Transient fertilization of a post-Sturtian Snowball ocean margin with dissolved phosphate by clay minerals.

Marine sedimentary rocks deposited across the Neoproterozoic Cryogenian Snowball interval, ~720-635 million years ago, suggest that post-Snowball fertilization of shallow continental margin seawater with phosphorus accelerated marine primary productivity, ocean-atmosphere oxygenation, and ultimately the rise of animals. However, the mechanisms that sourced and delivered bioavailable phosphate from land to the ocean are not fully understood. Here we demonstrate a causal relationship between clay mineral production by the melting Sturtian Snowball ice sheets and a short-lived increase in seawater phosphate bioavailability by at least 20-fold and oxygenation of an immediate post-Sturtian Snowball ocean margin. Bulk primary sediment inputs and inferred dissolved seawater phosphate dynamics point to a relatively low marine phosphate inventory that limited marine primary productivity and seawater oxygenation before the Sturtian glaciation, and again in the later stages of the succeeding interglacial greenhouse interval.

Compositions and mobility of major, δD, δ18O, trace, and REEs patterns in water sources at Benue River Basin-Cameroon: implications for recharge mechanisms, geo-environmental controls, and public health.

Hydro-geochemical data are required for understanding of water quality, provenance, and chemical composition for the 2,117,700 km2 Niger River Basin. This study presents hydro-geochemical analysis of the Benue River Basin, a major tributary of the Niger River. The distribution of major ions, Si, δD, and δ18O, trace and rare-earth elements (TE and REEs, respectively) composition in 86 random water samples, revealed mixing of groundwater with surface water to recharge shallow aquifers by July and September rains. Equilibration of groundwater with kaolinite and montmorillonites, by incongruent dissolution, imprints hydro-chemical signatures that vary from Ca + Mg - NO3 in shallow wells to Na + K - HCO3 in boreholes and surface waters, with undesirable concentrations of fluoride identified as major source of fluorosis in the local population. Our results further indicate non-isochemical dissolution of local rocks by water, with springs, wells and borehole waters exhibiting surface water-gaining, weakest water-rock interaction, and strongest water-rock interaction processes, respectively. Poorly mobile elements (Al, Th and Fe) are preferentially retained in the solid residue of incongruent dissolution, while alkalis, alkaline earth and oxo-anion-forming elements (U, Mo, Na, K, Rb, Ca, Li, Sr, Ba, Zn, Pb) are more mobile and enriched in the aqueous phase, whereas transition metals display an intermediate behavior. Trace elements vary in the order of Ba > Sr > Zn > Li > V > Cu > Ni > Co > As > Cr > Sc > Ti > Be > Pb > Cd, with potentially harmful elements such as Cd, As, and Pb mobilized in acidic media attaining near-undesirable levels in populated localities. With the exception of Y, REEs distribution in groundwater in the order of Eu > Sm > Ce > Nd > La > Gd > Pr > Dy > Er > Yb > Ho > Tb > Tm differs slightly with surface water composition. Post-Archean Average Australian Shale-normalized REEs patterns ranging from 1.08 to 199 point to the dissolution of silicates as key sources of trace elements to groundwater, coupled to deposition by eolian dust.

Hydrogeochemistry and quality of surface water and groundwater in the vicinity of Lake Monoun, West Cameroon: approach from multivariate statistical analysis and stable isotopic characterization.

With the use of conventional hydrogeochemical techniques, multivariate statistical analysis, and stable isotope approaches, this paper investigates for the first time surface water and groundwater from the surrounding areas of Lake Monoun (LM), West Cameroon. The results reveal that waters are generally slightly acidic to neutral. The relative abundance of major dissolved species are Ca(2+) > Mg(2+) > Na(+) > K(+) for cations and HCO3 (-) â‰« NO3 (-) > Cl(-) > SO4 (2-) for anions. The main water type is Ca-Mg-HCO3. Observed salinity is related to water-rock interaction, ion exchange process, and anthropogenic activities. Nitrate and chloride have been identified as the most common pollutants. These pollutants are attributed to the chlorination of wells and leaching from pit latrines and refuse dumps. The stable isotopic compositions in the investigated water sources suggest evidence of evaporation before recharge. Four major groups of waters were identified by salinity and NO3 concentrations using the Q-mode hierarchical cluster analysis (HCA). Consistent with the isotopic results, group 1 represents fresh unpolluted water occurring near the recharge zone in the general flow regime; groups 2 and 3 are mixed water whose composition is controlled by both weathering of rock-forming minerals and anthropogenic activities; group 4 represents water under high vulnerability of anthropogenic pollution. Moreover, the isotopic results and the HCA showed that the CO2-rich bottom water of LM belongs to an isolated hydrological system within the Foumbot plain. Except for some springs, groundwater water in the area is inappropriate for drinking and domestic purposes but good to excellent for irrigation.

