HR: 1340h
AN: B23C-1493    [Abstracts]
TI: Ecological Succession, Land use Changes and Soil Organic C Stock in a Lake Retreat Area (Main Ethiopian Rift Valley)
AU: * Nyssen, J
EM: jan@ethionet.et
AF: Mekelle University, Department of Land Resource Management and Environmental Protection, P.O.Box 231, Mekelle, ET, Ethiopia
AU: * Nyssen, J
EM: jan@ethionet.et
AF: Ghent University, Geography Department, Krijgslaan 281, Gent, B 9000, Belgium
AU: Temesgen, H
EM: habte023@yahoo.com
AF: Mekelle University, Department of Land Resource Management and Environmental Protection, P.O.Box 231, Mekelle, ET, Ethiopia
AU: Temesgen, H
EM: habte023@yahoo.com
AF: Alage TVET College, Department of Natural Resources, P.O.Box 18, Ziway, ET, Ethiopia
AU: Lemenih, M
EM: elrohi@yahoo.com
AF: Wondo Genet College of Forestry, P.O.Box 128, Shashamane, ET, Ethiopia
AU: Zenebe, A
EM: amanuelza@yahoo.com
AF: Mekelle University, Department of Land Resource Management and Environmental Protection, P.O.Box 231, Mekelle, ET, Ethiopia
AU: Zenebe, A
EM: amanuelza@yahoo.com
AF: K.U.Leuven, Physical and Regional Geography Research Group, Celestijnenlaan 200E, Leuven, B 3001, Belgium
AU: Kindu, M
EM: mengistiek@yahoo.com
AF: Ethiopian Agricultural Research Institute, Forestry Research Centre, P.O.Box 30708, Addis Ababa, ET, Ethiopia
AU: Haile, M
EM: gualmitiku@yahoo.com
AF: Mekelle University, Department of Land Resource Management and Environmental Protection, P.O.Box 231, Mekelle, ET, Ethiopia
AB: In the Main Ethiopian Rift Valley, ecological succession is related to continuous lake retreat (Nyssen et al., 2004). Human activities, through their impact on land use and cover, affect this ecological succession. Through a remote sensing study, we extricated ecological succession and human activity as causative factors for land use and cover changes (LUCC) and explored which impact this has on soil organic C (SOC) stock in lake retreat areas. Remote sensing data used include a Landsat MSS from 1973, a Landsat TM from 1986 and a Landsat ETM+ from 2000. A conventional type of classification was used whereby supervised classification of the 2000 image was supplemented by unsupervised classification of the older datasets. Due to decreased rainfall and water abstraction for intense irrigated agriculture and floriculture in its catchment, Lake Abijata lost 46 % of its area between 2000 and 2006. On the emerged lands, a good ecological succession was observed between 1973 and 1986, with clear evidence for: emerged land -> grassland -> Acacia bushes -> open woodland. Between 1986 and 2000, LUCC tendencies were totally reversed and woody vegetation decreased strongly, indicating increased human impact (Habtamu et al., 2007). Based on an analysis of the Landsat imagery, coupled with soil and land use studies, determinants for SOC stock were found. Firstly, SOC stock significantly differs between cultivated land and grazing land (3301 and 2626 g m-2) on the one hand, and woodland (4594 g m-2) on the other. The strongest explanation of SOC stock is related to the duration of emergence and hence of pedogenesis. Its proxy, elevation, explains much of the variability of SOC (R2 = 0.48). Using a multiple regression model involving elevation and IR reflectance, the SOC stock in the study area could be assessed at 2196 (+ - 1517) g m-2 SOC in 2000, against 3222 (+ - 1639) g m-2 in 1973 (Nyssen et al., 2007), which is related to the post-1986 reversing of ecological succession in the lake retreat areas. Habtamu Temesgen, Nyssen, J., Amanuel Zenebe, Mengistie Kindu, Mitiku Haile, 2007. Ecological succession and land use changes in a lake retreat area (Main Ethiopian Rift Valley). Journal of Arid Environments, submitted. Nyssen, J., Poesen, J., Moeyersons, J., Deckers, J., Mitiku Haile, and Lang, A., 2004. Human impact on the environment in the Ethiopian and Eritrean Highlands – a state of the art. Earth Science Reviews, 64: 273-320. Nyssen, J., Habtamu Temesgen, Mulugeta Lemenih, Amanuel Zenebe, Mitiku Haile, 2007. Soil organic C stock in a lake retreat area under increased human pressure (Main Ethiopian Rift Valley). Global Change Biology, submitted.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0442 Estuarine and nearshore processes (4235)
DE: 0480 Remote sensing
DE: 1813 Eco-hydrology
SC: Biogeosciences [B]
MN: 2007 Fall Meeting