Role of Possible Soil toxicity in Die back of Montane Forests in Sri Lanka.
Abstract
Rapid dying back of Tropical Upper Montane Rain forests of Sri Lanka which are considered as "Biodiversity Hotspots" is a nationally as well as globally important environmental issue. Although various hypotheses were tested during recent past, nothing could be proved except the possible involvement of soil toxicity due to excess levels of certain elements. This study investigated the extractable soil trace and major element levels in 3 pilot plots situated in dieback and healthy forests. Based on the results, Al, Mn, Fe and Pb concentrations in 30 individuals of 08 most susceptible plant species at different dieback stages and in soils in the immediate vicinity in Hakgala Strict Nature Reserve of Sri Lanka were determined in order to recognize the contribution of these element in forest die back. Collected Plant leaves were analyzed for total element levels and soils were analyzed for the extractable element levels. This study reveals the presence of high DTPA extractable Pb (0.6 - 2.4 ppm), Mn (1.7-57.2ppm), Fe (48.1- 372.1ppm) and KCl extractable Al (0.7-390.8 ppm) in soils. The most important observation was the presence of high accumulations of Pb (2.2-36.3 ppm) and Al (18.9 - 20047.6 ppm) in plant leaves which are high above the normal range. Acidic conditions in soils (pH 4.2-5.6) may increase Al+3 from Al bearing feldspar rich soils. Increased soil acidity due to lowering the pH of precipitation by air pollution may also contribute in dissolution of toxic Al+3. Extractable Soil Pb levels are higher on wind exposed slope areas. Increased Pb levels in soils on slope areas, differences between total and extractable soil Pb levels, amounts of washable Pb on leaves before and after the banning of Pb containing gasoline usage and comparisons of Pb levels in plants with known Pb polluted areas of the country prove that air pollution could be the main Pb source in this montane forests soils. Although no direct relationship could be recognized between element levels in plants and die back stage, possibly due to physiological factors of plants, high concentration of Al and Pb might impose stresses on plants facilitating die back.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.B43B0439R
- Keywords:
-
- 0461 Metals;
- 1865 Soils (0486);
- 4251 Marine pollution (0345;
- 0478)