Sang-Mo Lee

Natural 15N abundances of maize and soil amended with urea and composted pig manure

To investigate the effect of inorganic fertilizer and composted manure amendments on the N isotope composition (delta15N) of crop and soil, maize (Zea mays L.) was cultivated under greenhouse conditions for 30, 40, 50, 60, and 70 days. Composted pig manure (delta15N= +13.9‰) and urea (-2.3‰) were applied at 0 and 0 kg N ha−1 (C0U0), 0 and 150 kg N ha−1 (C0U2), 150 and 0 kg N ha−1 (C2U0), and 75 and 75 kg N ha−1 (C1U1), respectively. The delta15N of total soil-N was not affected by both amendments, but delta15N of NH+4 and NO−3 provided some information on the N isotope fractionation in soil. During the early growth stage, significant differences (P < 0.05) in delta15N among maize subjected to different treatments were observed. After 30 days of growth, the delta15N values of maize were +6.6‰ for C0U0, +1.1‰ for C0U2, +7.7‰ for C2U0, and +4.5‰ for C1U1. However, effects of urea and composted manure application on maize delta15N progressively decreased with increasing growth period, probably due to isotope fractionation accompanying N losses and increased uptake of soil-derived N by maize. After 70 days of growth, delta15N of leaves and grains of maize amended with composted pig manure were significantly (P < 0.05) higher than those with urea. The temporal variations in delta15N of maize amended with urea and composted manure indicate that plant delta15N is generally not a good tracer for N sources applied to field. Our data can be used in validation of delta15N fractionation models in relation to N source inputs.

Evaluation of contamination sources of groundwater NO3 − using nitrogen isotope data: A review

It has been accepted that variations in stable N isotope ratios (15N/14N) can potentially provide useful, sometimes unique, information on the sources of nitrate in groundwater, because N isotope compositions are generally different among various N pools such as atmospheric N2, soil, chemical fertilizer, and manure. However, this review strongly suggests that interpretation of the nitrate source based on a single measurement of δ15N may not be accurate because the isotopic composition of groundwater nitrate is a function of its source and any isotope fractionation that may occur during its generation or transport to groundwater. This review, therefore, shows that to evaluate the nitrate contamination source using δ15N technique, it is more reasonable to use correlation between the concentrations and δ15N of NO3−. For example, a positive correlation indicates15N-enriched source such as manure, while15N-depleted source results in a negative correlation. The correlation analysis can also be used in evaluation of denitrification and nitrification. Denitrification is a key process affecting δ15N of NO3−, i.e. if significant amount of nitrate is removed through denitrification, it is not easy to discriminate fertilizer-derived nitrate from manure-or compost-derived one because denitrification increase the δ15N of the remaining NO3−. Therefore, it is important to assess whether denitrification may be occurring or not when evaluating isotope data on nitrate. By using dual (δ15Nair and δ18Ovsmow) isotopic indicators, denitrification can be evaluated more accurately.

Evaluation of nitrate contamination sources of unconfined groundwater in the North Han River basin of Korea using nitrogen isotope ratios

To evaluate the nitrate contamination sources of unconfined groundwater in the North Han River basin (127°45′E, 37°55′N), groundwater samples were collected monthly for three years (1997–1999) from 20 wells, and analyzed for the concentration (n=599) and δ15N (n=96) of NO3−N. Frequency distribution of NO3−N concentration showed that 43.9% of samples exceeded the national standard for drinking water (10 mg NO3−N L−1). During dry season between October and March, only 36.1% of a total of 296 samples had NO3−N concentration above 10 mg L−1. However, 51.5% of a total of 303 samples exceeded the standard level during wet season between April and September. Concentrations of nitrate increased with direction of groundwater flow. Wells located in vicinity of livestock feedlots showed consistently high nitrate concentration irrespective of precipitation pattern. The δ15N signatures of NO3− showed that in general, both15N-depleted source (e.g., chemical fertilizer) and15N-enriched source (e.g., compost and manure) impacted groundwater quality concurrently. The δ15N ranges of groundwater NO3− were +1.5–+12.9‰ in dry season and +3.2–+9.9‰ in wet season. These δ15N data suggested that the effects of compost and/or manure on nitrate concentration were apparent in dry season. A positive correlation (r2=0.32) between N concentration and δ15N of NO3− in dry season also suggested that nitrate concentration increased with increasing loading of nitrate from compost and/or manure wastewater. On the other hand, the relatively narrow range of δ15N and high nitrate concentration in wet season suggested that increased flush of nitrate derived from mixed sources such as fertilizer, compost, and manure during storm event resulted in high nitrate concentration. In this area, neither high δ15N values nor a negative correlation between δ15N and N concentration of NO3−, indicating denitrification was observed because of the coarse textured soil matrix. Therefore, reduction of nitrogen inputs through curtailment of fertilizer and compost application rates and appropriate treatment of livestock manure are the most effective and practical ways to prevent groundwater contamination.

