Zeekoevlei / Rondevlei Rehabilitation Study ... - Southern Waters

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Southern Waters Ecological Research and Consulting Phosphorus as a limiting nutrient. “Life can multiply until all the phosphorus has gone and then there is an inexorable halt which nothing can prevent” (Isaac Asimov). Phosphorus is a key component of the molecule commonly known as ATP (adenosine triphosphate) – the molecule that provides the requisite energy for cell life. Accordingly, phosphorus is the limiting factor to life, both in water and on land. Phosphorus does not exist in nature in its elemental (P) form, but rather as one or other form of phosphate. Phosphorus cycles and recycles through organic (living) and inorganic (non-living) matter. The deleterious impacts of the disposal of phosphate-rich sewage effluent and/or detergent-rich grey water to lakes and rivers first became evident during the 1950s, and is now recognized as a global threat to water quality, ecosystem health and the recreational use of rivers and lakes. Phosphorus is not a pollutant or a toxicant, but a naturally scarce and life-supporting element that, when present in oversupply, frequently results in biological overgrowth. Its effective management and control, especially in shallow lakes and vleis, can reverse or prevent this process. 2.2 Approach Adopted For This Study A considerable and informative base of well-researched data exists for Zeekoevlei, and to a lesser extent for Rondevlei. As its fundamental points of departure, the Zeekoevlei / Rondevlei Rehabilitation Study encompassed the following key elements in its approach: • to not undertake or initiate any new collections of primary data other than to determine the role played by groundwater in the hydrological cycling and nutrient loading of these two vleis (an understanding of the role of groundwater in the hydrological and ecological functioning of the Cape Flats vleis has, for too long, been neglected; • to model the cause and effect linkages between the identified phosphorus loads, and the resultant in-lake condition; • to develop rehabilitation scenarios based on phosphorus reduction which, in conjunction with other management and/or biomanipulatory practices, would serve to reverse the extant extreme levels of eutrophication in each vlei. The primary focus of the study was to convert the existing knowledge and information into guidelines for rehabilitation. 4 Zeekoevlei / Rondevlei Rehabilitation Study: Action Plan
Southern Waters Ecological Research and Consulting 2.3 The Concept Of Rehabilitation vs Restoration And Remediation In terms of formulating management needs and recommendations for Zeekoevlei and Rondevlei, it is important that the concepts of restoration, rehabilitation and remediation be defined. The concept of restoration implies an inherent degree of naturalness, viz. that whatever efforts are undertaken will strive to restore aspects such as vegetation, hydraulic and/or hydrological patterns, water quality or faunal composition to their natural condition. By contrast, rehabilitation recognizes that restoration may be neither pragmatic nor possible. However, the enhancement of core aspects of ecological functioning and processes, in order to resemble a semi-natural condition, is attainable. Remediation procedures are common for systems that have been grossly abused (e.g. mine tailing wetlands), and any semblance of original condition is no longer possible. Here the goal would be to improve the ecological condition, to an endpoint that is unlikely to mirror any previous natural state. The specialist investigations conducted for this study indicate that, for Zeekoevlei, any management approach should encompass a blend of rehabilitation and remediation options. In the case of Rondevlei, future management should be rehabilitation-focussed. Zeekoevlei / Rondevlei Rehabilitation Study: Action Plan 5
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Zeekoevlei / Rondevlei Rehabilitation Study ... - Southern Waters

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