Sedimentary sequences in western Uganda as records

Sedimentary sequences in western Uganda as records of human environmental impacts Taylor, D. 1, 2 and Robertshaw, P.3 1

Department of Geography

2

From January 1 2001:

National University of Singapore

Department of Geography

10 Kent Ridge Crescent

Trinity College

Singapore 119260

University of Dublin

Email: [email protected]

Ireland

3

Department of Anthropology

California State University 5500 University Parkway San Bernardino, CA 92407-2397 USA Key words: charcoal; climate change; equatorial Africa; deforestation; human impact; pollen Accepted: Palaeoecology of Africa & Surrounding Islands (Balkema, Rotterdam), June 2000

ABSTRACT Relatively few sediment-based studies in equatorial Africa have as their focus improved understanding of the history of human-environment interrelationships. Instead their emphasis has tended to be reconstructions of past climate or vegetation, or in some cases both. A review of this previously published work for western Uganda reveals evidence for forest clearance and changes in soil conditions that can be attributed to human activity. Human-induced signals remain strong in periods of concomitant climate change. A holistic view of environmental change results from a combination of this evidence with palaeoclimatic and archaeological information from independent sources and leads to the conclusion that environmental factors contributed to some changes in human activity.

None of the sediment records

described in this paper were originally collected as part of archaeological studies and the sediments may include as yet uncovered evidence of human-environment interrelationships. There is a need for sediment-based studies that are closely tied to archaeological research, and for the development and incorporation within these of a much wider range of models and proxies of human-environment interrelationships than is presently the case. INTRODUCTION Establishing the level of human impact on the environment and nature of related feedbacks and hystereses are currently among the most pressing scientific questions. Answers to these form a basis for anticipating the nature of future environmental conditions following changes in human populations and are mainly sought through observations and simulations of very recent to contemporary environmental changes. To this end, technologies such as remote sensing and computer modelling have proved extremely useful. Such technologies have their limitations as anticipatory tools, however, as human-environment relationships rarely follow linear, deterministic trajectories. Rather, the response of people to environmental vicissitudes is highly variable and depends partly upon socio-economic conditions, while relatively minor changes in environmental processes and conditions, including those influenced by humans, can have catastrophic outcomes. One issue that has yet to be resolved fully is the separation of those environmental changes that are principally anthropogenic from those that are not. For example, the

extent to which today’s apparently exceptionally high levels of atmospheric CO2 are anthropogenic remains a subject of debate (compare, for example, the opinions of Hulme et al (1999) with those of Calder (1999)). Attempts to identify the level of contribution from one forcing mechanism (causal agent) are problematic when its impact is closely entwined with the affects of other processes. In some cases, such as hill-slopes under increased precipitation or coastlines subjected to raised sea levels, human activity may act to enhance or moderate environmental processes that have an initial, natural cause. In other cases, switches from one form of human activity to another, such as the ways in which food is produced, could be facilitated or even caused by natural environmental change. Reflecting on past environmental changes over time-scales of the last hundreds and thousands of years can provide a depth of view that is unavailable from satellite data, as well as a means of verifying the functioning of computer models. Retrospection can also provide a guide to the ways in which the agents of environmental change and the changes themselves might be linked.

The construction and application of

environmental histories is not straight forward, however. One problem is that the evidence is often partial and poorly resolved. For example, anticipating how biota in a particular region of the tropics might respond to habitat loss in the future, based on the available palaeoecological data, is difficult. Although studies of plant fossils indicate that around the peak of the last ice age rain forests in Africa were less extensive than they are today, the actual degree of isolation is unknown and probably unknowable. The actual degree for rain forest animals, for instance, is a function of their abilities to traverse intervening areas of non-rain forest habitat and, having done so, to establish breeding populations in their new location. Isolation now, as in the past, is therefore determined by factors such as the presence of inter-connecting, rain forest ‘corridors’ (perhaps in the form of gallery forest), the level of activity of humans and other predators, the incidence of disease etc, that are generally indeterminable in palaeoecological records.

A second problem can arise when

environmental changes are viewed in chronological sequence as this can suggest post hoc cause-effect relationships.

It is worth stressing that the identification of

chronological order in environmental histories is not the same as the determination of causal links.

One potential source of information for past environmental conditions is lake and swamp sediments.

