Solute concentrations in the lower niger river and the source rock contribution

Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO₃ > SO₄ > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1^?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals.     

Resolution of freshwater and saline water aquifers by composite geophysical data analysis methods

Abstract

The resolution of the freshwater and saline water aquifers in a coastal terrain (Mahanadi Basin, India) is updated. We analysed electrical borehole log data at four sites and compared the water resistivity regime of the freshwater and saline water zones obtained from electrical borehole logging, with the resistivity regime obtained by interpreting vertical electrical sounding (VES) data. The multilayer VES data interpretation is modified to a simple model, containing only the freshwater zone and the saline water zone. The composite geophysical parameters of the freshwater and saline water zones, in particular the resistivity and longitudinal unit conductance regime, are identified. The resolution obtained from the composite geophysical data analyses is very clear and convincing. The composite longitudinal unit conductance regime of the saline water zones is very high compared to that of the freshwater zones. This makes the identification of the two aquifers easy and increases its reliability. A technique which enables analysis of composite geophysical data of freshwater and saline water zones at VES sites in the vicinity of the borehole log sites is proposed. The significance of longitudinal unit conductance in resolving the freshwater and saline water aquifers is illustrated graphically. The proposed technique is validated by correlating the longitudinal unit conductance and resistivity with the total dissolved solids. The efficiency of the technique is validated by carrying out discriminant function analysis.

Citation Hodlur, G. K., Dhakate, R., Sirisha, T. & Panaskar, D. B. (2010) Resolution of freshwater and saline water aquifers by composite geophysical data analysis methods. Hydrol. Sci. J. 55(3), 414–434.     

The truth and beauty of chemical potentials

This essay in honour of Mike Brown addresses aspects of chemical equilibrium and equilibration in rocks, with a focus on the role that chemical potentials play. Chemical equilibrium is achieved by diffusive flattening of chemical potential gradients. The idea of equilibration volume is developed, and the way equilibration volumes may evolve along a pressure–temperature path is discussed. The effect of the environment of an equilibration volume is key to understanding the evolution of the equilibration volume with changing conditions. The likely behaviour of equilibration volumes is used to suggest why preservation of equilibrium mineral assemblages and mineral compositions from metamorphism tends to occur. This line of logic then provides the conceptual support to conventional equilibrium thermodynamic approaches to studying rocks, using, for example, thermobarometry and pseudosections.     

Characterization of total suspended solid dynamics in a large shallow lake using long‐term daily satellite images

Large, shallow‐water lakes located on floodplains play an important role in creating highly productive ecosystems and are prone to high concentrations of suspended solids due to sediment resuspension. In this study, the aim was to determine the dominant processes governing the total suspended solid (TSS) concentration at the water surface in Tonle Sap Lake, Cambodia, which is a large, shallow‐water lake. Satellite remotely sensed daily reflectance data from 2003 to 2017 were used. Seasonal changes in TSS concentration indicated that bottom sediment resuspension during dry seasons was mostly caused by wind and the TSS concentration was closely correlated with the water depth of the lake. The TSS concentration during flood periods was controlled by both wind and inflow currents from the Tonle Sap River. Additionally, we confirmed that surface/subsurface flow with a low TSS concentration from forests on the floodplain lowered the TSS concentration year round, except during August and September. This fact implied that the floodplain forest area decrease may increase the lake TSS concentration. An analysis of the long‐term changes in TSS indicated that a decrease in the water level during flood periods resulted in the high TSS concentrations observed during the subsequent dry periods. Therefore, climate change and water resource development, which are likely to cause water level reductions in the Mekong River during flood periods, may increase the TSS concentration in Tonle Sap Lake, particularly during the dry season.     

中国岩溶作用产生的大气CO2碳汇的分区计算

根据中国岩溶碳汇计算的需要,将我国岩溶地区划分为南方岩溶区、北方岩溶区、青藏高原岩溶区和埋藏岩溶区4种类型区,各区的岩溶面积分别为56.48万km2、32.58万km2、55.60万km2和200.1万km2。各区岩溶水的径流模数和岩溶作用强度存在差异,南方岩溶区比其他区的岩溶作用强度明显大得多。以取得的调查监测和统计资料为依据,对4种类型区和中国的岩溶碳汇量进行了重新计算,南方岩溶区、北方岩溶区、青藏高原岩溶区和埋藏岩溶区岩溶碳汇量分别为1909.9万tCO2/a、600.5万tCO2/a、580.1万tCO2/a、608.6万tCO2/a,由此获得中国岩溶碳汇总量为3699.1万tCO2/a。该结果比前人的研究更全面地反映了当前我国岩溶地区碳水钙无机循环产生的大气CO2汇量。      

Postulated responses of phytoplankton and bacteria to predicted increases of inorganic suspended sediments in oligotrophic lakes

