Remediation technologies for heavy metal contaminated groundwater.

The biological clogging of natural porous media, often in conjunction with physical or chemical clogging, is encountered under a wide range of conditions. Wastewater disposal, artificial groundwater recharge, in situ bioremediation of contaminated aquifers, construction of water reservoirs, or secondary oil recovery are all affected by this process. The present review provides an overview of the techniques that are used to study clogging in the laboratory, or to monitor it in field applications. After a brief survey of the clogging patterns most commonly observed in practice, and of a number of physical and chemical causes of clogging, the various mechanisms by which microorganisms clog soils and other natural porous media are analyzed in detail. A critical assessment is also provided of the few mathematical models that have been developed in the last few years to describe the biological clogging process. The overall conclusion of the review is that although information is available on several aspects of the biological clogging of natural porous media, further research is required to predict its extent quantitatively in a given situation. This is particularly true in cases that involve complicating factors such as predation or competition among organisms.

Environmental impact and mechanisms of the biological clogging of saturated soils and aquifer materials

A method of soil analysis

Strontium isotopes are a powerful tool which provide information about provenance directly from the tissues of humans rather than the grave context and burial goods. Geographical variation in strontium isotopes is primarily controlled by the underlying geology but there are many other factors that need to be considered before migratory individuals can be identified. Consequently, despite many studies which have shown that the method works well, it is clear that much remains to be clarified and it will not work for every question or in every place. It rests on the assumption that people were sourcing their food locally and that there is a measurable strontium isotope difference between the place the person migrated from and the place they migrated to. As migrants may deliberately seek out familiar soil types and terrains in their new homeland, some questions surrounding major migration events may prove intractable for this technique. Other factors that can create heterogeneity or homogeneity leading to false positives or false negatives, such as human choices or coastal subsistence, are explored and the metabolism of strontium into human tooth enamel is discussed. Several models of land-use choices by humans are presented to highlight the subtleties inherent in the isotope data and these are used to interpret archaeological human isotope ratios from three studies.

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Passports from the past: Investigating human dispersals using strontium isotope analysis of tooth enamel.

Previous studies indicate that biochar additions sometimes increase soil respiration and CO 2 emissions which could partially offset C credits associated with soil biochar applications. Little is known, however, about the impact of biochar on the mineralization of manure in soil systems and how interactions between biochar and manure impact C sequestration and greenhouse gas (GHG) emissions from soils. We studied the effect of biochar and dried swine manure additions on changes in soil bulk density (D b ), total soil organic carbon (SOC), and emissions of N 2 O and CO, during a 500-d soil column incubation study. The addition of biochar to the soil increased SOC content measured after the 500-d incubation by 17.6 to 68.8%, depending on the treatment. Biochar additions reduced N 2 O emissions measured once near the end of the incubation. The N 2 O emissions were weakly correlated with D b , suggesting that enhanced soil aeration contributed to the reductions in N 2 O emissions. Biochar additions consistently increased CO 2 emissions (measured 13 times during the incubation) relative to no-biochar controls with cumulative CO 2 ―C emissions equivalent to 17 to 23% of biochar C applied. However, a distinct biochar-by-manure interaction for CO 2 flux indicated that biochar either helped stabilize manure C or the presence of manure reduced the effect of biochar on the mineralization of SOC. For the studied system, we conclude that biochar additions sequestered large amounts of highly stable C, reduced N 2 O emissions, increased CO 2 emissions from the soils, and reduced rates of CO 2 emissions following a manure addition.

Impact of Biochar on Manure Carbon Stabilization and Greenhouse Gas Emissions

. The soil hydraulic parameters for analyzing soil water movement can be determined by fitting a soil water retention curve to a certain function, i.e., a soil hydraulic model. For this purpose, the program "SWRC Fit," which performs nonlinear fitting of soil water retention curves to 5 models by Levenberg-Marquardt method, was developed. The five models are the Brooks and Corey model, the van Genuchten model, Kosugi's log-normal pore-size distribution model, Durner's bimodal pore-size distribution model, and a bimodal log-normal pore-size distribution model propose in this study. This program automatically determines all the necessary conditions for the nonlinear fitting, such as the initial estimate of the parameters, and, therefore, users can simply input the soil water retention data to obtain the necessary parameters. The program can be executed directly from a web page at http://purl.org/net/swrc/ ; a client version of the software written in numeric calculation language GNU Octave is included in the electronic supplement of this paper. The program was used for determining the soil hydraulic parameters of 420 soils in UNSODA database. After comparing the root mean square error of the unimodal models, the van Genuchten and Kosugi's models were better than the Brooks and Corey model. The bimodal log-normal pore-size distribution model had similar fitting performance to Durner's bimodal pore-size distribution model.