Sedimentary basins are sumps for a range of environmental

records, including chronologies of vegetation history and human impacts. The use of sediments as proxy records of human history is commonly based upon a model of environmental impacts that assumes major changes in human activity, such as the introduction or intensification of agriculture, will alter catchment conditions and therefore the quantity and quality of material accumulating in sedimentary basins. The general problem of distinguishing and separating the impacts of changes in human activity from those of other causal agents remains, however. Thus, clearance of rain forest by humans and its replacement by grassland and scrub vegetation may have an effect on sub-fossil pollen assemblages – a component of many sedimentary records that is similar to that of increased aridity. This paper reviews previously published, sedimentological evidence for human activity in one part of the interlacustrine region of equatorial Africa, western Uganda, over the last 3000 years (the late Holocene).

None of the studies reviewed

specifically focused upon human-environment interrelationships. Indeed all are based on sites that are some distance from major archaeological excavations. The following section describes in brief some of the problems of determining signals of human impact in sedimentary records from the region.

Subsequent sections detail the

sequences of sediment and independently derived, archaeological and palaeoclimate records. The paper concludes by highlighting the relevance of sedimentary evidence to understanding human-environment interactions in equatorial Africa. ANTHROPOGENIC ACTIVITY FROM SEDIMENTARY EFFECTS Although it seems reasonable to assume that sedimentary basins will record human impacts, there are cases where the identification of a human-induced effect is difficult if not impossible. One such case comes from the Nigerian Sahel where, despite archaeological finds indicating that pastoralists have settled the semi-arid Manga grasslands for much of the last 4000 years, analyses of numerous sedimentary records revealed no evidence of their presence (Salzmann and Waller, 1998). There are a number of reasons for unexpectedly weak or non-existent signals of human activity in sedimentary records. For example, human-induced alterations in

some vegetation types, such as the semi-arid Manga grasslands, may simply remain hidden in sedimentary records, because those vegetation types are generally insensitive to the orthodox model of human impacts. Alternatively, it could be that the relevant part of the sediment column is missing, either because of non-deposition or post-depositional erosion.

Breaks, or hiati, in sedimentation are common to

sedimentary basins in the interlacustrine region, particularly for the early and mid Holocene periods.

For example, Lake Albert (Beuning et al., 1997), Mubwindi

Swamp (Marchant et al., 1997) and Kabata Swamp (Taylor et al., 1999) – all in western Uganda – have failed to yield sediments dating to most of the early and middle Holocene.

Kashiru Swamp (Burundi, Bonnefille and Riollett, 1988) and

Muchoya Swamp (Taylor, 1990) appear to lack an early Holocene record, whereas Kamiranzovu Swamp, Rwanda, lacks entirely sediments of Holocene age (Hamilton, 1982).

Lake Simbi, located in savanna to the east of Lake Victoria, may lack

sediments that are younger than around BC 500 (Mworia-Maitima, 1997). Even sites where Holocene sequences appear virtually intact (such as Ahakagyezi, Uganda and Kuruyange, Burundi), sedimentation rates during the early and middle part of the period are low. Only sediments from Pilkington Bay, Lake Victoria (Kendall, 1969) and Rusaka Swamp, Burundi (Bonnefille et al., 1996), appear to buck this trend by showing a virtually constant, high sedimentation rate. It could be that climate was responsible for slower rates of, or hiati in, sediment accumulation. However, one would expect that the relatively wet conditions associated with the early and mid Holocene periods promoted peat growth, as seems to have been the case during the same period in tropical Southeast Asia (Rieley et al., 1994), and lake productivity, rather than the reverse. Another possible reason for weak of absent signals is that only a relatively narrow range of human activities is presently determinable form sediment sequences. This is particularly relevant to a discussion of studies that have generally lacked a human focus but which have been carried out in a part of the world where humans have probably long been present. It stems ultimately from a worldview that sees human activity as ecologically disruptive, intrusive and negative. For example, it is usually assumed that the onset of food production is, in the absence of direct indicators such as pollen from domesticated plants, marked in sediment records by evidence of forest clearance and burning. This assumption appears to ignore the growing evidence from

other African sources for a history of, for example, shifting cultivators utilising natural forest gaps and the promotion of forest by certain forms of agriculture, such as low intensity cultivation of oil palm (Elaeis guineensis) (Fairhead and Leach, 1998). Thus sediment records may only, as currently constructed, actually document the occurrence of relatively intensive and permanent forms for human impact and land uses that, in general, come late in the history of food production in Africa. As yet under-utilised components of sediments that show some potential as proxies of human activities, in particular farming, are macrofossils, such as seeds, and phytoliths (silica bodies that are produced by many plants, including grasses). These forms of evidence are not so dependent upon the orthodox model of human impacts, but do require skills that are presently lacked by most tropical palaeoecologists.