We establish the relationships between concentrations of inorganic suspended sediments (ISS) on light, nutrients, phytoplankton, and bacteria in three oligotrophic lakes (four sites) and we use these relationships to predict the impacts of increasing concentrations of ISS on the biomass and productivity of phytoplankton and bacteria in the lakes. Increased concentrations of ISS contributed little available nutrient to the lakes. The relationships between ISS and underwater light attenuation differed among lakes because of variation in sediment size‐structure, and composition. Only at the site with the highest ISS concentrations and a relatively deep mixing depth, were phytoplankton apparently light‐limited and, thus, predicted to decline with increased ISS concentrations. In contrast to previously published studies, bacterial abundance and production were not highly correlated to suspended sediment concentrations in these lakes. However, bacterial biomass, productivity, and specific productivity were more strongly correlated to phytoplankton production. As a result of light limitation and stimulation of bacterial production, increases in ISS concentrations are not predicted to significantly shift the metabolic balance in the planktonic ecosystem of three of the sites towards greater heterotrophy. Where light limits phytoplankton production, increases in ISS are predicted to reduce the productivity of both phytoplankton and bacteria by direct inhibition of phytoplankton production, again without a large shift towards greater importance of the microbial loop. By reducing phytoplankton production and inhibiting larger cladoceran grazers, we predict that high concentrations of ISS will reduce available energy and its flow up the food chain.     

Geochemical assessment of groundwater around Macherla-Karempudi area,Guntur district,Andhra Pradesh

Groundwater in Palnad sub-basin is alkaline in nature and Na⁺-Cl⁻-HCO₃⁻ type around Macherla-Karempudi area in Guntur district, Andhra Pradesh. Total dissolved solids (TDS) show strong positive correlation with Cl⁻, Na⁺, Ca²⁺ and Mg²⁺, and positive correlation with SO₄²⁻, K⁺ and HCO₃⁻. Calcareous Narji Formation is the dominant aquifer lithology, and water-rock interaction controls the groundwater chemistry of the area. Chloro-alkaline indices (CAI) are positive at Miriyala, Adigopula, Mutukuru, Macherla and Durgi suggesting replacement of Na⁺ and K⁺ ions from water by Mg⁺⁺ and Ca⁺⁺ ions from country rock through base exchange reactions. Negative CAI values are recorded at Terala, Rayavaram and Nehrunagar, which indicate exchange of Na⁺ and K⁺ from the rock as cation-anion exchange reaction (chloro-alkaline disequilibrium). TDS range from 91 to 7100 ppm (Avg. 835 ppm) and exceed the prescribed limit of drinking water around Mutukuru, Durgi, Rayavaram, Khambampadu and Ammanizamalmadaka areas. Scanty rainfall and insufficient groundwater recharge are the prime factors responsible for high salinity in the area. Fluoride content ranges from <1 to 3.8 ppm and contaminated areas were identified around Macherla (1 sq km; 3.8ppm), Mandadi (1 sq km, 2.1ppm) and Adigopula (2 sq km, <1 to 3.7 ppm). The % Na⁺ content varies from 17 to 85 with the mean value of 57, and eighty (80) samples showed higher %Na⁺ in comparison to the prescribed limit of 60 for irrigation water. Sodium Adsorption Ratio (SAR) and % Na⁺ in relation to total salt concentration indicate that groundwater (51%) mostly falls under doubtful to poor quality for irrigation purpose. Groundwater of Adigopula village is fluoride contaminated and remedial measures are suggested to improve the water quality.     

Granitic rocks of Yosemite Valley and an ideal granite model

Stochastic models of an ideal, a degenerate ideal granite, and two models for metasomatically transformed granites have been compared with sequences of grains observed in granitic rocks of Yosemite Valley, California. Properties of the granitic rocks appear to show a relationship to the topography and stream directions, and may reflect the behavior of the granitic rocks with respect to fracturing and weathering.     

Responses of the green-lipped mussel Perna viridis (L.) to suspended solids

Laboratory experiments were conducted to investigate the lethal and sublethal effects of suspended solids on the survival and physiological, behavourial and morphological changes of the green-lipped mussel Perna viridis collected from Tolo Harbour, Hong Kong. Results showed that P. viridis survived in all test conditions of suspended solids from 0 to 1200 mg/l over a period of 96 h. Physiological responses of the green-lipped mussel under 14-d exposure of suspended solids from 0 to 600 mg/l, followed by 14-d recovery in natural seawater, revealed no significant changes (p>0.05) in oxygen consumption and dry gonosomatic index for treatments in different concentrations of suspended solids and exposure time. Changes in clearance rate were only found to be significant (p<0.001) with exposure time. Responses in behavourial and morphological changes of the green-lipped mussel were also studied under similar experimental treatments and exposure time. Byssus production was significantly (p<0.001) related to exposure time. Gill damage, however, was significantly greater in treatments (p<0.001). Present findings suggested that P. viridis could tolerate a high level of suspended solids in the laboratory. There were dose-dependent effects of suspended solids on morphology of gill filaments. Implications of survival and responses of the green-lipped mussel to suspended solids in the marine environment are discussed.     

某围护结构上土压力实例分析

对某公路大桥超深锚锭基础围护结构上实测的土压力、孔隙水压力分布及其位移变化规律进行了详细分析。围护结构上土压力的实测值远小于计算的主动土压力值,且随开挖加深而不断减少,变化规律也随土层分布的差异而有所不同,围护结构上的侧向位移随开挖加深不断减少,孔隙水压力的变化受坑外水位影响较大。