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The distribution of trace metals in active stream sediments from the mineralized Lom Basin has been evaluated. Fifty-five bottom sediments were collected and the mineralogical composition of six pulverized samples determined by XRD. The fine fraction (< 150 µm) was subjected to total digestion (HClO4 + HF + HCl) and analyzed for trace metals using a combination of ICP-MS and AAS analytical methods. Results show that the mineralogy of stream sediments is dominated by quartz (39–86%), phyllosilicates (0–45%) and feldspars (0–27%). Mean concentrations of the analyzed metals are low (e.g. As = 99.40 µg/kg, Zn = 573.24 µg/kg, V = 963.14 µg/kg and Cr = 763.93 µg/kg). Iron and Mn have significant average concentrations of 28.325 and 442 mg/kg, respectively. Background and threshold values of the trace metals were computed statistically to determine geochemical anomalies of geologic or anthropogenic origin, particularly mining activity. Factor analysis, applied on normalized data, identified three associations: Ni–Cr–V–Co–As–Se–pH, Cu–Zn–Hg–Pb–Cd–Sc and Fe–Mn. The first association is controlled by source geology and the neutral pH, the second by sulphide mineralization and the last by chemical weathering of ferromagnesian minerals. Spatial analysis reveals similar distribution trends for Co–Cr–V–Ni and Cu–Zn–Pb–Sc reflecting the lithology and sulphide mineralization in the basin. Relatively high levels of As were concordant with reported gold occurrences in the area while Fe and Mn distribution are consistent with their source from the Fe-bearing metamorphic rocks. These findings provide baseline geochemical values for common and parallel geological domains in the eastern region of Cameroon. Although this study shows that the stream sediments are not polluted, the evaluation of metal composition in environmental samples from abandoned and active mine sites for comparison and environmental health risk assessment is highly recommended.

Knowledge of groundwater recharge and apparent age constitutes a valuable tool for its sustainable management. Accordingly, shallow groundwater (n = 72) in the Ndop plain has been investigated using the stable isotopes of oxygen ( 18 O) and hydrogen ( 2 H or D) and tritium ( 3 H) to determine the recharge process, timing and rate of recharge, and residence time. The shallow groundwater showed low variability in d18 O values (-2.7 to -4.1 %) and 3 H content (2.4-3.1 TU). The low variability suggests a similar origin, homogenous aquifer, good water mixing and storage capacity of the groundwater reservoir. Like surface water, a cluster of groundwater along the Ndop Meteoric Water Line (NMWL) and Global Meteoric Water Line indicates meteoric origin/recharge. The rainfall recharge occurs under low relative humidity conditions and negligible evaporation effect. About 80 % of the recharge is from direct heterogeneous/diffuse local precipitation at low altitude (\1,260 m) within the Ndop plain. Approximately 20 % is from high altitude precipitation (localised recharge) or is recharged by the numerous inflowing streams and rivers from high elevations. A homogenous cluster of d-values in groundwater (and surface water) between May and June monsoon rains on the NMWL suggests dominant recharge during these months. The recharge represents at least 16 % ([251 mm) of the annual rainfall (1,540 mm) indicating high annual recharge; high enough for development of the groundwater resource for agriculture. The 3 H content ([2.4 TU) in groundwater indicates post-1952 recharged water with an estimated residence time \30 years, suggesting short subsurface circulation, and subsequently a renewable aquifer.

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Abstract:The present work highlights the influence of lithology on water quality in Méiganga and its surroundings. The main geological formations in this region include gneiss, granite and amphibolite. The soils developed on these rocks are of ABC type, which are acidic to slightly acidic. Electrical conductivity (EC), organic matter, total nitrogen, nitrate-nitrogen, sulfate, chloride, phosphorus and exchangeable base values were low to very low in the soil samples. Groundwater samples were investigated for their physicochemical characteristics. The wide ranges of EC values (15.1-436 µS/cm) and total dissolved solids (9-249 mg/L) revealed the heterogeneous distribution of hydrochemical processes within the groundwater of the area. The relative abundance of major dissolved species (mg/L) was Ca 2+ > Na + > Mg 2+ > K + for cations and HCO 3 − >> NO 3 − > Cl − > SO 4 2− for anions.All the groundwater samples were soft, with total hardness values (2.54-136.65 mg/L) below the maximum permissible limits of the World Health Organization (WHO) guideline. The majority of water samples (67%) were classified as mixed CaMg-HCO 3 type. Alkaline earth metal contents dominated those of alkali metals in 66.66% of samples. Thus, for the studied groundwater, Mg 2+ and Ca 2+ ion adsorption by clay minerals was almost nonexistent; this implies their release into the solution, which accounts for their high concentrations compared to alkali metals. Ion geochemistry revealed that water-rock interactions (silicate weathering) and ion exchange processes regulated the groundwater chemistry. One water sample points towards the evaporation domain of this diagram, indicating that groundwater probably does not originate from a deeper system. Kaolinite is the most stable secondary phase in the waters in the study area, in accordance with the geochemical process of monosiallitization, which predominated in the humid tropical zone.

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Purpose The aim of this study is to assess the seasonal variation in major ion distribution patterns and identify the origin and geochemical behavior of some trace metals of streamwaters bathing the mineralized Lom Basin. Methods Eighty-one water samples were collected during the dry and wet seasons and analyzed for major ions using AAS and 12 trace metals (Fe, Mn, V, Cr, Co, Ni, Cu, Zn, As, Cd, Pb, Hg) by ICP-MS. Results All physicochemical parameters besides pH and Cl -varied narrowly between both seasons. No seasonal variability was observed for Cl -given its conservative nature, while NO 3 -levels decreased in the wet period due to the dilution effect. Similarly, SO 4 2-concentrations were low for both seasons reflecting the dissolution of low sulphide minerals associated with gold deposits. In contrast, the concentration of Ca 2? , Mg 2? , Na ? , K ? and HCO 3 -slightly increased during the wet season as they are flushed from the soil layers by rain. Water samples had very low concentrations (\ 1 lg/l) of V, Cr, Co, Cu, Zn, Cd, Pb and significant concentrations of Fe and Mn.Conclusions The seasonal regime of streamwater chemistry is controlled by groundwater supply of major cations and HCO 3 -from chemical weathering, leaching of ions from surface soil layers during precipitation and dilution of nitrate by surface runoff during the wet season. In this tropical basin, low acidity and trace metal loadings revealed lateritic weathering of sulphides, entrapment of trace metals in Fe and Mn oxides and leaching into deep groundwater. Although the streams have not been impacted, these findings may guide policymakers for water chemistry evaluation in Cameroon.