For

example, the successful use of phytoliths depends upon first establishing diagnostic types for key indicator species, and second recognising analogues of sub-fossil phytolith assemblages among modern plant communities. Analyses of phytoliths have recently been carried out on sediments from equatorial African lakes Simbi and Victoria (Mworia-Maitima, 1997; Stager and Johnson, 2000) with some success, although the temporal scope of these studies lies largely outside the focus of this paper. Farther afield, the use of phytoliths in sediments from the Sahelian region of Senegal has allowed the reconstruction of forest-savanna woodland dynamics (Alexandre et al., 1997). SEDIMENTARY

EVIDENCE

FOR

LATE

HOLOCENE

HUMAN

ENVIRONMENTAL IMPACTS Figure (1) provides a summary of variations in sediments collected from four sites in western Uganda. These are presently peat forming mires, although evidence exists in the sediments of two (Muchoya and Kabata) that suggests that they were formerly lakes. Sediments from a fifth location, Pilkington Bay, Lake Victoria, are also shown in the figure. Although Pilkington Bay is not strictly part of western Uganda, the latter does form part of the catchment for Lake Victoria. The five locations were chosen on the basis of the level of dating control and resolution of the sedimentary evidence yielded. Figure (2) indicates the locations of the sites within Uganda and of other places mentioned in the text.

Variables along the ‘X’ axis of Figure (1) were selected from among the data published because they are believed to be indirect proxies of human activity, although none are unequivocally linked to the presence of humans. In the orthodox model of human impact, disturbance of vegetation and soils is expected to lead to increases in the amount of inorganic material delivered to sedimentary basins (and therefore a reduced proportion of organic matter in sediment cores) and to increased rates of sedimentation.

Fire is one tool of disturbance; a direct relationship is assumed

between the frequency of fire and the abundance of sedimentary charcoal. Changes in pollen from taxa associated with primary (e.g. Olea) and secondary (e.g. Celtis and Trema) forest, degraded soils (e.g. Dodonaea) and open vegetation (e.g. Vernonia and Poaceae) may also indicate disturbance of vegetation by humans and the development of more permanent forms of land use. Pilkington Bay is located in the northern part of Lake Victoria (1130 m above sea level, 0° 18’ N 33° 20’ E) to the south of the present outlet to the White Nile at Jinja. The deepest part of what is a near-landlocked bay is 20 m. A mixture of savanna and cultivated fields, with some remnants of swamp and medium altitude, moist semideciduous forest, is found over extensive areas in the northern part of the Lake Victoria catchment. Kendall (1969) analysed sediments in three cores (P-2, 64-4 and Entebbe-B). Laboratory work focused on the c. 18 m-long core P-2, for which 28 radiocarbon dates were obtained (seven of these relate to the last 3000 years, although one was regarded as ‘invalid’). Kabata Swamp (1370 m above sea level, 0° 291’ N 30° 162’ E) is a small, in-filled volcanic crater with a very limited catchment, set within an area of settled agricultural land (Taylor et al., 1999). The walls of the crater rise to some 100 m above the surface of the swamp and are under cultivation (mainly maize and bananas). An extensive tract of medium altitude, moist semi-deciduous forest (Kibale Forest) lies less than 5 km from the swamp, within which are patches of elephant grass thicket. A 5.97 m long core of sediment, core Ka, extending down to the rock base of the crater, was collected from the centre of the swamp.

Six

radiocarbon dates (five AMS) have been acquired for core Ka, four of which relate to the last 3000 years.

