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fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Dawit, Mekibib David
Languages: English
Types: Doctoral thesis
The methylamines (MAs) are chemical analogues of ammonia and contain one, two or three methyl groups. This study looked at their occurrence in inter-tidal sediments and at changes in their abundance during tidal cycling, including forced and naturally occurring sediment resuspension. Two sites in the UK, Burnham Overy Staithe (BOS) and the Thames Estuary (TE), and the Ria Formosa (RF), Portugal,\ud were chosen for the study.\ud \ud The MAs were abundant in all samples collected. MA concentrations were compared to NH ₄⁺ at BOS and TE. A consistent trend emerged, with NH ₄⁺ more abundant in the pore-waters and the MAs dominating the solid phase. Most NH ₄⁺ and MAs were found on the solid-phase, and the general magnitude of adsorption was:\ud TMA > DMA > MMA > NH ₄⁺. This was inconsistent with their pKb values but could be explained by the ability of each cation to form hydrogen bonds with water.\ud \ud Pore-water MA concentrations at BOS were compared with salinity but no correlation was observed. However, the clam Ruditapes decussatus (L.) released TMA during tidal inundation. The mechanism of release is unclear as these organisms do not osmoregulate, but the calculated TMA loss from these sediments (169 mmol m⁻² per tide) could be increasing dissolved organic nitrogen concentrations in the Ria\ud Formosa.\ud \ud TE sediments were used in desorption experiments. Desorption of NH ₄⁺ was more rapid than the MAs and their mean chemical response times were 15 and 25 minutes, respectively. Increases in concentrations of dissolved \ud NH ₄⁺ and MAs over a tidal cycle were coincident with remobilisation of seabed sediments. Desorption of NH ₄⁺ and MAs from the remobilised sediments accounted for approximately 50% and > 90% of the increase, respectively. The results are proposed as a predictor for the sorption behaviour of other ON compounds and emphasise the importance of sediment resuspension as a mechanism of ON release to the water column.
  • The results below are discovered through our pilot algorithms. Let us know how we are doing!

    • Sampling at Site 2.
    • 2.2.3 Thames Estuary.
    • Sample collection for determination of depth profiles ofN species.
    • Determination of suspended particulate material (SPM).
    • 2.3 Determination of nitrogen compounds.
    • 2.3.1 Reagents and standard solutions for NH/ and MA analysis.
    • 2.3.2 Determination ofNH4 +.
    • N~ + extraction techniques Procedure for N~ + analysis Calibration of the spectrophotometric technique for N~ +analysis.
    • Glassware preparation.
    • Design of the micro-diffusion flask.
    • Selection of internal standard.
    • Synthetic seawater preparation.
    • Calibration of the analytical technique.
    • Calculation of analyte recovery through micro-diffusion.
    • Application of the micro-diffusion process.
    • Gas chromatography.
    • Reproducibility of environmental samples.
    • 2.3.3 MA determination of Site 2 samples.
    • Mantle cavity-water.
    • Surrounding sediment and clam tissue.
    • 2.3.4 Calculations of potential exchangeable MA concentrations in clam samples.
    • 2.3.5 Calculation of adsorption coefficients for N~ +and MAs.
    • 2.4 Determination of sedimentary total organic carbon (TOC) and total nitrogen (TN) content. Determination of selected physico-chemical parameters. Measurement of pore-water content. Porosity measurement. Grain size analysis. Salinity measurement. Laboratory simulated tidal action experiment. Extraction of sediments. Calculation of extraction efficiencies.
    • Carpenter, E. 1 and Capone, D. G. (1983). In Nitrogen in the Marine Environment (eds.), Plenum Press, New York, pp649-678.
    • Carpenter, EJ. and Dunham, S. (1985). Nitrogenous nutrient uptake, pnmary production, and species composition of phytoplankton in the Carmans River Estuary, Long Island, New York. Limnol. Oeeanogr., 30:513-526.
    • Chorst, RJ. and Riemann, B. (1994). Storm-simulated enzymatic decomposition of organic matter in benthic/pelagic coastal mesocosms. Mar. Eeol. Prog. Ser., 108:185- 192.
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    • Fitzsimons M.F., Millward G.E., Revitt D.M. and Dawit M.D. (2006). Desorption kinetics of ammonium and methylamines from estuarine sediments: Consequences for the cycling of nitrogen. Mar. Chem., 101:12-26.
    • Fitzsimons, M.F., Dawit, M., Revitt, D.M. and Rocha, C. (2005). Effects of early tidal inundation on the cycling of methylamines in inter-tidal sediments. Mar. Ecol. Prog.
    • Ser., 294:51-61.
    • ~ Fitzsimons, M.F., Kamhi-Danon, B. and Dawit, M. (2001). Tidal control on distributions of the methylamines in an East-Anglian estuary: a potential role for benthic invertebrates? Environ. Experim. Bot., 46:225-236.
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    • > Laima, M.1C. (1992). Extraction and seasonal variation of NH/ pools in different types of coastal marine sediments. Mar. Ecol. Prog. Ser., 82:75-84.
    • > Lam, D.C.L. and Jaquet, 1M. (1976). Computations of physical transport and regeneration of phosphorus in Lake Erie, Fall 1970. Journal of Fisheries Resources Board, Canada, 33:550.
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    • ~ Shiedler, G.L. (1984). Suspended sediment responses in a wind dominated estuary of the Texas Gulf Coast. J. Sed. Petr., 54:731-745.
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  • No similar publications.

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