Spatial variability of geogenic contaminants in drinking water sources : Insights into hydrogeological controls, geospatial data for safe water supply and groundwater resource management

The presence of geogenic contaminants in drinking water is a major health concern in many parts of the world. The interaction of groundwater with different rock types and sediments in the natural geochemical environment play an important role in controlling their mobility. Due to limited resource allocations, water quality investigations are mostly limited only to the drinking water sources serving the communities. As a consequence, most aquifer systems remain unexplored in terms of groundwater quality through conventional methods. The present study aims to investigate the status of groundwater quality in the nine drainage basins of Tanzania focusing on the occurrence of fluoride (F¯) and other potentially toxic elements especially in the northern development zone (NDZ). The specific objectives were to model the spatial distribution of geogenic F¯- in groundwater systems and the health risk among the population as well as to evaluate the key influencing hydrogeological factors for the observed variability in F¯ concentrations in water sources using modern geospatial methods and technologies. Both literature and community perspectives indicate a serious problem in terms of F¯ in the Internal, Pangani, and Lake Victoria basins in the NDZ where the prevalence of mild to severe fluorosis is a health risk among the communities dependent on groundwater for drinking. In order to understand the spatial variability, machine learning methods were developed during this research by applying a combination of the concepts of spatial statistics, geostatistics, different Geographical Information Systems (GIS) tools as well as non-parametric methods to study the occurrence of geogenic contaminants in groundwater systems. Spatial statistical methods such as Moran’s I statistics and GIS tools revealed two positive significant high-high spatial patterns along the Pliocene-recent volcanic and the Mozambique belt as well as around Meru and Hanang’ stratovolcanoes in the northeast and southwestern part of the study regions, respectively. The positive low-low spatial patterns were determined around the major and minor rift valley escarpments both in the west and east of the East African Rift Valley (EARV) graben and around the stratovolcanoes within the graben. Other potentially toxic elements were found in elevated concentration around the Meru stratovolcano creating another risk of health concern to the communities which depend on such sources of drinking water. Factors controlling the spatial variability of fluoride in groundwater included, in the descending order, the mineralization, topography, tectonic processes, pH and water exchange between hydrogeological units during water movement. Other factors included depth to groundwater, well depth, screen depth and irrigation practices in the Sanya alluvial plain. The spatial heterogeneity of geological characteristics may lead to the spatial variability of various geogenic contaminants at spatial scales besides several other factors like topography, soil type, surface water-groundwater interaction, climate, volcanic activities, tectonic processes.The results of this study are important to the water safety planning implementation in the naturally contaminated aquifer systems especially in the EARV regions and volcanic areas.Förekomsten av geogena föroreningar i dricksvatten är ett stort hälsoproblem i många delar av världen. Interaktionen mellan grundvatten och olika bergarter och sediment i den naturliga geokemiska miljön har en avgörande betydelse för rörligheten av olika föreningar. På grund av begränsad resurstilldelning är vattenkvalitetsundersökningar oftast begränsade till de dricksvattenkällor som betjänar samhällena. Som en konsekvens förblir de flesta akvifersystem outforskade när det gäller grundvattenkvalitet med konventionella metoder. Den föreliggande studien syftar till att undersöka statusen för grundvattenkvaliteten i Tanzanias nio dräneringsbassänger med fokus på förekomsten av fluor (F¯) och andra potentiellt giftiga ämnen (PTE), särskilt i den norra utvecklingszonen (NDZ). De specifika målen var att modellera den rumsliga fördelningen av geogent F¯ i grundvattensystem och hälsorisken bland befolkningen samt att utvärdera de viktigaste påverkande hydrogeologiska faktorerna för den observerade variationen i F¯ koncentrationer i vattenkällor med hjälp av moderna geospatiala metoder och tekniker. Både litteratur och samhällsperspektiv indikerar ett allvarligt problem när det gäller F¯ i avrinningsområdena Internal, Pangani och Victoriasjön i NDZ där förekomsten av mild till svår fluoros är en hälsorisk bland befolkning som är beroende av grundvatten som dricksvattenkälla. För att förstå den rumsliga variabiliteten utvecklades maskininlärningsmetoder under denna forskning genom att tillämpa