Southwestern Ghana Research Articles

Anthropogenic sources of mercury pollution in the Ankobra river basin in the south western Ghana

Anthropogenic sources of mercury pollution in the Ankobra river basin in the south western Ghana

Geochemistry of an ultramafic-rodingite rock association in the Paleoproterozoic Dixcove greenstone belt, southwestern Ghana

Rodingite occurs in ultramafic rocks within the Paleoproterozoic (Birimian) Dixcove greenstone belt in southwestern Ghana. U–Pb analyses of zircons from granitoids intrusive into the greenstone belt constrain the age of the rodingite-ultramafic association to be older than 2159 Ma. The ultramafic complex consists of variably serpentinized dunite and harzburgite overlain by gabbroic rocks, which together show petrographic and geochemical characteristics consistent with their formation by fractional crystallization involving olivine and plagioclase cumulates. Major and trace element concentrations and patterns in the ultramafic–mafic cumulate rocks and associated plagiogranite are similar to rocks in ophiolitic suites. The rodingites, which occur as irregular pods and lenses, and as veins and blocks in the serpentinized zones, are characterized by high Al 2O 3 and CaO contents, which together with petrographic evidence indicate their formation from plagioclase-rich protoliths. The peridotites are highly depleted in REE and display flat, chondrite-normalized REE patterns with variable, but mostly small, positive Eu anomalies whereas the rodingites, which are also highly depleted, with overall REE contents from 0.04 to 1.2 times chondrite values, display distinct large positive Eu anomalies. It is proposed that the rodingite-bearing Birimian ultramafic complex and associated pillowed greenstone belt basalts may represent fragments of a Paleoproterozoic oceanic lithosphere.

Risk of crop raiding by elephants around the Kakum Conservation Area, Ghana

This Augsut 2000-September 2002 study monitored crop damage by elephants in the vicinity of Kakum CA. The Conservation Area, comprised of about 370 sq kms formerly known as Kakum NP and Attandanso FR, has a population of about 220 elephant. The forest in the protected area is a fragment of the lowland forest the once occupied much of southwestern Ghana. (Adjewodah, et al. 2005: Barnes, et al. 2003) The CA is almost completely surrounded by agricultural land under both subsistance and commerical cropping. 10 study sites of one sq each were randomly chosen around the periphery of the CA. A local villager was trained and hired to monitor and record elephant caused damage to crops. In 2001 a total of 213 fields were monitored. 55 of these fields suffered damage and a 120 incidents were recorded. It was apparent that distance from the CA boundary, size of field, type and number of crops in the field of crop, and isolation of the field all played a role is whether of not the field was raided. Maize and cassava were the most commonly raided crops and plantains were third. Smaller and more isolated fields close to the park were most often raided, however elephant also seemed to be attacted and larger farms with many crops in the fields. Recommendations suggest 'a farmer could drastically reduce risk by moving away from the park boundary, joining other farmers in a cluster, limiting farm size and growing fewer kinds of crops. This study was part of the training programme for officer interested elephant biology and management.

Heavy Metals in Sediments of the Gold Mining Impacted Pra River Basin, Ghana, West Africa

