Keurbooms Estuary Vegetation

Growth and distribution pattern of the Spartina maritima intertidal salt marsh in the dynamic microtidal Keurbooms estuary.

Coastal vegetated wetlands, including seagrasses, salt marshes and mangroves, are one of the most productive ecosystems in the world. These vegetated coastal wetlands provide numerous ecosystem-based services such as coastal defence against flooding, habitat, breeding, feeding and nursery grounds for many marine organisms as well as coastal protection against flooding by extreme events like storm surges and tsunamis.

Globally these ecosystems are recognized as one of the most effective carbon sinks, playing an important role in climate change mitigation and adaptation. The long-term existence of these ecosystems is threatened by global sea-level rise related to global climate change, and anthropogenic activities such as habitat destruction and coastal developments.

The Keurbooms Estuary is one of a few estuaries along the south coast of South Africa that has a large floodplain (∼ 186 ha) vegetated by salt marsh. The intertidal Spartina maritima salt marsh, a native cordgrass species to the South African coast, occupies an area of only ~7 ha. Cordgrass species are vital in nature-based solutions for coastal erosion control and trapping of sediment, stabilising shorelines, keeping pace with sea-level rise, and assisting with carbon sequestration.

The study aims to assess the importance of the sediment characteristics on the growth and distribution of S. maritima intertidal marsh and the implications for potential carbon storage capacity in the Keurbooms Estuary. The GIS mapping results showed an overall decline in S. maritima distribution, with coverage remaining largely the same in the lower reaches of the Bitou tributary compared to the Keurbooms tributary.

Field investigation revealed that the root systems of S. maritima in both tributaries were mostly restricted to the sub-surface substrate layer. Transplant experimentation showed that individuals planted in clayey soil produced a larger number of new stems compared to those in silty soil. Estimated soil carbon storage was higher in the clayey sand than in the silty sand sites. Despite showing a decline in area cover, the results suggest that the S. maritima is likely to colonise open stable intertidal mudflats/sandflats, maintaining its distribution as an intertidal species in the salt marshes of the Keurbooms Estuary. This is important to ensure the continued provision of essential ecosystem-based services.

The South African Environmental Observation Network (SAEON) continues to monitor this important component into the future through regular Long-Term Ecological Monitoring (LTER) surveys and the installation of Rod Surface Elevation Tables (RSETs).

Each session consists of 20-minute presentations, followed by a joint Q&A session of 15 minutes.

ABOUT DR ATHI MFIKILI

Dr Athi Mfikili is a post-doctoral research fellow with the Elwandle Coastal Node of the South African Environmental Observation Network of the National Research Foundation. Dr Mfikili has a doctoral degree from the Department of Oceanography at Nelson Mandela University. His PhD utilised a combination of sedimentary and micro-palaeontological records to investigate the evidence of palaeo-tsunami events and implications for coastal zone management of the South African coast.

Dr Mfikili’s research interests include, amongst others, coastal sedimentation, extreme marine wave events (tsunamis and storm surges) deposits, marine micropalaeontology (foraminifera), and blue carbon stock assessments. Researching his MSc, Dr Mfikili investigated the effects of sedimentary and hydrological dynamics on the growth and distribution pattern of the Spartima maritima intertidal salt marsh.

Currently, Dr Mfikili’s post-doctoral research investigates blue carbon sequestration and storage in coastal vegetated wetland ecosystems, mainly on temperate salt marshes on the South African coast. Dr Mfikili also serves as a post-doctoral representative to the management committee and board of the Institute for Coastal and Marine Research of Nelson Mandela University.