S Pillay, Dr. A. J. Smit, Dr Deborah Robertson-Andersson. Submitted to the ninth Scientific Symposium of the Western Indian Ocean Marine Science (WIOMSA) 2015.

1. Linking nitrogen pollution in estuaries to rocky shores: A stable isotope approach
Shivanee Pillay1
, Deborah Robertson-Andersson1
; AJ Smit1,2
1
UKZN
2
UWC
Many coastal regions in KwaZulu-Natal (KZN) are impacted by sewage effluent, but the
knowledge and extent of this impact remains poor. Additionally, previous impact studies
were restricted to community dynamics and nutrient trends in estuaries and coastal habitats.
However, this information can be supplemented by tracing the fate of nitrogen and its sources
to coastal systems. An accepted methodology is the use of stable isotopes of Nitrogen (N) to
determine anthropogenic origin to both terrestrial and marine systems. This study aimed to
determine anthropogenic sources and impacts of N-pollution to three estuaries in southern
KZN. To achieve this, stable isotope analysis together with nutrient and community
composition data, were used in the selected temporarily open/closed estuaries. Source
differentiation between the open (summer) and closed (winter) phase of the estuaries and the
importance of anthropogenic nitrogen (via estuarine input), was made possible using two
species of rocky shore macroalgae, Hypnea spicifera and Jania intermedia. The δ15N in
algae and mussels` provided evidence that estuarine inputs were more important during the
open phase than closed phase and were from anthropogenic sources in two sites (Mhlugwa
and Kongweni). Additionally, stable isotope analysis, physicochemical water properties and
determination of community composition, when integrated, were found to be useful tools in
nutrient pollution studies. The condition of sites chosen for this study indicated a need for
mitigation of nutrient pollution in estuaries and a greater need for development of
Wastewater Treatment Works along the coast of KZN.