Paper No. 9
Presentation Time: 10:55 AM


GOMAN, Michelle F., Dept of Geography, Environment and Planning, Sonoma State University, 1801 East Cotati Ave, Rohnert Park, CA 94928, ASHLEY, Gail M., Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, NJ 08854, OWEN, R. Bernhart, Dept of Geography, Hong Kong Baptist Univ, Kowloon Tong, Hong Kong, China, HOVER, Victoria C., Geology, Washtenaw Community College, 4800 E. Huron River Drive, Ann Arbor, MI 48105-4800 and MAHARJAN, Dev K., Geoscience, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010,

Wetlands are an underutilized archive of paleoclimate and environmental changes in the semi-arid regions. We present multi-proxy data from Lake Solai a small (9 km2) shallow (< 1.5 m) playa lake located near the equator in the semi-arid East African Rift Valley, Kenya. The lake is situated in a small rift basin and fed by groundwater emerging as springs and seeps on the flanks of the Solai escarpment and two groundwater-fed perennial rivers that drain the highlands to the east and south. P is ~650 mm/yr on valley floor; ET ~1800 mm/yr. The area is heavily populated and diversion of source river water from the lake is occurring for irrigation. Indeed, the lake has dried out several times in the last 40 years, possibly due to a combination of irrigation pressure and ENSO climate events. However, deltaic and peripheral wetlands persist about the lake and archive records of hydrologic and environmental change.

A two meter long core of organic-rich clays capped by a 68 cm peat was extracted from a freshwater Typha wetland (~0.3 km2). A suite of biological proxies (pollen, non-pollen palynomorphs, macrofossils, microscopic charcoal and diatoms) was examined in order to reconstruct the hydrological history. The biostratigraphy is divided into 3 distinct zones and records changes in the wetland hydrology and increasing anthropogenic impact of pastoralism and agriculture. Zone 3 (182-70 cm) is characterized by saline, shallow water conditions. In Zone 2 (70-40 cm) the proxies indicate drier and possibly erosive conditions; abundant charcoal suggests fire also becomes a significant driver on the landscape. Zone 1 (40-0 cm) is marked by overall wetter conditions, the development of the wetland, and possibly periods of higher lake level. The top 20 cm of sediments reflect eutrophication likely caused by agriculture and pastoral activities. The inception of the peat dates to 880 +/- 40 BP which is consistent with data from throughout East Africa indicating wetter conditions at the start of the Little Ice Age.