Electrokinetically enhanced transport of organic and inorganic phosphorus in a low permeability soil

The transport of P sources (organic and inorganic phosphorus) using electrokinetic process through a low-permeability soils was investigated. A series of batch experiments was conducted to construct the adsorption isotherms of KH2PO4 and triethyl phosphate (TEP) on kaolin soils. Approximately 60.3% of phosphorus from KH2PO4 was adsorbed within 24 hours, and the maximum adsorption (73%) was attained at 6 days after adsorption. In contrast, TEP showed no P adsorption in 7 days, thus suggesting an alternative P source that may maintain a favorable proportion of C∶N∶P through the effective delivery duringin situ bioremediation in low permeability soils. Experiments using electrokinetic process were carried out with electrokinetic reactor having a hydraulic conductivity of 1.99×10−7 cm s−1 for a 0.01 M NaCl aqueous solution. TEP and KH2PO4 were used as organic P source and inorganic P source, respectively, and introduced individually into a chamber near the platinum anode and near the platinum cathode, respectively. Potassium dihydrogen phosphate was not distributed uniformly along the soil column and most of transported phosphorus was changed to water-insoluble aluminum phosphate after 12 days of treatment, indicating the decrease of bioavailability of the phosphorus. In case of TEP, the advancing P front progressed with time, resulting in uniform P distribution through the kaolin column. In terms of transport, organic phosphorus, TEP, would be a more effective P source than inorganic phosphorus, KH2PO4, in electrokinetic enhanced bioremediation.

Reconstructing Atmospheric CO 2 Concentration Using Its Relationship with Carbon Isotope Variations in Annual Tree Ring of Red Pine

Carbon isotope ratio ( 13 C/ 12 C, expressed as δ 13 C) of tree ring can be proxy of atmospheric CO2 concentration ((CO2)) due to the inter-correlation between atmospheric (CO2), δ 13 C of atmospheric CO2, and δ 13 C of plant tissue that assimilates atmospheric CO2. This study was conducted to investigate if δ 13 C of tree ring of Pinus densiflora in polluted area may show a lower value than that in unpolluted area and to explore the possibility of reconstructing atmospheric (CO2) using its relationship with δ 13 C of tree ring. During the period between 1999 and 2005, δ 13 C of tree annual ring tended to decrease over time, and the δ 13 C in polluted area (-27.2‰ in 2009 to -28.3‰ in 2005) was significantly (P<0.001) lower than that (-26.0‰ in 1999 to -27.1‰ in 2005) in unpolluted area. This reflects a greater emission of CO2 depleted in 13 C in the polluted area. Atmospheric (CO2) was significantly (P<0.01) correlated with δ 13 C of tree ring in a linear fashion. Using the linear regression equation, atmospheric (CO2) in the polluted area was estimated to range from 392.3 ppm in 1999 to 410.9 ppm in 2005, and these values were consistently higher than the national atmospheric (CO2) monitored at the Anmyoundo meteorological station (from 370.7 ppm in 1999 to 387.2 ppm in 2005). Our study suggested that it is possible to reconstruct atmospheric (CO2) in a certain area using the relationship between tree ring δ 13 C and atmospheric (CO2).

Sorption of Pb in chemical and particle-size fractions of soils with different physico-chemical properties

PurposeLead (Pb) sorption capacity (PbSmax) and distribution in chemical and particle-size fractions of six soils with different physico-chemical properties were investigated to explore the principal properties of soils that affect Pb sorption.Materials and methodsA series of experiments of Pb sorption and soil chemical and particle-size fractionation of sorbed Pb were conducted with six soils of different texture, mineralogy, organic matter concentration, cation exchange capacity (CEC), and Fe-Mn concentrations.Results and discussionSoils either developed from volcanic ash or containing smectite showed relatively higher PbSmax than the other soils. Across the soils, clay content, organic matter concentration, and total Fe concentrations were significantly (p < 0.05) correlated with PbSmax. Concentrations of Pb bound with Fe-Mn and exchangeable Pb sorbed on to negatively charged sites were greater than the other chemical fractions. In the particle-size fractions, clay-sized particles had the greatest Pb concentration, suggesting that this fraction was most responsible for Pb sorption. The Pb concentration in coarse particle fractions (silt and sand) showed a positive relationship with organic matter concentration, indicating that organic matter in coarse particles was a factor determining Pb sorption. However, such relationship was not found for clay-sized particles, suggesting that complexation with organic matter was not a key mechanism for Pb sorption onto clay-sized particles.ConclusionsOur study which combined sorption and chemical and particle-size fractionation experiments suggests that complexation of Pb with Fe and Mn oxides and interaction with negatively charged sites of clay-sized particles are the key processes of Pb sorption in the studied soils. For coarse particles, it was suggested that association with organic matter is a Pb sorption mechanism.

Historical responses of Quercus variabilis growth to environmental changes in Southern Korea: Evidence from tree ring width and δ13C

Historical growth response of Quercus variabilis, which is the most important deciduous timber species in Korea, was investigated using the width and C isotope ratio (13C/12C denoted as δ13C) of the annual ring from 1975 to 2007. Tree disks were collected from three Q. variabilis trees with different growth statuses from a site in the Mt. Naejang area, and analyzed for annual ring width and δ13C. Basal area increment (BAI) of the annual ring was calculated from the width data, and carbon isotope discrimination (Δ) was calculated using δ13C. The intercorrelations among BAI, Δ, and environmental variables were explored. The BAI was positively (p <0.001) correlated with atmospheric CO2 concentration ([CO2]), reflecting increased net photosynthesis with [CO2], whereas the negative correlations of BAI with either NO2 (p <0.05) or O3 (p <0.05) concentrations suggested that atmospheric pollution might have restricted tree growth to some degree. The Δ was positively correlated with both temperature (p <0.05) and [CO2] (p <0.001), and BAI was also positively correlated with Δ (p <0.001). However, precipitation was correlated with neither BAI nor Δ, indicating that the precipitation amount is sufficient for tree growth in the study site. Such relationships suggest that stomatal rather than non-stomatal control is the predominant mechanism of photosynthetic acclimation of Q. variabilis under changing environmental conditions in the study site where water availability is not limited.