This article was downloaded by: [Agora Consortium] On: 15 April 2014, At: 02:47 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

The Professional Geographer Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rtpg20 Paleoenvironmental Changes in the Baringo Basin, Kenya, East Since AD 1650: Evidence from the Paleorecord Lawrence M. Kiage a & Kam-biu Liu b a Georgia State University , b Louisiana State University , Published online: 21 Sep 2009.

To cite this article: Lawrence M. Kiage & Kam-biu Liu (2009) Paleoenvironmental Changes in the Lake Baringo Basin, Kenya, East Africa Since AD 1650: Evidence from the Paleorecord , The Professional Geographer, 61:4, 438-458 To link to this article: http://dx.doi.org/10.1080/00330120903143425

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Lawrence M. Kiage Georgia State University

Kam-biu Liu Louisiana State University

This article presents some of the findings of a multi-indicator investigation of the history of vegetational changes and land degradation in the Lake Baringo basin, Kenya, East Africa, during the Late Holocene. 14C- and 210Pb-dated record of the lithostratigraphy is used to reconstruct the paleoenvironment in the region of the lake. The stratigraphic record from Lake Baringo reveals the presence of two abrupt dry episodes at ca. AD 1650 and AD 1720 in east Africa that led to drying up of the lake. The record also shows evidence of a third period of desiccation at ca. AD 1880, which resulted in lowering of the lake level and is corroborated by oral tradition from the area. This article shows the potential of how the paleoenvironmental record can be combined with the historical record to understand East Africa’s paleoenvironment. Key Words: East Africa, Lake Baringo, land degradation, paleoenvironment, vegetation change.

En este artıculo´ se presentan algunos de los hallazgos logrados en una investigacion´ de multi-indicadores de la historia de cambios vegetacionales y degradacion´ de la tierra durante el Holoceno tardıo´ en la cuenca del Lago Baringo de Kenya, Africa´ Oriental. El metodo´ 14C and 210Pb para datar la litoestratigrafıa´ fue utilizado para reconstruir el paleoentorno en la region´ del lago. El registro estratigrafico´ del Lago Baringo revela dos episodios secos abruptos que ocurrieron en Africa´ Oriental alrededor de 1650 d.C. y 1720 d.C., durante los cuales el lago se seco.´ En los registros tambien´ se encuentra evidencia de un tercer perıodo´ de

Downloaded by [Agora Consortium] at 02:47 15 April 2014 desecacion´ en ca. 1880 d.C., que ocasiono´ descenso en el nivel del lago, lo cual esta´ corroborado en el area´ por tradicion´ oral. Este artıculo´ muestra el potencial que tienen los registros paleoambientales en combinacion´ con los datos historicos´ para comprender el paleoentorno de Africa´ Oriental. Palabras clave: Africa´ Oriental, Lago Baringo, degradacion´ de la tierra, paleoentorno, cambios de la vegetacion.´

he ability of climatically sensitive fluences, and other environmental signals in T of the East African rift system to archive their sedimentary records makes them excel- regional climate dynamics, anthropogenic in- lent for investigating the paleoenvironment

∗ The authors would like to thank Dr. Jason T. Knowles, James Kiage, and John Omonywa for their invaluable help in the field. Mary Lee Eggart and Clifford Duplechin are thanked for professional assistance with illustrations. This research was supported by generous grants from the National Science Foundation (Grant No. BCS-0503334), the Geological Society of America (Grant No. 7712-04), the Sigma-Xi National Research Society, the R. J. Russell Field Research Award-Louisiana State University, and the R. C. West Field Research Award-Louisiana State University.

The Professional Geographer, 61(4) 2009, pages 438–458 C Copyright 2009 by Association of American Geographers. Initial submission, August 2008; revised submissions, February and March 2009; final acceptance, May 2009. Published by Taylor & Francis Group, LLC. Paleoenvironmental Changes in the Lake Baringo Basin, Kenya 439 Downloaded by [Agora Consortium] at 02:47 15 April 2014

Figure 1 Geographical position of Lake Baringo in East Africa. The lake is one of the lakes within the Eastern (Gregory) Rift Valley.

(Johnson and Svensson 1993; Russell et al. identifying the timing and magnitude of de- 2003). Changes in the stratigraphy and sedi- forestation, land degradation, or both. Lake mentation rates of such lakes can complement Baringo (Figure 1), one of the lakes within other proxy records in the reconstruction of cli- the eastern arm of the East African Rift Val- mate change and anthropogenic influences on ley, is well positioned to archive local and re- the paleoenvironment. Where human impact gional environmental changes. The lake is of on the watershed varies through time, changes great ecological interest because it has recently in sedimentation rates can provide a means of undergone dramatic change in surface area 440 Volume 61, Number 4, November 2009

