Abstract
During the past 40 years, eutrophication has become an increasing threat to the usability of South African freshwater resources. Despite legislation moderating the discharge of phosphorus from some wastewater treatment works since the 1980s, eutrophication of freshwater resources is now widespread. Two important consequences are blooms of cyanobacteria, carrying the threat of cyanotoxin contamination, and excessive growth of macrophytes, which clog water-supply structures and reduce the recreational value of aquatic resources. Eutrophication-management options include reduction of phosphorus in detergents, biomanipulation of the food web, accurate prediction of cyanobacterial growth cycles, and mechanical disturbance of the epilimnion. The implementation of adaptive management to deal with eutrophication would ensure the testing and application of the most appropriate methodology to each eutrophic water body. Continued monitoring and reporting of trophic status are essential to establish whether interventions are having any effect.Keywords: biomanipulation, cyanobacteria, eutrophication, forward prediction, management, low-p detergents, phosphorus, zero-phosphate
Highlights
Eutrophication is the process of nutrient enrichment and the associated excessive plant growth in water bodies
Cultural eutrophication is related to anthropogenic activities – human, social and economic activities
On the basis of these findings the target water quality aimed to control eutrophication was set ‘to maintain mean chlorophyll concentrations in the receiving water bodies at such levels that severe nuisance conditions would not occur for more than 20% of the time. This translated into a phosphorus management objective (PMO) or endpoint of maintaining mean total phosphorus concentrations in reservoirs at 130 μg/l P or lower (DWA, 1988; ANON, 1988a; ANON, 1988b)
Summary
Eutrophication is the process of nutrient enrichment and the associated excessive plant growth in water bodies. On the basis of these findings the target water quality aimed to control eutrophication was set ‘to maintain mean chlorophyll concentrations in the receiving water bodies at such levels that severe nuisance conditions would not occur for more than 20% of the time This translated into a phosphorus management objective (PMO) or endpoint of maintaining mean total phosphorus concentrations in reservoirs at 130 μg/l P or lower (DWA, 1988; ANON, 1988a; ANON, 1988b). During the late 1990s and early 2000s, the Department of Water Affairs and the WRC assessed the shortcomings in eutrophication research and management with a specific focus on the WRC’s contribution and the impact of its research (Walmsley, 2000; Harding, 2006; Frost & Sullivan, 2010). The result was a renewed focus on eutrophication-related problems and management options after 2000 (Quayle et al, 2010; Van Ginkel et al, 2009)
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