A potential human footprint on Western Central African rainforests before the Common Era has become the focus of an ongoing controversy. Between 3,000 y ago and 2,000 y ago, regional pollen sequences indicate a replacement of mature rainforests by a forest-savannah mosaic including pioneer trees. Although some studies suggested an anthropogenic influence on this forest fragmentation, current interpretations based on pollen data attribute the ''rainforest crisis'' to climate change toward a drier, more seasonal climate. A rigorous test of this hypothesis, however, requires climate proxies independent of vegetation changes. Here we resolve this controversy through a continuous 10,500-y record of both vegetation and hydrological changes from Lake Barombi in Southwest Cameroon based on changes in carbon and hydrogen isotope compositions of plant waxes. [Formula: see text]C-inferred vegetation changes confirm a prominent and abrupt appearance of C plants in the Lake Barombi catchment, at 2,600 calendar years before AD 1950 (cal y BP), followed by an equally sudden return to rainforest vegetation at 2,020 cal y BP. [Formula: see text]D values from the same plant wax compounds, however, show no simultaneous hydrological change. Based on the combination of these data with a comprehensive regional archaeological database we provide evidence that humans triggered the rainforest fragmentation 2,600 y ago. Our findings suggest that technological developments, including agricultural practices and iron metallurgy, possibly related to the large-scale Bantu expansion, significantly impacted the ecosystems before the Common Era.
Groundwater quality of the Banana Plain (Mbanga, Njombe, Penja-Cameroon) was assessed for its suitability for drinking, domestic, and agricultural uses. A total of 67 groundwater samples were collected from open wells, springs, and boreholes. Samples were analyzed for physicochemical properties, major ions, and dissolved silica. In 95% of groundwater samples, calcium is the dominant cation, while sodium dominates in 5% of the samples. Eighty percent of the samples have HCO(3) as major anion, and in 20%, NO(3) is the major anion. Main water types in the study area are CaHCO(3), CaMgHCO(3), CaNaHCO(3), and CaNaNO(3)ClHCO(3). CO(2)-driven weathering of silicate minerals followed by cation exchange seemingly controls largely the concentrations of major ions in the groundwaters of this area. Nitrate, sulfate, and chloride concentrations strongly express the impact of anthropogenic activities (agriculture and domestic activities) on groundwater quality. Sixty-four percent of the waters have nitrate concentrations higher than the drinking water limit. Also limiting groundwater use for potable and domestic purposes are contents of Ca(2+), Mg(2+) and HCO(3) (-) and total hardness (TH) that exceed World Health Organization (WHO) standards. Irrigational suitability of groundwaters in the study area was also evaluated, and results show that all the samples are fit for irrigation. Groundwater quality in the Banana Plain is impeded by natural geology and anthropogenic activities, and proper groundwater management strategies are necessary to protect sustainably this valuable resource.
To assess the water quality in the locality of Bétaré-Oya affected by an intensive artisanal and semi mechanized mining activities, 71 samples were collected from sixteen points during the 2015-2016 hydrological year. These points include: three in Lom river which is the main stream of the study area, five in Mari river which is one of the left bank tributaries of the Lom, in Bétaré-Oya and eight in the left and the right bank of Mari. Different physicochemical parameters such as pH, electrical conductivity (EC), alkalinity, turbidity, total suspended solids (TSS), cyanide (CN − ), major elements and heavy metals (Pb, Zn, Cd, Fe, Cu, As, Mn and Cr) were analyzed. Water Quality Indices (WQI), Heavy metal Pollution Index (HPI), sodium adsorption ratio (SAR) and percent sodium (Na%) were also computed to evaluate the suitability of water for drinking and irrigation. The results showed that the surface water from Bétaré-Oya was acidic to basic (5.40 < pH < 8.84), weakly mineralized (11.60 < EC < 122.10 μS/cm) with a high concentration of TSS (2 < TSS < 8996.00 mg/L) and turbidity (1.22 to 4758.00 NTU). The WQI scores show excellently to unsuitable quality in almost all the sampling sites. The water quality is found to be most deteriorated in Lom river and in the downstream of Mari river where an extensive mining activity is carried out, with the high WQI value of 5137.40. Based on heavy metal pollution index, the mean value was 1195.36 and thus under the critical pollution index. We thus notice a serious physical degradation by organic and mineral suspended particles as well as chemical degradation by heavy metals. This results from mining activities in the Lom river and its main tributaries such as the Mari river in the upstream part of the Sanaga basin. According to the percentage of sodium and SAR, these waters can be used for irrigation purposes in almost all types of soils.
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