en kombination av begreppen rumslig statistik, geostatistik, olika verktyg för geografiska informationssystem (GIS) samt icke-parametriska metoder för att studera förekomsten av geogena föroreningar i grundvattensystem. Rumsliga statistiska metoder såsom Morans I-statistik och olika GIS-verktyg avslöjade två positiva signifikanta rumsliga mönster (high-high) längs Pliocen-Holocen-vulkanen och Moçambiques bälte samt runt Mt. Meru och Hanang' stratovulkaner i de respektive nordöstra och sydvästra delarna av studieregionerna. De positiva rumsliga mönstren (low-low) hittades runt de stora och mindre sprickdalsbranterna både i väster och öster om östafrikanska förkastningsänkor (East African Rift Valley (EARV)) och runt stratovulkanerna i dessa. Andra potentiella giftiga ämnen hittades i förhöjd koncentration runt stratovulkanen Mt. Meru vilket skapar ytterligare en risk för hälsoproblem för den befolkning som är beroende av sådana dricksvattenkällor. Faktorer som styr den rumsliga variabiliteten av fluor i grundvattnet inkluderade, i fallande ordning, mineralisering, topografi, tektoniska processer, pH och grundvattenflöde mellan hydrogeologiska enheter. Andra faktorer inkluderar grundvattennivå, brunnsdjup, skärmdjup och bevattningsmetoder i den alluviala slätten kring Sanya floden. Den rumsliga heterogeniteten hos geologiska egenskaper kan leda till rumslig variation av olika geogena föroreningar på rumslig skala förutom flera andra faktorer som topografi, jordtyp, interaktion mellan ytvatten och grundvatten, klimat, vulkaniska aktiviteter och tektoniska processer. Resultaten av denna studie är viktiga för genomförandet av vattensäkerhetsplaneringen i de naturligt förorenade akvifersystemen, särskilt i EARV-regionerna och vulkanområdena.Kuwepo kwa uchafu wa kijiografia katika maji ya kunywa ni wasiwasi mkubwa kwa afya katika sehemu mbalimbali duniani. Uchafu huo hutokana na migusano kati ya maji ya ardhini na miamba mbalimbali pamoja na udongo katika mazingira ya asili ya kijiografia. Kutokana na ufinyu wa bajeti, tafiti nyingi katika ubora wa maji hufanyika kwa kutumia vyanzo vya maji ya kunywa vinavyohudumia jamii. Matokeo yake, mifumo mingi ya vyanzo vya maji ya ardhini bado haifanyiwa tafiti za kutosha kuhusu ubora wa maji hayo kwa kutumia njia za kawaida. Utafiti huu unalenga kuchunguza hali ya ubora wa maji chini ya ardhi katika mabonde tisa ya maji nchini Tanzania ukilenga kutokea kwa floridi (F¯) na kemikali nyingine zinavyoweza kuwa sumu hasa katika ukanda wa maendeleo wa kaskazini (NDZ). Malengo mahususi yalikuwa ni kuelezea jiografia ya F¯katika mifumo ya maji ya ardhini na athari zake kiafya miongoni mwa wakazi pamoja na kutathmini mambo muhimu yanayoathiri hali ya hidrojiolojia inayosababisha utofauti katika viwango vya F¯ kwenye vyanzo vya maji ya kunywa kwa kutumia mbinu za kisasa za kijiografia na teknolojia. Fasihi na mitazamo ya jamii inaonyesha kuna tatizo kubwa la F¯ katika mabonde ya Ndani, Pangani, na Ziwa Viktoria katika NDZ ambapo ugonjwa wa fluorosis ni tishio kiafya miongoni mwa jamii zinazotegemea maji ya ardhini kwa kunywa. Katika utafiti huu, mbinu za kisasa kama vile zile zenye kutumia dhana za takwimu za kijiografia, Mifumo ya Taarifa za Kijiografia (GIS) mbalimbali pamoja na mbinu zisizo za kigezo katika kuelewa jiografia ya chemikali hatarishi katika maji ya kunywa zilibuniwa na kutumika. Takwimu za kijiografia kwa kutumia Moran's I na GIS zilifichua mifumo miwili yenye uchafuzi kwa kiwango cha juu katika kando mpaka kati ya volkeno ya hivi majuzi ya Pliocene na ukanda wa Msumbiji pamoja na kuzunguka volkeno za Meru na Hanang' kaskazini mashariki na kusini magharibi mwa maeneo ya utafiti, kwa mtiririko huo. Maji yenye kiwango kidogo cha F- yalionekana kwenye miinuko mikubwa ya Bonde la Ufa la Africa Mashariki (EARV) na kwenye miinuko ya milima ya volcano ndani ya bonde hilo. Pia kemikali nyingine hatarishi kwa afya ya binadamu ziligundulika katika maeneo yenye kiwango kikubwa cha F- kuzunguka mlima Meru. Mambo yanayosababisha utofauti wa kiwango F- katika maji ya chini ya ardhi ni pamoja na, katika mpangilio wa kushuka, kiwango cha madini, topografia, michakato ya tectonic, pH na kubadilishana maji baina ya miamba wakati wa kusafiri kutoka sehemu moja kwenda nyingine. Mambo mengine ni pamoja na kina cha maji chini ya ardhi, kina cha kisima, sehemu ya kuchukulia maji kwenye kisima na mbinu za umwagiliaji katika hasa uwanda wa Sanya. Utofauti wa aina za miamba katika mazingira unaweza kusababisha uchafuzi mbalimbali wa kijiografia katika mizani licha kwamba mambo mengine kadhaa kama vile topografia, aina ya udongo, mwingiliano wa maji ya uso wa maji na ardhini, hali ya hewa, shughuli za volkeno, michakato ya tectonic vinaweza changia katika kuongeza tatizo la kemikali husika kwenye mfumo wa maji. Matokeo ya utafiti huu ni muhimu kwa utekelezaji wa mipango ya usalama wa maji katika mifumo ya maji iliyochafuliwa kiasili hasa katika maeneo ya EARV na maeneo ya volkeno.QC 20220124</p

