Late-Holocene palaeolimnological and climate dynamics at Princessvlei, South Africa: Evidence from diatoms

The 'Cape Flats' region, situated in the winter rainfall zone of South Africa, is a low-lying tombolo underlain by recent fluvial and aeolian sands and characterised by numerous small lakes and wetlands. One of these is Princessvlei, a eutrophic, freshwater coastal lake. The lake lies in an inter-dunal depression encroached on in the more recent past by high-density residential, industrial and agricultural land uses. A 210-cm core extracted from the lake periphery yielded high diatom fossil concentrations for the upper 174 cm. Princessvlei appears to oscillate between two ecologically stable states, namely, a state characterised by clear water, oligotrophic, benthic communities and a turbid state dominated by eutrophic, planktonic species. The two stable ecological states are interpreted to be a function of the relative dominance of catchment precipitation or groundwater influx which augments the open water conditions. From 2600 to 1500 cal. BP (173-135 cm), the system is predominantly turbid with greater moisture availability before a relatively rapid development of oligotrophic and dilute conditions from 1300 to 610 cal. BP (135-30 cm). A brief period of deeper water depths and meso-eutrophic conditions is observed between 550 and 445 cal. BP (23-13 cm). Following a short-lived hiatus, poly-hypertrophic, alkaline species are abundant in the top 10 cm coinciding with European colonisation in the region from the 17th century.