A re-analysis of nutrient mass balances in the Hartbeespoort Dam
No Thumbnail Available
Date
2020
Authors
Carroll, Alexandra
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The Hartbeespoort Dam, located 40 km west of Tshwane on the Crocodile River, has
recently been described as the most eutrophic dam in Africa. The dam is situated in one
of the most economically active areas of South Africa and receives a high nutrient input
from 11 wastewater treatment plants, leaking sewers and urban and agricultural runoff.
The Metsi a Me programme, which ran from 2006 to 2016, aimed to mitigate in-lake
nutrient stocks using biomanipulation, including the physical removal of water hyacinth
and algae. This study reassesses the debate regarding nutrient stocks and fluxes in the
Hartbeespoort Dam. Using Department of Water and Sanitation water quality and flow
data, the annual input and output fluxes of total nitrogen (TN) and total phosphorus (TP)
to the Hartbeespoort Dam from 2010 to 2018 were calculated, which formed the principal
focus of this study. Through literature review and previous studies the relative
importance of nutrient removal from biomass harvesting in relation to retained nutrients
was assessed. Between 2010 and 2017, the range of P to the Hartbeespoort Dam from
rivers was 578 to 610 t/a and the range of N was 4437 to 4687 t/a. On average, the P
inflow flux increased by 54.2 to 77.8 t/a and the N inflow flux increased by 368 to 465 t
each year, a reversal of a long-term decreasing trend. A generous estimation of the total
annual nutrient removal from hyacinth and algae harvesting combined is 1% of the
nutrient influx. Much of the nutrient flux to the dam is sedimented. A summary of the
flux calculations of this study is shown on the diagram on the next page. Thus, the
upgrading of WWTWs in the catchment and the refurbishing of leaking and overflowing
sewers is the most appropriate long-term solution to the eutrophication problem at the
Hartbesspoort Dam.
Description
Master of Science (Coursework and Research Report) in Environmental Science, School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, 2019