Spatial variability of geogenic contaminants in drinking water sources : Insights into hydrogeological controls, geospatial data for safe water supply and groundwater resource management

The presence of geogenic contaminants in drinking water is a major health concern in many parts of the world. The interaction of groundwater with different rock types and sediments in the natural geochemical environment play an important role in controlling their mobility. Due to limited resource allocations, water quality investigations are mostly limited only to the drinking water sources serving the communities. As a consequence, most aquifer systems remain unexplored in terms of groundwater quality through conventional methods. The present study aims to investigate the status of groundwater quality in the nine drainage basins of Tanzania focusing on the occurrence of fluoride (F¯) and other potentially toxic elements especially in the northern development zone (NDZ). The specific objectives were to model the spatial distribution of geogenic F¯- in groundwater systems and the health risk among the population as well as to evaluate the key influencing hydrogeological factors for the observed variability in F¯ concentrations in water sources using modern geospatial methods and technologies. Both literature and community perspectives indicate a serious problem in terms of F¯ in the Internal, Pangani, and Lake Victoria basins in the NDZ where the prevalence of mild to severe fluorosis is a health risk among the communities dependent on groundwater for drinking. In order to understand the spatial variability, machine learning methods were developed during this research by applying a combination of the concepts of spatial statistics, geostatistics, different Geographical Information Systems (GIS) tools as well as non-parametric methods to study the occurrence of geogenic contaminants in groundwater systems. Spatial statistical methods such as Moran’s I statistics and GIS tools revealed two positive significant high-high spatial patterns along the Pliocene-recent volcanic and the Mozambique belt as well as around Meru and Hanang’ stratovolcanoes in the northeast and southwestern part of the study regions, respectively. The positive low-low spatial patterns were determined around the major and minor rift valley escarpments both in the west and east of the East African Rift Valley (EARV) graben and around the stratovolcanoes within the graben. Other potentially toxic elements were found in elevated concentration around the Meru stratovolcano creating another risk of health concern to the communities which depend on such sources of drinking water. Factors controlling the spatial variability of fluoride in groundwater included, in the descending order, the mineralization, topography, tectonic processes, pH and water exchange between hydrogeological units during water movement. Other factors included depth to groundwater, well depth, screen depth and irrigation practices in the Sanya alluvial plain. The spatial heterogeneity of geological characteristics may lead to the spatial variability of various geogenic contaminants at spatial scales besides several other factors like topography, soil type, surface water-groundwater interaction, climate, volcanic activities, tectonic processes.The results of this