The role of hydrothermal fluids in sedimentation in saline alkaline lakes: Evidence from Nasikie Engida,Kenya Rift Valley

Saline alkaline lakes that precipitate sodium carbonate evaporites are most common in volcanic terrains in semi‐arid environments. Processes that lead to trona precipitation are poorly understood compared to those in sulphate‐dominated and chloride‐dominated lake brines. Nasikie Engida (Little Magadi) in the southern Kenya Rift shows the initial stages of soda evaporite formation. This small shallow (<2 m deep; 7 km long) lake is recharged by alkaline hot springs and seasonal runoff but unlike neighbouring Lake Magadi is perennial. This study aims to understand modern sedimentary and geochemical processes in Nasikie Engida and to assess the importance of geothermal fluids in evaporite formation. Perennial hot‐spring inflow waters along the northern shoreline evaporate and become saturated with respect to nahcolite and trona, which precipitate in the southern part of the lake, up to 6 km from the hot springs. Nahcolite (NaHCO₃) forms bladed crystals that nucleate on the lake floor. Trona (Na₂CO₃·NaHCO₃·2H₂O) precipitates from more concentrated brines as rafts and as bottom‐nucleated shrubs of acicular crystals that coalesce laterally to form bedded trona. Many processes modify the fluid composition as it evolves. Silica is removed as gels and by early diagenetic reactions and diatoms. Sulphate is depleted by bacterial reduction. Potassium and chloride, of moderate concentration, remain conservative in the brine. Clastic sedimentation is relatively minor because of the predominant hydrothermal inflow. Nahcolite precipitates when and where pCO₂ is high, notably near sublacustrine spring discharge. Results from Nasikie Engida show that hot spring discharge has maintained the lake for at least 2 kyr, and that the evaporite formation is strongly influenced by local discharge of carbon dioxide. Brine evolution and evaporite deposition at Nasikie Engida help to explain conditions under which ancient sodium carbonate evaporites formed, including those in other East African rift basins, the Eocene Green River Formation (western USA), and elsewhere.     

War,by Conservation

In this paper I argue that there has been a critical shift towards war by conservation in which conservation, security and counter insurgency (COIN) are becoming more closely integrated. In this new phase concerns about global security constitute important underlying drivers, while biodiversity conservation is of secondary importance. This is a significant break from earlier phases of fortress conservation and war for biodiversity. In order to develop a better understanding of these shifts, this paper analyzes the existing conceptual approaches, notably environmental security which seeks to understand how resources cause or shape conflict, and political ecology approaches that focus on the struggles over access to and control over resources. However, this paper indicates the limitations of these existing debates for understanding recent shifts, which require a fresh approach. I chart the rise of the narrative I call poachers-as-terrorists, which relies on the invocation of the idea that ivory is the white gold of Jihad, a phrase which is closely associated with an Elephant Action League (EAL) report in 2012 which claimed Al Shabaab used ivory to fund its operations. This narrative is being extended and deepened by a powerful alliance of states, conservation NGOs, Private Military Companies and international organizations, such that it is shaping policies, especially in areas of US geo-strategic interest in Sub-Saharan Africa. As a result conservation is becoming a core element of a global security project, with significant implications for conceptual debates and for conservation practice on the ground.     

Calibrating a FDR sensor for soil moisture monitoring in a wetland in Central Kenya

The recent transformation of wetlands into farmland in East Africa is accelerating due to growing food-demand, land shortages, and an increasing unpredictability of climatic conditions for crop production in uplands. However, the conversion of pristine wetlands into sites of production may alter hydrological attributes with negative effects on production potential. Particularly the amount and the dynamics of plant available soil moisture in the rooting zone of crops determine to a large extent the agricultural production potential of wetlands. Various methods exist to assess soil moisture dynamics with Frequency Domain Reflectometry (FDR) being among the most prominent. However, the suitability of FDR sensors for assessing plant available soil moisture has to date not been confirmed for wetland soils in the region. We monitored the seasonal and spatial dynamics of water availability for crop growth in an inland valley wetland of the Kenyan highlands using a FDR sensor which was site-specifically calibrated. Access tubes were installed within different wetland use types and hydrological situations along valley transects and soil properties affecting soil moisture (organic C, texture, and bulk density) were investigated. There was little variation in soil attributes between physical positions in the valley, and also between topsoil and subsoil attributes with the exception of organic C contents. With a root mean squared error of 0.073 m³/m³, the developed calibration function of the FDR sensor allows for reasonably accurate soil moisture prediction for both within-site comparisons and the monitoring of temporal soil moisture variations. Applying the calibration equation to a time series of profile probe readings over a period of one year illustrated not only the temporal variation of soil moisture, but also effects of land use.     