and volume that threatens the rich biodiversity episodes affecting humans in the East African within its ecosystem (Johansson and Svensson region occur on decadal to centennial scales. 2002; Kurgat 2003; Hickley et al. 2004; Kiage Considering that climatic fluctuations occurred et al. 2007). at all timescales the challenge currently facing Previous studies of East Africa’s past envi- the paleoenvironmental researchers is how ronment and climatic conditions based on the to uncover the century-scale environmental examination of lake sediment cores provide changes and elucidate their causal mechanisms a broad picture of the paleoenvironment at (Verschuren 2004). This article is drawn millennial time scales (Livingstone 1962, 1967; from a study that aimed at investigating the Bakker 1964; Coetzee 1967; Bonnefille and vegetational history and land degradation in Riollet 1988; Taylor 1990; Street-Perrott and the Lake Baringo basin, Kenya, to enhance Perrott 1993; Street-Perrott et al. 1997; Gasse our understanding of the paleoenvironment of 2000; Kiage and Liu 2006). Although the East East Africa using fossil pollen, fungal spores, African region has a long history of paleoenvi- and microscopic charcoal in lake-sediment ronmental research, the record of centennial- cores. Situated in the broad ecotone between or decadal-scale landscape disturbance and savanna and steppe in East Africa, the Lake climate variability needs to be strengthened Baringo basin has a rich biodiversity that (cf. Thompson et al. 2002; Verschuren 2004). is currently threatened by land degradation The few high-temporal-resolution studies due to mounting population pressure and from the region have illuminated submillennial climate fluctuations in East Africa. Part of this oscillations in African paleoclimatic conditions study reviewed the paleoenvironment in East akin to the Holocene Bond Cycle (Bond et al. Africa since the Last Glacial Maxima (LGM; 1997), including the Younger Dryas (Roberts see Kiage and Liu 2006). The focus of this et al. 1993; DeMenocal et al. 2000; Barker et al. article is on paleoenvironmental changes in the 2001), the Medieval Warm Period (MWP), and Lake Baringo basin since AD 1650 based on the (LIA; Marchant and Taylor the examination of a high-temporal-resolution 1998; Verschuren, Laird, and Cumming 2000; lithostratigraphic record. Lamb, Darbyshire, and Verschuren 2003; Garcin et al. 2007). These high-temporal Study Area resolution studies have challenged the previ- ously held hypothesis of a climatically stable Lake Baringo is medium sized (∼129 km2) and uneventful Late Holocene in the African and shallow (mean depth ∼2.5 m; Aloo 2002; tropics (Livingstone 1975, 1980; Hamilton Hickley et al. 2004; Kiage 2007), located at 970 1982). The older assumptions of climatic m elevation just north of the equator (latitude stability arose largely from poor dating control 0◦30Nand0◦41N, longitude 36◦00Eand and coarse sampling intervals that obscured 36◦10E) in Kenya’s Rift Valley (Figure 1). decadal- and century-scale climate variability Due to the present shallow conditions of the coupled with failure to recover the soft surface lake, the sediments could be disturbed by Downloaded by [Agora Consortium] at 02:47 15 April 2014 sediments that contain more recent environ- perturbation, especially near the lake shores, mental data (cf. Verschuren 2004). The use where hippopotamus and crocodiles spend of AMS radiocarbon analyses, which can make much of their time. Bioturbation is a common use of small samples, coupled with 210Pb and phenomenon in shallow lakes as evidenced 137Cs, has led to the revision of the hypothesis. from the Late Pleistocene and Holocene Increasing evidence (e.g., Crossley, record from the neighboring Lake Bogoria Davison-Hirschmann, and Owen 1984; Lamb, (Scott et al. 2009). However, sediments Darbyshire, and Verschuren 2003; Verschuren retrieved toward the center of Lake Baringo 2004; Shanahan et al. 2009) now suggests that do not show signs of bioturbation. The lake climatic conditions throughout tropical Africa is part of the Gregory Rift Valley system of over the last millennia might have been quite lakes and is one of the two lakes in the eastern unstable, characterized by moisture-balance fork of the Rift Valley that have , fluctuations that must have seriously dis- the other being Lake Naivasha. The eastern rupted indigenous civilizations. Also, existing Rift Valley extends northward from Tanzania evidence appears to indicate that drought through Kenya and Ethiopia. Paleoenvironmental Changes in the Lake Baringo Basin, Kenya 441

Lake Baringo is situated in a semiarid envi- Materials and Methods ronment with low annual rainfall averaging 600 mm, confined to sporadic downpours within Thirteen cores were raised from Lake Baringo a few days in the months of April and May on different dates over two field seasons in and October and November, consistent with the months of January 2004 and 2005, us- the northward and southward migration of the ing a modified Livingston corer (Wright, Intertropical Convergence Zone (ITCZ). Vari- Mann, and Glaser 1984) from different water ation in rainfall in Lake Baringo occurs on depths ranging from 2.5 m to 3.4 m of water a range of timescales, including El Nino˜ and (Figure 4). The cores were raised in segments of La Nina˜ periods, about every five to seven varying lengths, and all were in excellent condi- years (LaVigne and Ashley 2002). Rainfall vari- tion at recovery. The coring process was termi- ability in the region has also been correlated nated when the sediments became too stiff for strongly with changes in sea surface temper- recovery using the modified Livingstone. The ature (SST) in the western Indian Ocean, a cores were retained in PVC tubes that were phenomenon that is also known as the Indian carefully sealed at the collection sites and then Ocean Dipole (IOD; Nicholson 1997; Mutai, transported to the Louisiana State University Ward, and Colman 1998; Saji et al. 1999; Clark, (LSU) Biogeography and Quaternary Paleoe- Webster, and Cole 2003). The average temper- cology Laboratory for processing and analysis. atures are fairly high (25–30◦C) and the poten- At the laboratory, each core was longitudinally tial evapotranspiration exceeds 2,500 mm (cf. split into two equal halves, photographed, and LaVigne and Ashley 2002; Driese et al. 2004). macroscopically described. The littoral vegetation community around The longest cores (LB-3, LB-4, LB-5, and much of Lake Baringo is poorly developed LB-6; Figure 5) were selected for detailed except for some marshes on the southern analysis. Several 1-cm3 samples were taken shores. Although the lake is located within the sequentially throughout the four cores at 1 vegetation zone classified by White (1983) as cm intervals and subjected to loss-on-ignition deciduous bushland and thicket (drier savanna analysis. Weight loss was measured after ◦ types; Figures 2A and 2B), its ecosystem away drying the samples overnight at 105 C, after ◦ ◦ from the littoral zone is highly heterogeneous combustion at 550 C, and 1000 C to establish with high species diversity and significant the water, organic, and carbonate content, intraspecific variations in physiognomic char- respectively (Dean 1974; Heiri, Lotter, and acteristics along the elevational gradient. The Lemcke 2001; Boyle 2004). Samples from the majority of the people in the lowlands are cores were sent to Beta Analytic, Inc., for AMS pastoralists, although some irrigation farming 14C analysis to establish the chronology. The is also practiced near the lake. As the elevation material that was sampled for the AMS 14C increases away from Lake Baringo, a wide vari- analysis included the hard clay peat material ety of woody plant species combine with acacias that was at the base of core LB-5 between to form the main vegetation layer with an 343 and 363 cm. Once the chronology for Downloaded by [Agora Consortium] at 02:47 15 April 2014 under-storey vegetation of moderate to dense the oldest sediments was established, the perennial forbs and grasses. Diverse woodlands younger sediments were sampled at 20 cm and remnants of formerly widespread montane intervals and analyzed for 210Pb dating at the forests consisting of Celtis spp., Urticaceae, Coastal Studies Institute at LSU. Samples Myrtaceae, Croton, Holoptelea, Prunus, Juniper, for radionuclide measurements were dried ◦ Podocarpus, Acacia, and Olea, among others, for twenty-four hours at 60 C, ground with a are found in the highlands that constitute the porcelain mortar and pestle, and sealed in air- upper reaches of the main that feed tight Petri dishes. Weighed masses were then Lake Baringo. Widespread transformation counted for twenty-four hours on Canberra of vegetated areas to degraded sites and bare low-background planar gamma detectors; surfaces, consisting of grazing lands, croplands correction for self-absorption of 210Pb was (mainly maize, beans, millet, sorghum, wheat, done using the method of Cutshall, Larsen, and tea), and human settlements, is readily and Olsen (1983). Total 210Pb was determined visible (Figure 3; Johansson and Svensson by measurement of the 46.5-KeV 210Pb gamma 2002; Kiage et al. 2007). peak. Supported 210Pb from the decay of 226Ra 442 Volume 61, Number 4, November 2009 Downloaded by [Agora Consortium] at 02:47 15 April 2014

