Eric O. Odada

The Holocene History of Lake Victoria

Abstract Recent investigations by the International Decade for the East African Lakes (IDEAL) have significantly advanced our knowledge on the history of Lake Victoria. Seismic reflection profiles confirm the origin of the lake as a result of regional tilting and provide an estimated age of 400 000 years for the lake basin. Three major desiccation events are recorded in the seismic records that may reflect the 100 000 year Milankovitch cycle of climate forcing. The most recent arid period resulted in complete desiccation of the pre-existing lake. Lake Victoria arose from a dry landscape 14 600 calendar years ago (14.6 ka). Primary production was extremely high as lake level rose in its first 500 years, nourished by the high input of nutrients from the flooded landscape. A few species of cichlids and other fish swam out of their fluvial refugia to colonize the new lake, generating hundreds of new endemic species over the ensuing 14 000 years. Lake level rose until a brief overflow event at about 14.2 ka to 13.6 ka. Closed-basin conditions returned during the Younger Dryas until 11.2 ka, when major outflow and open-basin conditions were permanently established. The lake experienced progressively stronger stratification and water-column stability through the first half of the Holocene, and diatom productivity dropped to a minimum from 9.8 to about 7.5 ka. This period coincides with, but is much longer than, the 8.2 ka climatic event that has been observed in many Holocene records from throughout the world. The degree of water-column mixing appears to have steadily increased over the last 6000 years. Short cores from the open lake, document a shift in lake conditions beginning in the 1930s that progressed to the major ecosystem collapse of the early 1980s. The coincidence of the shift in sediment properties in the 1930s with the beginning of rapid expansion of human population and agricultural activity suggests cause and effect. It is conceivable that the lake experienced similar conditions due to natural causes between about 9800 and 7500 years ago.

Sensitivity of global river discharges under Holocene and future climate conditions

A comparative analysis of global river basins shows that some river discharges are more sensitive to future climate change for the coming century than to natural climate variability over the last 9000 years. In these basins (Ganges, Mekong, Volta, Congo, Amazon, Murray-Darling, Rhine, Oder, Yukon) future discharges increase by 6-61%. These changes are of similar magnitude to changes over the last 9000 years. Some rivers (Nile, Syr Darya) experienced strong reductions in discharge over the last 9000 years (17-56%), but show much smaller responses to future warming. The simulation results for the last 9000 years are validated with independent proxy data.

Mitigation of environmental problems in Lake Victoria, East Africa: causal chain and policy options analyses

Abstract Lake Victoria is an international waterbody that offers the riparian communities a large number of extremely important environmental services. Over the past three decades or so, the lake has come under increasing and considerable pressure from a variety of interlinked human activities such as overfishing, species introductions, industrial pollution, eutrophication, and sedimentation. In this paper we examine the root causes for overfishing and pollution in Lake Victoria and give possible policy options that can help remediate or mitigate the environmental degradation.

