Wienhues, Giulia; Lami, Andrea; Bernasconi, Stefano; Jaggi, Madalina; Morlock, Marina A.; Vogel, Hendrik; Cohen, Andrew S.; Courtney Mustaphi, Colin J.; Heiri, Oliver; King, Leighton; Kishe, Mary A.; Misra, Pavani; Muschick, Moritz; Ngoepe, Nare; Matthews, Blake; Seehausen, Ole; Temoltzin-Loranca, Yunuen; Tinner, Willy; Grosjean, Martin (2024). Latest Pleistocene and Holocene primary producer communities and hydroclimate in Lake Victoria, eastern Africa. Quaternary science reviews, 330(108599) Elsevier 10.1016/j.quascirev.2024.108599
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The Lake Victoria ecosystem is emblematic of the catastrophic effects that human activities, particularly cultural
eutrophication, can have on freshwater biodiversity. However, little is known about the long-term spatial and
temporal pattern of aquatic primary paleo-production (PPaq) and producer communities in Lake Victoria and
how these patterns relate to past climate variability, landscape evolution, lake hydrology, mixing regimes,
nutrient cycling, and biodiversity dynamics in the past 17 kyr. We use sediments from four well-dated cores
along a transect from offshore to nearshore sites, and exploit XRF element scanning and hyperspectral imaging
data, TC, TN, bSi, δ13C and δ15N, and sedimentary pigments to investigate paleolimnological variability and
change. Our findings demonstrate that changes in PPaq and algal communities during the past 17 kyr were closely
related to hydroclimatic changes, lake mixing, and nutrient availability. During the wetland phase (16.7–14.5 cal
ka BP), PPaq levels remained generally low, while chromophytes and chlorophytes dominated the algal community.
Following the rapid lake level rise (~14.2 cal ka BP) during the early African Humid Period (AHP), PPaq
levels steadily increased, accompanied by a shift towards cyanobacteria and chromophytes. During the Holocene,
our results suggest repeated short-lived arid intervals (~10.5, ~9, 7.8–7.2, ~4, and 3.2–3.0 cal ka BP) and two
distinct periods of enhanced lake mixing associated with high PPaq and high diatom productivity: the first one
between 11 and 9 cal ka BP, which coincided with the maximum of the AHP (high precipitation, high wind,
enhanced mixing), and the second, less pronounced one, between 7 and 4 cal ka BP. Between these two periods
(i.e. 9–7 cal ka BP) we observe reduced diatom productivity, relatively low PPaq, and high C/N ratios, suggesting
conditions with more stable lake stratification, likely associated with reduced wind strength, and some nutrient
limitation (N and P). Finally, the drier conditions around the end of the AHP (ca. 4 cal ka BP) and during the late
Holocene were associated with decreasing lake mixing and increasing dominance of cyanobacteria. Given our
reconstruction of PPaq over the past 17 kyr, we conclude that the levels in the 20th century are unprecedentedly
high, consistent with the massive human-mediated impact on the Lake Victoria ecosystem including biodiversity
loss.
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