Figure 2 Pictures of the typical vegetation of the lowland plains in the vicinity of Lake Baringo dominated by Acacia species, Euphorbia, and scrub vegetation with little or no undergrowth. The vegetation in the Lake Baringo basin is generally classified by White (1983) as the drier savanna type. Paleoenvironmental Changes in the Lake Baringo Basin, Kenya 443 Downloaded by [Agora Consortium] at 02:47 15 April 2014

Figure 3 Land cover and change detection map of the Lake Baringo drainage basin obtained from comparing the 1986 and the 2000 land covers based on satellite imagery. The sites labeled A to F represent areas within the Lake Baringo drainage basin that have experienced significant change in land cover in recent years. A detailed discussion of land cover change and land degradation is provided in Kiage et al. (2007).

within the lake bed was determined by mea- analysis were taken at 5 cm intervals through- surement of the granddaughters of 226Ra, 214Pb out the core. The pollen and microscopic char- (at 295 and 352-KeV), and 214Bi (at 609-KeV). coal were processed following the standard Palynomorphs and microscopic charcoal procedures (Faegri and Iverson 1989). The pro- were processed from core LB-5, which had the cessed samples from core LB-5 were mounted longest record. Sediment samples for pollen onto slides and counts were made for pollen 444 Volume 61, Number 4, November 2009

Figure 4 A Bathymetric map of Lake Baringo modified from Hickley et al. (2004). The contour lines progress at 0.5 m (beginning at 1.5 m) and the dots numbered 1–7 are the coring sites for the cores collected in January 2005. Contour lines less than 3 m around the islands are mostly omitted. The deepest points in the lake are also indicated. The Bathymetric map offers broad generalization of the

Downloaded by [Agora Consortium] at 02:47 15 April 2014 depth and some sections of the lake might not fall within the scheme.

types, fungal spores, and abundance of micro- (Grimm 2004). The identifications were based scopic charcoal at each level. Viewing was done on the reference collection at the LSU Global on a Nikon HFX-II compound microscope Change Laboratory and on specialized publica- mostly at 400X magnification. For each sam- tions relevant to East Africa’s pollen morphol- ple, counting ceased when 1,000 Lycopodium ogy (Bonnefille 1971a, 1971b; Hamilton 1976; spores were counted; the resultant counts rep- Bonnefille and Riollet 1980). Other pollen ref- resented pollen concentration at each level. erences that proved useful for pollen identifi- The counts were recorded by hand and then cation included publications of pollen from the entered into a spreadsheet and sorted and tropical regions (Heusser 1971; Willard et al. plotted using Tilia and Tilia-Graph software 2004). Paleoenvironmental Changes in the Lake Baringo Basin, Kenya 445

Figure 5 (A) Stratigraphic correlations of the major cores (LB-5, LB-6, LB-4, and LB-3) from Lake Baringo. The cores are arranged from the longest to the shortest and the delineation of the different zones (A–G) is based on the lithostratigraphic characteristics of the cores. (B) A 210Pb activity versus depth. (C) Age versus depth based on 210Pb based on samples from core LB-5.

Results results for loss on ignition (LOI) and pollen percentage curves were used to divide the The main chronological features of core LB-5 cores into five major units (zones) in the pollen are summarized in Table 1. Lake Baringo’s diagram: V (363–343 cm), IV (343–295 cm), III stratigraphy since AD 1650 consists of seven (295–260 cm), II (260–35 cm), and I (35–0 cm; lithological horizons (labeled A–G in Figure 5). Figure 6). The pollen and other palynomorphs These stratigraphic horizons along with the are generally well preserved with the exception Downloaded by [Agora Consortium] at 02:47 15 April 2014

Ta b l e 1 Chronology of the sediment record from Lake Baringo based on core LB-5

Core depth (cm) Dated material Beta no. 210Pb or 14C (year AD or BP) Calendar year

0–1 cm Bulk sediment 2004 23 cm Bulk sediment 1982 51 cm Bulk sediment 1954 82 cm Bulk sediment 1924 Age based on stratigraphic marker horizons 98 cm Pinus pollena 1920s 193 cm Zea mays pollena Mid- to late 1800s Radiocarbon date 363 cm Grass seeds and roots 207988 Cal. 300± 50 AD 1650 (1δ range Cal. 1640–1690)

aSediment age at depth is estimated based on pollen of introduced species. 446 Volume 61, Number 4, November 2009

Figure 6 Pollen percentage diagram showing the results of the analysis based on core LB-5 from Lake Baringo. The pollen zonation (I–V) is based on mainly on pollen percentages and loss-on-ignition analysis and is different from the zones (A–G) in Figures 5 and 7.

