HR: 0800h
AN: PP21A-1549    [Abstracts]
TI: Sediment Records of Recent Cultural Eutrophication in Lake Malawi/Nyasa, East Africa
AU: * Puchniak, M K
EM: mkpuchni@uwaterloo.ca
AU: Hall, R I
EM: rihall@sciborg.uwaterloo.ca
AF: University of Wateloo, 200 University Avenue West, Waterloo, ON N2L 3G1 Canada
AU: Hecky, R E
EM: rehecky@sciborg.uwaterloo.ca
AF: University of Wateloo, 200 University Avenue West, Waterloo, ON N2L 3G1 Canada
AB: Tropical lacustrine sediment records are developing into excellent sources of information for assessing climate change, but these historical records may become obscured by the compounding effects of anthropogenic impacts. For example, massive alterations to Lake Malawi's landscape in the form of deforestation, cultivation and population growth have impacted the hydrological regime with increased runoff from the catchment, increased loading of total suspended solids to the rivers and increased burial of particulate organic carbon to the sediments. Assessment of the lake's long-term water quality has not been possible until now. Here, we present results of analyses from four short sediment cores (44-52cm) recovered in 1997/98 along a north-south transect, spanning the past ca. 300 years. Lead-210 dating techniques, diatom community composition, biogenic silica content and analyses of nutrients (carbon, nitrogen and phosphorus) have been used to infer past catchment disturbances. There was no obvious trend over the past century in Lake Malawi sediment cores until ca. 1960 when cores from the south end displayed a dramatic increase in diatom concentrations and burial rates, dominated by nutrient-rich indicator species. Subsequently, silica influx to the sediment increased in the southern cores, most likely due to the increased supply of nitrogen and phosphorus from human activities within the catchment. As a result, diatom community composition shifted to less siliceous species in the 1990's, which is inferred as a greater trend towards cultural eutrophication in the south end of Lake Malawi. The contrasting north end of Lake Malawi shows no evidence of similar anthropogenic impacts. Our study highlights the importance of coring site selection in documenting the existence of a north-south gradient of eutrophication and provides an early warning of human impacts on water quality in the southern portions of Lake Malawi.
DE: 0402 Agricultural systems
DE: 0410 Biodiversity
DE: 0458 Limnology (1845, 4239, 4942)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1803 Anthropogenic effects (4802, 4902)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005