The east African great lakes : limnology, palaeolimnology and biodiversity

Introduction. Acknowledgements. Geological and Structural Setting of the East African Lakes. A 300 Million Years History of Rift Lakes in Central and East Africa: An Updated Broad Review J.-J. Tiercelin, K.-E. Lezzar. Climate Dynamics and Climate Variability in the East African Lakes Region. Extreme Rainfall Events and Lake Level Changes in East Africa: Recent Events and Historical Precedents D. Conway. Mesoscale Patterns of Rainfall, Cloudiness and Evaporation Over the Great Lakes of East Africa S.E. Nicholson, X. Yin. Observations, Evaporation and Preliminary Modelling of Over-Lake Meteorology on Large African Lakes P.F. Hamblin, et al. Development of a Coupled Regional Climate Simulation Model for the Lake Victoria Basin Y. Song, et al. Hydrology and Physical Limnology. A Modelling Approach for Lake Malawi/Nyasa/Niassa: Integrating Hydrological and Limnological Data D.C.L. Lam, et al. Ventilation of Lake Malawi/Nyasa M.K. Vollmer, et al. Application of Satellite AVHRR to Water Balance, Mixing Dynamics, and the Chemistry of Lake Edwards, East Africa J.T. Lehman. Lake-Groundwater Relationships, Oxygen Isotope Balance and Climate Sensitivity of the Bishoftu Crater Lakes, Ethiopia S. Kebede, et al. A Review of Sediment Gas Cycling in Lakes with reference to Lake Victoria and Sediment Gas Measurements in Lake Tanganyika D.D. Adams, S.O. Ochola. Biodiversity, Food Webs and Fisheries. Redundancy and Ecosystem Stability in the Fluctuating Environments of Long-Lived Lakes K. Martens. Invasion of Lake Victoria by the Large Bodied Herbivorous Cladoceran Daphnia Magna R. Jonna, J.T. Lehman. Effects of Climate and Human Activities on the Ecosystem of Lake Baringo, Kenya P.A.Aloo. Limnological Profiles and their Variability in Lake Tanganyika P.-D. Plisnier. Sedimentary Processes, Paleoclimate and Paleoenvironment. Sedimentology and Geochronology of Late Pleistocene and Holocene Sediments from Northern Lake Malawi S.L. Barry, et al. A 24,000 yr Diatom Record from the Northern Basin of Lake Malawi F. Gasse, et al. Lake Tanganyika Holocene Record on Variability in Precipitation in the Malagarasi Catchment Basin A.N. Muzuka, N. Nyandwi Late Quaternary Sedimentation and Climate in the Lakes Edward and George Area, Uganda-Congo T. Laerdal, et al. Pigment Analysis of Short Cores from the Central Ethiopian Rift Valley Lakes M.U. Mohammed, et al. Origin and Isotopic Composition of Aragonite Laminae in an Ethiopian Crater Lake H. Lamb, et al. Vegetation Changes and their Climatic Implications for the Lake Victoria Region during the Late Holocene I. Ssemmanda, A. Vincens. Organic Content and X-ray Density of Lacustrine Sediments from Hausberg Tarn, Mount Kenya W. Karlen, et al. Human Dimensions: Impacts and Management. Restoring and Protecting the African Great Lake Basin Ecosystems -- Lessons from the North American Great Lakes and the GEF A.M. Duda. Geological Hazards and Anthropogenic Impacts on the Environment in Malawi: Lesson from a Case Study of Debris Flows in Zomba J. Mwenelupembe, H.-G. Mylius. The Human Dimensions Studies on the East African Lake Regions: A Review M.M. Opondo.

Stratigraphic and Earth System approaches to defining the Anthropocene

Stratigraphy provides insights into the evolution and dynamics of the Earth System over its long history. With recent developments in Earth System science, changes in Earth System dynamics can now be observed directly and projected into the near future. An integration of the two approaches provides powerful insights into the nature and significance of contemporary changes to Earth. From both perspectives, the Earth has been pushed out of the Holocene Epoch by human activities, with the mid-20th century a strong candidate for the start date of the Anthropocene, the proposed new epoch in Earth history. Here we explore two contrasting scenarios for the future of the Anthropocene, recognizing that the Earth System has already undergone a substantial transition away from the Holocene state. A rapid shift of societies toward the UN Sustainable Development Goals could stabilize the Earth System in a state with more intense interglacial conditions than in the late Quaternary climate regime and with little further biospheric change. In contrast, a continuation of the present Anthropocene trajectory of growing human pressures will likely lead to biotic impoverishment and a much warmer climate with a significant loss of polar ice.

Regional-Global Change Linkages: Southern Africa

Unravelling the skein of global change effects in southern Africa is a non-trivial task. It is made all the more interesting since Africa is the birthplace of humanity. Southern Africa preserves an impressive five-million-year record of human-environmental interaction. From the evolutionary cradle onwards, environmental change has profoundly affected the development of the early and later hominids into Homo sapiens (Vrba et al.1995). More recently, over the past two millennia, environment was a major factor affecting migrations of Bantu people into southernmost Africa. Until as late as the nineteenth century, environment continued to be a dominant factor affecting the settlement and survival of the population of the region.