study are important to the water safety planning implementation in the naturally contaminated aquifer systems especially in the EARV regions and volcanic areas.Förekomsten av geogena föroreningar i dricksvatten är ett stort hälsoproblem i många delar av världen. Interaktionen mellan grundvatten och olika bergarter och sediment i den naturliga geokemiska miljön har en avgörande betydelse för rörligheten av olika föreningar. På grund av begränsad resurstilldelning är vattenkvalitetsundersökningar oftast begränsade till de dricksvattenkällor som betjänar samhällena. Som en konsekvens förblir de flesta akvifersystem outforskade när det gäller grundvattenkvalitet med konventionella metoder. Den föreliggande studien syftar till att undersöka statusen för grundvattenkvaliteten i Tanzanias nio dräneringsbassänger med fokus på förekomsten av fluor (F¯) och andra potentiellt giftiga ämnen (PTE), särskilt i den norra utvecklingszonen (NDZ). De specifika målen var att modellera den rumsliga fördelningen av geogent F¯ i grundvattensystem och hälsorisken bland befolkningen samt att utvärdera de viktigaste påverkande hydrogeologiska faktorerna för den observerade variationen i F¯ koncentrationer i vattenkällor med hjälp av moderna geospatiala metoder och tekniker. Både litteratur och samhällsperspektiv indikerar ett allvarligt problem när det gäller F¯ i avrinningsområdena Internal, Pangani och Victoriasjön i NDZ där förekomsten av mild till svår fluoros är en hälsorisk bland befolkning som är beroende av grundvatten som dricksvattenkälla. För att förstå den rumsliga variabiliteten utvecklades maskininlärningsmetoder under denna forskning genom att tillämpa en kombination av begreppen rumslig statistik, geostatistik, olika verktyg för geografiska informationssystem (GIS) samt icke-parametriska metoder för att studera förekomsten av geogena föroreningar i grundvattensystem. Rumsliga statistiska metoder såsom Morans I-statistik och olika GIS-verktyg avslöjade två positiva signifikanta rumsliga mönster (high-high) längs Pliocen-Holocen-vulkanen och Moçambiques bälte samt runt Mt. Meru och Hanang' stratovulkaner i de respektive nordöstra och sydvästra delarna av studieregionerna. De positiva rumsliga mönstren (low-low) hittades runt de stora och mindre sprickdalsbranterna både i väster och öster om östafrikanska förkastningsänkor (East African Rift Valley (EARV)) och runt stratovulkanerna i dessa. Andra potentiella giftiga ämnen hittades i förhöjd koncentration runt stratovulkanen Mt. Meru vilket skapar ytterligare en risk för hälsoproblem för den befolkning som är beroende av sådana dricksvattenkällor. Faktorer som styr den rumsliga variabiliteten av fluor i grundvattnet inkluderade, i fallande ordning, mineralisering, topografi, tektoniska processer, pH och grundvattenflöde mellan hydrogeologiska enheter. Andra faktorer inkluderar grundvattennivå, brunnsdjup, skärmdjup och bevattningsmetoder i den alluviala slätten kring Sanya floden. Den rumsliga heterogeniteten hos geologiska egenskaper kan leda till rumslig variation av olika geogena föroreningar på rumslig skala förutom flera andra faktorer som topografi, jordtyp, interaktion mellan ytvatten och grundvatten, klimat, vulkaniska aktiviteter och tektoniska processer. Resultaten av denna studie är viktiga för genomförandet av vattensäkerhetsplaneringen