of stratigraphic zones G and E (Figure 5). common in this zone. Nevertheless, Zone Overall, aquatic and emergent marsh taxa are V is characterized by high concentrations poorly represented in the record, reflecting of Gramineae, Cyperaceae, Combretaceae, limited development of marshland or littoral Podocarpus, Olea, Tarchonanthus, Phyllanthus, vegetation. Grass (Gramineae) pollen domi- Acacia, and Euclea, most of which are dry- nated the spectra with percentages averaging 20 indicator species. to 40 percent, typical of regional African pollen Lithostratigraphic Zone F (343–298 cm) assemblages (Msaky, Livingstone, and Davis consists of soft, dark gray muds, lack- 2005). Low percentages of arboreal pollen (less ing any laminations. There is an increase than 20 percent) are observed throughout the in the concentration of microscopic char- core. coal in Zone IV (Figure 6), which is Lithostratigraphic zone G (Figure 5), from also characterized by a general increase in 363–343 cm, is composed of stiff, dark- the percentages of Macaranga, Phoenix, and gray, largely unconsolidated clay (crumbly Gramineae pollen. The pollen of Acacia, Ses- appearance), and peat material. At the bot- bania, Euclea, and Phoenix increase, whereas tom of the unit, well-preserved macrofossils Olea, Tarchonanthus, Phyllanthus, and Com- (rootlets and seeds), probably of plants of bretaceae decrease. The organic content in this Downloaded by [Agora Consortium] at 02:47 15 April 2014 marsh and wetland environment, were recov- zone remains above 10 percent as in the pre- ered and constituted part of the organic mate- ceding horizon (lithostratigraphic zone G, Fig- rial that was submitted to Beta Analytic, Inc., ure 7) and the carbonate content was higher by for AMS 14C analysis. The bottom of this about 1 percent. Figure 5 provides the details unit was dated to approximately 300 years BP of the changes in the lithostratigraphic record. (Cal AD 1650; Beta-207988). The results of Although pollen Zone III (Figure 6) records LOI (Figure 7) show that the sediments in a general decrease in pollen sum, there is an this unit consist of approximately 36 to 40 abrupt but remarkable decrease in the percent- percent water, 10 to 12 percent organic mat- ages of grass and sedge pollen, matched by an ter, and less than 2 percent carbonate con- increase in shrubs and woodland trees (Cheno- tent, the lowest observed throughout the core. Am and Acacia). Pollen preservation in Zone V is poor; many Lithostratigraphic Zones D and B (Figure pollen grains are corroded and difficult to 5, 260–40 cm) are dominated by brown dark identify. Microscopic charcoal is relatively un- brown clay sediments that are well laminated. Paleoenvironmental Changes in the Lake Baringo Basin, Kenya 447

Figure 7 The stratigraphy of Lake Baringo and results of loss-on-ignition analysis based on core LB-5. The seven zones (A–G) are based on the lithostratigraphic characteristics of the core.

Although the water content is fairly uniform 200–150 cm. There is also a remarkable in- Downloaded by [Agora Consortium] at 02:47 15 April 2014 (45–50 percent) throughout this zone, the other crease in the percentages of Podocarpus, Junipe- constituents of the LOI analysis and the color rus, and Myrtaceae. The percentages of most of the sediments varied throughout the zone. of the other pollen types are also marked by For instance, at 110–40 cm and 240–170 cm oscillations at different points within Zone II, the organic content is consistently above 8 per- but remain largely below 10 percent. cent, whereas the rest of the zone has an average The sediments in lithostratigraphic Zone A of 5 to 6 percent (Figure 7). Also, the carbonate (Figure 5, 55–0 cm) are made of dark brown clay content records a core maximum of 4.6 percent material that is largely unconsolidated. This is and maintains an average of 4 percent between the case, particularly in the top 10 cm, that 128 cm and 188 cm, whereas the rest of the is also characterized by fairly low water con- zone has values of 2 to 3 percent. Pollen Zone II tent (33–35 percent). The rest of the zone con- (Figure 6) shows a recovery of grass and sedge sists of brown and dark brown soft clay sedi- (Cyperaceae) pollen, especially at about 260– ments that have no apparent laminations, which 200 cm. The grass and sedge pollen drops back contrast sharply with the zones beneath. The to the same low levels as Zone III from about organic and carbonate content in this section 448 Volume 61, Number 4, November 2009

is similar to that of lithostratigraphic Zone B ment from which pollen enters the lake is large with average values of 7 to 8 percent and 2 to and covers a wide altitudinal range, between 3 percent, respectively. The sediments in litho- 900 m and beyond 2,200 m above sea level. stratigraphic Zone A appear to suggest the pos- Also, vegetation in the Lake Baringo drainage sibility of bioturbation, increased sedimenta- basin changes from dry woodlands and savanna tion, or both, in Lake Baringo in recent years. in the low elevations to montane forests in This view is supported by the curve of 210Pb the high elevations. However, the lithostrati- activity versus depth (Figure 5) that is char- graphic record highlights most of the paleoen- acterized by an erratic decay of 210Pb toward vironmental changes that could be overlooked background supported lead in the upper 50 cm in the pollen record. of core LB-5. The key to the paleoenvironmental and sed- imentation history of Lake Baringo is provided by the core LB-5 profile between 363 and 343 Discussion cm and again at 280 to 260 cm (Zones G and E, respectively; Figure 5). The low water content, The Lake Baringo pollen record shows domi- crumbly appearance, presence of traces of nance of dry-indicator species such as Podocar- rootlets, and well-preserved seeds suggests pus, Olea, Acacia, Balanitaceae, Gramineae, and terrestrial environments, probably marsh con- Cyperaceae, which is consistent with preva- ditions in the lake that had dried up following lence of largely dry conditions throughout the an extended drought episode. The unconsol- period covered by the core. The Olea species idated clay material with a crumbly structure represented in the Lake Baringo sediments is is a typical pedogenic feature of floodplain probably Olea hochstetteri, an important compo- soils. AMS 14C analysis of the well-preserved nent of the dry montane forests often occurring seeds that were recovered along with the peat in abundance in association with Podocarpus material at the bottom of core LB-5 yielded a (Olago 2001). However, accurate interpreta- date of 300 ± 50 yr BP, calibrated to approxi- tion of the climate signal is hampered by the mately AD 1650 (Beta No. 207988). That date fact that various species of Olea with very simi- places the peak of the first dry episode at Lake lar pollen grow together in a wide spectrum of Baringo at some time before the late sixteenth forest types (cf. Kiage and Liu 2009). The two or early seventeenth century and the second common species of Podocarpus in the Kenyan episode in the early to mid-eighteenth century. highlands have distinct ecological preferences. A comparison of the lithostratigraphic features P. falcatus occurs in drier environments that from the all the major cores recovered from receive 1,000 to 1,500 mm yr–1 of rainfall, Lake Baringo revealed that the sediments at whereas P. latifolius dominates in much wetter the bottom of core LB-5 (Zone G, Figure 5) environments, yet their pollen grains are iden- had no equivalents in the other cores collected tical (Beentjee 1994; Lamb, Darbyshire, and from the lake. Based on the thickness of Verschuren 2003). Although the pollen assem- the marker horizon of the second dry event Downloaded by [Agora Consortium] at 02:47 15 April 2014 blage surrounding the first intense dry event in (Zone E, Figure 5) it can be posited that the the Baringo record offers evidence for aridity, late sixteenth- and early seventeenth-century some ambiguity surrounds the interpretation drought must have persisted for over a decade. of Podocarpus and Olea pollen in the record. The poor state of pollen preservation and dom- There are no marked changes in the pollen inance of dry-indicator species such as Acacia, profiles, with the exception of introduced Sesbania, Euclea, and Phoenix increase, whereas species, maize (Zea) and pine (Pinus), that can be Olea, Tarchonanthus, Phyllanthus, and Com- directly linked to human impact. Although the bretaceae provide further evidence of the twentieth century is marked by subtle changes, extended dry episodes. especially in the percentages of arboreal pollen, A comparison of the Baringo record with which are consistent with increasing deforesta- records from the Nile and other lakes tion, those changes are somewhat muted. The in the East African region such as Lake interpretation of the climatic implications of Naivasha, Lake Victoria, Lake Edward, the vegetational changes of the pollen record Lake Masoko, Lake Malawi, Lake Chilwa, is interesting because the Lake Baringo catch- and Lake Tanganyika (Table 2; Crossley, between 1570 and 1830. The lowest levels occur at ca. 1780–1830 Low lake level

