Abstract The ability of three plant species: Helianthus annuus, Nicotiana tabacum, and Vetiveria zizanioides for phytoaccumulation of Pb was studied. Plants were grown in hydroponic solution containing Pb(NO3)2 at concentration of 0.25 and 2.5 mM Pb in the presence or absence of chelating agents (EDTA or DTPA). Lead (Pb) transport and localization within the tissues of the plant species was determined using scanning electron microscope equipped with energy dispersive X-ray spectrometers (SEM-EDS). The addition of chelators increased Pb uptake as compared to plants grown in solution containing Pb alone. Lead taken up by the plant species were concentrated in both leaf and stem at the region of vascular bundles with greater amounts in the leaf portion. Lead granules were also found in the H. annuus root tissue from the epidermis layer to the central axis. After four weeks of growth a 23-fold increase in shoot Pb content for H. annuus and N. tabacum and 17-fold increase in shoot Pb for V. zizanioides resulted from plants grown in the 2.5 mM Pb-EDTA treatment. The higher Pb treatment (2.5 mM Pb containing EDTA) resulted in higher concentrations of Pb in plant tissue at the fourth week of exposure as compared to Pb treatment containing DTPA. Overall, Pb accumulation potential of H. annuus was greater than that of N. tabacum and V. zizanioides as indicated by the bioconcentration factor (171, 70, and 88, respectively). The highest measured Pb concentrations were found in H. annuus roots, stems, and leaves (2668, 843, and 3611 μg/g DW, respectively) grown in the 2.5 mM Pb-EDTA treatment. The addition of chelators caused some reduction in plant growth and biomass. Results showed that the three plant species tested have potential for use in phytoaccumulation of Pb since the Pb was concentrated in leaf and stem as compared to control plants. H. annuus however best meet the prerequisites for a hyperaccumulator plant and would have the potential for use in the restoration of abandoned mines and factories sites contaminated with elevated Pb levels in the soil. Keywords: PhytoremediationLeadHyperaccumulatorsSynthetic chelatorsNutrient film technique (NFT)SEM-EDS ACKNOWLEDGMENTS This research work was supported by the grant from the PostGraduate Education, Training and Research Program in ESTM through Higher Education Development Project of the Ministry of University Affairs. The authors also thank Field Crop Research Institute, Department of Land Development (Regional Office 1), Dr. S. Panasahatham of the Thailand Tobacco monopoly and Mae Jo Tobacco Experiment Station for providing the plant materials for the Pb uptake experiments. The assistance of P. Poochianya of the Scientific Equipment Center, Kasetsart University in using the SEM and EDS system is duly acknowledged.
Within the last century the Louisiana coastline began an accelerated rate of retreat primarily due to rapid subsidence. Implications of changes occurring along the rapidly subsiding Louisiana coast could be of concern worldwide, because of similar situations that may be encountered in the future if the predicted global rise in sea level occurs. The lack of sediment deposition with respect to rapid coastal subsidence cause increased submergence which in turn causes numerous habitat changes. Various human (canal cutting, leveeing, dredging, etc.) and natural processes (hurricanes, tropical storms, etc.) conjunctively influence the rate of deterioration. Landward retreat of the wetlands, in addition to causing land loss, promotes secondary effects such as saltwater intrusion, aquifer contamination, loss of freshwater marshes and disappearance of the present biota. Flooding will cause increases in salinity, waterlogging, and anaerobiosis, killing native vegetation and eventually resulting in open bodies of water.
