Pra River Basin Research Articles

Water balance responses to land-use/land-cover changes in the Pra River Basin of Ghana, 1986–2025

The unfavorable effect of human disturbances in major river basins resulting in extensive variations in the ecosystem has necessitated this research within the Pra River Basin of Ghana. Knowledge about how individual land use influences water balance components will massively improve natural resources planning, management and sustainable development. Land use/cover change in the basin was evaluated by the assessment of six historical and one future land use/cover maps relating to the land use/cover stages in 1986, 2000, 2004, 2008, 2013, 2016 and 2025. The land use/cover maps were deployed to generate seven land use/cover scenarios relating to diverse states of land use/cover change in the basin which were then deployed to simulate the hydrological components. The Soil and Water Assessment Tool was deployed for hydrological simulation. The results revealed that there was a continuous increase in cropland, settlement and mining at the detriment of forest areas from 1986 to 2016, which is expected to continue into 2025. The variations in land use/land cover brought about increment of surface runoff (124.51%) and water yield (40.13%), and reduced baseflow (30.08%) and ET (13.248%). Conversely, the results showed a reduction in surface runoff and water yield during dry season and increased baseflow and evapotranspiration during wet season. These trends are expected to further increase in 2025. Moreover, settlement and mining are the major contributors to changes in water balance components. These results show how important control of land use/cover is in order to maintain water balance components to guarantee water accessibility for all generations.

Monitoring land use and land cover changes due to extensive gold mining, urban expansion, and agriculture in the Pra River Basin of Ghana, 1986–2025

AbstractThis study used the double cumulative curve and visual image interpretation methods for the selection of spatiotemporal Landsat data to evaluate the land degradation by anthropogenic activities in the Pra River Basin (PRB) of Ghana. Unsupervised and supervised classification procedures were used to map the land use and land cover (LULC) distribution from 1986 to 2016. Assessment of LULC showed that the PRB has been subjected to six different rates of land degradation in the years 1986, 2000, 2004, 2008, 2013, and 2016. This is due to increase in settlement, cropland, and mining activities to about 130%, 198%, and 304%, respectively. The Markov chain and cellular automation integrated model was successful in predicting LULC distribution in 2016 and the outcomes were comparable to the actual LULC for 2016. The projected LULC for 2025 showed that land degradation is significant in the western and the eastern parts where cropland and forest are, respectively, converted to mining activity. The northern, southern, and middle parts of PRB are expected to experience high settlement expansion, sedimentation in the rivers, and cropland expansion, respectively. The results will aid natural resources management, planning, and sustainable development at PRB. In addition, the research method serves as guideline for other related studies in an attempt to investigate, quantify, and project LULC change in forest ecological areas.

Variable resolution modeling of near future mean temperature changes in the dry sub-humid region of Ghana

The study used two models from Rossby Centre Regional Atmospheric Model (RCA4) and two from Weather Research and Forecasting Model (WRF) plus the Statistical Downscaling Model—Decision Centric (SDSM-DC) at 44 km, 12 km and 2 m resolution respectively to project the impact of climate change on mean temperature in the Pra River Basin for the period 2020–2049. Results showed that the minimum temperature increased (+ 1.47 °C) faster than the increase (+ 1.11 °C) in maximum temperature for observed period 1981–2010. An evaluation of the performance of the models with time-series based metrics showed that SDSM-DC and RCA4 are better for projecting mean temperature in the study area compared to WRF despite its resolution. Analysis of variance (p < 0.05) indicated significant difference between the projected mean temperature of the five models but there was no significant difference between SDSM-DC and RCA4 models. Correlation between models was highest at R = 0.727 between SDSM-DC and RCA4. The years 2041, 2042 and 2047 were projected as hottest by minimum two different models. The mean temperature change was projected at + 1.36, + 1.42 and + 1.12 °C by SDSM-DC, RCA4 and WRF respectively. The ensemble of projection depicted same trend of February—April as the high mean temperature and July—September as the lowest as was for the observed period. However, January is projected to have the highest change in mean temperature of + 1.51 °C. The maximum temperature for observed period was found to be the mean temperature in the period 2020–2049. Future study will focus on the impact of projected temperature change on ecosystem services delivery in the region.