The remaining three sites considered here are all swamps and located in the Rukiga Highlands of southwestern Uganda. Cultivated land has replaced moist montane forest over much of the Rukiga Highlands. Ahakagyezi Swamp (1830 m above sea level, 1° 5’ S 30° 162’ E), described in Taylor (1993), is part of a much larger mire and is set within a mosaic of intensively cultivated fields, planted wood-lots and regenerating scrub. Over the last 15 years, the swamp has been drained and much of its surface converted to pasture. Core Ah2 extends to over 22.84 m. A total of 13 radiocarbon dates was obtained for the core, three of which relate to the last c. 3000 years. Mubwindi Swamp (2100 m above sea level, 1° 5’ S 29° 45’ E) is set within the southern part of Bwindi (Impenetrable) Forest, which occupies land to an altitude of 2450 m above sea level. Bwindi Forest is classed as moist montane forest. More than 20 cores of sediment have been extracted from Mubwindi Swamp (Marchant et al., 1997). Core Mb6, discussed here, is 8.84 m long. Nine radiocarbon dates are available for this core; four of these (all AMS) relate to the period of interest. Muchoya Swamp (2260 m above sea level, 1° 17’ S 29° 48’ E) is the highest altitude site considered here and is close to the maximum altitude for permanent agriculture in the region today. The swamp is set within Echuya Forest, which contains a mix of broad-leaved moist montane forest and bamboo taxa.

Sediments from Muchoya

Swamp are described in Taylor (1990). The 20.54 m-long core Mc2, referred to here, is one of four cores collected the site. It is the best dated; 18 radiocarbon dates are available for core Mc2, three of which relate to the last c. 3000 years. All sites chosen show variations in sediments throughout the late Holocene. Sedimentary sequences from Muchoya and Kabata swamps and from northern Lake Victoria appear to show the earliest, most obvious evidence of major catchment disturbance, in the form of increases in pollen from taxa that are presently associated with regenerating forest and degraded soils. This phase of disturbance, dated to the first millennium BC, is most visible in sediments from Muchoya Swamp. Much more striking in all five sequences is evidence, including increased charcoal, of significant disturbance that dates to around AD 1000. A further phase of major forest clearance is visible in pollen and spores from Kabata Swamp and northern Lake Victoria and is dated at Kabata Swamp with a radiocarbon date of 400 ± 60 yr. BP (AD 1441-1627). This disturbance was preceded by a period of burning, the onset of which is also dated

with a radiocarbon date (550 ± 45 BP, AD 1330-1429).

Evidence of forest

regeneration, in the form of pollen from plants presently associated with regenerating forest in the region, is dated around AD 1250 at Muchoya Swamp and younger than 400 ± 50 BP (AD 1443-1621) at Kabata Swamp. Recovery of forests around Kabata Swamp may have been restricted to particular habitats or soil types, because there is evidence for a concomitant increase in the extent of grassland (possibly elephant grass thicket). A very recent phase of forest disturbance is apparent around Mubwindi from around 200 years ago. PALAEOCLIMATE AND ARCHAEOLOGICAL EVIDENCE Assessing variations in sediment in the context of reconstructions drawn from independent sources of palaeoclimate and archaeological evidence has the potential to provide a holistic view of environmental change. Several lake basins with parts of their catchments in western Uganda have yielded evidence of major variations in rainfall over the last three millennia (Johnson et al., 1991; Cassanova and HillaireMarcell, 1992; Nicholson, 1996; 1998; Cohen et al., 1997; Stager et al., 1997; Rickets and Anderson, 1998; Johnston et al., 2000; Stager and Johnston, 2000) in the form of the remains of aquatic organisms, such as diatoms and gastropods, written accounts, strand lines and stable isotopes. A second proxy of rainfall variations is the record of fluctuations in Nile River levels, particularly flood minima, from the Rodah Nilometer, Cairo. These records are more or less complete for the period beginning AD 622. Flood minima are most relevant to this discussion because they relate to the volume of water supplied by tributaries of the White Nile during the main wet season of the interlacustrine region.

A combination of linguistic, archaeological and

historical evidence forms the basis of reconstructions of human activity in western Uganda over the period of interest. Linguistic studies have provided evidence of the earliest farmers, who appeared to have herded cattle and grew grain in the centuries before BC 500, particularly sorghum. Their neighbours, settled between the Rwenzori Mountains and northern Rwanda, were speakers of proto-interlacustrine Bantu, who planted root crops in the forest margins and supplemented their diet with fish and game (Schoenbrun, 1993a). Some or all of these communities began to forge iron from around BC 500

