Sediment conundrum
While sediment is welcome in a healthy river
system, when contaminated, it can be a source
of toxicity in an aquatic environment.
By Dr Eunice Ubomba-Jaswa at the WRC
S
ediments are formed by the
natural process in which material
(such as stones and sand) is
carried to the bottom of a body of water
and forms a solid layer. It is a source
of life in a healthy river system, as it
forms a variety of habitats for benthic
organisms and facilitates the nutrient
cycle of the aquatic ecosystem.
However, just as the sediments can be a
source of life, when contaminated, the
sediment can be the actual source of
pollutants releasing into the overlying
aquatic environment.
This can only be countered with an
integrated approach that can assess
and understand the relationships
between the various components
of the water resource. Current
monitoring programmes focus mainly
on determining water quality and not
additional factors that can influence the
quality of the environmental resource
and the potential risk contained. This
has resulted in a lack of methods to
assess the other environmental
variables, such as the sediment.
The Water Research Commission
(WRC) hosted a workshop entitled
‘The Sediment Conundrum’, which
aimed to discuss and develop an
integrated approach that can lead to
better coordination in the monitoring
and management of contaminated
sediments. The workshop was
attended by sediment researchers,
users, laboratories, consultants, mining
companies, environment practitioners
responsible for Environmental Impact
Assessments (EIAs), government
departments, practitioners responsible
for Microbial Monitoring Programmes,
and citizen science groups working
with sediment analysis.
Dr Eunice Ubomba-Jaswa from the
WRC opened the proceedings by saying
that the sediment environment is highly
variable and inevitably complex, both
which contribute to the difficulty in
monitoring and managing contaminated
sediments. She explained that scientific
decisions are based on the results
received from laboratories; yet, it is only
with the use of consistent methods for
sample collection, manipulation, and
storage that accurate data can be
obtained to co-ordinate programmes
that prevent, remediate, and manage
contaminated sediment.
Dr Sebastion Jooste from the
Department of Water and Sanitation
(DWS) Resource Q uality Information
Services said that what is missing in
water quality research is the sediment,
“The stuff that sits at the bottom
[bedload]. We are interested in the
suspended load when it comes to the
water quality perspective.” Jooste
added that there is a need for a
national particulate surveillance and
monitoring programme.
Executive manager from the WRC,
Dr Stanley Liphadzi, said that the
thinking around sediment is getting
more serious and research needs to
move beyond the physical chemistry
side to surrounding issues of water
systems, such as the impact of
sediment on the economy and food
production. The WRC R&D portfolio is
moving in that direction, addressing
issues like where sediments