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SWRC fit - a nonlinear fitting program with a water retention curve for soils having unimodal and bimodal pore structure

The causes of soil alkalinization in the Songnen Plain of Northeast China were mainly analyzed from two aspects, natural and anthropogenic. Natural factors of alkalinization are parent materials, topographic positions, freeze-thaw action, wind conveyance, water properties and semi-arid/sub-humid climate. Some of them were always being neglected, such as freeze-thaw action and wind conveyance. Anthropogenic causes are mainly population pressure, overgrazing and improper agricultural and economic policies. In recent decades, overgrazing played a main role in secondary soil alkalinization, which led to the decline of Leymus chinensis grasslands. Now, the alkalinization is very severe, and more than 3.2 × 106 ha area has been affected by salt, which becomes one of the three largest sodic–saline areas in the world.

The causes of soil alkalinization in the Songnen Plain of Northeast China

We develop a theory that explains the decrease in saturated hydraulic conductivity Ks due to biological clogging of porous media. Experiments show that discontinuous microcolonies in fine-textured soils decrease Ks more severely than biofilms do. However, most existing models for biological clogging assume that bacteria cells form biofilms which uniformly cover pore walls. We propose a mathematical model for biological clogging with a quantitative evaluation of the nonuniform microbial distribution of colonies. A series of equations describing the relation between the biological clogging and the saturated hydraulic conductivity are derived. The data of previous researchers are used to validate the model.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001WR000395

A mathematical model for biological clogging of uniform porous media

Summary
Natural wetlands are a significant source of atmospheric methane, an important greenhouse gas. Compared with numerous papers on measurements of methane emission from natural wetland surfaces, there are few reports on methane configuration and distribution within wetland soil profiles. By using a newly designed gas sampler, we succeeded in collecting free-phase gas from beneath the water table down to 120 cm in a peat. The volumetric percentage of methane in the gas phase increased with depth and was generally more than 50% beneath the zone within which the water table fluctuates. The volume of the gas phase in the peat beneath the water table was estimated to be from 0 to 19% with significant variation with depth, suggesting uneven distribution of gas bubbles. Using the volume ratio of the gas and liquid phases and methane concentration data in the gas phase, as well as assuming that methane was in equilibrium (based on Henry's Law between the two phases), we calculated that ∼60% of the methane accumulates in the form of bubbles. These results suggest the importance of ebullition in methane emission, which might be a major cause for the reportedly large variation of methane emission in both space and time. Most importantly, our results show the need to consider gaseous-phase methane for understanding the production, transport and emission mechanisms of methane in wetlands, which has been overlooked to date.

In situ accumulation of methane bubbles in a natural wetland soil

Permeable reactive barriers (PRBs) are an alternative technique for the biological in situ remediation of ground water contaminants. Nutrient supply via injection well galleries is supposed to support a high microbial activity in these barriers but can ultimately lead to changes in the hydraulic conductivity of the biobarrier due to the accumulation of biomass in the aquifer. This effect, called bioclogging, would limit the remediation efficiency of the biobarrier. To evaluate the effects bioclogging can have on the flow field of a PRB, flow cell experiments were carried out in the laboratory using glass beads as a porous medium. Two types of flow cells were used: a 20- 3 1- 3 1-cm cell simulating a single injection well in a onedimensional flow field and a 20- 3 10- 3 1-cm cell simulating an injection well gallery in a two-dimensional flow field. A mineral medium was injected to promote microbial growth. Results of 9 d of continuous operation showed that conditions, which led to a moderate (50%) reduction of the hydraulic conductivity of the one-dimensional cell, led to a preferential flow pattern within the simulated barrier in the two-dimensional flow field (visualized by a tracer dye). The bioclogging leading to this preferential flow pattern did not change the hydraulic conductivity of the biobarrier as a whole but resulted in a reduced residence time of water within barrier. The biomass distribution measured after 9 d was consistent with the observed clogging effects showing step spatial gradients between clogged and unclogged regions.

Katsutoshi Seki

Papers

SWRC fit - a nonlinear fitting program with a water retention curve for soils having unimodal and bimodal pore structure

The causes of soil alkalinization in the Songnen Plain of Northeast China

A mathematical model for biological clogging of uniform porous media

In situ accumulation of methane bubbles in a natural wetland soil

Moderate Bioclogging Leading to Preferential Flow Paths in Biobarriers