Environmental change over the last millennium recorded in two contrasting crater lakes in western Uganda, eastern Africa (Lakes Kasenda and Wandakara)

Abstract

The last millennium is a key period for understanding environmental change in eastern Africa, as there is clear evidence of marked fluctuations in climate (effective moisture) that place modern concern with future climate change in a proper context, both in terms of environmental and societal impacts and responses. Here, we compare sediment records from two small, nearby, closed crater lakes in western Uganda (Lake Kasenda and Lake Wandakara), spanning the last 700 (Wandakara) and 1200 years (Kasenda) respectively. Multiproxy analyses of chemical sedimentary parameters (including C/N ratios,  13 C of bulk organic matter and  13 C and  18 O of authigenic carbonates) and biotic remains (diatoms, aquatic macrofossils, chironomids) suggest that Kasenda has been sensitive to climate over much of this period, and has shown substantial fluctuations in conductivity, while Wandakara has a more muted response, likely due to the increasing dominance of human activity as a driver of change within the lake and catchment over

Sensitivity of East African savannah vegetation to historical moisture-balance variation

“…Archaeological and linguistic data from regions north and west of Lake Victoria (Reid, 2000;Robertshaw and Taylor, 2000;Killick, 2009;de Filippo et al, 2012) suggest that more humid western areas of the East African Plateau experienced human landscape modification for a substantially longer period of time. Unfortunately, ambiguity in the pollen records of past vegetation history and/or dating mismatches with the separate proxy records of past climate change have so far hampered efforts to distinguish more clearly the climatic and human influences on vegetation history in this region (e.g., Marchant and Taylor, 1998;Taylor et al, 1999;Ssemmanda et al, 2005;Russell et al, 2009;Ryves et al, 2011). As a result, it remains difficult to estimate the magnitude of climatic moisture-balance variation responsible for a certain vegetation change inferred from fossil pollen, and to translate pollen assemblage changes into reconstructions of past vegetation change across the landscape.…”

Palaeo-seasonality of the last two millennia reconstructed from the oxygen isotope composition of carbonates and diatom silica from Nar Gölü, central Turkey

“…While C. meneghiniana has a high conductivity optimum in the European diatom database (6600 mS cm À1 ; Juggins, 2012), it tolerates a wide range of alkalinity (Gasse, 1986), with a conductivity optimum of 912 mS cm À1 and a tolerance of 218e4168 mS cm À1 in a Ugandan crater lake training set (Mills and Ryves, 2012) and an optimum of 2000 mS cm À1 in the Turkish training set (Reed et al, 2012). In the Ugandan lakes, nutrient input, not salinity, is seen as the most important driver of changes in the abundance of this species (Ryves et al, 2011;Mills and Ryves, 2012). With species such as C. meneghiniana, the importance of salinity relative to nutrients can be difficult to unravel (Fritz et al, 2010).…”

The development of iron technology in precolonial western Uganda

“…A further significant development was the undertaking of extensive, systematic surveys (in Bwera, Rakai, Mubende, Kibale, Mwenge and Hoima) to examine site location and settlement patterns (Reid 1990(Reid , 1991Robertshaw 1991bRobertshaw , 1994Connah 1996;MacLean 1996), bolstering the shift away from a focus on large sites towards a more regional perspective. Critical examinations of oral histories and oral traditions (Buchanan 1974;Tantala 1989), historical linguistics (Schoenbrun 1993a(Schoenbrun , 1993b(Schoenbrun , 1998, ethnoarchaeology (Childs 1998a(Childs , 1998b(Childs , 1999(Childs , 2000, anthropology and environmental research * historical, palaeoclimatic and palaeoecological * Marchant 1994/1995;Jolly et al 1997;Doyle 1998;Marchant and Taylor 1998;Lejju et al 2003;Ssemmanda et al 2005;Lejju 2009;Ryves et al 2011) also grew in range and scope during this time. Ultimately, however, archaeological research has remained comparatively scant and sparsely situated across this expansive and socially complex landscape, making the construction of a fluent social history of iron no simple task.…”

“…Palaeoenvironmental evidence indicates that western Uganda was mostly wet and forested before AD 1000 (Ssemmanda et al 2005;Ryves et al 2011), with a decline in forest vegetation during the period AD 1000Á1200 coinciding (counter intuitively) with a time of high rainfall, a strong suggestion of humaninduced forest clearance (Lejju 2009). Palaeoenvironmental evidence indicates that western Uganda was mostly wet and forested before AD 1000 (Ssemmanda et al 2005;Ryves et al 2011), with a decline in forest vegetation during the period AD 1000Á1200 coinciding (counter intuitively) with a time of high rainfall, a strong suggestion of humaninduced forest clearance (Lejju 2009).…”

“…This drier phase of the region's history saw a decline in nucleated settlements and large, sedentary populations reflected in regrowth of semi-deciduous and swamp forest across many areas as well as expanding grasslands Taylor et al 2000;Ssemmanda et al 2005;Ryves et al 2011). Incursions by incoming northern agropastoralists secured and consolidated power, and society became more stratified.…”