Total concentrations of Hg, Al, Fe, As, Pb, Cu, Cr, Ni, Mn, Co, V, and Zn were determined in surface sediments collected from 21 locations within the gold mining impacted Pra River basin in southwestern Ghana. Samples were collected during both the rainy and dry seasons. We hypothesized that in the rural southwestern portion of Ghana, the lack of industrial activities makes artisanal gold mining (AGM) by Hg amalgamation the main source of water resource contamination with heavy metals. Therefore, metals showing concentration trends similar to that of Hg in the studied system are likely impacted by AGM. We found that total-Hg (THg) concentrations in riverine sediments are rather low as compared to other aquatic systems that are impacted by similar mining activities. Measured THg concentrations ranged from 0.018 to 2.917 mg/kg in samples collected in the rainy season and from about 0.01 to 0.043 mg/kg in those collected during the dry season. However, the determination of the enrichment factor (EF) calculated using shale data as reference background values showed signs of severe contamination in most of the sampled sites. In the dry season, THg concentrations correlated positively and significantly to the concentrations of As (r = 0.864, p < 0.01), Cu (r = 0.691, p < 0.05), and Ni (r = 0.579, p < 0.05). Based on our previously stated hypothesis, this could then be an indication of the impact of AGM on ambient levels of these 3 elements. However, the determined concentrations of Cu, and Ni co-varied significantly with Al, suggesting that natural sources do account for the observed levels. Accordingly, both AGM and metal inputs from weathered natural deposits are likely co-responsible for the observed levels of Cu and Ni. In contrast, the lack of correlation between As and Al tends to suggest an impact of AGM on As levels. Overall, our data suggest that besides Hg and to some extent As, the impact of AGM on ambient levels of investigated metals in the gold mining impacted Pra River remains negligible. Finally, the increase in metal concentrations from the dry to the rainy season underlines the impact of changes in hydrologic conditions on levels and fate of metals in this tropical aquatic system.

Mercury in different environmental compartments of the Pra River Basin, Ghana

Artisanal gold mining (AGM) with metallic mercury has a long history in Ghana. It is believed to be over 2000 years old. Today, AGM has escalated in a new dimension consuming about half of the country where gold lode deposits exist along riverbanks or rivers are alluvial-gold rich. The Pra River in southwestern Ghana is a site of on going application of metallic mercury in prospecting gold, and this paper examines mercury (Hg) contamination in the different environmental compartments in its watershed. Samples of water, sediment, soil and biota (i.e., human hair and fish) were collected from locations along the course of the river during the rainy and dry seasons of 2002 and 2003, respectively. Besides the obvious Hg point sources along the Pra and its tributaries, the obtained results show that Hg levels and speciation in the studied aquatic system are controlled by precipitation, which drives the hydrology and differences in flow regimes versus seasons. The seasonal difference in Hg speciation suggests that methyl mercury (MeHg) found in the aqueous phase and riverine sediments is likely of terrestrial origin where its production is favored during the rainy season by high soil water and organic matter content. The use of the enrichment factor (EF) for the assessment of sediment quality indicated moderate to severe contamination of surface sediments in the rainy season, while in the dry season, the EF index indicates nearly no pollution of surface sediments. Accordingly, most of the Hg introduced into this river system is likely transported to depositional downstream terminal basins (e.g. the river delta and the Gulf of Guinea). With regard to biota, Hg measured in hair in the dry period was higher than data obtained on samples collected during the wet period. This could be explained at least in part by the shift in diet as a result of abundance of fish in the local markets and the concurrent increase and more active fishing during the dry season. Mercury data obtained on a very limited number of fish samples collected during the dry period only are also presented.

Structure and Operation of a Bushmeat Commodity Chain in Southwestern Ghana

Abstract: The bushmeat trade is perceived as a major threat to wild animal populations in the tropics. Little is known of how the trade is organized, however, or of the actors involved in it, impeding the development of effective conservation policy. We investigated the structure and operation of a bushmeat commodity chain in West Africa that supplies a typical urban market, the city of Takoradi in southwestern Ghana. Data were collected from January through February 2000, describing 2430 bushmeat transactions encompassing 17 different taxa from 70 different actors, through a combination of direct observation and semistructured interviews. Five different types of actor traded along the commodity chain: commercial hunters, farmer hunters, wholesalers, market traders, and chopbar (cafe) owners. Bushmeat was traded freely among all these actors, although the primary trade route for terrestrial mammals was from commercial hunters via wholesalers to chopbars. In contrast, invertebrates were only traded by farmer hunters, market traders, and chopbars. Wholesalers captured the largest per capita share of the market (4% of all sales were handled by each wholesaler), whereas the most important vendors were chopbars, which as a group made 85% of all bushmeat sales to the public. Variation in the price of bushmeat was largely explained by transport costs and taste preferences. Transport costs were most significant for hunters and greatest on long journeys involving large loads. Nevertheless, hunters obtained the greatest income per kilogram of bushmeat sold of all actor groups. Our results suggest that there is no single best entry point along the bushmeat commodity chain for conservation intervention. On the contrary, the successful monitoring and management of the bushmeat trade is likely to require a multiactor approach that encompasses most or all actor groups.

