Unger, Lilian Eva; (2023) Using palaeolimnology to inform lake restoration in Madagascar. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Madagascar is a biodiversity hotspot with many endemic species, including the Madagascar Pochard. Once present at Lake Alaotra, this species was feared extinct by the 1990s. It was rediscovered at Lake Matsaborimena in 2006, where it probably persisted due to its isolation. After a captive breeding programme, ducks were released onto Lake Sofia in 2018, chosen because of its extensive papyrus marsh, the pochard’s nesting habitat. However, the lake is somewhat degraded and levels of macroinvertebrates, the pochard’s food source, are low, so it is being restored by the Wildfowl and Wetlands Trust. It is crucial to understand the current and historical physical, chemical, and biological features of these three lakes to inform their management for the pochard. This was achieved by conducting surveys and installing sediment traps at Lakes Matsaborimena and Sofia, as well as extracting sediment cores from all three sites to be dated and analysed for multiple biological and chemical indicators. In Lake Matsaborimena a pulse of the erosional indicators ca. 1470 AD corresponds with a diatom indicated switch to a turbid state. The lake takes 400 years to recover. In Lake Sofia a similar shift occurs after increasing erosional inputs ca. 1830 AD, indicated by a loss of macrophyte, and associated macroinvertebrate remains. Here erosion remains high, and the lake does not recover. It is hypothesised that the source of erosion at these sites is increasing human activity. There are high erosional inputs to Lake Alaotra prior to human arrival, this is likely due to a corresponding period of limited papyrus marsh. The key implication for lake restoration is that erosional inputs must be reduced, either through land use management or papyrus marsh restoration, for ecological recovery. This will boost the pochard’s food source at Lake Sofia to ensure the population’s long-term survival.

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