The economic value of nutrient cycling in the Swartkops and Sundays River estuaries

Nutrient cycling, a fundamental ecological process, directly impacts the health and functionality of marine environments and plays a pivotal role in maintaining water quality and supporting diverse marine life and human health. To date, there has been no ecosystem service valuation assessment for nutrient cycling in South Africa, mainly because of the scarcity of nutrient cycling capacity measurements. The lack of valuation assessments necessitates reliance on data-transfer valuation techniques that can produce misleading valuations. Given the similarity between estuary nutrient cycling processes and wastewater treatment work processes, as well as the relative abundance of published data on the latter’s cost, the latter can be used as a proxy for the former. Cost and efficiency data for wastewater treatment works in Algoa Bay were sourced along with the published concentrations of dissolved inorganic nutrients in the Swartkops and Sundays River estuaries. The value of nutrient cycling in the Swartkops estuary has increased by about 1330% from USD466 076 in 1994 to USD6.7 million in 2022 but declined in the Sundays River estuary from USD1.6 million to about USD428 140 over the same period. In dollar terms, this value of nutrient cycling translates to USD18 681/ha for the Swartkops estuary when using the smallest area denominator and USD1747/ha for the Sundays River estuary (USD1 = ZAR18.4519). These estuaries offset the need for capital investment of this magnitude, reflecting their importance and the need for continued restoration and conservation. Significance: Few published valuations of the benefits of nutrient cycling in South African estuaries exist. An estimate is provided using the Swartkops and Sundays River estuaries as examples.