Browsing by Author "Awadzi, T.W."
Now showing 1 - 8 of 8
Results Per Page
Sort Options
Item Characteristics and genesis of pisolitic soil layers in a tropical moist semi-deciduous forest of Ghana(Geoderma, 2007-09) Breuning-Madsen, H.; Awadzi, T.W.; Koch, C.B.; Borggaard, O.K.In the tropical moist semi-deciduous forests of West Africa, gravelly soil horizons common on the summits and upper slopes in the landscape, are often covered by a thin layer of gravel-free soil. Previous investigations have shown that these top layers are formed by termites transporting gravel-free soil material from the subsoil to fallen logs and branches on the soil surface. The present study located at the upper part of a catena at Kade in Ghana shows that the gravel consists of iron nodules or pisolites of varying degree of cementation, quartz and a few remnants of unweathered metamorphic stones. According to chemical and mineralogical studies of pisolites from E, Bt and Bt/Cg horizons, pisolites in the three horizons consist of well crystallized goethite and hematite, and the pisolite content and hardness decrease with increasing soil depth. Furthermore, the very hard pisolites from the E horizon are richer in total iron oxides, especially hematite, than the pisolites in the horizons below but iron oxide crystallinity is similar in the three horizons indicating that pisolite hardening depends on the total content of iron oxides, in particular hematite. Based on the location of the gravel-rich soil horizon in the landscape, a general route for development of pisolite-rich soil horizons in West Africa is proposed including the following processes: (i) An upward transport of gravel-free material to the soil surface due to termite activity, (ii) ongoing removal of this material by water erosion, (iii) weathering of the rather soft metamorphic bedrock present at shallow depth and (iv) gley formation. These processes will over time lead to a lowering of the land surface and concentration of pisolites at the soil surface or in a layer near the soil surface. © 2007 Elsevier B.V. All rights reserved.Item The combined effect of termite bioturbation and water erosion on soil nutrient stocks along a tropical forest catena in Ghana(Catena, 2019-03) Kristensen, J.A.; Boëtius, S.H.; Abekoe, M.; Awadzi, T.W.; Breuning-Madsen, H.In the tropical moist semi-deciduous forests of West Africa, soil catenas with extremely gravel-rich soil horizons at the summits and upper slopes and largely gravel-free profiles at the lower slope are common. Previous investigations have suggested that these gravel layers are the result of macro-invertebrates mining of fine-grained soil material from the subsoil leaving behind the gravel, to build galleries at the surface subsequently exposing it to water erosion transport downslope. We examined the indirect effect of this process on the distribution along a soil catena of crucial base cations (Ca2+, Mg2+, K+) and plant available phosphorous (P), which is often growth-limiting in these tropical ecosystems. We found that the export of fine-grained soil material at the top of the catena reduces the soil stocks (to 1 m) of these elements by up to 60%, while the soil fertility downslope did not change significantly. This important long-term (100–1000 yr scale) reduction in soil fertility at the top of slopes resulting from bioturbation and water erosion is overlooked in contemporary literature, which primarily focus on the beneficial impact termites and ants have on ecosystem functioning in more level savannah landscapes. As the type of catena studied is widespread across tropical environments, this effect is likely ecologically substantial. Future research should aim at understanding such long-term consequences of bioturbation on landscape ecology as well as soil heterogeneity and fertility, so we do not overlook potential negative ecosystem effects.Item Deposition of Nutrients From Harmattan Dust in Ghana, West Africa(Pedosphere, 2015-08) Breuning-Madsen, H.; Awadzi, T.W.; Lyngsie, G.In order to measure dust's nutrient input on farmland in different agro-ecological zones, Harmattan dust was sampled by mats with plastic straw in Ghana between 2002–2006. The inputs of total nutrients by Harmattan dust in Ghana per Harmattan period were about 1–2 kg Ca ha−1, 0.5–2 kg K ha−1, 0.5–1.5 kg Mg ha−1 and less than 0.5 kg P ha−1. Compared with the annual input of nutrients by precipitation, the dust accounted for 10% or less of Ca, Mg and K but approximately 20%–40% of P. The input of nutrients by dust was only valid for areas with vegetation, because in areas with none or sparse vegetation, loss of soil due to wind erosion and hereby loss of nutrients might be significant. In farmland areas with bare and vegetated fields there seemed to be an internal redistribution of the nutrients and not a net gain of nutrients from outside the area (long-range transported dust). The input of P by dust might be of some importance in the traditional shifting cultivation systems, while the inputs of other three nutrients of Ca, Mg and K were so low that they must be considered insignificant. In the intensive agriculture systems with huge inputs of manures and fertilizers the nutrient input by dust is insignificant and could be neglected. Deposition of Nutrients From Harmattan Dust in Ghana, West Africa | Request PDF. Available from: https://www.researchgate.net/publication/279865257_Deposition_of_Nutrients_From_Harmattan_Dust_in_Ghana_West_Africa [accessed Sep 12 2018].Item Harmattan dust deposition and particle size in Ghana(Catena, 2005-09) Breuning-Madsen, H.; Awadzi, T.W.In Ghana, a dust-laden Harmattan wind blows from the Sahara from November to March. Some of the dust is trapped in the vegetation, in the lakes and other inland waters, while the rest is blown further away into the Ivory Coast or into the Atlantic Ocean. Several methods have been used to trap the Harmattan dust, mainly bowls with or without water, but also plates or sheets of various materials have been used. This paper compares three different methods to trap the Harmattan dust and describes the differences in amount and particle size distribution of dust trapped in various agroecological