Pyrethroid resistance/susceptibility and differential urban/rural distribution of Anopheles arabiensis and An. gambiae s.s. malaria vectors in Nigeria and Ghana.

Resistance to pyrethroid insecticides and DDT caused by the kdr gene in the malaria vector Anopheles gambiae Giles s.s. (Diptera: Culicidae) has been reported in several West African countries. To test for pyrethroid resistance in two more countries, we sampled populations of the An. gambiae complex from south-western Ghana and from urban and rural localities in Ogun State, south-west Nigeria. Adult mosquitoes, reared from field-collected larvae, were exposed to the WHO-recommended discriminating dosage of exposure for 1 h to DDT 4%, deltamethrin 0.05% or permethrin 0.75% and mortality was recorded 24 h post-exposure. Susceptibility of An. gambiae s.l. to DDT was 94-100% in Ghana and 72-100% in Nigeria, indicating low levels of DDT resistance. Deltamethrin gave the highest mortality rates: 97-100% in Ghana, 95-100% in Nigeria. Ghanaian samples of An. gambiae s.l. were fully susceptible to permethrin, whereas some resistance to permethrin was detected at 4/5 Nigerian localities (percentage mortalities 75, 82, 88, 90 and 100%), with survivors including both An. arabiensis Patton and An. gambiae s.s. identified by PCR assay. Even so, the mean knockdown time was not significantly different from a susceptible reference strain, indicating absence or low frequency of kdr-type resistance. Such low levels of pyrethroid resistance are unlikely to impair the effectiveness of pyrethroid-impregnated bednets against malaria transmission. Among Nigerian samples of An. gambiae s.l., the majority from two urban localities were identified as An. arabiensis, whereas the majority from rural localities were An. gambiae s.s. These findings are consistent with those of M. Coluzzi et al. (1979). Differences of ecological distribution between molecular forms of An. gambiae s.s. were also found, with rural samples almost exclusively of the S-form, whereas the M-form predominated in urban samples. It is suggested that 'urban island' populations of An. arabiensis and of An. gambiae s.s. M-form in the rainforest belt of West Africa might be appropriate targets for elimination of these malaria vectors by the sterile insect technique.

Deforestation and the spatio-temporal distribution of savannah and forest members of the Simulium damnosum complex in southern Ghana and south-western Togo

Spatio-temporal data on cytotaxonomic identifications of larvae of different members of the Simulium damnosum complex collected from rivers in southern Ghana and south-western Togo from 1975 until 1997 were analysed. When the data were combined, the percentages of savannah blackflies ( S. damnosum sensu stricto and S. sirbanum) in the samples were shown to have been progressively increasing since 1975. The increases were statistically significant ( P < 0·001), but the rates of increase were not linear. Further analyses were conducted according to the collection seasons and locations of the samples, to account for possible biases such as savannah flies occurring further south in the dry season or a preponderance of later samples from northern rivers having more savannah flies. These analyses showed that the increasing trend was statistically significant ( P< 0·0001) only during the periods April to June and October to December. The presence of adult savannah flies carrying infective larvae (L3) indistinguishable from those of Onchocerca volvulus in the study zone was confirmed by examinations of captured flies. The percentages of savannah flies amongst the human-biting populations and the percentages with L3s in the head were higher during dry seasons than wet seasons and the savannah species were found furthest south (5 °25′N) in the dry season. Comparisons of satellite images taken in 1973 and 1990 over a study area in south-western Ghana encompassing stretches of the Tano and Bia rivers demonstrated that there have been substantial increases in urban and savannah areas, at the expense of forest. This was so not only for the whole images but also for subsamples of the images taken at 1, 2, 4, 8 and 16 km distant from sites alongside the River Tano. At every distance from the river, the percentages of pixels classified as urban or savannah have increased in 1990 compared with 1973, while those classified as degraded or dense forest have decreased. The possibility that the proportionate increases in savannah forms of the vectors of onchocerciasis, and hence in the likelihood of the transmission of savannah strains of the disease in formerly forested areas, were related to the decreases in forest cover is discussed.