nson (2005); Stager et al. period , lowest lake levels recorded at ca. 1550–1750 Extensive dry b years (1580–1650) years (1700–1760) years (1830–1860) years (1880–1900) Thirteen low flow Fourteen low flow Thirteen low flow Nine low flow Low flows of within a long dry period (1650–1860) period Driest period Extended dry ca. 1610–1680 ca. 1780–1820 Low lake levels at Low lake levels at at ca. 1580 period with lowest lake levels at ca. 1730 at ca. 1800 Downloaded by [Agora Consortium] at 02:47 15 April 2014 Lowest lake level Extended dry Lowest lake level at ca. 1560–1620 episode at ca. 1760–1840 Low lake levels Brief dry Low lake levels a

Comparison of the lithostratigraphic record from Lake Baringo with records from select lakes in Eastern Africa and the Nile flood data First intense dry episode ended ca. 1650 Second intense dry episode ? Low lake level: Low lake level: Low lake level

Drought episodes not apparent inData the missing stratigraphic for record several years. but available in oral history and recorded by early explorers. 1600 1810 1820 1830 1620 1730 1710 1720 1840 1880 Drought 1890 episodes 1660 1670 1680 1690 1700 1630 1640 1650 1740 1750 1760 1610 1770 1780 1790 1800 Year 1580 1900 a b (AD) Lake Baringo Lake Naivasha Lake Tanganyika Lake Victoria Lake Masoko the Nile Lake Edward Lake Malawi Ta b l e 2 (1580–1900) according to different sources 1850 1860 1870 Note: The dry periods thatSources: resulted Cohen in et low al. lake(2005); (1997); levels Russell, Verschuren are Verschuren, et and shown al. Eggermont in (2007). (2000); gray. Alin and Cohen (2003); Ortlieb (2004); Verschuren (2004); Cohen et al. (2005); Russell and Joh 449 450 Volume 61, Number 4, November 2009

Davison-Hirschmann, and Owen 1984; Johnson, Brown, and McManus 2004). These Whetton and Rutherfurd 1994; Cohen et al. climate controls also strongly influence rainfall 1997; Verschuren, Laird, and Cumming 2000; amounts received in East Africa (Nicholson Alin and Cohen 2003; Lamb, Darbyshire, and 2000); it is therefore reasonable to compare the Verschuren 2003; Ortlieb 2004; Verschuren Lake Baringo record to that of Lake Malawi. 2004; Russell and Johnson 2005; Stager et al. Indeed, Lake Malawi’s annually laminated 2005; Garcin et al. 2007) reveals interesting record of diatom silica suggests the presence of parallels. For instance, a record of the Nile a well-defined low-lake-level period between River floods and low flows shows a series of about AD 1570 and 1850 (Owen et al. 1990; low-flow periods at about AD 1640–1641, Johnson, Brown, and McManus 2004), which 1650, and 1661 (Quinn 1992; Whetton is contemporaneous with the dry episodes and Rutherfurd 1994; Ortlieb 2004), which recorded in Lake Baringo. The duration of the coincide with the first intense dry episode Lake Malawi lowstand appears to be part of recorded in Lake Baringo that ended in the a gradual but extended period of aridity that late sixteenth or early seventeeth century. runs through the two distinct dry episodes in The second dry episode that ended at about the Lake Baringo record. Considering that the the mid-eighteenth century also appears to Lake Malawi’s diatom-inferred record shows be coeval with eleven records of low flows in the most pronounced lowstand between 1780 the Nile between about AD 1723 and 1753. and 1830 (Owen et al. 1990; Johnson, Brown, In Lake Victoria, which is the source of the and McManus 2004; Verschuren 2004), it Nile River, the lowest lake levels during that might be reasonable to assume the possibility time occurred at about AD 1610 to 1680 of two or more decadal-scale intense dry and also AD 1780 to 1820 (Stager et al. episodes within the extensive period of aridity 2005). between about AD 1570 and 1850. Crossley, A paleoenvironmental record reconstructed Davison-Hirschmann, and Owen (1984) put based on ostracode species-abundance data the peak of the aridity in the Lake Malawi from Lake Tanganyika, located to the south of record between the late 1700s and early 1800s, Lake Baringo, shows persistent drought condi- which is a couple of years after the occurrence tions between AD 1550 and 1850 that resulted of the second drying episode at Lake Baringo. in rapid declines in lake level at about AD 1580, At the peak of the Lake Malawi drying episode, 1730, and 1800 (Cohen et al. 1997; Alin and large tropical trees grew in what is now part Cohen 2003). These recurrent drought events of the lake surface (cf. Crossley, Davison- appear to be coeval with the drying episodes Hirschmann, and Owen 1984). Lake Chilwa, in the Lake Baringo record. Further evidence situated at the southern end of the Gregory for the severe drought episodes in the Lake Rift Valley and to the south of Lake Malawi, Tanganyika basin is provided by microscopic also recorded an extended lowstand sometime charcoal abundance that shows evidence for in- between AD 1750 and 1850 (Lancaster 1981). creased fire frequency between about AD 1550 Magnetic, organic carbon, geochemical, and Downloaded by [Agora Consortium] at 02:47 15 April 2014 and 1850 (Alin and Cohen 2003). These dry pollen evidence from Lake Masoko in south- conditions appear to have been widespread in ern Tanzania all seem to indicate intense dry equatorial East Africa because they are also periods at about AD 1650 and AD 1730 and recorded in Lake Edward and in two crater between AD 1800 and AD1860 (Garcin et al. lakes (Lake Kitagata and Lake Kibengo) in 2007). Also, lake level and salinity records from western Uganda (Russell and Johnson 2005; Lake Naivasha shows what must have been a Russell, Verschuren, and Eggermont 2007). period of intense drought around AD 1560 to Although Lake Malawi (10–15◦S) is located 1625 (Verschuren, Laird, and Cumming 2000). farther south of Lake Baringo and in a slightly Although the timing of the AD 1560 to 1625 different climate region, its rainfall exhibits Lake Naivasha drought episode is consistent seasonality that is strongly influenced by with the first intense drought episode in the the migration of the ITCZ, the Congo Air Lake Baringo record that ended in the late Boundary, El Nino-Southern˜ Oscillation sixteenth or early seventeenth century, there events, and the Indian Ocean SST anomalies are neither written documents nor reliable ar- (Tyson 1986; Nicholson 1996; Reason 2001; chaeological surveys from that locality with Paleoenvironmental Changes in the Lake Baringo Basin, Kenya 451

