The role of geology and climate in soil nutrient variability - potential drivers for large ungulate migrations in the Serengeti ecosystem (Northern Tanzania, East Africa)

2020 ◽  
Author(s):  
Eileen Eckmeier ◽  
Simon Kübler ◽  
Akida Meya ◽  
Stephen Mathai Rucina
Keyword(s):  
Volcanic Eruptions ◽  
East African ◽  
Near Surface ◽  
Serengeti Ecosystem ◽  
Geological Processes ◽  
Basement Rocks ◽  
Nutrient Variability ◽  
Archean Basement

<p>The East African Serengeti ecosystem hosts a great range of mammals and one of the world’s largest seasonal ungulate movements, with over 1.3 wildebeest and several hundreds of thousands of zebras and antelopes migrating through the region in a regular pattern. While climatic and biological drivers for this migration have been studied in great detail, the role of rock chemistry, weathering and resulting soil diversity as a source for nutrient provision has so far been largely neglected and needs detailed and systematic study.</p><p>Geological processes provide important controls on long-term ecosystem dynamics. Volcanic eruptions, earthquakes, and rock weathering influence soil edaphic properties, which represent the ability of soils to provide vital plant-available nutrients, which therefore control grazing patterns of herbivores, particularly during birthing and lactating seasons. Studying the geological role in providing and distributing essential nutrients is critical to understand long-term drivers and stability of animal migrations in dynamic ecosystems. We have carried out a field reconnaissance study in the Serengeti National Park, with the aim to study variations in nutrient variability in soils and vegetation in relation to the chemical composition of soil parent material, i.e. volcanic or metamorphic rocks and sediments derived from those rock units, and under consideration of climatic variations. First results show that the Serengeti ecosystem can be subdivided into three geo-edaphic subregions that correlate with seasonal wildebeest grazing habitats.</p><p>(1) The southeastern Serengeti (wet-season grazing), is characterized by soils developed on volcanic ash derived from recent eruptions of the Ol Doinjo Lengai carbonatite volcano. Here, we have identified deeper organic-rich soils with andic and vitric properties and varying amounts of carbonate concretions or near-surface calcrete horizons. High Na, K, and Ca levels of volcanic ashes suggest high levels of those elements in soils and vegetation in this region, also because the precipitation is lowest in this area.</p><p>(2) In the central Serengeti (short-term transitional grazing), soils develop on Archean basement rocks including granitic gneisses, phyllites and banded iron formations. Geochemical signatures of these rock types suggest that soils in this region have lower levels in Ca, Mg, and plant available P, compared to the SE Serengeti, which is supported by the transitional nature of this grazing habitat.</p><p>(3) Soils in the Northern Serengeti (dry-season grazing) develop on a diverse patchwork of Archean basement rocks as well as basaltic lavas and thick fluvial deposits. North of Mara river, the Insuria fault – a large normal fault of the East African Rift  - creates a wide sedimentary basin dominated by soils developed on basaltic sediments. Here, higher precipitation leads to stronger weathering and leaching of nutrient elements.</p><p>Our preliminary results suggests that geochemical variations together with continuous (syngenetic) pedogenesis through active volcanism or tectonic faulting and related fault scarp erosion created regions of high edaphic quality in the north and southeast of the Serengeti ecosystem, and that the patchy nature of soil edaphics is important to understand the underlying drivers of large scale migration of grazing animals in this region. </p>

The fate of volcanic ash aggregates: premature or delayed sedimentation?

