted a negative correlation between β‐glucosidase activity and DOC concentrations, and a positive correlation between arylsulphatase activity and sulphate concentration. Phenol oxidase activity was negatively correlated with DOC concentrations in pore water, but for ditch water phenol oxidase correlated negatively with the ratio of phenolics to DOC. Our results imply that drainage could exacerbate gaseous and fluvial carbon losses and that peatland restoration may not reverse the effects, at least in the short term.     

Pyrite and siderite oxidation in swamp sediments

Differences in the processes of pyrite and siderite oxidation, in reclaimed swamp sediments of the Skjernå delta (Denmark), are described from sediment chemistry, mineralogy and pore water chemistry. Pyrite oxidation leads to extreme soil acidification, with pH dropping to about 2, the release of large amounts of weathering products to the pore water, and the precipitation ofiron oxides, jarosite and gypsum. Siderite oxidation results only in moderate soil acidification where the pH does not drop below 3.5, while part of the acidification is due to the oxidation of small amounts of sulphur compounds together with siderite. The release of weathering products to the pore water is limited and only iron oxide is precipitated. Calculations indicate that equilibrium with amorphous FeOOH, gypsum and amorphous Al(OH)₃ sets an upper limit to the Fe³⁺, SO₄ and Al concentrations in the pore water.     

Unsaturated zone pore water chemistry and the edge effect in a beech forest in Southern England

Twenty one pore water chemistry profiles were obtained for a range of inorganic solutes from the Chalk unsaturated zone in or adjacent to Black Wood, a 2.4 kM² mature beech wood in southern England. The depth sampled was normally 10 m, but some boreholes were shallower and one was deeper (30 m). Towards the centre of the wood, average pore water concentrations were: Cl (17–25 mg l^-1), SO₄ (20–40 mg l^-1) and NO₃-N (5–10 mg 1^-1). In small clearings within the wood, concentrations of Cl (12–20 mg l^-1) and SO₄ (27–36 mg 1^-1) were somewhat lower but the average concentration of nitrate-N was higher (16 mg 1^-1). Pore water chloride and nitrate concentrations under a small area of ash were lower than under the beech. There was a significant increase in the concentration of a number of solutes, especially Cl, Na, Mg and SO₄, close to the exposed western edge of Black Wood. This ‘edge effect’ decreased exponentially with a half distance of about 9 m. The effect was less consistent at the more sheltered eastern edge. Average pore water concentrations of up to 310 mg 1^-1 Cl and 312 mg 1^-1 SO₄ were found at the western edge. Paradoxically, close to the western edge pore water nitrate concentrations were often very low, frequently less than 1 mg 1^-1 NO₃-N. Using the parameters derived from a simple exponential model of the Black Wood data, calculations suggested that the edge effect would lead to significantly enhanced Cl and SO₄ pore water concentrations in forests of a few hectares, a size typical of many of those currently being planted. The consistently lower moisture content of the Chalk close to the forest edges suggested that groundwater recharge may have been lower there.     

Simple and Rapid Laboratory Method for Rewetting Dry Soil for Incubations

Soil microbial activity is greatly affected by soil water content. Determining the appropriate moisture content to rewet soils that have been dried in preparation for laboratory incubations to determine microbial activity can be laborious and time-consuming. The most common methods used achieve sufficient moisture content for peak microbial respiration are gravimetric water content, soil matric potential, or percentage of water-filled pore space (WFPS). Alternatively, a fast, simple, and accurate way to ensure that a given soil receives the appropriate amount of water for peak soil microbial respiration is to rely on natural capillary action for rewetting the dry soil. The capillary method is related to the gravimetric method for water uptake and has a strong correlation with WFPS. A microbial respiration test was conducted to compare rewetting methods. The 24-h carbon dioxide (CO₂) / carbon (C) results were very similar and strongly correlated using the gravimetric method and the capillary method for rewetting dried soil.     