which to compare. Documentary records of cli- periods on at least three occasions since 4000 mate data from the region are rare, and instru- to 3000 years BP (Talbot and Livingstone mental records, where available, are limited to 1989). The first drying out at Lake Rukwa only the last 120 years in spite of the region’s occurred sometime prior to 3000 BP and the long and rich cultural history (Nicholson 2001; latest episode, the exact date of which remains Nicholson and Yin 2001). unknown, occurred during sub-historical times The late sixteenth- and early seventeenth- and might be contemporaneous with the AD century intense aridity episode in Lake Baringo 1750 to 1850 lowstand in Lake Malawi (Talbot that corresponds to the Naivasha lake level and Livingstone 1989; Crossley, Davison- record is generally coeval with the precolonial Hirschmann, and Owen 1984) that appears history of East Africa that records drought- consistent with the Lake Baringo record. induced famine (Nyarubanga drought)and The lithostratigraphy of core LB-5 (Zone F, sociopolitical unrests that match the periods Figure 5) reveals what we interpret as a period of lowstand at Lake Naivasha (Webster 1979; of high precipitation after the late sixteenth Verschuren, Laird, and Cumming 2000; or early seventeenth century and before the Verschuren 2004). However, this evidence second period of intense drought that ended from the precolonial history of East Africa around the mid-eighteenth century. This sec- needs to be interpreted with caution because tion of the core is characterized by soft, dark of methodological issues surrounding the gray sediments that are devoid of any apparent dating of the drought and famine episodes. horizontal lamination that characterizes much Apparently, Webster’s (1979) estimation of of the rest of the core. However, the duration chronology of the famines was based on the was not long enough to be accompanied by sig- calculation of the reigns of the Kabakas (kings) nificant vegetational change, although there is of Buganda kingdom (each reign made up evidence of reduction in the pollen of dry in- of twenty-year durations), an estimation that dicator species (Figure 6). The amount of pre- can be quite inaccurate. Unfortunately, that cipitation during that time period was probably is the trend that characterizes East Africa’s higher than any other period covered by core precolonial history, which is largely based on LB-5 considering that data from the nearby oral tradition that tends to be both variable Lake Naivasha showed the highest lake levels and lacking in chronological precision. during the same period (Verschuren 2001). It is The challenges with the dating of these likely that the first intense drought episode was precolonial droughts and famines notwith- succeeded by a period of heavy precipitation standing, the two episodes of aridity in the Lake that was probably accompanied by flooding. Baringo record were evidently more severe The presence of well-preserved seeds in Zone than any drought recorded in the twentieth V might suggest that the material could have century. Even the much remembered series been buried rapidly, resulting in the excellent of droughts that affected the Baringo area in preservation. The Lake Chilwa record shows the 1920s and 1930s (Anderson 2002) did not evidence of lake-level peak (9 m above mod- Downloaded by [Agora Consortium] at 02:47 15 April 2014 result in the drying up of the lake. It must ern mean level) sometime between AD 1650 have taken a combination of low or failure of and 1750 (Crossley, Davison-Hirschmann, and precipitation, incredible land cover change (no Owen 1984). Applying modern evapotranspi- evidence of this in the pollen record), increased ration rates to this peak at Lake Chilwa would wind speeds, high temperatures, and high evap- translate to approximately a 35 to 40 per- otranspiration within the drainage basin for cent increase in precipitation (Lancaster 1981). significant portions of Lake Baringo’s surface An increase in precipitation around that pe- area to dry up. However, the drying up of Lake riod is consistent with the tree ring record ob- Baringo is not without precedent in the East tained from baobab trees at Nchisi Island near African region, as evidenced by paleorecords the western shore of Lake Chilwa (Crossley, of other lakes drying up (Talbot and Delibrias Davison-Hirschmann, and Owen 1984). Un- 1977; Riehl and Meıtin´ 1979; Talbot and fortunately, many paleorecords from the East Livingstone 1989). Geochemical evidence and African region have low time resolution or lake level record indicates that Lake Rukwa in poor chronological control, to the extent that southern Tanzania has dried out for significant centennial- to decadal-scale events such as 452 Volume 61, Number 4, November 2009

