1,720,990 research outputs found
Remote Sensing of African Lakes: A Review
No full textThe optical complexity and small size of inland waters make the application of remote sensing more challenging than for the open ocean. However, in Africa, where in situ monitoring of important water bodies is financially, institutionally and spatially constrained, there is strong demand for remote sensing to fill the critical information gap. Here we review a wide range of applications of both passive and active remote sensing to African lakes. The applications fall into five main categories: (1) visible, NIR, thermal and microwave sensing of lake area; (2) altimetric and gravimetric sensing of lake level; (3) thermal sensing of lake surface temperature; (4) visible, NIR and microwave sensing of macrophytes; and (5) optical sensing of trophic conditions including chlorophyll-a and euphotic depth. Sensors used include Landsat MSS, TM and ETM+, MERIS, MODIS, SeaWiFS, AVHRR, Meteosat, TOPEX/Poseidon, Jason-1, OSTM/Jason-2, ERS-1, ERS-2, Envisat, GFO, ICESat, ALOS-PALSAR and GRACE. The majority of studies have been applied to the "great" lakes such as Chad, Malawi, Tanganyika and Victoria; however, there is a growing body of literature on smaller lakes. We examine the possibilities that remote sensing offers to monitoring and management of African lakes as well as the potential limitations of the technology using Lake Victoria as an illustrative case
Organochlorine pesticides in rain, rivers and groundwater in the Lake Naivasha basin and implications for their management
Full text linkOrganochlorines (OCs) have a high persistence in the environment and toxicity to humans and wildlife. Despite their ban in several countries, they are still found in agricultural areas. Their presence in drinking water resources (rivers, rain and groundwater) in Lake Naivasha area, which has had a booming horticultural industry in the last three decades was investigated. Twenty-two water samples from the rift floor around Lake Naivasha were collected in June 2017 and analysed for organochlorines. Findings show that all the water samples are contaminated with various organochlorine pesticides and metabolites. The abundance of OCs in water resources can be ranked as follows, rain> river >groundwater in which 18 compounds were identified; alpha, beta, gamma and delta HCH, endrin, aldrin, heptachlor, chlordane, b-endosulfan, methoxychlor, p,p′-DDE, p,p′-DDD, endrin aldehyde, endosulphan sulphate, p,p′-DD and endrin ketone. Their concentrations range from 0.1 to1 μg/L. The OCs with high concentrations are aldrin, endrin aldehyde and endosulphan sulphate. Twelve banned compounds were found present, several decades after their ban (1986 - 2014) shows either occasional usage in the region or the residues drift from use elsewhere. Despite the low concentrations, many of these pollutants can exceed acceptable daily intake (ADI) for humans. Thus, the National Environment Management Authority, Kenya needs to set OCs guidelines on drinking water quality and concerted efforts with agriculture, water and health ministries is needed to ensure public health safety
The occurrence of high fluoride in groundwater and its health implications in Nakuru County in the Kenyan Rift Valley
Full text linkM.Sc. (Geology)Abstract: Most semi-urban and rural communities in developing countries rely on groundwater for their daily domestic supply. Unfortunately, contamination from the local geology can render the often only source of water unhealthy for consumption. Such case is in Nakuru County in the Central Kenyan Rift Valley where high fluoride in groundwater causes dental and skeletal fluorosis. Public water supply by the government in the area has been faced with many challenges such as insufficient water for the increasing population, deterioration of infrastructure, and poor maintenance and only 36% of the households are reported to have access to piped water. As a result, most of the local population relies on private and community owned boreholes. Despite the known high fluoride in groundwater, its concentrations in the local aquifers is not yet known. The aim of this study was to identify fluoride concentrations and distributions in the Nakuru aquifers and its correlation to the status of dental fluorosis affecting the local population. Waterquality data from 32 boreholes acquired from the Catholic Diocese of Nakuru-Water program (CDN), a water service organization in Nakuru, were used to determine fluoride’s correlation and association with the physico-chemical parameters in groundwater and how they influence its concentrations and spatial distribution in the local aquifers. The prevalence and severity of dental fluorosis in the local population was investigated in 170 patients from two dental clinics in the area and correlated to fluoride distribution. All the data were statistically and spatially analyzed. The results show a sodium-bicarbonate and slightly sodium-bicarbonate-chloride groundwater type in the area dominated by sodium, fluoride, chloride, sulphate, bicarbonate, TDS, pH, borehole depth, water hardness, and calcium, which where the principal parameters. More than 86% of the boreholes had fluoride levels higher than the WHO recommended value of 1.5 mg/l for safe drinking water. Fluoride levels ranged from 0.5 to 72 mg/l with a mean of 11.08 mg/l and had a strong positive correlation with most of the principal parameters except calcium, borehole depth, and water hardness, which had a weak negative correlation. The strong positive correlations between fluoride and the dominant parameters suggest that mineral dissolution and evaporative..