2020 ◽  
Author(s):  
Eduardo Rossi ◽  
Frances Beckett ◽  
Costanza Bonadonna ◽  
Gholamhossein Bagheri
Keyword(s):  
Volcanic Ash ◽  
Dispersion Model ◽  
Volcanic Eruptions ◽  
Fall Velocity ◽  
Field Evidence ◽  
Aggregation Processes ◽  
Lagrangian Dispersion ◽  
Theoretical Evidence

<p>Most volcanic ash produced during explosive volcanic eruptions sediments as aggregates of various types that typically have a greater fall velocity than the particles of which they are composed. As a result, aggregation processes are commonly known to affect the sedimentation of fine ash by considerably reducing its residence time in the atmosphere. Nonetheless, speculations also exist in the literature that aggregation does not always result in a premature sedimentation of their constitute particles but that it can also result in a delayed sedimentation (i.e. the so-called rafting effect). However, previous studies have considered rafting as a highly improbable phenomenon due to a biased representation of aggregate shapes.</p><p>Here we provide the first theoretical evidence that rafting may not only occur, but it is probably more common than previously thought, helping to elucidate often unexplained field observations. Starting from field evidence of rafted aggregates at Sakurajima Volcano (Japan), we clarify the conditions for which aggregation of volcanic ash results either in a premature or a delayed sedimentation.</p><p>Moreover, using the Lagrangian dispersion model NAME, we show the practical consequences of rafting on the final sedimentation distance of aggregates with different morphological features. As an application we chose the case study of the 2010 eruption of Eyjafjallajökull volcano (Iceland), for which rafting can increase the travel distances of ash <500 m up 3.7 times with respect to sedimentation of individual particles.</p><p>These findings have fundamental implications both for real-time forecasting and long-term hazard assessment of volcanic ash dispersal and sedimentation and for weather modelling. The constraints on rafting presented and discussed in this work will help the scientific community to clarify the often unexpected role of aggregation in creating a delayed sedimentation of coarse ash.</p>

scholarly journals Shifting patterns: malaria dynamics and rainfall variability in an African highland

2007 ◽  
Vol 275 (1631) ◽  
pp. 123-132 ◽  
Author(s):  
M Pascual ◽  
B Cazelles ◽  
M.J Bouma ◽  
L.F Chaves ◽  
K Koelle
Keyword(s):  
Time Series ◽  
Rainfall Variability ◽  
Climate Forcing ◽  
East African ◽  
Endogenous Cycles ◽  
Model Time Series ◽  
African Highlands ◽  
East African Highlands

The long-term patterns of malaria in the East African highlands typically involve not only a general upward trend in cases but also a dramatic increase in the size of epidemic outbreaks. The role of climate variability in driving epidemic cycles at interannual time scales remains controversial, in part because it has been seen as conflicting with the alternative explanation of purely endogenous cycles exclusively generated by the nonlinear dynamics of the disease. We analyse a long temporal record of monthly cases from 1970 to 2003 in a highland of western Kenya with both a time-series epidemiological model (time-series susceptible–infected–recovered) and a statistical approach specifically developed for non-stationary patterns. Results show that multiyear cycles of malaria outbreaks appear in the 1980s, concomitant with the timing of a regime shift in the dynamics of cases; the cycles become more pronounced in the 1990s, when the coupling between disease and rainfall is also stronger as the variance of rainfall increased at the frequencies of coupling. Disease dynamics and climate forcing play complementary and interacting roles at different temporal scales. Thus, these mechanisms should not be viewed as alternative and their interaction needs to be integrated in the development of future predictive models.

Detailed Description of a Long-Term Low-Level Waste Degradation Experiment

1996 ◽  
Vol 465 ◽  
Author(s):  
F. Caron ◽  
J. Torok ◽  
M. K. Haas ◽  
G. Manni
Keyword(s):  
Landfill Leachates ◽  
Near Surface ◽  
Low Level ◽  
Dissolved Organics ◽  
Safety Case ◽  
Waste Degradation ◽  
Paper Towels ◽  
Low Level Radioactive Waste

