Manoch Kongchum

Methyl Mercury and Heavy Metal Content in Soils of Rivers Saale and Elbe (Germany)

Abstract The rivers Saale and Elbe, including their catchment areas (Germany), have been heavily polluted by ore mining and other anthropogenic emission sources during the last centuries. Heavy metal contamination along the Elbe River floodplains can vary depending on location. In this study data on methyl mercury, mercury, and other heavy metal contents in three soil profiles from a representative site under the influence of the rivers Elbe and Saale are presented. The relationship of metal distribution to chemical and physical characteristics in the soil profiles is outlined. Methyl and total mercury were detected in extremely high concentrations in the soil profiles. Results showed that Zn, Cu, and Pb were elevated, above the reported levels considered as excessive in soils. Concentrations of Ni, Cd, and Se were not elevated, while other elements (Al, Na, K, Ca, Mg, Mn, and Fe) were at geological or background levels. The research was supported by National Science Foundation (Grant # INT 9901301).

Effect of Straw Incorporation on 15N‐Labeled Ammonium Nitrogen Uptake and Rice Growth

Abstract A greenhouse experiment was conducted to determine the effect of rice straw residue on growth and uptake of added 15N‐labeled ammonium nitrogen (NH4‐N) (3% 15N abundance at the rate of 150 kg N ha−) by rice in Crowley silt loam soil (Typic Albaqualfs). Higher rates of rice straw addition had an adverse affect on plant growth from the first to sixth week. After 6 weeks, the high rice straw treatment had a positive effect on plant growth (P<0.05). The 15N‐labeled ammonium or fertilizer nitrogen (N) uptake by rice was significantly lower (P<0.05) in the high rice straw treatment as compared to lower rice straw treatments. Greater plant growth was recorded under alternate flooding and draining condition as compared to continuously flooded treatment (P<0.01).

Total Hg and methyl Hg distribution in sediments of selected Louisiana water bodies

Sediment samples (543) collected from selected Louisiana streams and lakes were analyzed for total Hg and methyl Hg content. The average total Hg content among 543 samples was 92.3 ± 95.1 μg kg−1. The average methyl Hg content in the samples was 0.68 ± 0.80 μg kg−1. Methyl Hg accounted for an average of 0.73% of the total Hg in sediment. Linear regression analysis of total Hg versus methyl Hg content of the sediment showed methyl Hg content was significantly correlated to total Hg content of sediment (P > 0.01, n = 537) and sediment organic matter content. (P > 0.01, n = 536) Methyl Hg was also positively correlated to clay (P > 0.01, n = 537) and inversely correlated to sand content of sediment (P > 0.01, n = 537). Total Hg and methyl Hg content in these sediments was within the normal range reported elsewhere indicating no significant industrial or municipal Hg contamination. A comparison of selected water bodies with fishing advisories showed no relationship to total Hg and methyl Hg in sediment.

Effect of Plant Residue on Germination of Selected Rice Cultivars

Abstract The effects of rice straw and alligator weed (Alternanthera philoxeroides) residue on germination of selected rice cultivars grown in Louisiana were studied. Germination was influenced by both plant residue source and application rate. Alligator weed, which caused a rapid decrease in soil redox and pH, had a greater impact on germination than rice straw addition. There were distinct differences in rice cultivars ‘response’ to plant residue application rate and source. Alligator weed showed significant germination inhibition for all cultivars tested as compared to rice straw.

Mercury adsorption in the Mississippi River deltaic plain freshwater marsh soil of Louisiana Gulf coastal wetlands

Mercury adsorption characteristics of Mississippi River deltaic plain (MRDP) freshwater marsh soil in the Louisiana Gulf coast were evaluated under various conditions. Mercury adsorption was well described by pseudo-second order and Langmuir isotherm models with maximum adsorption capacity of 39.8 mg g-1. Additional fitting of intraparticle model showed that mercury in the MRDP freshwater marsh soil was controlled by both external surface adsorption and intraparticle diffusion. The partition of adsorbed mercury (mg g-1) revealed that mercury was primarily adsorbed into organic-bond fraction (12.09) and soluble/exchangeable fraction (10.85), which accounted for 63.5% of the total adsorption, followed by manganese oxide-bound (7.50), easily mobilizable carbonate-bound (4.53), amorphous iron oxide-bound (0.55), crystalline Fe oxide-bound (0.41), and residual fraction (0.16). Mercury adsorption capacity was generally elevated along with increasing solution pH even though dominant species of mercury were non-ionic HgCl2, HgClOH and Hg(OH)2 at between pH 3 and 9. In addition, increasing background NaCl concentration and the presence of humic acid decreased mercury adsorption, whereas the presence of phosphate, sulfate and nitrate enhanced mercury adsorption. Mercury adsorption in the MRDP freshwater marsh soil was reduced by the presence of Pb, Cu, Cd and Zn with Pb showing the greatest competitive adsorption. Overall the adsorption capacity of mercury in the MRDP freshwater marsh soil was found to be significantly influenced by potential environmental changes, and such factors should be considered in order to manage the risks associated with mercury in this MRDP wetland for responding to future climate change scenarios.