this are completely missing (cf. Verschuren cated networks of irrigation, and agricultural 2004). Very few climate- and anthropogenic- success during an era of Maasai pastoralist ex- proxy records have good enough centennial- pansion in the Rift Valley (Anderson 2002). or decadal-scale resolution and age control that Before AD 1850, the Lake Baringo basin was cover the last 500 years. Therefore, apart from well known to Arab traders and early European the information gained from oral tradition and explorers as an area rich in ivory and an impor- the few high-temporal-resolution records that tant source of food provisions for trade caravans are available, a big chasm of information char- moving to the north and west from the East acterizes East Africa’s paleorecord of the last African coast (Thomson 1887; Gregory 1896; five centuries. Ambler 1988; Anderson 2002). However, Eu- After the second drying-out episode at ropean missionaries and explorers during the Lake Baringo at about the mid-eighteenth 1880s found Baringo in the middle of a serious century (Zone E, Figure 5) the climate of the drought. For instance, Joseph Thomson could region appears to have stabilized to modern not find food for his caravan in the Njemps conditions characterized by high seasonal villages in 1883. The irrigation networks had variability in precipitation. This is reflected in collapsed following a succession of years with the stratigraphic features in nearly all the cores no rainfall and the local people (the Njemps) characterized by a dominance of horizontal were largely dependent on hunting and gather- laminations made of dark and light brown ing wild roots and berries for food (Thomson layers of varying thickness. The laminations 1887). Another European expedition led by (light and dark brown/gray couplets) are not Gregory in 1893 also recounted experiences of “varves.” We hypothesize that the light and drought and famine in Baringo, which had not dark couplets correspond to alternating wet received rains for two consecutive years and and dry periods on an interannual basis. In the area was characterized by dry riverbeds Zones D and B (260–40 cm) of core LB-5 the (Gregory 1896; Huxley 1935). The precolonial laminations are finer in the lower portion of histories of the Baringo area recounted from the core and become less defined toward the oral tradition testify that the late nineteenth top of the core. A gradual transition in the century experienced a series of droughts and sediments to coarse light brown muds devoid famines, as well as violent contacts between pas- of lamination occurs between 160 and 125 cm toralists and agriculturalists (Ambler 1988). All (Zone C, Figure 7). We interpret these changes these accounts attest the presence of droughts in the stratigraphy to be indicative of a decrease in the region prior to and around 1880 that in lake level related largely to climate-driven led to severe lake-level reduction in Baringo. shifts in the pattern of precipitation from fairly However, it is likely that the severity of this wet to arid conditions with the consequent drought event was more localized and less decrease in river discharge. The resultant shal- intense compared to the earlier 1650 and 1720 low lake conditions encouraged resuspension to 1750 droughts that resulted in the drying of sediments and complete mixing ensued that out of the lake because there is no record of it Downloaded by [Agora Consortium] at 02:47 15 April 2014 terminated the lamination process in the lake. in the other lakes from the East African region. The sediment transition that occurred prior That cessation of laminations in the Lake to AD 1900 can be compared to the pre- Baringo sediments is consistent with reduction European history of the Baringo region as in lake level is not in doubt because more re- recounted from oral tradition and recorded cent sediments in the lake (the top portions accounts of early European explorers in the of the cores) have no laminations. All the cores area. Whereas the later part of the nineteenth show that the top 20 to 40 cm, which represents century was characterized by wars, droughts, sediments deposited over the past forty to fifty famine, human turmoil, and pestilence, after years, are missing laminations that resumed af- AD 1750 the Lake Baringo basin, especially ter the mid- to late-nineteenth-century series the Il Chamus (also known as Njemps) villages of droughts. This change in stratigraphy is at- to the immediate south of the lake witnessed a tributed to a combination of low lake levels due continuous era of prosperity. During the era of to the present high evapotranspiration rates in prosperity the Il Chamus villages became syn- the region and decreasing precipitation, as well onymous with fortified settlements, sophisti- as increased land degradation and soil erosion. Paleoenvironmental Changes in the Lake Baringo Basin, Kenya 453

The mean depth of the lake was approximately However, it is somewhat surprising that the 7.5 m in 1932 (Beadle 1932), 5.6 m in the 1960s Lake Baringo record shows no change in sed- (Ssentongo 1995) and had declined to 2.5 m by iment inflow for both the prehistoric period, 2005 when we conducted fieldwork. The cur- prior to European settlement in the Baringo rent shallow lake conditions limit stratification ecosystem (AD 1900), and after, including more and encourage mixing and daily resuspension recent times. We expected to find a significant of sediments, which, coupled with the inflow difference in sediment inflow between the two of high sediment load from heavy erosion in time periods based on the widely held hypoth- the catchment, have caused lamination to cease esis that land degradation became synonymous in the lake. The other possible explanation for with Baringo following European settlement lack for laminations in the sediments toward and colonization in East Africa (cf. Sorrenson the top of the cores is disturbance. Bioturbation 1968; Sindiga 1984; Anderson 2002). During from large animals is a very common problem the colonial period the European settlers alien- in shallow rift lakes. Lake Baringo is no excep- ated the indigenous pastoralists from their dry tion and it is known for its hippo populations. season grazing lands by occupying and fencing Given the fluctuation of the lake level over the off the well-watered highlands to the south and last century, a pod of hippos could have used east of Lake Baringo (cf. Anderson 2002). The nearly all areas within the lake basin, thereby local pastoralists were confined to the climat- disturbing the sediments. ically harsh and ecologically fragile lowlands. The high sediment inflow into Lake Baringo The Baringo lowlands had been part of a wider is accentuated by the steep slopes that con- production system that involved transitory use stitute over 46 percent of the Baringo land- of grazing resources attuned to the fragile semi- scape (cf. Hickley et al. 2004). The slope of the arid environment that developed out of adap- land and the soil properties often combine to tation to the variable semiarid conditions. By enhance the erodibility (i.e., soil resistance to taking possession of the well-watered high- detachment and transport) of any given land- lands, the European settler community severed scape (Morgan 1995; Lal 2001; Vrieling 2006). the seasonal grazing areas and watering points The climate of Baringo, especially the rainfall from the African herders and condemned them pattern, only compounds the soil erosion and to the permanent use of the fragile lowlands, land degradation problem. Low rainfall only which then might have become quickly de- supports sparse vegetation cover in a region graded (Sindiga 1984). After Kenya gained in- that experiences high evapotranspiration rates dependence in 1963, wealthy individuals took (< 2,500 mm per year) and the sporadic nature possession of previously held European lands of the rainstorms has high erosive power on and maintained the status quo. bare grounds or low vegetation cover. There is There are two possible explanations for the a close relationship between vegetation density high pre- and postcolonial or modern sedimen- and soil loss, especially in environments that tation record at Lake Baringo. First, it is possi- are characterized by abrupt rainstorms. A study ble that land degradation in the Lake Baringo Downloaded by [Agora Consortium] at 02:47 15 April 2014 in the flats adjacent to Lake Baringo recorded basin commenced much earlier than has been soil loss values of over 80 g m–2 for thirty- previously documented, and the rates of pre- minute storms and 30 g m–2 for sixty-minute historic land degradation are similar to those storms during single rainstorm events (Snelder evident in modern time. If that assertion is and Bryan 1995). Thus, storm duration and in- true, the hypothesis of the invariably environ- tensity greatly influence soil erosion rates. It mentally friendly use of grazing resources by is, therefore, no wonder that almost 90 percent the indigenous pastoralists and their indigenous of the catchment (6,820 km2) is considered de- knowledge of conservation will need some revi- graded (Johansson and Svensson 2002; Hickley sion (Anderson 2002; Kiage and Liu 2009). Al- et al. 2004; Onyando, Kisoyan, and Chemelil though the precolonial population in the Lake 2005; Kiage 2007). The high rates of soil ero- Baringo basin was much lower compared to the sion are evidenced by the erratic nature of the present level, the effect on the landscape was as 210Pb decay toward background in the upper 50 profound as that witnessed in modern times. cm of core LB-5 (Figure 5), which is consistent The second explanation for the high and un- with abrupt and massive sediment input. changed sedimentation rates at Lake Baringo 454 Volume 61, Number 4, November 2009

