Kelly L Kirsten

A 700‐year record on the effects of climate and human impact on the southern cape coast inferred from lake sediments of eilandvlei, wilderness embayment, south africa

Abstract The southern Cape coast, outh frica, is sensitive to climate fluctuations as it is influenced by different atmospheric and oceanic circulation systems. Palaeoecological evidence of Holocene climate variations in this region is presently limited. Here, we present a lake sediment record spanning approximately the last 670 years from ilandvlei, a brackish coastal lake situated mid‐way between Cape Town and Port lizabeth. The results from geochemical and sedimentological analyses point to an increase in minerogenic sediment input from the catchment starting around ad 1400. Changes in the seasonal distribution of rainfall during the Little Ice Age may have altered river discharge and increased erosion rates and fluvial sediment transport in pre‐colonial times. A rising mean lake level, possibly associated with an altered water balance or relative sea‐level rise, may offer an explanation for the deposition of finer sediments. After ad 1450, reduced burial flux of elements associated with autochthonous sediment formation may have resulted from ecological changes in ilandvlei. Enhanced sedimentation rates, increasing carbon, nitrogen, phosphorous and biogenic silica concentrations, as well as high concentrations of proxies for allochthonous sediment input (e.g. aluminium, titanium, zirconium) point to increasing sediment and nutrient flux into ilandvlei from the late nineteenth century onwards. The most likely factor involved in these recent changes is land‐use change and other forms of human impact.

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.