Will water abstraction from the Table Mountain Aquifer threaten endemic species? A case study at Cape Point, Cape Town

February, E C; Bond, W J; Taylor, R; Newton, R

Will water abstraction from the Table Mountain Aquifer threaten endemic species? A case study at Cape Point, Cape Town

Journal Article

2004

Journal Title

South African Journal of Science

Link to Journal

http://www.sajs.co.za/

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

THE PRINCIPAL SOURCE OF CAPE TOWN’S future water needs is the Table Mountain Group aquifer. The floral characteristics of the region overlying this aquifer are unique with five endemic and one near-endemic families. Many of these endemics are restricted to areas such as wetlands and marshes that are supplied by aquifer water, making them vulnerable to groundwater abstraction. Here we report the results of a study undertaken at two sites in the Cape Point Nature Reserve using stable hydrogen isotopes to determine the water source of plants to establish dependence on a permanent water supply. The results from the Suurdam site suggest that Erica labialis has a more diverse rooting strategy than Erica multumbellifera, with two plants sourcing water close to the surface, whereas others extract water much deeper down. The results from the Anvil Hill site, however, suggest that the rare Mimetes hirtus uses water very close to the surface that has undergone extensive isotopic fractionation. These results indicate that this species is shallow-rooted and dependent on surface soil water for survival. As such, it would be vulnerable to an even slight lowering of the water table during the dry summer months, when the surface soil water would be replenished mainly from the permanently saturated zone of the wetland. These results have implications for other endemic plant families with the same water requirements.

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