54956 Anthony A. Duah et al./ Elixir Pollution 148 (2020) 54956-54964 Available online at www.elixirpublishers.com (Elixir International Journal) Pollution Elixir Pollution 148 (2020) 54956-54964 Hydrochemical Characteristics of Surface Waters and their Suitability for Irrigation in the Artisanal Mining Environment in Ghana Anthony A. Duah, Anthony Y. Karikari, Bismark A. Akurugu and Humphrey F. Darko. CSIR Water Research Institute, P. O. Box M.32, Accra, Ghana. ARTICLE INFO ABSTRACT Article history: Surface water resources play a crucial role in potable water delivery to many Received: 12 September 2020; communities in Ghana. They support recreational, agricultural and industrial water needs. Received in revised form: However, several interrelated factors of spatial and temporal variation impact on and 2 November 2020; control the quality of these water bodies. Due to lack of protection, surface water bodies Accepted: 12 November 2020; are highly vulnerable to the impacts of climate change and anthropogenic activities. This study sought to evaluate the main factors influencing the hydrochemistry of the Pra, Keywords Ankobra and Tano rivers of the south-western rivers system using statistical, spatial and Hydrochemistry, conventional hydrochemical plots. The results revealed high turbidity and TSS levels in Water Quality, the rivers reaching values of 4 645 NTU and 3 615 mg/l, respectively. Significant levels Surface Water, of Fe exceeding recommended WHO guideline level were also identified. The main Irrigation, hydrochemical facies in the rivers were Ca-HCO3 (47%) and Mg-HCO3 (44%), with Artisanal Mining. relative abundance of the order Ca > Mg > Na > K for the cations and HCO3 > Cl > SO4 for anions. Precipitation, mineral dissolution in the soil zone and anthropogenic activities, particularly artisanal mining, were identified as the main factors influencing the quality of these rivers. However, irrigation assessment shows that the rivers are of excellent quality for irrigation. © 2020 Elixir All rights reserved. Introduction Asare 2014; Afum and Owusu 2016; Asare‑Donkor et al. In Ghana, surface water resources play a very crucial role 2018). in the delivery of potable water to most urban and some rural Studies focusing on the sources of variation in river water communities. They also support recreational, agricultural and chemistry and the main factors controlling the quality of the industrial water needs, especially the manufacturing and rivers in Ghana, as well as studies on the suitability of these construction industry, hydroelectric power plants, tourism, rivers for irrigation purposes are very limited. This study and irrigated agriculture (Venkatramanan et al. 2014; Dunca adopts similar approaches, with particular focus of the main 2018). Most rivers in the country dry up during the long dry factors influencing the hydrochemistry of rivers in season when the rains cease, leaving a few perennial rivers. southwestern Ghana, adopting statistical and conventional Most of these rivers which traverse diverse environments, hydrochemical plots, coupled with model irrigation water especially mining communities have been reported to be quality assessment diagrams. It further attempts to assess the heavily polluted (Boamponsem et al. 2010) and, in some spatial character of water quality parameters, which could instances, led to the closure of water treatment plants that rely help determine major pollution sources that contribute to the on these rivers for their „raw‟ water supply. deterioration of these rivers and for a better understanding Several interrelated and complex factors with spatial and and management of water resources, which could aid water temporal variation impact on and control the quality of resources management decisions. surface water bodies. Due to their exposure and lack of Study Area protection, surface water bodies are highly vulnerable to the This study was conducted in Pra, Tano and Ankobra impacts of climate change, runoff from farmlands containing Rivers of the Southwestern Rivers System of Ghana, and agrochemicals, domestic and industrial effluents etc. covers a land area of about 47 780 km2, which translates into However, pollution of rivers is usually not localized, and about 20% of the entire land area of the country. It lies could be transboundary even, such as in the case of Ghana between the boundaries of longitudes 3°7ꞌ and 0°25ꞌ west, and and Cote d‟Ivoire where pollution of the Tano and Bia rivers latitudes 4°53ꞌ and 7°39ꞌ north. The study area is bordered to in Ghana impacted negatively on the surface water supply the east by Afram, Densu, Ayensu, Nakwa and Amisa River needs of the former (Asamoah 2017). Most studies on surface basins, to the west by Cote d‟Ivoire, Black Volta and Pru water bodies in Ghana focus mainly on the suitability of the River basins to the north and the Gulf of Guinea to the south water for domestic purposes, and adopt methods such as the (Fig. 1). Among rivers of the Southwestern River System, the water quality