Investigating geogenic lead contamination and its associated health effects in Kilifi area, Kenya
Full text linkM.Sc. (Geology)Abstract: Lead (Pb) is ranked second in the most toxic substance list by Agency of Toxic Substances and Disease Registry (ATSDR). As a non-essential trace element, Pb presence in blood has no threshold safe limit with prolonged exposure affecting body systems especially brain development in children. In Kilifi area, sedimentary rocks of Triassic to Recent age host a base metal deposit of galena (PbS) that was extensively mined in the 1970s. Over 70% of the local population depends on natural land resources for their daily livelihood. To bridge the existing knowledge gap between ore deposit geology and associated chronic health conditions in the area, this study aimed at investigating the possible link between geogenic Pb and the prevalent chronic health issues affecting Kilifi residents. Soil, food crops and water samples were analyzed for Pb as well as other associated trace metals (Zn, Cu, Mn, Fe and Ba). Medical records collected from the County Health Office were reviewed for prevalent chronic diseases reported in ages below and above 5 years from 2011-2014. Neurodevelopmental disorders (NDD) prevalence in children aged 6-9 years old recorded between March 2015 and August 2016 were also obtained from KEMRI. Soil (n=55), plants (n=8) and water (n=15) samples were collected from random locations covered by Kilifi Demographic and Health Surveillance System (KDHSS) and beyond. Using X-Ray Fluorescence (XRF) technique, soil and plants samples were analyzed for Pb and associated metals. Water samples were analyzed for major cations and anions using inductively coupled plasma optical emission spectrometry (ICP-OES) and colorimetric discrete techniques. All the data was statistically and geospatially processed. Metals concentration in soil is found to be in the ranges of Pb=0.02-370.13; Zn=5.65-389.59; Cu=2.37-30.45; Mn=559.58-3962.81; Ba=3436.8-153675 and Fe=287.06-52472.9 mg/kg respectively. Out of the 55 soil samples, 20% of them had Pb levels exceeding WHO limit of 0.1-20 mg/kg for normal ranges of Pb in soil. In cassava tubers (Manihot esculenta) metals concentration is found to be in the ranges of Pb=0.39-0.49; Zn=17.10-59.54; Cu=2.39-5.74; Mn=132-315.25 and Fe=261.72-789.18 mg/kg respectively. In maize (Zea mays) the metals concentration is Pb=0.42; Zn=35.43; Cu=4.51; Mn=367.63 and Fe=751.53 mg/kg respectively. Metals concentration in cowpea leaves (Vigna unguiculata) are Pb=0.45; Zn=39.72; Cu=5.74; Mn=190.76 and Fe=204.84 mg/kg respectively while in baobab fruit (Adansonia digitata) the metals concentration is Pb=0.39; Zn=23.74; Cu=3.80; Mn=290.03 and Fe=634.17 mg/kg respectively. 100% plant samples (n=8) show Pb quantities above WHO limits of 0.3, 0.2 and 0.1 mg/kg for leafy vegetables, cereals/grains and..
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