i de naturligt förorenade akvifersystemen, särskilt i EARV-regionerna och vulkanområdena.Kuwepo kwa uchafu wa kijiografia katika maji ya kunywa ni wasiwasi mkubwa kwa afya katika sehemu mbalimbali duniani. Uchafu huo hutokana na migusano kati ya maji ya ardhini na miamba mbalimbali pamoja na udongo katika mazingira ya asili ya kijiografia. Kutokana na ufinyu wa bajeti, tafiti nyingi katika ubora wa maji hufanyika kwa kutumia vyanzo vya maji ya kunywa vinavyohudumia jamii. Matokeo yake, mifumo mingi ya vyanzo vya maji ya ardhini bado haifanyiwa tafiti za kutosha kuhusu ubora wa maji hayo kwa kutumia njia za kawaida. Utafiti huu unalenga kuchunguza hali ya ubora wa maji chini ya ardhi katika mabonde tisa ya maji nchini Tanzania ukilenga kutokea kwa floridi (F¯) na kemikali nyingine zinavyoweza kuwa sumu hasa katika ukanda wa maendeleo wa kaskazini (NDZ). Malengo mahususi yalikuwa ni kuelezea jiografia ya F¯katika mifumo ya maji ya ardhini na athari zake kiafya miongoni mwa wakazi pamoja na kutathmini mambo muhimu yanayoathiri hali ya hidrojiolojia inayosababisha utofauti katika viwango vya F¯ kwenye vyanzo vya maji ya kunywa kwa kutumia mbinu za kisasa za kijiografia na teknolojia. Fasihi na mitazamo ya jamii inaonyesha kuna tatizo kubwa la F¯ katika mabonde ya Ndani, Pangani, na Ziwa Viktoria katika NDZ ambapo ugonjwa wa fluorosis ni tishio kiafya miongoni mwa jamii zinazotegemea maji ya ardhini kwa kunywa. Katika utafiti huu, mbinu za kisasa kama vile zile zenye kutumia dhana za takwimu za kijiografia, Mifumo ya Taarifa za Kijiografia (GIS) mbalimbali pamoja na mbinu zisizo za kigezo katika kuelewa jiografia ya chemikali hatarishi katika maji ya kunywa zilibuniwa na kutumika. Takwimu za kijiografia kwa kutumia Moran's I na GIS zilifichua mifumo miwili yenye uchafuzi kwa kiwango cha juu katika kando mpaka kati ya volkeno ya hivi majuzi ya Pliocene na ukanda wa Msumbiji pamoja na kuzunguka volkeno za Meru na Hanang' kaskazini mashariki na kusini magharibi mwa maeneo ya utafiti, kwa mtiririko huo. Maji yenye kiwango kidogo cha F- yalionekana kwenye miinuko mikubwa ya Bonde la Ufa la Africa Mashariki (EARV) na kwenye miinuko ya milima ya volcano ndani ya bonde hilo. Pia kemikali nyingine hatarishi kwa afya ya binadamu ziligundulika katika maeneo yenye kiwango kikubwa cha F- kuzunguka mlima Meru. Mambo yanayosababisha utofauti wa kiwango F- katika maji ya chini ya ardhi ni pamoja na, katika mpangilio wa kushuka, kiwango cha madini, topografia, michakato ya tectonic, pH na kubadilishana maji baina ya miamba wakati wa kusafiri kutoka sehemu moja kwenda nyingine. Mambo mengine ni pamoja na kina cha maji chini ya ardhi, kina cha kisima, sehemu ya kuchukulia maji kwenye kisima na mbinu za umwagiliaji katika hasa uwanda wa Sanya. Utofauti wa aina za miamba katika mazingira unaweza kusababisha uchafuzi mbalimbali wa kijiografia katika mizani licha kwamba mambo mengine kadhaa kama vile topografia, aina ya udongo, mwingiliano wa maji ya uso wa maji na ardhini, hali ya hewa, shughuli za volkeno, michakato ya tectonic vinaweza changia katika kuongeza tatizo la kemikali husika kwenye mfumo wa maji. Matokeo ya utafiti huu ni muhimu kwa utekelezaji wa mipango ya usalama wa maji katika mifumo ya maji iliyochafuliwa kiasili hasa katika maeneo ya EARV na maeneo ya volkeno.QC 20220124</p