Spatial and Temporal Patterns of Variation in Environmental Quality of Water and Sediments of Streams in Mined and Unmined Areas with Emphasis on Mercury (Hg) and Arsenic (As)

Heavy metal pollution from both anthropogenic and natural processes can have significant effect on environmental quality of stream and river systems. However, in Ghana, heavy metal pollution of waterbodies is attributed mainly to mining activities but the role of natural mechanisms in altering stream water and sediment quality in relation to heavy metals has received little attention. Spatial and temporal variation in water quality parameters and heavy metal concentrations in water and sediments were studied comparatively in a river and two streams in a gold-rich watershed impacted by heavy mining activities. Samples were collected monthly over a twelve-month period from November 2010 to October 2011 from upstream (unmined) and downstream (mined) sections of the studied streams. Parameters measured include temperature, dissolved oxygen, conductivity, pH, turbidity, colour, mercury (Hg) and arsenic. High spatial variability of water quality parameters was found. Hg concentrations in water were extremely low in both upstream and downstream areas. Maximum geochemical background levels of Hg in unmined pristine areas were 2.45 mg/g whilst arsenic was 29.10 mg/g. By contrast, gold-mined downstream areas recorded Hg and arsenic concentrations of 8.75 mg/g and 82.53 mg/g in stream sediments respectively. Levels of Hg and arsenic in sediments were several orders of magnitude greater than concentrations in surface water in downstream sections and this may be explained by substances originating from mining activities, upstream transport or remobilized sedimented materials in the overlying water column. Our study showed that both natural and human activities may contribute to heavy metal pollution in the highly mineralized watershed of the Pra River Basin. Human factors are however likely to amplify the natural background levels of heavy metals.

Analysis of climate and anthropogenic impacts on runoff in the Lower Pra River Basin of Ghana

The Lower Pra River Basin (LPRB), located in the forest zone of southern Ghana has experienced changes due to variability in precipitation and diverse anthropogenic activities. Therefore, to maintain the functions of the ecosystem for water resources management, planning and sustainable development, it is important to differentiate the impacts of precipitation variability and anthropogenic activities on stream flow changes. We investigated the variability in runoff and quantified the contributions of precipitation and anthropogenic activities on runoff at the LPRB. Analysis of the precipitation–runoff for the period 1970–2010 revealed breakpoints in 1986, 2000, 2004 and 2010 in the LPRB. The periods influenced by anthropogenic activities were categorized into three periods 1987–2000, 2001–2004 and 2005–2010, revealing a decrease in runoff during 1987–2000 and an increase in runoff during 2001–2004 and 2005–2010. Assessment of monthly, seasonal and annual runoff depicted a significant increasing trend in the runoff time series during the dry season. Generally, runoff increased at a rate of 9.98 × 107m3yr−1, with precipitation variability and human activities contributing 17.4% and 82.3% respectively. The dominant small scale alluvial gold mining activity significantly contributes to the net runoff variability in LPRB.

Estimating the “Forgone” ESVs for Small-Scale Gold Mining Using Historical Image Data