ABSTRACTThis work gives a detailed description of the important aspects of a long-term Low-Level Radioactive Waste (LLRW) degradation experiment, performed at Chalk River Laboratories (CRL). This experiment utilized actual LLRW. The wastes consist of unconditioned compacted refuse (paper, mop heads, paper towels, used clothing, etc), which represents the bulk of the waste volume intended for near-surface disposal at CRL. Waste material was collected and compacted to make a total of 11 bales for this experiment. Each bale was then placed and sealed in separate steel containers which were connected to sampling lines. After a dry monitoring period, water was added to promote leaching and decomposition of the wastes. The leachate sampled had a composition similar to landfill leachates. Some applications of this experiment, used to support the safety case of near-surface disposal, are briefly discussed in this paper, e.g., the production of colloidal material, the nature and role of dissolved organics of microbial origin, etc.

A global study of dolomite stoichiometry and cation ordering through the Phanerozoic

2021 ◽  
Vol 91 (5) ◽  
pp. 520-546
Author(s):  
Cameron J. Manche ◽  
Stephen E. Kaczmarek
Keyword(s):  
Laboratory Experiments ◽  
Temporal Variations ◽  
Depositional Environments ◽  
Cation Ordering ◽  
Carbonate Platforms ◽  
Seawater Chemistry ◽  
Near Surface ◽  
Origin And Evolution ◽  
Geological Processes

ABSTRACT Various geochemical proxies are used to constrain the diagenetic origin and evolution of ancient dolomites. Dolomite stoichiometry (mole % MgCO3) and cation ordering, two mineralogical attributes that define dolomite, have also been shown to demonstrate utility in this regard. Observations from laboratory experiments and field studies suggest that these attributes broadly reflect the fluid chemistry and temperature of the dolomitizing environment. The degree to which these parameters reflect global conditions during dolomitization (e.g., seawater chemistry, eustasy, atmospheric pCO2) and long-term geological processes is poorly understood, however. Here, a large dataset consisting of mineralogical data from over 1,690 Phanerozoic dolomites from various geographic locations, stratigraphic ages, platform types, and depositional environments are queried to investigate the broader geological controls on dolomite stoichiometry and cation ordering in dolomites formed by early, near-surface dolomitization. A suite of statistical analyses performed on the global dataset indicate: 1) despite wide ranges at the eon, period, and epoch level, dolomite stoichiometry and cation ordering broadly increase with geologic age; 2) significant variations in dolomite stoichiometry and cation ordering throughout the Phanerozoic do not correlate with global parameters, such as seawater chemistry, eustasy, orogenic events, and ocean crust production; 3) dolomites associated with restricted depositional settings, such as restricted lagoons, and the intertidal and supratidal zones, are more stoichiometric than dolomites associated with open marine settings, such as the deep-subtidal and shallow-subtidal zones; and 4) dolomites from shallow ramps and epeiric carbonate platforms are generally more stoichiometric than dolomites from open shelves and isolated carbonate platforms. These observations permit a number of inferences to be drawn. First, the principal signal observed in the data is that local environmental conditions associated with platform type and depositional setting are the strongest control on dolomite mineralogy. The observation that more stoichiometric dolomites correlate with shallow and restricted depositional environments is consistent with laboratory experiments that show environmental factors, such as higher Mg:Ca, temperature, and salinity of the dolomitizing fluids yield more stoichiometric dolomite. Second, a weaker secondary signal is also observed such that dolomite stoichiometry and cation ordering both increase with geologic age, suggesting that progressive recrystallization driven by mineralogical stabilization during burial is also occurring. Collectively, these data suggest that spatial and temporal variations in stoichiometry and cation ordering reflect the interplay between local dolomitizing conditions near the surface and long-term mineralogical stabilization during burial.