(Schoenbrun, 1993a). Distinctive Early Iron Age pottery, assigned to the Urewe tradition (Soper, 1971), has been found throughout the interlacustrine region, often in association with iron-smelting furnaces. The sites are generally located in areas of cultivation and abundant rainfall, as in Rwanda and Burundi, and along the western shores of Lake Victoria, indicating the importance of rain-fed agriculture (MacLean, 1996). There are few Early Iron Age sites known from western Uganda where archaeological surveys have been carried out. By comparison, the Later Iron Age is more conspicuous in archaeological records, its onset being marked by a change in pottery decoration, notably the widespread use of fibre roulettes. The onset of the Later Iron Age is dated elsewhere in the interlacustrine region to around the eighth or ninth century AD (Van Grunderbeek et al., 1983; Van Noten, 1983: 35; Desmedt, 1991; Robertshaw, 1997: 17) and is associated with a plethora of social, political and economic changes (Robertshaw, 1987). Climate appears to have become more arid during the first millennium BC, on the basis of evidence preserved in sediments from northwest Lake Victoria (Stager et al., 1997). This increased aridity may have driven the uptake of new technologies and an expansion of cultivation by Bantu-speaking farmers (Schwartz, 1992). According to Nile River records, however, a return to relatively humid conditions occurred early in the second millennium AD (Nicholson, 1996; 1998). A transition to more humid climates may have coincided with the beginning of the Later Iron Age in western Uganda. Archaeological surveys in western Uganda indicate a movement of pastoral people into the grasslands south of the Katonga River early in the second millennium AD (Reid, 1991). Increased humidity at this time may have been associated with the Little Climatic Optimum of more temperate regions. There is also evidence for an expansion of religious and political offices (Schoenbrun, 1993b: 55) and the development, beginning in the eleventh century, of what seems to be a major settlement at Ntusi (Lanning, 1970; Reid, 1991; Reid and Meredith, 1993; Sutton, 1993: 52-57).

A mixed pastoral and agricultural economy is indicated by the

abundant cattle bones and grindstones, and by the recovery of carbonised seeds of sorghum.

Increased population densities in the early centuries of the second

millennium AD are also evident from archaeological surveys in the wetter and more forested landscapes to the north of the Katonga River (Robertshaw, 1994).

A prolonged period of increased aridity is evident from the late AD 1300s to the late AD 1700s in records of variations in levels of Nile River and lakes Tanganyika and Victoria (Nicholson, 1996; 1998; Cohen et al., 1997; Stager et al., 1997). This period was interrupted by a relatively humid spell, from the late AD 1400s to the late AD 1500s (Nicholson 1996; 1998). A return to drier climate conditions from the late AD 1500s appears to correlate with the onset of the Little Ice Age of higher latitudes. The prolonged period of increased aridity appears to coincide with the decline of Ntusi, while the relatively brief, humid interlude coincides with the emergence of large polities to the north of the Katonga River. These were centred upon settlements that were characterised by systems of earthen ditches (earthworks), sometimes extending over several kilometres. Bigo, Munsa and Kibengo are the largest of these settlements that have so far been uncovered (Robertshaw et al., 1997). Abandonment of the earthworks, during the subsequent dry phase and probably around the end of the 1600s AD, appears to have coincided with a further shift in settlement pattern, from nucleated permanent settlements to dispersed, peripatetic homesteads (Robertshaw, 1994). DISCUSSION Two obvious variations in the sedimentary sequences from western Uganda fall within the first millennium BC and the first few centuries of the second millennium AD. They appear to represent two phases of major disturbance of forest. The later signal is more widespread and includes charcoal peaks, as a possible indicator of increased burning of vegetation, and pollen from taxa associated with open vegetation types and degraded soils. Sediments from Lake Victoria and Kabata Swamp appear to show a third phase of forest disturbance, around AD 1500.

Sediments from

Mubwindi Swamp have provided evidence of a fourth and most recent phase of disturbance, dated to the last 200 years. Changes in sediment dated to the first millennium BC could represent the introduction of iron working and agriculture in western Uganda. Higher altitude sites, such as the catchment for Muchoya Swamp, may have been favoured for reasons such as a lower incidence of disease. Alternatively they may have offered land that was ‘vacant’ because it was regarded as being less suitable for existing land uses, such as the keeping of cattle.