Spatial analysis and GIS mapping of regional hotspots and potential health risk of fluoride concentrations in groundwater of northern Tanzania

Safe drinking water supply systems in naturally contaminated hydrogeological environments require precise geoinformation on contamination hotspots. Spatial statistical methods and GIS were used to study fluoride occurrence in groundwater and identify significant spatial patterns using fluoride concentrations. The global and local Morans I indices were used. While the significant positive global Morans I index indicated spatial structure in fluoride occurrence, the significant spatial clusters were identified using local Morans I index and mapped at p-value of 0.05. The spatial clusters demonstrated patterns of drinking water sources with fluoride concentrations below or above WHO guideline and Tanzania standard for drinking water and were considered as ‘regional fluoride cool spots’ and ‘regional fluoride contamination hotspots’, respectively. Two regional fluoride contamination hotspots were identified and mapped around the Stratovolcano Mountains in the north-east and south-west of the study area; and along the Neogene Quaternary volcanic formations and Palaeo-Neoproterozoic East African Orogen (Mozambique Belt). The two largest regional fluoride cool spots dominated the major and minor rift escarpments in the west and east of the study area respectively while the small ones emerged around the volcanic mountains in the north and south. Furthermore, significant spatial outliers emerged at the boundary of regional fluoride hotspots and cool spots as an indication of the spatial processes controlling the mobilization of fluoride in groundwater. While all water sources in the cool spots had fluoride concentrations below 1.5 mg/L, some had extremely low concentrations below 0.5 mg/L which is not safe for human consumption. For hotspots, 96% of water sources had fluoride concentrations above 1.5 mg/L. The probability of having safe source of drinking water varied from one geological unit to another with sources in the Neogene Quaternary volcanic formations having least probabilities.QC 20200716</p

Hydrogeological Controls of Spatial Variabiity of Arsenic in the Volcano-Sedimentary Complex of Geita District, Northern Tanzania

Accurate and precise understanding of water quality variables distribution is a pre-requisite to proper design of safe water supply systems especially in countries endowed with gold mineralization like Tanzania. In this study, the effect of topography, pH and well depth on variability of arsenic (As) have been investigated using measured concentration levels in shallow wells, intermediate deep wells and boreholes. The modelling process involved testing spatial dependence in measured concentration levels using global Moran’s Index and spatial regression analysis. A moderate significant Moran’s index (I = 0.366, p-value = 0.001) was obtained indicating that As occurrence in this local geologic formation is clustering in space. During spatial regression analysis, significant (p-value=0.002) model fit of 20% was obtained. Arsenic occurrence in the volcano-sedimentary complex was significantly negative correlated with altitude from mean sea level (p-value=0.012). In contrast, As concentration was positively correlated with pH and well depth, though the correlation with the latter was not significant. This is because some wells had no reliable depth information. This approach is very useful in understanding the space dependent natural processes controlling the distribution and mobility of geogenic contaminants such as As in drinking water sources