zones. The investigation shows that bowls with water trap more dust than plastic mats with 1.5 cm straw which again trap more dust than wooden plates. The bowl values can be used as a measure of the total Harmattan dust deposition, the mat values can be used as a measure of how much Harmattan dust is retained by vegetation, while the plates provide a measure of how much dust is retained on vegetation free areas. The amount of Harmattan dust captured is largest in the north, the amount of dust retained differs significantly from year to year, and a severe Harmattan in the north is not necessary coincident with severe Harmattan in the south. The dust particle size becomes finer towards the south and with increasing amounts of organic matter, and the particle size distribution shows that the major part of the dust trapped is long-term suspended material with a significant input of local dust. The dust particle size is coarser on the mats than in the bowls due to re-suspension from the mats. The presence of diatoms in the samples from Bawku indicates that a substantial part of the dust originates from former lakes in the Sahara. The amount of dust retained in the north gives a deposition rate of about 15 mm per 1000 years. This may explain why loess layers have not developed in Ghana. © 2005 Elsevier B.V. All rights reserved.Item Influence of the inter tropical discontinuity on Harmattan dust deposition in Ghana(Geochemistry, Geophysics, Geosystems, 2013-09) Lyngsie, G.; Olsen, J.L.; Awadzi, T.W.; Fensholt, R.; Breuning-Madsen, H.The Harmattan is a dry dust-laden continental wind, and in the boreal winter Harmattan dust plumes affects many West African countries, including Ghana. When the Harmattan is strongest the southern part of Ghana is affected by the Inter Tropical Discontinuity (ITD). In this study, we investigate if the ITD functions as a barrier, preventing long transported Harmattan dust to settle south of, and below, it. This is done by analyzing a Harmattan dust outbreak, mapped using Earth observation (EO) data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the Meteosat Second Generation (MSG) platform, coupled with data from West African AERONET stations, and comparing these observations with wind data from NOAA's Air Resources Laboratory (ARL) program and the mineral suite of samples from seasonal dust deposits in north and south Ghana. In northern Ghana traces of minerals indicate a weak influence of particles from an arid environment, which is found consistent with the mapped dust plumes and NE wind directions. In southern Ghana the mineral composition show no sediments of an arid origin, the mapped dust plumes is less intense, and the surface wind directions and wind mass trajectories are more varying with lower wind speeds. Based on the results of this study it is concluded that dust deposited, or measured near ground, in the Harmattan period under the ITD, and south of it, does not contain material from the Chad Basin due to the local winds conditions. © 2013. American Geophysical Union. All Rights Reserved.Item Mineralogy of dust deposited during the Harmattan season in Ghana(Geografisk Tidsskrift, 2007-01) He, C.; Breuning-Madsen, H.; Awadzi, T.W.In Ghana, a dust-laden Harmattan wind blows from the Sahara in the period November to March. Some of the dust is trapped in the vegetation, in lakes and other inland waters, and a little on the bare land, whereas the rest of the dust is blown further away to the Ivory Coast or out into the Atlantic Ocean. In this project, we studied samples of dust and topsoils in various agroecological zones, from the north to the south of Ghana, focussing mainly on the mineralogy of these materials. Some data about grain sizes and morphology of the samples are also presented. Feldspars, together with quartz, are the common minerals found in Harmattan dust, but the relative contents of K-feldspars and plagioclase vary markedly in the different zones. This variation is consistent with changes in the relative content of the feldspars in the topsoil, indicating a substantial local contribution to the Harmattan dust. This conclusion is supported by the clay mineralogy of the samples. However the pH of the dust is significantly higher than that of the local soils, indicating that a substantial amount of the dust comes from the Sahara.Item The role of termites in soil formation in the tropical semi-deciduous forest zone, Ghana(Geografisk Tidsskrift, 2004-01) Awadzi, T.W.; Cobblah, M.A.; Breuning-Madsen, H.Soil Macrofauna especially insects have been recognized as being an important factor in regulating soil processes and thereby the soil profile development. The influence of earthworms is well documented and it is the dominant member of the soil macrofauna influencing the soil formation processes in the temperate zone. In the tropics, termites and ants play the major role in the nutrient recycling and the movement and transportation of soil material. This paper describes the influence of termites on the soil formation in the tropical wet semi-deciduous forest in Ghana at the north coast of the Gulf of Guinea. The termites form distinct soil horizons especially at the summits of the landscapes where gravel free soil horizons are formed upon gravel rich horizons, and in some cases soil heaps are formed after the decomposition of huge trees.Item A scientific evaluation of the agricultural experiments at Frederiksgave, the Royal Danish plantation on the Gold Coast, Ghana(Geografisk Tidsskrift, 2001-01) Awadzi, T.W.; Bredwa-Mensah, Y.; Breuning-Madsen, H.; Boateng, E.In the 1830s agricultural experiments were carried out at the Danish state plantation Frederiksgave at the Danish Gold Coast Establishments, in order to establish an economical sustainable plantation system which could produce export crops to among others the European market. Experiments were made with coffee, tobacco, sugar cane and some other crops and spices, but they failed. Based on climatic data from Frederiksgave for the year 1835 and from nearby climatic stations in the 20th century combined with soil data from the dominant soil types analysed in 1999, the natural reasons for the lack of success are discussed.