Mercury in Human Blood, Urine, Hair, Nail, and Fish from the Ankobra and Tano River Basins in Southwestern Ghana

Mercury in Human Blood, Urine, Hair, Nail, and Fish from the Ankobra and Tano River Basins in Southwestern Ghana

Mercury in human blood, urine, hair, nail, and fish from the Ankobra and Tano River Basins in southwestern Ghana.

Mercury in human blood, urine, hair, nail, and fish from the Ankobra and Tano River Basins in southwestern Ghana.

Elephant census in the Ankasa Conservation Area in south-western Ghana

Results from a dry season dung count carried out during January 2001 in Ankasa Conservation Area estimate a population of approximately 21 elephant. Most of the animals were found in the vicinity of the Suhien River. A pre-study reconnaissance had statified the areas into three stata, low, medium and high, based on assumed density. However, the study suggests it would be better to have a two stata system and arrange the high density stratum along the Suhien River. All 43 dung piles observed were on the 16 transects in the high density strata near the River. This 509 sq km Conservation Area which covers the two adjacent forests of Nuni-Suhian NP and the Ankasa Resource Reserve in southwestern Ghana appears to house the smallest elephant population in Ghana's forest zone. It is an important plant diversity region and has been only lightly logged thus far. It is important to monitor the elephant population in order to assess whether it is isolated or if the estimated 21 elephant move between Ankasa and the Draw River FR.

Temephos-resistant larvae of Simulium sanctipauli associated with a distinctive new chromosome inversion in untreated rivers of south-western Ghana.

Larvae of the Simulium damnosum Theobald complex (Diptera: Simuliidae) were sampled in June 1996 from two sites in south-west Ghana where larviciding has not been applied: Sutri Rapids on the Tano river (05 degrees 23 minutes N 02 degrees 38 minures W) and Sekyere-Heman on the Pra river (05 degrees 11 minutes N 01 degrees 35 minutes W). All specimens were identified as Simulium sanctipauli Vajime & Dunbar sensu stricto (Diptera: Simuliidae). Bioassays with temephos (organophosphorus larvicide employed by the Onchocerciasis Programme for systematic treatment of most rivers across West Africa since the 1970s) showed about five-fold resistance in the Tano population (LC95 2.37-3.14 mg/L) and slight tolerance to temephos in the Pra population (LC95 0.67-0.76 mg/L), vs. the diagnostic concentration of 0.625 mg/L. Larval salivary polytene chromosomes of S. sanctipauli showed fixed inversions 1S-24/24, standard IIL-6 and a new inversion IL/36 polymorphism at Sutri on the Tano. These karyotype characteristics differ from those of temephos-resistant S. sanctipauli in rivers of C te d'Ivoire and other sites on the Tano in Ghana. Thus, temephos resistance in S. sanctipauli at Sutri is associated with distinct chromosomal configurations, showing that immigration was unlikely. This resistance could have been locally selected by exposure of S. sanctipauli larval populations to agrochemicals run-off from cocoa, coffee and oil plantations flanking the rivers.

Electrical resistivity of quartzite obtained from the gold-belt of the Tarkwaian rock formation in South-Western Ghana

