Effects of soil moisture content on CO2 triggered soil physicochemical properties in a near-surface environment

Journal of Soils and Sediments - Carbon capture and storage (CCS) has been frequently discussed as a strategy for meeting CO2 emission reduction and its targets. However, some critical issues have...     

Electrokinetic remediation of heavy metal-contaminated soils: performance comparison between one- and two-dimensional electrode configurations

Journal of Soils and Sediments - Electrokinetic (EK) soil remediation is significantly affected by the electrode configurations. Therefore, this study was conducted to compare the performance of...     

Geochemical studies on the contamination and dispersion of trace metals in intertidal sediments around a military air weapons shooting range

Purpose  

A number of publications have raised trace metal contamination of soils and sediments within and around shooting ranges used for sport or military training. To our knowledge, however, there is no publication on the contamination of sediments derived from military shooting ranges in a marine environment. Therefore, this work was purposed to assess the dispersion and fractionation of ammunition- and bomb-derived trace metals in intertidal sediment.     

Hydrochemical and stable isotopic assessment of nitrate contamination in an alluvial aquifer underneath a riverside agricultural field

Major ions and stable isotopic (δD_water, δ¹⁸O_water, δ¹⁵N_nitrate, δ¹⁸O_nitrate) measurements in concert with hydrochemical modeling were used in order to elucidate the sources and geochemical processes controlling nitrate contamination of shallow alluvial groundwater underneath a riverside agricultural field in the Buyeo area, Korea. Beneath vegetable fields in the sandy soil, the mean nitrate concentration of groundwater was 148.6 mg/L, which is significantly higher than in groundwater (mean 28.8 mg/L) beneath silty soils underneath rice paddy fields. Nitrogen isotope data indicate that synthetic fertilizers are the predominant source of groundwater nitrate in the study area. Denitrification during recharge through rice paddy soils appears to be responsible for the lower nitrate concentrations in groundwater beneath the silty soil zone. The relationship between nitrogen and oxygen isotope data of nitrate also suggests mixing of two different groundwater bodies with nitrates from the silt zone and the sand zone. Geochemical mass balance modeling on hydrochemical data indicates that various agricultural chemicals such as urea, lime, magnesium sulfate and potassium chloride dissolve in vegetable fields of the sandy zone, resulting in significant enrichment of various solutes such as K⁺, Ca²⁺, Mg²⁺, NO₃⁻, SO₄²⁻ and Cl⁻. As a consequence of over-utilization of synthetic nitrogen fertilizers, the sand zone is characterized by very high nitrate concentrations in the groundwater. This study suggests that a reduction of over-fertilization especially on vegetable fields in the riverside sand zone is required to minimize the nitrate contamination of groundwater. This study also shows that combination of geochemical and isotopic techniques with simple mass balance modeling provides information about the causes and processes of nitrate contamination of groundwater underneath a riverside agricultural field. The study also provides sustainable measures to optimize fertilization rate as an important basis of eco-friendly agriculture.     

Influence of Different Substrates in Wetland Soils on Denitrification

Different substrates were evaluated to investigate their effect on nitrate removal and denitrifying bacterial community in soils obtained from wetland. Serial batch kinetic tests were conducted on soils obtained from wetland mixed with glucose and sawdust using KNO₃ solution. Column tests were also conducted on soils obtained from wetland mixed with three different substrates (glucose, sawdust, and scoria coated with zero-valent iron) using KNO₃ solution. For the batch tests, the nitrate removal efficiency for soil mixed with glucose was comparable to that for soil mixed with sawdust, but the nitrate removal rate for soil mixed with glucose (23.3 NO ₃ ^? -N mg/L-d) was approximately eight times higher than that for soil mixed with sawdust (2.8 NO ₃ ^? -N mg/L-d). For column tests among soil samples, nitrate removal efficiency was highest in soil mixed with glucose, which is an easily biodegradable carbon source. Removal efficiency increased with increasing incubation time for both soil samples with glucose and sawdust. A phylogenetic analysis based on nitrate reductase gene demonstrated that the different carbon sources affected both the diversity and compositions of the denitrifying bacterial in soil samples.     