Pan-African high pressure granulites from SE-Kenya: Petrological and geothermobarometric evidence for a polycyclic evolution in the Mozambique belt

Two different Pan-African tectono-metamorphic events are recognised in the Taita Hill Tsavo East National Park/Galana river area, SE-Kenya (Mozambique belt) based on petrographic and geothermobarometric evidence. Structurally, this area can be subdivided into four units: (1) the easternmost part of the basement along the Galana river is characterized by subhorizontal slightly to the west and east dipping foliation planes. Migmatic paragneisses with intercalated marbles, calcsilicates and metapelites and bands of amphibolites are the dominant rock type. (2) The western part of the Galana river within the Tsavo East National Park is a ca. 25 km wide shear zone with subvertical foliation planes. The eastern part shows similar rocks as observed in unit 1, while towards west, metasedimentary units become rare and the main rock types are tonalitic gneisses with intercalated amphibolites. (3) A 10 km wide zone (Sagala Hills zone) between the strike slip zone (unit 2) and the Taita Hills (unit 4) is developed. This zone is characterized by elongated and folded felsic migmatic amphibole and garnet bearing orthogneiss bodies with intercalated bands of mafic rocks. (4) The Taita Hills are a slightly to the N dipping nappe stack. The main rock type in the Taita Hills are amphibole–biotite–plagioclase–quartz ± garnet ± clinopyroxene ± scapolite bearing migmatic gneisses with mafic bands. In the southern part, metapelites, marbles and some amphibolites are common.Although the geological structures are different in units 1 and 2, the calculated PT conditions are similar with peak PT of 760–820 °C and 7.5–9.5 kbar. Temperatures in unit 3 (Sagalla Hills zone) and unit 4 (Taita Hills) are slightly higher ca. 760–840 °C, but pressure is significantly higher, ranging from 10 to 12 kbar. Sillimanite growth around kyanite, garnet zonation pattern, mineral reaction textures, and PT calculations constrain a “clock-wise” PT-path with near isobaric cooling following the peak of metamorphism. The different PT conditions, tectonic setting, and a different age of metamorphism are evidence that units 1 and 2 (Galana river) belong to a different tectono-metamorphic event than unit 3 (Sagala Hills zone) and 4 (Taita Hills). The major shear zone (unit 2) marks a tectonic suture dividing the two different tectono-metamorphic domains. It is also likely that it played an important role during exhumation of the granulite facies rocks from units 3 and 4.     

Characterization of drought in the Kerio Valley Basin,Kenya using the Standardized Precipitation Evapotranspiration Index: 1960−2016

The Kerio Valley basin in Kenya has undergone several periods of drought, yet drought patterns in the region are not well understood due to limited climatic data. Drought events in the region have resulted in crop failure and livestock deaths, exacerbating food shortages. In this study, the Standardized Precipitation Evapotranspiration Index (SPEI), a multi‐scalar drought index was used to examine the onset, duration, severity, intensity, and frequency of agricultural and hydrological drought in the region. The gridded 0.5° × 0.5° climatic datasets from Climatic Research Unit for the period 1960?2016 was used for analysis. Temporal evolutions of SPEI at 6‐ and 12‐month lags were subsequently used to evaluate agricultural and hydrological drought, respectively. Additionally, the Mann‐Kendall trend test was used to test for trends in the time series. Results from the analysis show that: 1) droughts are becoming more frequent in the region, 2) drought intensities in the arid and semi‐arid lands have weakened, 3) regions west of the Kerio River have recently recorded a wetting trend, and 4) the southern and central regions of the basin are drought‐prone. Understanding the spatial and temporal patterns of drought in the basin can assist in drought preparation and mitigation planning.     