The variation of the electrical resistivity between room temperature (300 K) and elevated temperature (500 K) has been investigated for quartzite obtained from the Gold Belt of the Tarkwaian rock formation in the south-western part of Ghana. The resistivity was measured for the passage of current through the samples in two orthogonal directions, parallel and perpendicular to the rock foliation. The average value of the room temperature resistivity for electrical conduction in the two directions were respectively, 9.02 x 105 W m and 1.95 x 108 W m. These values indicate that the ease with which current flows in the direction of foliation is about 200 times greater than in the perpendicular direction which confirms the general anisotropic behaviour of rocks. The average anisotropic coefficient was found to be 14.7. It was observed that generally, the resistivity increased with increase in temperature, attaining a maximum value at about 430 K, above which the resistivity decayed exponentially. This trend in conductivity is suggestive that two types of conduction take place in the quartzite within the temperature range studied. Between 300 K and the maximum temperature, it appears, that conduction is due to ions within the electrolytes filling the pores of the rock samples. Above the maximum temperature, the pores become dry and most probably charge carriers are responsible for the conduction as it occurs in a semiconductor. The average activation energies obtained for conduction above the maximum temperatures, in the parallel and perpendicular directions were respectively, 0.20 ± 0.03 eV and 0.83 ± 0.04 eV. These values compare favourably with the activation energies of other rock samples and are also similar to the values for some semiconductor materials. JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 2 No. 2 (2000) pp. 114-120

Engineering geological assessment of a proposed waste disposal site in coastal southwestern Ghana

An engineering geological investigation has been undertaken of a proposed landfill site in coastal southwestern Ghana which is characterized by torrential rains, high relative humidity, shallow groundwater conditions and almost surrounded by a ridge. The study shows that the site has some desirable characteristics such as availability of suitable soils for the construction of the capping and bottom liners of the landfill, a large tract of land for landfilling operation and its location close to a major highway. However, the groundwater table was shallow and there was a high potential for leachate intrusion into and consequent contamination of nearby groundwater abstraction wells and surface potable water sources thereby constituting serious threat to life. Construction costs could be prohibitive as extensive dewatering and backfilling of vast portions of the project site would be required to enable the provision of a separation between the shallow water table and the bottom of the landfill.

The cytotaxonomy of Simulium sanctipauli sensu stricto (Diptera: Simuliidae) in Ghana and the Côte d’Ivoire

AbstractThe status of the different cytological variants of Simuliumsanctipaulisensu stricto Vajime &amp; Dunbar (sensu b8Post, 1986) found in Ghana and Côte d’Ivoire is cytotaxonomically evaluated in view of recent revisions of the S. sanctipauli subcomplex. Three geographical variants designated as ‘Pra’, ‘Comoé’ and ‘Sassandra’forms of S. sanctipauli are described. The ‘Pra’ form is genetically differentiated from the other two forms by a distinct sex-determining system. The ‘Comoé’ and ‘Sassandra’ forms are considered as the two ends of an interspecific stepped cline with the River Bandama basin as the zone of contact. The possibility that the ‘Comoé’ form populations breeding in southwestern Ghana could serve as reinvading S. sanctipauliinto the Onchocerciasis Control Programme (OCP) area in West Africa is discussed.

輸出作物生産と階層

This paper analyzes the economic differentiation in a cocoa-producing village in southwestern Ghana. The method of “wealth-ranking” developed by Grandin (1988) is used to identify the economic differences among households and individuals in the village, and the result is examined vis-à-vis various socioeconomic variables.The economic differentiation in the village is closely associated with the scale of cocoa production, land holdings, age, gender, and labor arrangement. Male farmers tend to enjoy larger landholdings and more cocoa harvest, thus higher economic status than female counterparts. In addition, women are likely to obtain their own land at their later age than men, contributing further disadvantage in cocoa production (which requires years before trees start bearing fruits). Rich farmers use more hired labor than poor counterparts, but poor farmers also employ farm laborers for certain tasks. This is especially true for poor female farmers who have no access to male labor in the household and whose reproductive duties prevent them from concentrating on farming. These disadvantages all contribute to the relatively lower economic status of women in the village.Other findings are: (1) Younger farmers tend to be classified as poor, but individual economic status may change considerably over one's life cycle as the result of land acquisition from relatives; (2) due to indigenous land tenure systems limiting the transfer of land, land accumulation in large scale by prosperous farmers (observed earlier by Hill (1963) in Southern Ghana) did not occur; (3) indigenous arrangements allow landless farmers and poor farmers to obtain or expand, with little capital, their own land, thus; (4) further differentiation between land accumulating class of rich farmers on the one hand, and the landless farm laborers on the other, is neither observed nor likely to occur in near future in the village.

