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Assessment of land‐use types has conventionally been on spatial rather than temporal scales, thus limiting the inference on relative potential of land‐use types against soil degradation, needed to validate their allotment to ecosystems on agricultural watersheds. The study assessed the changes in key indices of soil degradation among four land‐use systems of West African 'watershed' agroforestry development over about a decade (1999–2011) along a toposequence in Central Ghana. The land‐use systems were grass‐dominated natural fallow (Fallow), cocoa plantation (CPT), traditional rice farm (TRF), and Sawah ecotechnology for wet inland valley rice farm (Sawah), with sampled land areas covering 2,000, 1,500, 4,500, and 6400 m2, respectively. In 1999 and 2011, soil samples were taken from 0–20, 20–40, and 40–60‐cm depths. Samples were collected from about the same spots in both years. The samples were analyzed for selected physicochemical parameters and, for each land‐use option and depth, comparison made between 1999 and 2011. A mean‐weighted decadal change in degradation status was used to rank the land‐use options. Most of the decadal changes in soil properties (including available micronutrients) were negative, with about two‐third of the significant changes in the top (0–20 cm) soils. For instance, soil pH tended to decrease in 2011 compared with 1999; the decreases (14.51%) were significant in the topsoils under Sawah where no other index showed significant decline. Topsoil total carbon decreased under TRF (49.08%) and CPT (32.80%). Available phosphorus marginally increased only under Sawah. The overall aggregate scores for the mean‐weighted decadal change in degradation status showed that the land‐use options differed in their potential to resist degradation: Sawah (slight), Fallow (mild), and TRF/CPT (moderate). Our findings highlight the extent of temporal changes in soil degradation under different topo‐positions in tropical African ecosystems while pointing to the superiority of Sawah ecotechnology. Increased use of this soil‐and‐water management system in lowland rice farming could, therefore, have some soil conservation benefits. [ABSTRACT FROM AUTHOR]

The consumption of rice has increased in Ghana recently, but supply cannot meet demand; hence, there is a large annual important to make up for the deficit. In Ghana, rice is cultivated under three main system, namely rain-fed upland conditions, irrigated conditions, and rain-fed conditions has been very unstable. Fortunately, inland valley systems (IVs), which have been cited by many authors as the environment best suited for efficient and sustainable rice production, abound in this country. This study was therefore under taken to determine the soil nutrient status, and to document a plant species distribution that is useful for nutrient cycling in the IVs of the Ashanti region of Ghana. The goal is to develop a sustainable sawah-rice production system.** Valley bottom soil samples for laboratory analyses were collected from standard soil profiles in areas under use for rice cultivation or capable of supporting rice. Results showed these soils to be slightly acidic (topsoil mean pH=5.7) with low exchangeable acidity [0.10cmol(+)/kg.]. Mean topsoil total carbon (C), nitrogen (N), and available phosphorus (P) (Bray 1) were 1.8%, 0.20%, and 4.4 mg/kg, respectively. Exchangeable cation [cmol (+)/kg] values of surface soils were 0.3 for potassium (K), 5.1 for calcium (Ca), 1.8 for magnesium (Mg), and 0.2 for sodium (Na), respectively. The concentrations of C.N. and most cations decreased down the profile. However, the overall fertility levels were well within the normal ranges for IVs of West Africa. The species dominating the valley bottoms were fairly similar in their carbon content. However, Manihot esculenta and Mallatus oppositifolium of the family Euphorbiaceae were higher than other species in N content. Species belonging to the family Euphorbiaceae were lower in P content (which ranged from 0.9 to 3.7 g/kg) while Physalis angulata and Manihot esculenta contained the highest (3.9 and 3.6 g/kg) P, respectively. The variable nutrient composition of these species has implications for nutrient cycling in the ecosystem. Knowledge of nutrient status of IVs will greatly assist in efforts at adopting the Asian type of sawah rice cultivation. If supported with appropriate farming practices that return crop residues to the soil and utilized inorganic fertilizer or organic manures, the inland valley ecology can contribute significantly to food security, especially of rice, and also conserve the environment. [ABSTRACT FROM AUTHOR]

