Food web (bio-)manipulation of South African reservoirs – viable eutrophication management prospect or illusory pipe dream? A reflective commentary and position paper

Abstract

An overview of prospects and limitations for the application of ‘classical' top-down biomanipulation as a management tool to ameliorate the consequences of eutrophication under the conditions applicable to reservoirs in South Africa is presented. This is structured by considering successive stages in reservoir food-web structure and function as far as can be generalised for South African biophysical conditions. Features and conditions that influence the potential vulnerability of local reservoirs to the effects of eutrophication, and prospects for its amelioration by biomanipulation intervention are examined. Physical factors linked to latitude (irradiation pattern and water-column stability) enhance the potential severity of eutrophication consequences in local reservoirs, although conversely, these are offset by suspended-clay turbidity. The predominance of
Microcystis in local eutrophic waters is perceived as a primary major constraint in implementing ‘classical' food-web manipulation.
Intrinsic limitations on the ability of zooplankton grazers to control this cyanobacterium, and subsequent food-web linkages widely applicable in local reservoirs are discussed and evaluated accordingly. On balance, available evidence indicates
a range of limitations that are likely to apply in respect of familiar contemporary approaches to biomanipulation in use today, although the uniqueness of each reservoir ecosystem is recognised. Some novel alternative management approaches are suggested, and a range of associated research requirements necessary to advance locally relevant scientific comprehension of ‘biomanipulation' and its application are itemised. National revitalisation of reservoir limnology remains paramount.

Water SA Vol.32 (4) 2006: pp.567-575