index, pollution index and some statistical longest and largest is the Pra River, which stretches a course techniques in these assessments (Boamponsem et al. 2010; of about 240 km from source to mouth. Adiyiah et al. 2013; Attua et al. 2014; Humphrey and Ansa- 54957 Anthony A. Duah et al./ Elixir Pollution 148 (2020) 54956-54964 Headwater of the Pra River is located in the Kwahu taken place yet, trees reaching heights of about 15 to 45 m Plateau in the Eastern Region. It flows southwards, dominate, mostly at the summit of hills (Boamponsem et al. meandering through several communities, and finally 2010). discharges into the Gulf of Guinea in the Western Region Geology through a small village called Krobo. The study area traverses The geology of the study area is dominated by Crystalline several administrative regions; Precambrian rocks of the Birimian Supergroup (about 70%). Central, Bono, Bono East, Ahafo, Western North, These rocks occur almost throughout the study area, intruded Western, Eastern, Central and Ashanti. It has a population of by granitoids of the Eburnean and Tamnean Plutonic Suites approximately 8 790 421 people, with the densest city being (Figure 2). The Tamnean and Eburnean Plutonic Suites Kumasi, which has a population density of 5,419 persons per appear most as remote patches all over the area, but kilometre square, compared to a national average of 103 prominent in the northern, southern and central parts of the persons per square kilometre (Ghana Statistical Service study area. Common rock types associated with the Birimian 2012). Supergroup are phyllite, quartzite, granite-gneiss, gneiss, In most of the communities in the study area, illegal and migmatite and schist composed of basaltic flows, cherts, artisanal small-scale mining of bauxite and gold is highly hornblende, dykes and volcano-clastics (Gyau-Boakye and endemic. Conventional mining techniques in the area include Tumbulto 2006). The Eburnean and Tamnean granitoid panning, open pit mining and direct dredging (Adiyiah et al. intrusions are K-feldspar-rich, composed mainly of granite 2013; Afum and Owusu 2016). Well-established and popular and monzonite. The Tamnean and Eburnean Plutonic Suite mining sites in the study area include the gold mines at are thought to be of uncertain age, but believed to be post- Konongo, Dunkwa, Kenyase, Akwatia, and the AngloGold Birimian and Pre-Tarkwaian age (Kesse 1985; Abdul-Ganiyu Ashanti mine in Obuasi, one of the largest mines in Africa and Gbedzi 2015). (WRC, 2012). Agricultural activities, mainly farming of food and cash crops such as oil palm, rubber, cocoa, cassava, citrus, timber, coffee, maize and vegetables are other socio- economic activities and livelihood supporting activities in the study area. Towards the coast in the south, the topography of the study area appears relatively flat, with a few mountains in the east close to the Kibi area. Similarly, a few mountaintops can be located in the central parts around Bekwai and Obuasi, and towards the northern parts, in Ashanti Mampong area (Fig. 1). The topography seems to have an overall downward slope, trending in the north - south direction. In the southern parts of the study area, elevations range between 0 – 50 m towards the coast, and gradually reaching 800 m in the northern and central parts which are characterised by mountaintops. The study area falls in the sub-equatorial wet climate, characterized by a two rainfall peaks regime. The major rainy season occurs between May and July, and the minor September and November. The annual rainfall amount varies between 1300 and 2000 mm, with a mean of about 1500 mm. The amount of rainfall in the study area shows an increasing westward trend (WRC, 2012). The air is usually humid during the rainy season. Relative humidity in the area varies between 70% – 85%, and declines steadily during the dry season to about 41%. The peak of the dry season, which is around March, records the maximum temperatures of up to 30 oC, which steadily falls to a minimum of about 23 oC when Figure 1. Map of the study area showing sampled the harmattan sets in around December (Adomako et al. 2011; locations. WRC 2012). In the coastal parts of the study area, the vegetation is Furthermore, the Tarkwaian Group also underlie eastern mainly savannah and shrub forest due to the low rainfall sections of the study area, and trends towards the south, in a regime characteristic of such locations. It is characterized by north-east south-west direction. The rock types identified bush and grassland as well as mangrove swamps particularly within this formation are tuff, sandstone, argillite, where saline water dominates (Yidana et al. 2014). However, conglomerate and siltstone. The Late Cretaceous Apollonian the middle and northern parts are dominated by tropical rain Group also underlie the extreme southwestern corner of the forest vegetation, which is characteristically rich in study area. The Apollonian Group is one of the most recent undergrowth of climbers and shrubs of varying heights.