Inland valleys (IVs) of Ghana offer a very high potential for sustainable agricultural production due to their relatively high soil fertility and water availability. Within the IVs, different land use systems can be identified along the toposequence. The land uses selected for this study were: traditional rice farming in the valley bottom (TR): mixed cropping (MC), young fallow (YF), and cocoa plantation (CP) in the lower and upper slopes; and primary forest (PF) at the crest or summit. Soil reaction, cation exchange capacity (eCEC), and levels of major soil nutrients were determined for each. Results showed that the pH of the soils was moderately to slightly acid and that MC had the lowest pH. The observed topsoil mean values were TR, 5.5; MC,1.9; YF, 6.4; CP, 6.1; and PF, 6.2. With the exception of TR, pH generally decreased with depth. Exchangeable cations, especially potassium, calcium, and magnesium, and effective cation exchange capacity were higher in the upland systems than in the valley bottom, showing the degradation caused by traditional slash-and-burn rice cultivation. Recorded mean topsoil eCEC (cmnol (+)/kg) was TR, 7.2; MC, 6.1; YF, 11.1: CP, 14.1; and PF, 14.7. Total nitrogen (TN) levels ranged from 0.2% in TR to 0.4% in PF. Vegetation cover, litter fall, and organic matter accumulation seemed to influence the distribution of total carbon (TC) and TN. Available phosphorus (Bray 1), on the other hand, was higher in TR than in the upland land use systems, possibly due to the hydromorphic and relatively coarse nature of the soils. Sustainable lowland farming systems, such as the Asian type sawah system, need to be established. At the same time, because effective management of the upland is reflected in the valley bottom soils, proper management of the upland soils could help increase food production and conserve the environment. [ABSTRACT FROM AUTHOR]

Perfluoroalkyl acids (PFAAs) are persistent environmental pollutants that have been detected in various media including human serum. Due to concerns regarding their bioaccumulation and possible negative health effects, an understanding of routes of human exposure is necessary. PFAAs are recalcitrant in many water treatment processes, making drinking water a potential source of human exposure. This study presents the first report on contamination from PFAAs in river and drinking water in Ghana. The targeted PFAAs were perfluoroalkyl carboxylic acids (PFCAs) with C 4–14 carbon chain and perfluoroalkane sulphonic acids (PFSAs) with C 6, 8, 10 . Five PFAA congeners – PFOA, PFOS, PFHxA, PFDA and PFPeA – were commonly detected in river and tap water. The mean concentrations of ∑ PFAAs in the Kakum and Pra Rivers were 281 and 398 ng/L, while tap water (supplied from the treatment of water from those rivers) contained concentrations of 197 and 200 ng/L, respectively. PFOA and PFOS constituted about 99% of the ∑ PFAAs. The risk quotient (RQ) attributed to drinking of tap water was estimated at 1.01 and 1.74 for PFOA and PFOS, respectively. For a country that has not produced these compounds, the RQs were unexpectedly high, raising concerns particularly about contamination from such emerging pollutants in local water sources. The study revealed limitations of local tap water treatment in getting rid of these emerging pollutants. [ABSTRACT FROM AUTHOR]

Highlights: [•] A nationwide monitoring of atmospheric OCPs was conducted in Ghana. [•] DDT and its metabolites and endusulfans constituted the highest burden of OCPs. [•] There were recent signatures of DDT, endosulfans and heptachlor at some sites. [•] OCPs varied spatially as a function of crop types, legacy issues and recent applications. [ABSTRACT FROM AUTHOR]

A nationwide monitoring of atmospheric POPs (persistent organic pollutants) was conducted in Ghana between May and July 2010, applying polyurethane foam (PUF) disk passive air samplers (PAS). Reported here are preliminary findings on PCNs, an industrial organic contaminant currently under review for possible listing under the global chemical treaty. The present results constitute the first set of nationwide data on air PCNs from a West African country. Contrary to expectation, air PCNs levels were quite high in Ghana, at an average of 49 ± 5.4 pg/m³. The coastal (southern) zone of Ghana appeared the most impacted, with crude open burning of waste, industrial emissions, and the harbor environment identified among possible emission factors. Tri- and tetra-CNs (the lowly chlorinated homologues) predominated in the atmosphere, altogether constituting approximately 90% of total PCN homologues composition. Increased volatilization under tropical conditions was presumed a key factor that contributed to this high atmospheric input of lowly chlorinated homologues. We further observed a significant level of fractionation of PCN homologues across the breadth of the country. The percentage composition of the lowly chlorinated homologues increased northwards, probably because of their transportation in the direction of prevailing winds. From congener profile analysis, PCN-45/36 is proposed as a possible source marker for emissions preempted by uncontrolled waste burning activities. Dioxin-like toxicity of air PCNs in Ghana was estimated to range 0.49-5.6 fg TEQ/m³. This study brought to the fore the emerging problems of nonagricultural organohalogens that covertly might be confronting the environment in African nations like Ghana. [ABSTRACT FROM AUTHOR]