Widespread changes around the beginning of the second

millennium AD correlate with technological and settlement changes associated with the onset of the Later Iron Age. However, the changes are also associated with the onset of more humid climates and this transition may have had an impact on populations, although increased levels of rainfall are unlikely to have caused the changes in pollen and charcoal described. For example, reduced aridity may have prompted major movements of people and an expansion of the area settled. Thus population increase, changes in the incidence of diseases or the attractiveness of particular habitats, or some combination of these factors could have led to human environmental impacts becoming more widespread and intense. Sedimentary evidence that appears to demonstrate an intensification of forest disturbance in the catchment for Kabata Swamp around AD 1500 correlates with the onset of a phase of relatively dry climates. This transformation of vegetation was preceded by a period of increased burning that commenced during an earlier dry phase, around AD 1400. The intensification of forest clearance appears to support the notion that the nodes of power in western Uganda underwent a shift to wetter and more forested parts during the early centuries of the second millennium AD. This shift may have been prompted by a reduced productivity of pasture in drier parts of western Uganda, brought about by reduced humidity. Increased aridity may also have facilitated the clearance of forest by fire. The decline of permanent settlements around the end of the AD 1600s could have been a response to difficulties in ensuring sufficient supplies of food to a large, settled population and may mark the emergence of the pre-colonial kingdoms described by the first European visitors to the region.

The most recent changes in forest

composition apparent in sedimentary records, dated at Mubwindi Swamp to the last 200 years, may represent exploitation during the early colonial period, or the impact of political instability just prior to the imposition of colonial control. Forest around Mubwindi Swamp was selectively logged up to the early 1990s. This logging was particularly intensive during the early part of the present century, when timber (e.g. Podocarpus for the stocks of rifles) was required to support the war in Europe. Relatively little emphasis has to date been placed on sedimentary sequences as proxies of human impact. Instead, where sediments have been studied in detail, the

focus of study has tended to be reconstructions of long (i.e. glacial-interglacial) climate and vegetation histories. This is perhaps surprising, given the poor coverage in the region of sediments dating to the early and mid Holocene periods. It is also unfortunate, as sediments have the potential to provide a link between spatially and temporally disparate archaeological finds, as well to contribute to our understanding of the nature of human–environment interrelationships. Even if humans had been a focus, it is highly likely that interpretations would have been compromised by the form of analyses employed, as these are presently oriented towards the detection of certain – although by no means all – forms of human activity.

Archaeologists

working in equatorial Africa have been slow to embrace lake and swamp sedimentbased studies (Schoenbrun, 1991).

Future studies of the history of human-

environment interrelationships will benefit greatly from an increased involvement of archaeologists, as well as from the development and application of new models of anthropogenic activity and new analytical techniques. ACKNOWELEDGEMENTS The authors would like to thank the Royal Society, National Science Foundation (SBR-9320392), British Institute in East Africa, National Geographic Society, Uganda Council for Science and Technology, Uganda Department of Antiquities and the departments of Botany and History at Makerere University, Kampala. We would also like to acknowledge the assistance of numerous colleagues, notably Robert Marchant, Ephraim Kamuhangire, Andrew Reid and Ruth Young. REFERENCES Alexandre, A., Meunier, J.D., Lezine, A.M., Vincens, A. and Schwartz, D. 1997. Phytoliths: indicators of grassland dynamics during the late Holocene in intertropical Africa.

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Figure captions Figure 1:

Summary of sediment-based proxies of human environmental impacts from sites in western Uganda (see Figure 2 for locations and text for an explanation of the different proxies). Arrows (!) denote major phases of ecologically disruptive human impact.

Figure 2:

Map of western Uganda, showing the locations of sites mentioned in the text (stars = location of sedimentary evidence, dots = archaeological sites).

Figure 1

32

N

Nile River 2

2

A F R I C A

Kibiro Ri

ve

r

N

Ka

fu

LAKE ALBERT

0

LAKE KYOGA

2000km

Munsa

er

Ri ve r

Riv

Kasunga

Mubende Hill

i

Kabata Swamp

Se m lik

r

ziz i

Rive

Mu

Nile

Kibengo DEMOCRATIC REPUBLIC OF THE CONGO

KAMPALA

Pilkington Bay

Katonga River

Bigo Ntusi

0

0

U G A N D A LAKE

LAKE EDWARD

Mubwindi Swamp Ahakagyezi Swamp

30

Legend Archaeological sites Palaeoenvironmental sites

T A N Z A N I A 0

RWANDA

32

Figure 2

20

VICTORIA

50

100km