GROUNDWATER-FED WETLANDS HAS A RELIABLE WATER SOURCE FOR HUMANS IN ARID ENVIRONMENTS

Despite the relatively common occurrence of springs and groundwater-fed wetlands in modern arid environments, little is known about the sustainability of water particularly during wet-dry cycles. In arid settings, groundwater-fed wetlands are distinct from surface run-off wetlands (river floodplains, deltas, and lacustrine marshes) as surface systems are significantly affected by the relative difference of precipitation (P) vs. evapo-transpiration (ET). Aquifer-fed systems are shielded from surface effects and are driven mainly by groundwater recharge (P). Meteoric water moves from upland recharge areas under hydraulic head to lowlands exiting as groundwater seeps or artesian flow commonly along faults or fractures. Groundwater-fed wetlands were likely important to humans because they provided a perennial water source and possibly food in what might otherwise be a parched environment.

Studies of Holocene wetland sediments associated with archaeological records reveal that wetland records are hydric paleosols comprised of peats, localized tufas and organic-rich clay deposits that contain eolian-transported mineral matter, macrophyte plant remains (e.g. roots, stems) pollen, phytoliths, diatoms, charcoal, carbonate (calcite and siderite) and manganese-rich nodules. Older (> mid- Pleistocene) deposits retain little original organic matter and the plant remains are generally silicified, but otherwise the record is similar. Systematic analyses of biological records (diatoms, ostracods, pollen, and testate amoeba) document climate change, as well as the quality of the water (freshness, alkalinity, and oxygen levels) and its persistence during dry periods.

Two wetland sites associated with archaeological records reveal the importance of these water sources for humans. Wetland records from Olduvai Gorge, Tanzania (1.85-1.75 Ma) are associated with stone tools. Concentrations of artifacts and cut-marked bone were found to be higher in the wetlands than in adjacent environments. Holocene records form Lake Bogoria, Kenya revealed that drought occurred during the Medieval Warm Period, but higher rainfall in the region during the Little Ice Age (700-130 BP) lead to the expansion of Loboi Swamp and the migration people living on surrounding uplands into the normally dry rift valley.