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Late Holocene palaeoenvironmental reconstruction from Mpumalanga Province (South Africa) inferred from geochemical and biogenic proxies

Sjöström, Jenny, Norström, Elin, Risberg, Jan, Schoeman, Maria H.
Review of palaeobotany and palynology 2017 v.246 pp. 264-277
Bacillariophyceae, C4 plants, Holocene epoch, carbon, ecosystems, food production, grasses, grasslands, gravel, hills, mesic conditions, nitrogen content, paleoecology, peat, people, population growth, South Africa
Here we present a palaecological reconstruction covering the last 1700yr from Lydenburg fen, located in the north-eastern grassland biome, Mpumalange, South Africa. A 300cm peat sequence was analysed for biogenic (grass phytoliths, diatoms) and geochemical proxies (δ¹³C, δ¹⁵N, carbon/nitrogen content) to infer past grassland dynamics and hydro-climatic changes. The Lydenburg record reports a C4 dominated grassland throughout the studied period, with more or less pronounced fluxes between C4-Chloridoideae and C4-Panicoideae grass subfamilies. The record reflects moderate to dry conditions from AD 400 to 1000; more mesic conditions until around AD 1250; followed by a significantly drier period between c. AD 1250 and c. AD 1350, when Chloridoideae grasses expand at the expense of Panicoideae grasses. During this phase, the δ¹³C-record reports more enriched values indicating higher influx of C4 grasses. Furthermore, lithological evidence indicates highly erosive conditions, with significant gravel input from the surrounding hills. After AD 1350, proxy indications suggest a shift towards more mesic conditions. During this increasingly mesic but also unstable period, farming communities using specialized agricultural practices (e.g. the people in Bokoni) expanded their settlements into new regions (Delius et al., 2008). This expansion was also coupled to population growth, suggesting these communities applied techniques that enabled improved food production under environmentally challenging conditions. Over the last century, Lydenburg δ¹³C-values indicate increased input of C3 taxa. The phytolith record shows that this increase is not coupled to an increase in Pooideae (C3) grasses, suggesting that the C3 input may be related to woody encroachment.