The natural magnesite efficacy on arsenic extraction from water and alkaline influence on metal release in water

Arsenic (As) removal studies were carried out through batch experiments to investigate the performance of the locally available calcined magnesite mineral rocks from Tanzania. Natural water from a stream source in Tanzania and the prepared synthetic water at the laboratory were used for the studies. Parameters such as initial As concentration, calcined magnesite dosage, contact time and pH were evaluated for As removal using an overhead reax2 shaker. Arsenic concentration was reduced from 5.3 to 1.1 mg/L As(V) at 180 min when 0.5 g/L calcined magnesite was applied to a synthetic water sample, whereas the concentration of 117 & mu;g/L As(V) and 5.2 & mu;g/L As(III) was reduced to below 0.1 & mu;g/L in natural water. An increase in calcined magnesite dosage resulted in increased As removal up to below 0.01 mg/L. The calcined magnesite raised the pH of the water sample from 6.8 to 10 when the applied dosage increased between 0.002 g/L and 0.05 g/L. The pH was constant at around 10 even when the amount of 0.05 g/L was added 2000 times. Despite the high pH, the amount of magnesium released in water was low. The calcination of magnesite at 500 degrees C increased surface area by 4 times as compared to the natural magnesite and X-ray diffraction showed presence of MgCO3 phase as the dominant phase at this temperature. The reaction kinetics of As removal on 0.5 g/L calcined magnesite fitted with the pseudo-second-order (R2 = 0.96). Reaction isotherm was strongly fitted with Freundlich isotherm (R2 = 0.98). Linear regression and artificial intelligence neural network showed the As removal was influenced by both contact time and pH. Arsenic can be removed from As water using calcined magnesite and will be suitable for water treatment around gold mining areas

Visual MINTEQ simulation for prediction of the adsorption of arsenic on ferrihydrite

The surface of ferrihydrite adsorbs arsenic (As) effectively. In this investigation, the As laced water samples collected from Geita and Mara regions within the Lake Victoria Basin (LVB) under DAFWAT project were simulated onVisual MINTEQ 3.1 software to determine the amount of ferrihydrite required to adsorb a given amount of As from water. Model simulations show that As concentration of ≤1 mM can be completely adsorbed by 4 g L−1 ferrihydrite. Previous studies show that the lower pH 4 to 4.5 influences adsorption, while it decreases as pH increases as well as when As concentration increases. The increase of adsorbent dose to 4 g L−1 has shown to improve As(V) adsorption on pH 5 to 8 at 100%. The amount of adsorbent can now be used for laboratory adsorption experiments by using iron-based materials or commercial ferrihydrite.</p

Spatial uncertainties in fluoride levels and health risks in endemic fluorotic regions of northern Tanzania

Spatial uncertainty caused by large-scale variation in fluoride (F-) occurrence remains a setback for water supply authorities in the F- belts of the world. It is estimated that approximately 80 million people in the East African Rift Valley (EARV) regions and volcanic areas exhibit a wide variety of fluorosis symptoms due to drinking water with F- concentrations higher than 1.5 mg/L (WHO guideline limit). In this study, we combined geostatistical techniques, spatial statistical methods, and geographical information systems (GIS) to (i) map the probable places with F- &lt; 0.5 mg/L and F- &gt; 1.5, 4.0 and 10.0 mg/L using probability kriging (PK) method, (ii) estimate the probable total population at high or low F- risk levels using univariate local Moran's I statistic, and (iii) map the spatial distribution of population at high and low F- risk levels in Manyara, Arusha and Kilimanjaro regions using GIS. It was predicted that places along the major and minor EARV mountain ranges and around the flanks of major stratovolcanoes were dominated by groundwater sources with extremely low F-(&lt;&lt;0.5 mg/L). In contrast, places within EARV graben were dominated by groundwater sources with F- &gt; 1.5 mg/L. About 1 million people (similar to 20% of the total population) living around Mt. Kilimanjaro in Rombo, Moshi, and Mwanga districts are at high dental caries risk. Furthermore, it was estimated that about 2 million people (similar to 41% of the total population) in Siha, Hai, Arusha City, Hanang', Arusha, Simanjiro, and Meru districts are at high risk of dental, skeletal, and crippling fluorosis. Fluorosis, especially dental and crippling fluorosis, is an increasing disease burden at the community level due to prolonged consumption of F- contaminated water within EARV graben. The major findings of the present study are very crucial for authority to minimize the uncertainty caused by high spatial variability in geogenic F- occurrence.QC 20210929</p