Ghana’s economic development relies largely on the mining industry, but the ecological cost is very high, particularly for the small-scale sector. To ascertain and give an account of the ecological pressures from the small-scale gold mining sector, we quantified and appraised the ecosystems (land cover types) degradation due to mining land use along portions of the renowned Pra River basin of Ghana. The study classified and analysed high-quality Landsat image data (1986–2016) to monitor processes and changes in the river basin and adopted the Ecosystem Service Value (ESV) model to quantify the forgone value in monetary term. The results revealed that the initial ESV of 17.69 million US$ in 1986 increased to 18.40 million US$ in 2002 for the study landscape with the small-scale mining sector accounting for 8.4% of the trade-off costs. The expansion of forest areas and its higher value coefficient (VC) was, however, prevalent and this resulted in a net positive change during this period. However, in 2016, out of the total ESV of 14.63 million US$ obtained, the small-scale mining activities accounted for 36.8% of the trade-off costs. The substantial increase in trade-off costs with a subsequent decrease in ESV in the study landscape, following the intensification of small-scale gold mining, indicates that their activities have been degrading the watershed ecosystem and are, therefore, unsustainable. The study affirms the need for policymakers/government to review the laws, particularly on post-mining monitoring schemes to deter illegal miners and support the registered small-scale miners who are willing to implement land rehabilitation activities.

Sediment yield of a forest river basin in Ghana

The Pra River Basin, located in south central Ghana is a forest basin that has been engulfed by certain anthropogenic activities particularly illegal small scale mining (popularly called galamsey) and serious concerns have been raised by stakeholders within the basin of the level of pollution due to the release of sediments into the water bodies. This study was undertaken to assess sediment yield levels within the Pra Basin through field data collection to ascertain stakeholder's perceptions and suggest remedial measures to the land degradation problem in the basin.Suspended sediment concentration measurements were undertaken for 10months in selected stream discharge measuring stations within the basin by coupling dip and integrated sampling approaches. Samples were analyzed using the evaporation method. Daily mean suspended sediment concentration was calculated from which monthly and annual suspended sediment yields were derived. Suspended sediment concentration (mg/l) and sediment yield (tyr−1) of the Pra Basin were found to be very high resulting in a high annual specific suspended sediment yield (tkm−2yr−1). Illegal small scale gold mining along the rivers and alluvial gold mining within the basin were found to be the probable cause for the high sediment levels of the rivers. To promote coordinated development and sustainable management of the resources of the basin, there is the need to resource agencies in charge of regulating natural resource utilization to control land use activities particularly galamsey. This will reduce fluvial sediment concentration and sustain good water quality of the rivers and promote socio-economic development in the basin.

Artisanal mining of gold with mercury in Ghana

The paper examines the environmental impact of artisanal mining of gold with mercury (Hg) in Ghana. In spite of its positive socioeconomic contributions, it is well known that artisanal mining of gold contributes in no small measure to land degradation, loss of biodiversity and natural resources, deforestation, water pollution, etc. In Ghana, these environmental problems remain poorly studied. In the case of Hg pollution, caused by gold extraction using the amalgamation process, total Hg levels in different environmental compartments of the gold-mining-impacted Pra River basin in southwestern Ghana were determined using the latest sampling and analytical techniques. Artisanal gold mining activities in the Pra River basin are on the increase and even though Hg levels determined in water, soil, and sediments were below WHO safe guideline values, the current state of affairs poses a serious environmental threat. However, the majority of the populace, particularly those engaged in gold mining, are unaware of the dangers posed by the use of Hg in mining operations. This paper seeks to draw the attention of Ghanaians (as well as their foreign counterparts) to the need to take up the mantle in changing the general patterns of environmental damage caused by the artisanal gold miners. The need to regularize artisanal gold mining is long overdue. A legal regime for mines of every size, leading to a transformation of the artisanal mining sector into a legal, regulated industry, will help minimize the impact on the environment.

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.

Marker Indices for Assessing the Conditions of Water Bodies under Moderate Anthropogenic Impact: Case Study of the Pra River

A system of marker-based estimates of the environmental conditions of water bodies in the Pra River basin is proposed based on the results of field studies and archive data. Correlation equation were derived for relating the selected markers with other indices.

Structural Adjustment and Economic Efficiency of Rice Farmers in Northern Ghana

Structural Adjustment and Economic Efficiency of Rice Farmers in Northern Ghana