Saturday, 15 July 2006

The Current Status of the Soufriere Hill Volcanic Ejecta on the Andosols of Montserrat.

Kamala N. Bhat1, Robert Taylor2, Thilini D. Ranatunga1, Zachary N. Senwo1, Richard H. April3, and Bruce Jackson4. (1) Alabama A&M University, Department of Plant and Soil Science, P.O. Box 1208, Normal, AL 35762, (2) Department of Plant and Soil Science, Alabama A&M University, 4900 Meridian Street, Normal, AL 35762, (3) Colgate university, Department of Geology, Hamilton, NY 13346, (4) University of Massachusetts Lowell, Department of Biological Sciences, One University Avenue, Lowell, MA 01854

The intermittent volcanic ejecta from Soufière Hill volcanic eruption after 1995 has necessitated the evaluation of soil surface and its properties to better evaluate the future land use and management, once the exclusion zone is opened for re-habitation. Preliminary studies of ash and ash samples from this zone indicate the absence of secondary minerals. Further in the bulk, silt and clay fraction, no phyllosilicate clay mineral material has been found by XRD measurements. The main constituent of the Soufrière Hill ejecta to date consists of cristobalite and plagioclase. The ash and ash/soil samples from regions with and without any vegetation contain albite, anorthite, amphibole, some (hornblende) and cristobalite, which have been found up to a depth of 6 inches or more. The soils and ash samples are highly acidic with pH in the range of 3.6(ash) - 5.8(soil). The total concentration of ten different elements obtained by XRF measurement shows that the ratio of Si/Al is almost 4:1 in the samples analyzed to date. The total amount of each element, present in the form of their oxides, expressed as percentages, are Si> Al> Ca=Fe>Na>Mg>K>Ti>Mn>P. The amount of Al in the ash (using KCl method) and together with the Si / Al ratio can affect the productivity of the soil. Micronutrient element concentrations determined by 0.1M HCl, DTPA, Mehlich-1 and Mehlich -3 were relatively low in ash and soils. However high concentration of available Ca, Mg and P were found in the ash using Mehlich -1 and Mehlich -3 extractants. Such analysis gives insight into the bioavailability of these nutrient elements and the ash, as well as the ash's value as a soil amendment. However the presence of high levels of Al may cause Al toxicity and lead to stress in plants, so that when management and agricultural issues are debated suitable plants must be chosen that can withstand high acidity due to Al as well as Al toxicity.

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