Core Ideas Application of urea led to higher N 2 O emissions than urea–ammonium nitrate in sugarcane. Residue retention led to higher N 2 O and CH 4 emissions irrespective of N source. Both N source and residue management did not affect CO 2 emissions. Sugarcane ( Saccharum spp.) is a major row‐crop in the southern United States with high rates of N‐fertilizer application and unique harvest‐residue management. A 2‐yr field experiment was conducted to investigate different N‐fertilizer effects (urea and urea ammonium nitrate, UAN) and harvest‐residue managements (residue‐retain, RR, and residue‐burn, RB) on greenhouse gas (GHG) emissions from soils under sugarcane production. In 2012, a split‐plot design experiment was conducted with residue managements as main‐plots and N‐sources as sub‐plots. In 2013, two experiments were conducted to investigate UAN effect under RR and RB, and N‐source effect under RB on GHG emissions. Nitrogen was applied at 135 and 157 kg ha ‒1 in 2012 and 2013, respectively. Soil GHG emissions were monitored using a closed chamber method. Results showed the majority of N 2 O emissions occurred within 4 wk after N‐application. Average N 2 O emissions from urea‐treated plots were 1.43 to 1.67 times higher compared with UAN for 2 yr. Urea had a N 2 O emission factor of 3.52 and 4.45% under RB and RR, respectively, whereas UAN had 1.67 and 2.46% under the same residue management. Higher N 2 O emission under RR treatment was supported by 15 to 20% more water‐filled pore space (WFPS) in soil than RB plots, which also increased CH 4 emissions. Higher correlation was found between N 2 O emission and WFPS in 2012 compared with 2013 ( r 2 = 0.52 vs. 0.36) because a majority of the rainfall in 2012 was received within 3 wk following N application. Nitrogen sources had no effect on CH 4 and CO 2 emissions.
(1) A study was made of nitrogen cycling and the effect of added inorganic nitrogen on biomass production of Panicum hemitomon in the deltaic plain of the Mississippi River. Nitrogen is apparently a limiting nutrient since supplemental nitrogen increased above-ground biomass by 40%. (2) There is apparently little loss of internal nitrogen from the system since 80% of the nitrogen added at the rate of 3 g m-2 was recovered in the soil-plant system at the end of the growing season. (3) Nitrogen fixation was the principal source of nitrogen to this vast freshwater system with 6.7 g m-2 year-' being added. These marshes are apparently serving as large nitrogen sinks, with 12 g m-2 year-' being retained as organic nitrogen as a result of accretion as determined by 137Cs dating. (4) The results suggest that these freshwater marshes may improve water quality by removing nutrients from inflowing water.
Abstract Excess nitrate in Mississippi River water entering offshore areas is reported to contribute to low oxygen (hypoxia) conditions in the Gulf of Mexico. Excessive algal growth driven by the excess nitrogen results in a decrease in dissolved oxygen in bottom water. Reintroduction of Mississippi River waters into a Louisiana coastal wetland has the potential to reduce the amount of nitrate reaching offshore waters. In this study, reduction in the concentration of added NO3 − was determined in sediment–water-columns collected from a wetland site in Breton Sound estuary receiving nutrient inputs from the Mississippi River. The capacity of a wetland to process nitrate in floodwater was determined in the laboratory. The rates of NO3 − removal (determined from change in nitrate concentration in the floodwater) averaged 97 mg N m−2 d−1 over 16 d for a 1750-mg NO3-N m−2 addition, and 170 mg N m−2 d−1 over 16 d for a 3500-mg NO3-N m−2 addition. The total N2O-N emissions from the 1750- and 3500-mg NO3-N m−2 additions were 19 and 54 mg N m−2 accounting for 1.1% and 1.5% of the applied NO3-N, respectively. Using the acetylene-inhibition technique, the average denitrification rate was determined to be 57 and 87 mg N m−2 d−1 (21 and 32 g N m−2 yr−1) during the most active denitrification period of 5 d after incubation for 1750 and 3500 mg NO3 −-N m−2 of added nitrate in floodwater, respectively. The total N evolved over 11 d as N2O + N2 was equivalent to 436 and 921 mg N m−2 (24.9% and 26.3%, respectively, of added N). Increasing the amount of NO3 − applied to the overlying water increased the rate of NO3 − loss and N2O emission significantly. The thickness of the oxidized surface sediment layer was also influenced by the NO3 − application to the floodwater with a significant linear correlation between nitrate addition and thickness of the oxidized layer (r = 0.9998, p = 0.01). This study indicates that wetlands receiving diverted Mississippi River water have the potential to process and remove NO3 − in the river water, reducing the amount of NO3 − reaching to offshore areas. Keywords: NO3− loadingDenitrificationAcetylene blockage techniqueNO3− reductionN2O emission, Mississippi RiverWetland Acknowledgments Funding for this study was provided in part by the Louisiana Water Resource Research Institute and the Louisiana Department of Natural Resources, Coastal Restoration Division.
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