Origin of major ions in monthly rainfall events at the Bamenda Highlands, Northwest Cameroon.

Rainwater characteristics can reveal emissions from various anthropogenic and natural sources into the atmosphere. The physico-chemical characteristics of 44 monthly rainfall events (collected between January and December 2012) from 4 weather stations (Bamenda, Ndop plain, Ndawara and Kumbo) in the Bamenda Highlands (BH) were investigated. The purpose was to determine the sources of chemical species, their seasonal inputs and suitability of the rainwater for drinking. The mean pH of 5 indicated the slightly acidic nature of the rainwater. Average total dissolved solids (TDS) were low (6.7 mg/L), characteristic of unpolluted atmospheric moisture/air. Major ion concentrations (mg/L) were low and in the order K(+) > Ca(2+) > Mg(2+) > Na(+) for cations and NO3(-)≫HCO3(-)>SO4(2-)>Cl(-)>PO4(3-)>F(-) for anions. The average rainwater in the area was mixed Ca-Mg-SO4-Cl water type. The Cl(-)/Na(+) ratio (1.04) was comparable to that of seawater (1.16), an indication that Na(+) and Cl(-) originated mainly from marine (Atlantic Ocean) aerosols. High enrichments of Ca(2+), Mg(2+) and SO(2-)4 to Na(+) ratios relative to seawater ratios (constituting 44% of the total ions) demonstrated their terrigenous origin, mainly from Saharan and Sahelian arid dusts. The K(+)/Na(+) ratio (2.24), which was similar to tropical vegetation ash (2.38), and NO3(-) was essentially from biomass burning. Light (< 100 mm) pre-monsoon and post-monsoon convective rains were enriched in major ions than the heavy (> 100 mm) monsoon rains, indicating a high contribution of major ions during the low convective showers. Despite the acidic nature, the TDS and major ion concentrations classified the rainwater as potable based on the WHO guidelines.

Bacterial and archaeal communities in Lake Nyos (Cameroon, Central Africa).

The aim of this study was to assess the microbial diversity associated with Lake Nyos, a lake with an unusual chemistry in Cameroon. Water samples were collected during the dry season on March 2013. Bacterial and archaeal communities were profiled using Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) approach of the 16S rRNA gene. The results indicate a stratification of both communities along the water column. Altogether, the physico-chemical data and microbial sequences suggest a close correspondence of the potential microbial functions to the physico-chemical pattern of the lake. We also obtained evidence of a rich microbial diversity likely to include several novel microorganisms of environmental importance in the large unexplored microbial reservoir of Lake Nyos.

Geochemical provenance and spatial distribution of fluoride in groundwater of Mayo Tsanaga River Basin, Far North Region, Cameroon: implications for incidence of fluorosis and optimal consumption dose.

The 500,000 inhabitants of Mayo Tsanaga River Basin are vulnerable to a "silent" fluorosis from groundwater consumption. For the first time, the groundwater is investigated for the purpose of identifying the provenance of fluoride and estimating an optimal dose of fluoride in the study area. Based on the fluoride content of groundwater, fluorine and major oxides abundances in rocks from the study area, mean annual atmospheric temperature, and on-site diagnosis of fluorosis in children, the following results and conclusions are obtained: Fluoride concentration in groundwater ranges from 0.19 to 15.2 mg/l. Samples with fluoride content of <1.5 mg/l show Ca-HCO(3) signatures, while those with fluoride >1.5 mg/l show a tendency towards Na-HCO(3) type. Fluor-apatite and micas in the granites were identified as the main provenance of fluoride in the groundwater through water-rock interactions in an alkaline medium. The optimal fluoride dose in drinking water of the study area should be 0.7 mg/l, and could be adjusted downward to a level of 0.6 mg/l due to the high consumption rate of groundwater, especially during drier periods.