Environmental assessment of the East African Rift Valley lakes

An assessment of the East African Rift Valley lakes was initiated by the United Nations Environment Programme (UNEP) with funding from Global Environment Facility as part of the Global International Waters Assessment (GIWA). The purpose of GIWA was to produce globally comparable assessments and examine stresses on international waters: marine, coastal and fresh; surface and groundwaters. The assessment of the East African Rift Valley lakes was undertaken from the perspective of water quality and quantity, associated biodiversity and habitats, their use by society and societal causes of the regionally identified issues and problems. Assuming intrinsic values of aquatic ecosystems, the assessment of social perspective focused on human use of water and considered the incremental costs of measures to encourage sustainable development. The assessment identified the major concerns facing the East African Rift Valley lakes.By and large, pollution and unsustainable exploitation of fisheries and other living resources emerged as critical concerns attributable to human activities. East Africa has a very high concentration of humans and economic activities. Pollution is from uncontrolled discharge of wastes directly into the lakes. Unsustainable exploitation of fisheries and other living resources is caused by over-fishing, destructive fishing practices, and introduction of non-native species that affect the composition of the native communities, resulting sometimes in the collapse of certain species and dominance by resilient ones. Loss of biodiversity also was identified as a major concern; and the issues of excessive by-catch and discards are also relevant. Trawling using undersized mesh-nets for target species and indiscriminate fishing gear or poison is serious, in most cases resulting in indiscriminate catches, including juvenile fish. Given the transboundary nature of the issues identified in this assessment, appropriate multilateral policy and institutional arrangements need to be established in East Africa to address the main concerns of these large lakes. Riparian countries must pay attention to the regional management of these transboundary water bodies, and appropriate planning of human population sizes and their settlement, land-use and waste disposal to control pollution. Although East African lakes contribute relatively little emission of greenhouse gases, there is a need to reduce the rate of deforestation and even restore cleared areas since forests serve as sinks of greenhouse gases towards mitigating adverse climatic changes.

Long-term temporal characteristics of palaeomonsoon dynamics in equatorial Africa

Abstract In this paper we examine the long-term temporal characteristics of palaeomonsoon dynamics in equatorial Africa from a continuous lacustrine sequence retrieved from Sacred Lake, Mount Kenya (0°03′N, 37°32′E, 2350 m a.s.l.), covering the last interglacial–glacial transition to the present. The trends in mineral magnetics and stable carbon isotopes are proxy indicators of changes in precipitation on the mountain over the last glacial–interglacial cycle. Spectral analysis by a fast fourier transform method revealed that the stable carbon isotope trend (δ 13 C) has strong signals at the 23,000 and 11,500 year frequencies. The mineral magnetic signature does not register the 23,000 year cycle observed in the δ 13 C signature. It has, however, a strong signal at an 11,500 year frequency, and sharp but relatively weak peaks at ca. 7500 and 5000 year frequencies are recorded. The dominant 23,000 year frequency recorded in the δ 13 C signature reflects the strong effect of the precessional cycle on tropical climate and ecosystems, and is most probably effected via global atmospheric pCO 2 and temperature changes. The shorter cycles at 11,500 year (indicated by both mineral magnetics and δ 13 C trends), and 7500 and 5000 years BP (apparent in the mineral magnetic record) are attributed to precipitation variations, whose temporal cycles are dominated by the higher precessional harmonics.

Time for in situ renaissance

In situ monitoring of water dates to Pharaonic Egypt and remained the primary means of observation into the later part of the 20th century. Monitoring networks have declined ([ 1 ][1]–[ 4 ][2]) since the 1980s because of budgetary constraints and political instabilities. This decline paradoxically

Scale and diversity of the physical technosphere: A geological perspective

We assess the scale and extent of the physical technosphere, defined here as the summed material output of the contemporary human enterprise. It includes active urban, agricultural and marine components, used to sustain energy and material flow for current human life, and a growing residue layer, currently only in small part recycled back into the active component. Preliminary estimates suggest a technosphere mass of approximately 30 trillion tonnes (Tt), which helps support a human biomass that, despite recent growth, is ~5 orders of magnitude smaller. The physical technosphere includes a large, rapidly growing diversity of complex objects that are potential trace fossils or ‘technofossils’. If assessed on palaeontological criteria, technofossil diversity already exceeds known estimates of biological diversity as measured by richness, far exceeds recognized fossil diversity, and may exceed total biological diversity through Earth’s history. The rapid transformation of much of Earth’s surface mass into the technosphere and its myriad components underscores the novelty of the current planetary transformation.