Israel’s Deportation Policy of African Migrants: Internal and External Aspects

2018 ◽  
pp. 54-68
Author(s):  
Luiza Khlebnikova
Keyword(s):  
Asylum Seekers ◽  
Vulnerable Groups ◽  
Jewish State ◽  
East African ◽  
African Countries ◽  
Migration Strategy ◽  
Grassroots Initiatives ◽  
Socially Vulnerable Groups

In 2016 Prime Minister of Israel Benyamin Netanyahu declared its comeback to Africa and Africa’s return to the Jewish state. The key reason for a new Israeli-African cooperation (especially between Israel and East African countries) seems to be an intent to regulate crisis with illegal immigrants from Africa in Israel. The author examines the drivers of the big inflow of African asylum seekers from Eritrea and Sudan trying to find ‘safe heaven’ in the Jewish State. Netanyahu prefers to treat these African asylum seekers as economic migrants. He often stresses that Israel is too small to accept everyone who is afflicted. In the Israeli society negative sentiments towards African asylum seekers are generally prevailing. However, there are some grassroots initiatives aimed at protecting Africans and their rights. Opposition parties, Zionist Union and Meretz, are not united and have not succeeded in challenging the government’s course. The main goal of this research is to evaluate the Israeli government’s approaches, including deportation of immigrants to ‘third countries’ like Rwanda and Uganda, aimed at resolving the crisis. The deportation of African asylum seekers provoked some new debates about rights of socially vulnerable groups in Israel and, moreover, its democratic character. The critique of the Netanyahu’s policies spread well beyond the borders of the State of Israel. The United Nations tried to resolve the crisis by offering a deal that would relocate Africans from Israel to different countries, but the head of the Jewish state, first agreed to sign it, but later changed his mind. Special attention is paid to the role of the American Jewish organizations in stopping the deportation of Africans from Israel. The American liberal progressive groups, for example J street, have been openly protesting against Netanyahu’s policies. The conclusion is drawn that the way out of the crisis lays in elaborating a long-term comprehensive migration strategy.

scholarly journals Lithological and Topographic Impact on Soil Nutrient Distributions in Tectonic Landscapes: Implications for Pleistocene Human-Landscape Interactions in the Southern Kenya Rift

2021 ◽  
Vol 9 ◽  
Author(s):  
S. Kübler ◽  
S. Rucina ◽  
D. Aßbichler ◽  
E. Eckmeier ◽  
G. King
Keyword(s):  
Soil Nutrients ◽  
Soil Nutrient ◽  
Parent Material ◽  
Kenya Rift ◽  
Geological Processes ◽  
Heterogeneous Habitats ◽  
Shallow Soils ◽  
Human Landscape

Tectonically active regions are characterized by complex landscapes comprising soils with heterogeneous physicochemical properties. Spatial variability of nutrient sources enhances landscape biodiversity and creates heterogeneous habitats potentially attractive for animals and humans. In this study, we analyze the role of geological processes in the distributions of soil nutrients in the southern Kenya Rift, a key region in the interpretation of early human-landscape interactions. Our aim is to determine how spatial variations in rock chemistry, as well as topographic gradients and localized zones of rock fracturing from tectonic faulting determine the distributions of plant-available soil nutrients in soils. We hypothesize that present-day soil nutrient levels reflect the long-term chemical and geomorphological characteristics of the landscape and underlying parent material, and that regions with high nutrient availability occur along pathways correlating with locations of hominin fossil sites. Analyses of 91 topsoil samples from the main geological units show that Calcium (Ca) deficiencies predominately occur in shallow soils developed on trachytic volcanic rocks and granitic gneisses, while high Ca levels are associated with basaltic parent material and sedimentary deposits of mixed sources. XRF analysis of rock samples confirms that CaO levels in trachyte rocks are significantly lower than those in basalts, and Ca mobilization in basalt is more effective than in trachyte. Along two toposequences in densely faulted basaltic and trachytic rocks, we observed slope dependent soil nutritional gradients and a systematic increase of the concentrations of Ca, Mg and SOC in topsoils of colluvial sediments downslope of active normal faults. Known hominin sites in the region are located either along corridors of long-term Ca availability or at short-term nutrient hotspots potentially related to active CO2 degassing along active fault zones. This implies a strategic advantage of Ca-rich regions for hominin subsistence strategies, such as provision of predictable constraints on the distribution and mobility of grazing animals in complex tectonic landscapes. Our study implies that geological processes impact nutrient distributions in the southern Kenya Rift. Results of this study have further implications for understanding the role of soils in the interpretation of hominin-landscape interactions in the early stages of human evolution.

