WETLANDS, A PERENNIAL WATER RESOURCE, AND RECORD OF CLIMATE CHANGE IN ARID EAST AFRICA

Frequent and ongoing droughts often plague arid regions, highlighting a need to identify reliable freshwater resources for people and animals. Historical records of groundwater are rare, thus planning for future resources remains a challenge. This study reports on the results of a multiproxy analysis of a core collected from a freshwater wetland, Kisima Ngeda, on the shore of alkaline Lake Eyasi, a rift basin lake located in northern Tanzania. The lake is a playa with a negative hydrologic budget (annual precipitation is ~400 mm and evapotranspiration ~ 2500 mm). Whereas, precipitation on the adjacent highland, Mt Oldeani (3220 m) is ~>1000 mm/yr and sources multiple groundwater discharge sites (GWD) along the lake margin that support springs and freshwater wetlands. In order to determine groundwater history, a sediment core (43 cm) was collected from a modern wetland and analyzed for physical (percent sand), geochemical (TOC, TN and C/N), isotopic (bulk carbon and compound specific), and biologic (diatoms and pollen) parameters. Six radiocarbon dates document four phases of the wetland: (1) incipient wetland with wetland plants and palm trees (Hyphaene), lake margin sediment, a dry period (~650–1300 AD), (2) expansion of a Typha and Cyperaceae wetland at the expense of Hyphaene (Palm), reflecting increased groundwater discharge (~1300–1820 AD), (3) continued expansion seen by the presence of tall wetland vegetation at the core site and a time of increased lake incursions (~1820–2006 AD), and (4) the current phase, sustained wetland during through years of variable precipitation (~2006–2011 AD). Within this wetland record phase (1) appears to coincide with the Medieval Climate Anomaly (~900 – 1300 AD) and phases (2) and (3) with the Little Ice Age (~1300 – 1850 AD). With global climate changes and ongoing reduction in precipitation recorded since 1960 knowledge of groundwater response to past climatic events, such as the Medieval Climate Anomaly and Little Ice Age, provides critical insight for future freshwater resource planning.