The Council for Scientific and Industrial Research (CSIR) has estimated that commercial farmers in the Dwars River area of the Western Cape spend R600 000 a year ridding their irrigation systems of filamentous algae.
The CSIR is in the process of formulating a tradable permit system as a tool to avoid extreme pollution in the river, which serves as an important water source to the citizens of Cape Town.
Resource economist Dr Willem de Lange arrived at an estimated R1 887.92 per hectare a year as the cost of eutrophication. The figure also includes a management budget for filamentous green algae mitigation strategies specific to the area.
He explains that this figure enables the calculation of a reserve price for filamentous green algae pollution permits, which is estimated at between R2.25/g and R111/g of filamentous green algae.
Nutrient enrichment from raw or partially treated sewage, agricultural effluent and other forms of phosphorus-rich pollutants stimulate the growth of filamentous algae, which clogs farmers’ irrigation systems.
The standard practice to manage the impacts of filamentous algae is frequent cleaning of irrigation systems and this provides the basis for establishing a cost estimate on the impact of algae.
“Farmers were aware of the algae problem but did not know how big the problem was and how it affected their pockets,” says De Lange.
Commercial agriculture in the Dwars River is dominated by deciduous fruit and viticulture, with plums being grown on 70% of the area. Thus, De Lange used plums as a representative deciduous fruit crop in his study.
About 307 ha in the study area is dedicated to deciduous fruit and, assuming that all farmers are faced with the challenge of filamentous algae, the deduced R1 887.92 per hectare a year translates into R579 591.44 a year for deciduous fruit in the area – enough to establish 10 ha of plums.