Sedimentation and recent history of a freshwater wetland in a semi‐arid environment: Loboi Swamp, Kenya, East Africa

Abstract

Loboi Swamp is a 1·5 km2 freshwater wetland situated near the equator in the Kenya Rift Valley. The climate is semi‐arid: precipitation is ≈ 700 mm year−1, and evapotranspiration is ≈ 2500 mm year−1. Some of the wetland water is currently used for irrigation. An interdisciplinary study was conducted on the geology, hydrology, pedology and biology of the wetland to determine its origin and history and to assess its longevity under present hydrological conditions. Sedimentary records from two piston cores (1·8 and 4 m long) indicate that the present wetland developed during the late Holocene on a low‐relief alluvial plain. Floodplain deposits (sandy silts) are capped with wetland sediments (organic‐rich clay and peat), which began to form at ≈ 700 BP. The swamp is dominated by Typha domingensis Pers. (≈ 80%) and floating Cyperus papyrus L. (20%). It is fed by warm springs (T ≈ 35 °C; pH ≈ 6·4–6·9) emanating from grid faults of the rift floor. Water compositions suggest that sources are dominated by shallow meteoric water, with little contribution from deeper geothermal fluids. Siderite concretions in the floodplain silts reflect the Fe‐reducing conditions that developed as the surface became submerged beneath the water table. The pollen record captured both local and more regional vegetation, showing the prevailing dry rift valley climate despite development of the wetter conditions on the valley floor. The diatom record also suggests a dramatic change in local hydrology. The combined biological records of this semi‐arid wetland indicate an abrupt change to wetter conditions, most probably as a result of a regional change in climate. Rift tectonics provided accommodation space, maintained the wetland at or below the water table and enabled spring recharge. The size of the modern wetland has been reduced by about 60% since 1969, which suggests that the system may now be under hydrological stress due to anthropogenic impacts from land‐use change.

Morphological variations of wild populations of Nile tilapia (Oreochromis niloticus) living in extreme environmental conditions in the Kenyan Rift-Valley

“…) and has a higher pH (7.4-8.3) (Ashley et al 2004). Comparatively, Crocodile Lake is a crater formed island lake within the Lake Turkana.…”

“…) and slight acidity pH (6.4-6.9) (Ashley et al 2004). The springs drain into Loboi swamp of about 1.5 km 2 , which is covered by dense vegetation of Typha domingensis and Cyperus papyrus.…”

Sedimentological and Paleoecological Research Techniques, with Applications to the Environmental History of Loboi Swamp, Kenya

“…The cores were retrieved with a rod-operated single-drive piston corer (Wright, 1980) operated from the mud surface. The core site was selected with proximity to Ashley's et al, [14] previous core site as main reference (Figure 1), however better accessibility aided by reduced water levels within the wetland made it possible to access part of the deepest area on the western side of the wetland. The longest core section, LOB14-1P I, measured 101.8 cm and reached almost to the base of the swamp deposit.…”

“…The swamp is fed by water from three main surface springs: Lake Bogoria spa spring, Chelaba spring and Turtle spring. Due to the consistent seepage and flow of the springs, it is suggested that local aquatic ecosystems may have persisted even during past episodes of severe climatic aridity when Lake Baringo and other Rift lakes stood completely dry [14]. Loboi Swamp serves an important role of habitat provision for a wide range of biodiversity.…”

Dynamic response of desert wetlands to abrupt climate change

“…GWD deposits are preserved globally in the geologic record, contain information on the timing and magnitude of past changes in water table levels, and are a source of paleohydrologic and paleoclimatic information (4)(5)(6)(7)(8)(9)(10). Previous studies have shown that desert wetlands in the southwestern United States responded to climate change at glacial to interglacial timescales (e.g., refs.…”