is that humans might not be the main drivers umented in other high-temporal-resolution of land degradation in the area and the high records from the region. The lithostratigraphic sedimentation rates at the lake. This hypoth- record from Lake Baringo compares well with esis is reasonable considering that change in known high-impact infrequent environmental population and increased use of vegetation re- events like prolonged droughts that caused sources in the Lake Baringo basin over time immense human suffering in the East African has not affected the sedimentation rates. It is region. These results show the potential likely that the steep landscape, sparse vegeta- of how the paleoenvironmental record can tion cover, clay and volcaniclastic material, and be combined with the historical record to the climate within the Lake Baringo basin in- understand East Africa’s paleoenvironment. teract to yield the high sedimentation rates in- Although human activities often exacerbate dependent of anthropogenic impacts. Indeed, the land degradation process in the area, they the soil properties of clay, clay loams, and silty only serve to magnify the land degradation clay in the context of steep slopes, sparse veg- process. Consequently, the Lake Baringo etation, and heavy sporadic rainstorms could record shows no significant change in the hold the key to understanding the high sedi- sediment inflow into Lake Baringo for the mentation record in Lake Baringo. Einsele and precolonial and postcolonial period. These Hinderer (1998) have shown from studies else- findings contribute to our understanding of where in East Africa that areas with crystalline the paleoenvironmental changes in East Africa rocks and denser vegetation (e.g., around Lakes during prehistoric times. However, more Tanganyika and Kivu) experience lower sed- high-temporal-resolution studies need to be imentation rates compared to areas with vol- performed in different sites from East Africa caniclastic material and sparse vegetation cover to increase our understanding of the region’s (e.g., Lake Turkana). paleoenvironment during the late Holocene The Lake Turkana region, although many period. times larger, is similar to Lake Baringo in many ways (Halfman, Johnson, and Finney 1994; Mohammed, Bonnefille, and Johnson 1995); however, the latter has more steep landscapes, Literature Cited has high relief, and experiences higher pre- cipitation. Therefore, although both lakes are Alin, S. R., and A. S Cohen. 2003. Lake-level his- characterized by relatively high sedimentation tory of Lake Tanganyika, East Africa, for the rates, those for Lake Baringo are much higher past 2500 years based on ostracode-inferred water- and the difference can be accounted for by fea- depth reconstruction. Palaeogeography Palaeoclima- tures lacking in the Turkana landscape. That tology Palaeoecology 199:31–49. underscores the significance of high relief, Aloo, P. A. 2002. Effects of climate and human ac- steep landscapes, soil properties, and climate in tivities on the ecosystem of Lake Baringo, Kenya. heightening denudation and subsequent high In The East African great lakes: Limnology, palaeolim-

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Verschuren, D. 2001. Reconstructing fluctuations of AETFAT/UNSO vegetation map of Africa. Paris: a shallow East African lake during the past 1800 UNESCO. years from sediment stratigraphy in a submerged Willard, D. A., C. E. Bernhardt, L. M. Weimer, S. crater basin. Journal of Paleolimnology 25:297– R. Cooper, D. Gamez, and J. Jensen. 2004. At- 311. las of pollen and spores of the Florida Everglades. Verschuren, D. 2004. Decadal and century-scale cli- Palynology 28:175–227. mate variability in tropical Africa during the past Wright, H. E., D. H. Mann, and P. H. Glaser. 1984. 2000 years . In Past climate variability in Europe and Piston corers for peat and lake sediments. Ecology Africa, ed. R. W. Battarbee, F. Gasse, and C. Stick- 65:657–59. ley, 139–58. Dordrecht, Netherlands: Springer. Verschuren, D., K. R. Laird, and B. F. Cumming. 2000. Rainfall and drought in equatorial East LAWRENCE M. KIAGE is an Assistant Profes- Africa during the past 1,100 years. Nature 403:410– sor in the Department of Geosciences at Georgia 14. State University, Atlanta, GA 30302. E-mail: lkiage@ Vrieling, A. 2006. Satellite remote sensing for water gsu.edu. His research interests include bio- erosion assessment: A review. Catena 65:2–18. geography, palynology, paleotempestology, remote Webster, J. B. 1979. Noi! Noi! Famines as an aid to sensing, geographic information systems, and Interlacustrine chronology. In Chronology, migra- paleoecology. tion and drought in Interlacustrine Africa, ed.J.B. Webster, 1–37. Halifax, NS, Canada: Dalhousie KAM-BIU LIU is the George William Barineau III University Press. Distinguished Professor, Department of Oceanogra- Whetton, P. H., and I. Rutherfurd. 1994. Historical phy and Coastal Sciences at Louisiana State Univer- ENSO teleconnections in the eastern hemisphere. sity, Baton Rouge, LA 70803. E-mail: [email protected]. Climate Change 28:221–53. His research interests include biogeography, paly- White, F. 1983. The vegetation of Africa: A de- nology, paleotempestology, and global environmen- scriptive memoir to accompany the UNESCO/ tal change. Downloaded by [Agora Consortium] at 02:47 15 April 2014