TY - JOUR T1 - Human impacts, climate change, and aquatic ecosystem response during the past 2000 yr at Lake Wandakara, Uganda JF - Quaternary Research Y1 - 2009 A1 - Russell, James M. A1 - McCoy, S. J. A1 - Verschuren, D. A1 - Bessems, I. A1 - Huang, Y. AB - Analyses of carbon and hydrogen isotope ratios of terrestrial leaf waxes and the carbon and nitrogen abundance. ratio, and isotopic composition of bulk sediments from Like Wandakara, a crater lake in western Uganda, East Africa. document human and climatic controls on the aquatic system and oil the Surrounding terrestrial vegetation during the past two millennia Our data indicate that Wandakara was a relatively stable, productive lake Surrounded by C(3) vegetation from AD 70 to 1000. Abrupt changes in the delta(13)C of terrestrial leaf waxes indicate a series of abrupt shifts in the relative abundance of C(3) and C(4) vegetation caused by a combination of climate change and human activities around Wandakara beginning at AD 1000. Abrupt shifts in bulk sediment organic geochemistry. particularly C/N ratios and delta(15)N, indicate that human activities at this time caused permanent changes in the limnology of Lake Wandakara. including eutrophication Our results suggest that the biogeochemistry of Like Wandakara was more sensitive to shifting human impacts than to climate variations during the past millennium, highlighting the importance of understanding the intensity of pre-colonial human impacts on Africa's aquatic ecosystems (C) 2009 University of Washington Published by Elsevier Inc All rights reserved VL - 72 IS - 3 N1 - id: 2052; PT: J; UT: WOS:000271254000002 JO - Human impacts, climate change, and aquatic ecosystem response during the past 2000 yr at Lake Wandakara, Uganda ER - TY - JOUR T1 - Paleolimnological records of recent glacier recession in the Rwenzori Mountains, Uganda-D. R. Congo JF - Journal of Paleolimnology Y1 - 2009 A1 - Russell, J. A1 - Eggermont, H. A1 - Taylor, R. A1 - Verschuren, D. AB - The status of tropical glaciers is enormously important to our understanding of past, present, and future climate change, yet lack of continuous quantitative records of alpine glacier extent on the highest mountains of tropical East Africa prior to the 20th century has left the timing and drivers of recent glacier recession in the region equivocal. Here we investigate recent changes (the last 150-700 years) in lacustrine sedimentation, glacier extent, and biogeochemical processes in the Rwenzori Mountains (Uganda- Democratic Republic of Congo) by comparing sedimentological (organic and siliciclastic component determined by loss-on-ignition; LOI) and organic geochemical profiles (carbon and nitrogen abundance, ratio, and isotopic composition of sedimentary organic matter) from lakes occupying presently glaciated catchments against similar profiles from lakes located in catchments lacking glaciers. The siliciclastic content of sediments in the 'glacial lakes' significantly decreases towards the present, whereas 'non-glacial lakes' generally show weak trends in their siliciclastic content over time, demonstrating that changes in the siliciclastic content of glacial lake sediments primarily record fluctuations in glacier extent. Radiometric dating of our sediment cores indicates that prior to their late 19th-century recession Rwenzori glaciers stood at expanded 'Little Ice Age' positions for several centuries under a regionally dry climate regime, and that recession was underway by 1870 AD, during a regionally wet episode. These findings suggest that the influence of late 19th century reductions in precipitation in triggering Rwenzori glacier recession is weaker than previously thought. Our organic geochemical data indicate that glacier retreat has significantly affected carbon cycling in Afroalpine lakes, but trends in aquatic ecosystem functioning are variable among lakes and require more detailed analysis. VL - 41 IS - 2 N1 - id: 2048; PT: J; UT: WOS:000262651500002 JO - Paleolimnological records of recent glacier recession in the Rwenzori Mountains, Uganda-D. R. Congo ER - TY - JOUR T1 - Spatial complexity of 'Little Ice Age' climate in East Africa: sedimentary records from two crater lake basins in western Uganda JF - Holocene Y1 - 2007 A1 - Russell, J. M. A1 - Verschuren, D. A1 - Eggermont, H. AB - Lithostratigraphic analyses of the sedimentary record from two contrasting crater lake basins in western Uganda, Africa, provide evidence for three major century-scale and intervals during the last 2000 year. Variations in sedimentation and salt mineralogy of hypersaline Lake Kitagata, and a succession of fine-grained lake sediments and peat in the freshwater Lake Kibengo, suggest century-scale droughts centred on AD 0, similar to 1100, similar to 1550 and 1750. These results broadly support data from nearby Lake Edward on the timing of drought in western Uganda, but contrast with lake sediment records from eastern equatorial Africa. In particular, our results suggest regional variability of East African climate during the main phase of the 'Little Ice Age' (AD similar to 1500 to 1800), with westernmost East Africa experiencing drought while areas farther east were wet. This spatial pattern highlights the strongly regional nature of century-scale climate changes over the African continent, and holds implications for the mechanisms governing African rainfall during the 'Little Ice Age'. VL - 17 IS - 2 N1 - 144ztTimes Cited:36Cited References Count:55 JO - Spatial complexity of 'Little Ice Age' climate in East Africa: sedimentary records from two crater lake basins in western Uganda ER -