Spatial variability of the sources and distribution of fluoride in groundwater of the Sanya alluvial plain aquifers in northern Tanzania

Groundwater contamination from geogenic sources paces challenges to many countries, especially in the developing world. In Tanzania, the elevated fluoride (F-) concentration and related chronic fluorosis associated with drinking F- rich water arc common in the Fast African Rift Valley regions. In these regions, F- concentration is space dependence which poses much uncertainty when targeting safe source for drinking water. To account for the spatial effects, integrated exploratory spatial data analysis, regression analysis, and geographical information systems tools were used to associate the distribution of F- in groundwater with spatial variability in terrain slopes, volcanic deposits, recharge water/vadose materials contact time, groundwater resource development for irrigated agriculture in the Sanya alluvial plain (SAP) of northern Tanzania. The F- concentration increased with distance from steep slopes where the high scale of variation was recorded in the gentle sloping and flat grounds within the SAP. The areas covered with debris avalanche deposits in the gentle sloping and flat grounds correlated with the high spatial variability in F- concentration. Furthermore, the high spatial variability in F- correlated positively with depth to groundwater in the Sanya flood plain. In contrast, a negative correlation between F- and borehole depth was observed. The current irrigation practices in the Sanya alluvial plain contribute to the high spatial variability in F- concentration, particularly within the perched shallow aquifers in the volcanic river valleys. The findings of this study arc important to the overall chain of safe water supply process in historically fluorotic regions. They provide new insights into the well-known F- contamination through the use of modern geospatial methods and technologies. In Tanzania's context, the findings can improve the current process of drilling permits issuance by the authority and guide the local borehole drillers to be precise in siting safe source for drinking water.QC 20220120</p

Evaluating the land cover dynamics in the protected areas using GIS and Remote sensing techniques:the case of Nyerere National Park, Tanzania

Understanding land cover dynamics of protected areas is one area of active research and several studies have been done in this direction. However, such studies are limited with few parameters and lack a long-range spatial-temporal analysis to effectively understand land cover dynamics and thereby helping countries manage their protected areas sustainably. This research used Nyerere National Park (NNP) to explore its land cover dynamics from 1991 to 2021 and projected to 2050, vegetation health from 2000 to 2021 and surrounding human population from 1988 to 2021. The park’s land cover of 1991 and 2021 was explored using a smileCart classifier after training 897 samples of water, bareland, grassland, bushland and forest from the Landsat imagery. Its 2050 land cover was simulated using CA-Markov model. The park's vegetation health was studied using NDVI and EVI from the Landsat and MODIS imagery. Land cover classes with significant changes are forest and grassland. The forest areas showed a decreasing trend from 62%-to-52%-to-41% from 1991-to-2021-to-2050, while the grassland areas showed an increasing trend from 9%-to-17%-to-24%. The maximum NDVI values from the Landsat imagery showed a minimal decrease from 0.76 in 1991 to 0.75 in 2021. Many park’s areas have weak vegetation based on the overall NDVI and EVI results. The study also identified rapid increase in human population around the park, and agricultural activities taking place in some of its areas. The results of this study provide a new reference to NNP and other studies in all other protected areas