Evaluation of phosphorus mobilization potential in rewetted fens by an improved sequential chemical extraction procedure

After rewetting of peatlands, phosphorus (P) pore‐water concentrations were up to three orders of magnitude greater than under pristine conditions. It was hypothesized that different mobilization processes such as ion‐exchange reactions, biotic/abiotic redox reactions, acidification and ongoing anaerobic decomposition of particulate organic matter by hydrolytic cleavage and fermentation might be responsible. To identify P pools in peat samples of varying degrees of decomposition, we modified and improved a sequential chemical extraction method that allowed conclusions on potential mobilization mechanisms in rewetted peatlands. The results indicated that the earlier drainage of rewetted fens strongly increased the P mobilization potential in the upper decomposed peat layers. Accordingly, the amount of P bound to redox‐sensitive (bicarbonate/dithionite soluble) compounds (BD‐P) was, on average, one order of magnitude greater in decomposed peat of rewetted fens (5.4–14.3 μmol P g^?1 dry matter or DM) than in underlying less‐decomposed peat layers (0.2–1.9 μmol P g^?1 DM) or slightly decomposed peat derived from pristine fens (0.4–2.0 μmol P g^?1 DM). The BD‐P fraction found in the upper very decomposed peat layers appears to be most important for P mobilization in rewetted fens and accounted for 85% of the variability of P mobilization rates. Despite uncertainties regarding P diagenetic processes in peat, as well as the development of microbial decomposition processes, in the long‐term, high pore‐water P concentrations can be expected in rewetted fens for decades to come.     

Dissolved organic matter and inorganic N jointly regulate greenhouse gases fluxes from forest soils with different moistures during a freeze-thaw period

ABSTRACT

Antecedent soil moisture before freezing can affect greenhouse gases (GHG) fluxes from soils during thaw, but their critical threshold values for GHG fluxes and the underlying mechanisms are still not clear. By using packed soil-core incubation experiments, we have studied nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) fluxes from a mature broadleaf and Korean pine-mixed forest soil and an adjacent white birch forest soil with nine levels of soil moisture ranging from 10 to 90% water-filled pore space (WFPS) during a 2-month freezing at ?8°C and the following 10-day thaw at 10°C. The threshold values of soil moisture ranged from 50 to 70% WFPS for CH₄ uptake and from 70 to 90% WFPS for N₂O and CO₂ emissions from the two soils during the freeze-thaw period. Under the optimum soil moisture condition, fulvic-like compounds with high bioavailability contributed more than 60% of dissolved organic matter (DOM) in the soil. Cumulative N₂O emissions from forest soils during the freeze-thaw period were greatest when the concentration ratio of nitrate-N to dissolved organic carbon (DOC) was 0.04 g N g^?1 C. Cumulative soil CO₂ emissions and CH₄ uptake during the freeze-thaw period were both regulated by the interaction between soil DOC and net N mineralization. The activities of β-1,4-glucosidase and β-1,4-N-acetyl-glucosaminidase, microbial biomass C and N, and the microbial biomass C-to-N ratios, were all significantly correlated to the soil N₂O, CO₂, and CH₄ fluxes. Overall, upon a freeze-thaw period with different soil moistures, GHG fluxes from forest soils were jointly regulated by inorganic N and DOC concentrations, and related to the labile components of DOM released into the soil, which could be strictly controlled by the related microbial properties.     

Grain Yield and Mineral Element Composition of Maize Grown on High Phosphorus Soils Amended with Water Treatment Residual

ABSTRACT

The potential for phosphorus (P) movement from poultry-litter amended soils into surface waters heightens the need to manage elevated P concentrations. Amending high P soils with aluminum (Al) rich drinking water treatment residue in a greenhouse study reduced water extractable P levels and induced P deficiency in container grown wheat. Objectives of the current investigation were to determine the effect of water treatment residue on grain yield, leaf and grain mineral nutrient concentrations in corn (Zea mays L.) grown under field conditions and to examine pH, water and Mehlich 3-extractable P, and 0.01 M calcium chloride extractable Al in the amended soils at two sites. Poultry litter was amended with 0, 5.6, and 11.2 Mg ha^{? 1} of water treatment residual and applied to two sites prior to planting with corn in 1998. Additional rates (16.8 and 33.6 Mg ha^{? 1}) of water treatment residue were applied directly to half of each plot on site I in 1999. Results indicated that water treatment residue application did not adversely affect corn grain yields or alter concentrations of mineral nutrients in leaves and grain. Water and Mehlich 3-extractable P and calcium chloride extractable Al concentrations were unchanged with water treatment residue applications in both years on both sites. Further studies are needed concerning optimal annual dosages and long term loading rates for direct soil application of water treatment residue to reduce soluble phosphorus.