Analysis of agricultural drought in Iiuni,Eastern Kenya: application of a Markov model

In semi‐arid Kenya, episodes of agricultural droughts of varying severity and duration occur. The occurrence of these agricultural droughts is associated with seasonal rainfall variability and can be reflected by seasonal soil moisture deficits that significantly affect crop performance and yield. The objective of this study was to stochastically simulate the behaviour of dry and wet spells and rainfall amounts in Iiuni watershed, Kenya. The stochastic behaviour of the longest dry and wet spells (runs) and largest rainfall amounts were simulated using a Markov (order 1) model. There were eight raingauge stations within the watershed. The entire analysis was carried out using probability parameters, i.e. mean, variance, simple and conditional probabilities of dry and rain days. An analysis of variance test (ANOVA ) was used to establish significant differences in rainfall characteristics between the eight stations. An analysis of the number of rain days and rainfall amount per rain day was done on a monthly basis to establish the distribution and reliability of seasonal rainfall. The graphic comparison of simulated cumulative distribution functions (Cdfs) of the longest spells and largest rainfall amounts showed Markovian dependence or persistence. The longest dry spells could extend to 24 days in the long rainy season and 12 in the short rainy season. At 50% (median) probability level, the largest rainfall amounts were 91 mm for the long rainy season and 136 mm for the short rainy season. The short rains were more reliable for crop production than the long rains. The Markov model performed well and gave adequate simulations of the spells and rainfall amounts under semi‐arid conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

Virtual moralities: The mainstreaming of Fairtrade in Kenyan tea fields

Fairtrade was founded to alleviate poverty and economic injustice through a market-based form of solidarity exchange. Yet with the increasing participation of transnational food corporations in Fairtrade sourcing, new questions are emerging on the extent to which the model offers an alternative to the inimical tendencies of neoliberalism. Drawing on a qualitative research project of Kenyan Fairtrade tea, this paper examines how the process of corporate mainstreaming influences the structure and outcomes of Fairtrade, and specifically the challenges it poses for the realization of Fairtrade’s development aspirations. It argues firstly that whilst tea producers have experienced tangible benefits from Fairtrade’s social premium, these development ‘gifts’ have been conferred through processes marked less by collaboration and consent than by patronage and exclusion. These contradictions are often glossed by the symbolic force of Fairtrade’s key tenets - empowerment, participation, and justice - which simultaneously serve to neutralize critique and mystify the functions that Fairtrade performs for the political economy of development and neoliberalism. Second, building on recent critiques of corporate social responsibility, the paper explores how certain neoliberal rationalities are emboldened through Fairtrade, as a process of mainstreaming installs new metrics of governance (standards, certification, participation) that are at once moral and technocratic, voluntary and coercive, and inclusionary and marginalizing. The paper concludes that these technologies have divested exchange of mutuality, as the totemic features of neoliberal regulation - standards, procedures and protocols - increasingly render north south partnerships ever more virtual and depoliticized.     

肯尼亚交通优势度及其空间分异格局分析

基于2018年肯尼亚铁路、公路、机场、港口等交通基础设施数据,设定交通优势度指数及交通网络连接度指数和交通对外通达度指数2个分指数,采用探索性数据分析法对肯尼亚交通优势度及其空间分异格局进行分析,并对其影响因素进行探讨。研究发现:①肯尼亚交通优势度空间差异十分显著,以内罗毕、蒙巴萨和基苏木为主要交通节点的铁路沿线地区交通优势度水平明显高于其他地区;②肯尼亚交通优势度空间分异格局总体上呈现出较强的非均衡性,交通网络连接度呈现出以内罗毕为核心,以铁路沿线为轴带呈圈层状向四周递减的空间分异格局,而交通对外通达度呈现出北部和西北部较低而南部和东南部较高的空间分异格局。③地形地貌、气候、水文、人口集聚、经济发展等是形成肯尼亚交通优势度空间分异的主要影响因素。对交通基础设施空间分布进行优化调整,积极引导经济空间合理布局,是推动肯尼亚经济健康持续发展的重要途经。     

利用MOD13Q1产品监测肯尼亚2001-2010年荒漠化动态

使用MODIS MOD13Q1-NDVI数据,通过NDVI累计计算,得到肯尼亚2001年和2010年植被生长状况较好时期的NDVI影像.基于像元二分模型,估算植被盖度.利用植被盖度进行荒漠化评价.结果表明,肯尼亚近10年来生态环境总体趋于改善,荒漠化发展态势并不明显,但荒漠化问题仍然严重.不同程度的荒漠化土地变化趋势不尽相同,轻度荒漠化和重度荒漠化转出面积大于转入面积,呈现减少趋势,非荒漠化和中度荒漠化变化相反,各省区的荒漠化土地变化趋势也不相同.在小范围地区内,使用Landsat-5 TM影像进行验证,发现与MODIS数据评价结果相似,但更能详尽的描述重点区域的荒漠化问题.