Numerical and Experimental Studies on Cadmium (II) Transport in Kaolinite Clay under Electrical Fields

A numerical model was formulated to simulate cadmium (Cd) transport under an electric field using one-dimensional diffusion-advection equations describing the contaminant transport driven by chemical and electrical gradients in kaolinite clay. The numerical model includedcomplex physicochemical factors affecting the transport phenomena, such as soil pH value, zeta potential, aqueous phase reaction, adsorption, and precipitation. One-dimensional finite-difference computer models successfully predicted meaningful values for soil pH profiles and Cd concentration profiles. To verify the results of the proposed model by comparing them with experimental results, two different types of laboratory electrokinetic tests, unenhanced and enhanced tests, were conducted. The numerical and the experimental results showed good agreement. In addition, those results indicate that soil pH is the most important factor in governing the dissolution and/or desorption of Cd in the soil system under electrical fields. The removal efficiency of Cd in the unenhanced test was low (15.6%) due to a high accumulation in the region near the cathode. On the contrary, the cadmium concentration profile of the enhanced test showed a different pattern, and most of the residual concentrations appeared below the initial level at each local point within the soil cell after processing. The removal efficiency of the enhanced test was much higher (42.7%) than that of the unenhanced test, resulting from the prevention of hydroxide precipitation near the cathode using the acidic catholyte. Consequently, the result implies that the enhancement schemes such as conditioning of catholyte should be required to increase the effectiveness of the electrokinetic technology in removing metal contaminants from soils.     

Clustering of temporal profiles using a Bayesian logistic mixture model: Analyzing groundwater level data to understand the characteristics of urban groundwater recharge

The hydrogeologic conditions of groundwater can be examined by carefully studying the patterns of fluctuations in groundwater levels. These fluctuations are spatially and temporally influenced by many complicated factors, including rainfall, topography, land use, and hydraulic properties of soils and bedrock (i.e., aquifers). In this article we report a methodology based on the Bayesian logistic mixture model to simultaneously cluster profiles of groundwater level changes over time and estimate the relationships between the characteristics of each cluster and environmental variables. We apply the proposed method to analyze groundwater level profiles from 37 monitoring wells in Seoul, South Korea, and we find four clusters of wells. Using the estimated relationship between the clusters and the environmental variables, we discern the hydrogeologic conditions of each cluster, thus gaining insight into the recharge and subsurface flow of bedrock groundwater in an urban setting and the vulnerability of groundwater to the inflow of potential pollutants from ground surface. This article has supplementary material online.     

Studies of Spatial Variabilities of Airborne Metals Across Four Different Land-Use Types

The concentrations of seven metals (Fe, Pb, Mn, Ni, Cd, Cu, and Cr) associated with the total suspended particles (TSPs) were analyzed regularly from the four sampling sites of different land-use types within the boundary of Won Ju city, Korea during1991 through 1995. The mean concentration data for the four sitesselected to represent grassland, residential, commercial, and industrial areas fell in a relatively broad range of: 1440–2240 (Fe), 88–326 (Pb), 2–4 (Cd), 8–21 (Cr),194–469 (Cu), 32–95 (Mn), and 15–26 (Ni) ng m^-3. The data, when compared across the different study sites, generally exhibited systematic trends in accordance withthe site-selection scheme; most metals exhibited increase in their concentration levels across grassland through industrial site. Examinations of data also indicated the possibility that spatial factors play complicated roles on both long- and short-term distribution of metals. From all four sites studied, severalmetals (e.g., Fe, Pb, Mn, Ni, and Cd) consistently showed theirseasonal trends characteristic of high winter/spring values. In addition, the analysis of long-term distribution trendsindicated that the concentrations of many metals droppedsteadily at four sites (e.g., Fe, Pb, and Mn). When these metaldata were compared among different sites (land-use types), significant correlations were seen frequently for such metals asFe, Pb, Cd, and Cr. Investigations of inter-metal relationshipsindicated that strong correlations were more abundant from such metal pairs as Fe-Pb, Pb-Mn, and Mn-Fe. In addition, the cases for such strong correlations were seen more abundantly from grassland (and residential) than industrial (and commercial) site. Factor analysis was also conducted to distinguish sourceprocesses affecting metal distributions in the study area. Results of this analysis suggest that the metal distributions ofthe individual sites may be affected most significantly by distinctive source processes of their own.