Parenté, catégories économiques et théorie du pouvoir. Le cas des Nzema du Ghana

Abstract Kinship, Economie Categories and Theories of Power: The Case of the Nzema (Ghana). — The matrilineal Nzema of southwestern Ghana are mainly farmers and fishers belonging to the Akan language group. The author studied the Nzema economic system of thought with reference to the traditional kinship and political organization. The funda-mental aspects of that System have to do with the structural relation between matrilineal descent and patrilocal bonds in the sense of the Crow kinship terminology. The father-son relationship has crucial, economic and political, importance, even though it is also a source of conflict (at a level that is more theoretical and practical) in matters of inheritance. The analysis of economic categories sheds light on the coherence of the local system of thought, and on its adjustment to modemization as well as its adaptations to the political and matrimonial strategies that ruling groups adopt in order to keep power and wealth.

Gold mineralization in As-rich mesothermal gold ores of the Bogosu-Prestea mining district of the Ashanti Gold Belt, Ghana: remobilization of ?invisible? gold

The Bogosu-Prestea mining district of southwestern Ghana is a 33 km section of the Early Proterozoic Ashanti Gold Belt. Greenschist facies carbonaceous and carbonate-bearing turbidites and greywackes, and mafic dikes host numerous economic mesothermal gold deposits. Structurally higher ores in the Bogosu concession have brittle deformation and consist of disseminated-sulphide lodes in tectonically-disrupted sedimentary rocks and carbonate-altered mafic dikes. Most gold occurs as micrometre-size particles in arsenian pyrite, and as “invisible” gold in arsenian pyrite and arsenopyrite. The structurally deeper ores of the adjoining Prestea concession are associated with brittle-ductile deformation and consist of extensive crack-seal quartz-veins and graphitic shear zones. Only minor amounts of “invisible” gold were detected; in these deeper lodes, gold occurs dominantly as abundant microscopic and larger particles in sulphide/arsenide minerals and in gangue. The gold distribution patterns revealed by SIMS microprobe analysis and ion maps, EMP and colour staining suggest that most of the primary gold in the Bogosu-Prestea system precipitated in solid-solution with sulphide/arsenide minerals. However, post-depositional concentration and redistribution occurred, in increasing degree with: 1) increase in metamorphic/hydrothermal gradients in the gold system (depth), 2) decrease in the refractory properties of the host mineral, and 3) increase in the amount of post-depositional, host-mineral recrystallization and deformation. Gold evolved from primary solid-solution within sulphide/arsenide minerals, to colloidal and micrometre-size particles concentrated in voids, fractures and internal grain boundaries, and finally to microscopic and larger particles at sulphide/arsenide grain margins and in the gangue assemblage. The general conclusions presented here are applicable to As-rich gold deposits of all ages, worldwide. The presence of gold in late fractures is insufficient evidence for late-stage introduction of gold in mesothermal gold systems.

Sulfide Oxidation and Production of Gossans, Ashanti Mine, Ghana

At the Justice mine, in the Ashanti goldfields of southwestern Ghana, chemical weathering of gold- bearing sulfide-rich lodes has produced a series of characteristic mineralogical and geochemical features that are diagnostic. In this type of gold mineralization, the most abundant sulfides are arsenopyrite, pyrite, pyrrhotite, and chalcopyrite with minor bornite and sphalerite. Gold occurs predominantly as native gold, spatially associated and chemically bound with arsenopyrite. Elsewhere gold-silver tellurides are present in quartz veins. During sulfide oxidation, arsenopyrite is replaced by amorphous and crystalline Fe-Mn arsenates, goethite, hematite, and arsenolite in box- and ladderwork textures. In the extremely weathered gossans exposed at surface or in exploration pits, goethite, hematite, and scorodite are present as pseudomorphs of oxidized arsenopyrite, which can be used as a visual pathfinder for gold-arsenic mineralization. As with arsenopyrite, pyrite and pyrrhotite alteration produces boxwor...

Review of some chemical characteristics of selected acid soils of south-western Ghana

Review of some chemical characteristics of selected acid soils of south-western Ghana