Geochemical evidence of hydrothermal recharge in Lake Baringo, central Kenya Rift Valley

Abstract

Lake Baringo, a freshwater lake in the central Kenya Rift Valley, is fed by perennial and ephemeral rivers, direct rainfall, and hot springs on Ol Kokwe Island near the centre of the lake. The lake has no surface outlet, but despite high evaporation rates it maintains dilute waters by subsurface seepage through permeable sediments and faulted lavas. New geochemical analyses (major ions, trace elements) of the river, lake, and hot spring waters and the suspended sediments have been made to determine the main controls of lake water quality. The results show that evaporative concentration and the binary mixing between two end members (rivers and thermal waters) can explain the hydrochemistry of the lake waters. Two zones are recognized from water composition. The southern part of the lake near sites of perennial river inflow is weakly influenced by evaporation, has low total dissolved species (TDS), and has a seasonally variable load of mainly detrital suspended sediments. In contrast, waters of the northern part of the lake show evidence for strong evaporation (TDS of up to eight times inflow). Authigenic clay minerals and calcite may be precipitating from those more concentrated fluids. The subaerial hot-spring waters have a distinctive chemistry and are enriched in some elements that are also present in the lake water. Comparison of the chemical composition of the inflowing surface waters and lake water shows (1) an enrichment of some species (HCO3-, Cl, SO42-, F, Na, B, V, Cr, As, Mo, Ba and U) in the lake, (2) a depletion in SiO2 in the lake, and (3) a possible hydrothermal origin for most F. The rare earth element distribution and the F/Cl and Na/Cl ratios give valuable information on the rate of mixing of the river and hydrothermal fluids in the lake water. Calculations imply that thermal fluids may be seeping upward locally into the lake through grid-faulted lavas, particularly south of Ol Kokwe Island. Copyright © 2006 John Wiley & Sons, Ltd

The use of multivariate statistics to resolve multiple contamination signals in the oxygen isotope analysis of biogenic silica

“…). Depending on the strength and duration of the rainy seasons, the surface area varies between 108 and 160 km 2 and the lake drains a catchment encompassing a total area of 6200 km 2 (Tarits et al ., ). The region is semi‐arid, with mean annual rainfall rates that range from 600 to 900 mm on the valley floor to >1000 mm in the adjacent highlands.…”

“…Tarits et al . () suggest that this is the result of subsurface groundwater seepage through faulted lavas and permeable sediments. In the past, Lake Baringo is believed to have ranged from a highly alkaline and saline playa‐lake during different low‐level stages in its history, as marked by the presence of authigenic zeolites formed from NaCO 3 ‐rich lake and pore waters (Renaut et al ., ), to an extensive freshwater lake (Kingston et al ., ).…”

“…Here we analyse a 2.6 Ma diatomite sequence from the East African Rift Valley that contains numerous air‐fall ash deposits from volcanic activity (Deino et al ., ) and was deposited in a system known to experience high clay and silt influx from the catchment (Tarits et al ., ). We use multivariate statistics to identify the geochemical signatures of the different contamination components and develop a three end‐member model based on elemental oxide abundance data to accurately model climate‐driven changes in δ 18 O diatom .…”

Applying scores of multivariate statistical analyses to characterize relationships between hydrochemical properties and geological origins of springs in Taiwan

“…Major ions in spring water include HCO 3 − , Cl − , SO 4 2− , SiO 2 , Na + , K + , Ca 2+ and Mg 2+ , which mainly originates from dissolution and mineralization of rocks (Davisson et al, 1994;Minissale et al, 1997;Afşin et al, 2006). Therefore, water quality of springs is highly associated with their geological conditions and evolution, and the hydrochemical composition of spring water can indicate the geological origin (González-Partida et al, 2005;Sanada et al, 2006;Tarits et al, 2006). Furthermore, temperatures and pH of springs exhibit high variability, resulting in significant difference in species and quantities of hydrochemical parameters.…”

Characterizing hydrochemical properties of springs in Taiwan based on their geological origins

“…Major ions in spring water include HCO − 3 , Cl − , SO 2− 4 , SiO 2 , Na + , K + , Ca 2+ , and Mg 2+ , which mainly originates from dissolution and mineralization of rock (Davisson et al 1994;Minissale et al 1997;Afşin et al 2006;StambukGilijanovic 2008). Therefore, water quality of springs is highly associated with their geological conditions and evolution, and the hydrochemical composition of spring water can indicate the geological origin (González-Partida et al 2005;Sanada et al 2006;Tarits et al 2006). Furthermore, temperatures and pH of springs exhibit high variability (Hsu et al 2006), resulting in significant difference in species and quantities of hydrochemical parameters.…”