Ottoman Frontier Policies in North-East Africa, 1517–1914

2009 ◽  
Author(s):  
JOHN ALEXANDER
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
African History ◽  
East African ◽  
North East ◽  
Indian Ocean Trade ◽  
Secure Control ◽  
Islamic Empire

This chapter suggests that insufficient attention has been paid in accounts of north-east African history to the role of the Ottoman Turks. With the capture of Egypt from its Mamluk rulers in 1517, the Ottomans established their first foothold in Africa. However, several factors drew them further into the region. First, there was a threat presented by the Portuguese, who sought to establish a monopoly on the valuable Indian Ocean trade and who challenged Ottoman control of the Red Sea and the pilgrimage routes to Mecca and Medina. Second, the Ottomans wished to secure control over Africa's valuable exports, slaves and gold. Third, in accordance with the sultans' quest for legitimacy as rulers of an Islamic empire, their long-term aim was the inclusion of all north-east Africa into Ottoman territory and hence the Dar al-Islam.

scholarly journals Terrestrial stilling will continue during the 21st century

2021 ◽  
Author(s):  
Deliang Chen ◽  
Kaiqiang Deng ◽  
Cesar Azorin-Molina ◽  
Song Yang ◽  
Gangfeng Zhang ◽  
...  
Keyword(s):  
Wind Speed ◽  
21St Century ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
New Paradigm ◽  
Near Surface ◽  
The Pacific ◽  
Long Time

Abstract The near-surface wind speed over land has declined in recent decades, a trend known as terrestrial stilling (TS)1-2. However, recent studies have indicated a reversal of the TS in the Northern Hemisphere (NH) during the last decade3-6, triggering renovated interest in the wind speed changes. Here we show that the TS in the NH mid-latitudes will continue in all seasons throughout the 21st century, especially in summer. The recent reversal of TS is most likely a multi-decadal fluctuation related to the Pacific and Atlantic climate variations, rather than a secular trend. A new paradigm of the future TS is further proposed, which is related to an intensified subsidence inversion over the mid-latitudes, caused by enhanced tropical and subtropical convections. This study reveals the important role of global warming in reducing the near-surface wind speed on long time scales. The continuing TS means a long-term strategy for wind energy production needs to be developed, particularly for the NH mid-latitude countries.

scholarly journals On the Role of Volcanism in Dansgaard-Oeschger Cycles

2020 ◽  
Author(s):  
Johannes Lohmann ◽  
Anders Svensson
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Ice Cores ◽  
Volcanic Eruptions ◽  
Abrupt Climate Change ◽  
Last Glacial Period ◽  
Large Volcanic Eruptions ◽  
The Last Glacial

Abstract. A significant influence of major volcanic eruptions on regime shifts and long-term climate variability has been suggested previously. But a statistical assessment of this has been hampered by inaccurate synchronization of large volcanic eruptions to changes in past climate. Here, this is achieved by combining a new record of bipolar volcanism from Greenland and Antarctic ice cores with records of abrupt climate change derived from the same ice cores. We show that at > 99 % confidence bipolar volcanic eruptions occurred more frequently than expected by chance just before the onset of Dansgaard-Oeschger events, the most prominent large-scale abrupt climate changes of the last glacial period. Out of 20 climate change events in the 12–60 ka period, 5 (7) occur within 20 (50) years after a bipolar eruption. Thus, such large eruptions may act as short-term triggers for large-scale abrupt climate change, and may explain part of the variability of Dansgaard-Oeschger cycles.

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