Sun-Ho Yoo

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.

Distribution of Heavy Metals in Soils of Shihwa Tidal Freshwater Marshes

Shihwa tidal freshwater marsh was constructed recently to treat pollutants entering Shihwa lake. In this study, we examined the spatial and temporal patterns of heavy metal accumulation in soils of Shihwa marsh and sought correlations between several soil variables (pH, electrical conductivity, organic matter, and acid ammonium oxalate-extractable Fe and Al contents) and the heavy metal concentration of soils. Surface soil samples (0∼20 cm) were collected in June 2000, November 2000, and July 2001, and were analyzed for heavy metals (Zn, Cd, Pb, Cu, Cr, As, and Hg) and soil chemical properties. The neutral pH and water-saturated conditions of Shihwa marsh appeared to favor immobilization of heavy metal through adsorption onto soils. The concentrations of heavy metal (especially Zn, Cu, and Cr) in soils of Shihwa marsh increased along the sampling occasions, suggesting that soils of Shihwa marsh serve as a sink of heavy metal. Among the sub-marshes, metal concentrations were highest in Banweol high marshes and lowest in Samhwa marshes. The temporal and spatial variations in the heavy metal concentrations of soils were correlated positively with organic matter and oxalate extractable Fe and Al contents, but negatively with electrical conductivity. These results suggest that organic matter and hydrous oxide of Fe/Al may playa key role in removing heavy metals in soils of Shihwa marsh, and that heavy metal removing capacity would increase with desalinization. However, the removal patterns of heavy metal by reeds warrant further studies to evaluate the total removal capacity of heavy metals by Shihwa marsh.

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.