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Past and present environmental change at Lake St Lucia

past-and-present

Lake St Lucia is Africa’s largest and most important estuarine ecosystem. However, there is a critical need to understand the processes driving change at Lake St Lucia across a range of temporal scales. Virtually all research on St Lucia has taken place since 1950 and has therefore dealt with a system that has been severely impacted by human activities and management interventions. Previous attempts to manage the estuary in the past have been limited by our understanding of the long-term processes that govern change at the regional scale. In addition, the system is at a point in its geological evolution where it is extremely sensitive to changes in runoff, sediment supply, and nutrient inputs. Despite increasing concern regarding the influence of anthropogenic activities, there are few accurate records from Lake St Lucia against which future trends in accumulation can be assessed. By examining chemical and sedimentological changes, this study aims to provide insight into the underlying processes driving change within the St Lucia system. The long-term evolution and functioning of the system will be investigated through the development of a high-resolution, multi-proxy reconstruction, against which current anthropogenic stresses associated with sedimentation and eutrophication can be assessed. The study brings together specialists from four different universities and will provide essential knowledge that will ultimately underpin management strategies for future conservation at St Lucia.

The work is currently funded by the South African Water Research Commission (WRC) and the NRF.

High resolution records of past environmental changes

high-resoultion-records

Natural archives of environmental change, such as lakes and wetlands, are rare in the southern African subregion due to climatic and topographic factors. The Mfabeni Peatland in northern KwaZulu-Natal is one of Africa’s oldest and largest active peatlands, containing in excess of ten meters of continuous peat accumulation, representing a record of environmental change spanning more than 40000 years. This record covers the critical periods of the earth’s recent climatic history through the last glacial maximum and into the current interglacial, the Holocene period. Thus, the Mfabeni site presents a unique opportunity for global change research in subtropical Africa. A pilot study recorded excellent microfossil preservation at the site, and a stratigraphically consistent radiocarbon-derived age-depth model for the bulk of the core (Finch and Hill, 2008). The present research applied a more appropriate coring methodology for the nature and depth of sediment (viz. vibracoring), and has developed a robust AMS chronology, particularly for the last glacial maximum and Holocene. Through interdisciplinary collaboration, the study is conducting multiproxy analyses at high resolution, including pollen, charcoal, fungal spores, geochemistry and sedimentology. Given the rarity of well-dated sediments which extend beyond the last glacial maximum in southern Africa, detailed analysis of the Mfabeni Peatland is critical for understanding past environmental change in the summer rainfall zone.

Mfabeni also forms part of the RAIN (Regional Archives for Integrated iNvestigations) project (http://www.marum.de/en/R_A_i_N.html). Other sites currently under investigation include the Mkhuze wetlands, Kosi Bay, and Lake Bhangazi.

This research is funded by a UKZN CRG Grant (2011) and NRF Thuthuka Grant (2013-2014).

Groundwater Flow and Nutrient Fluxes along the east coast of South Africa

groundwater-flow

Increasing human pressure and climate change are predicted to alter coastal ecological processes, but at present we have no capacity to understand or predict these impacts. Making such predictions and managing complex ecosystems requires a mechanistic understanding of groundwater flow and nutrient dynamics.

Submarine groundwater discharge (SGD) has become increasingly recognized as a major pathway for the flow of nutrients, organic carbon, metals, and even contaminants from land into the coastal ocean. While there have been a number of studies that focus on the role of SGD in estuarine and coastal biogeochemistry, only a few of these studies have occurred in the southern hemisphere, and none in southern Africa. Such information is critical for understanding not only regional SGD and its influence on the local environment, but our understanding of how SGD impacts global ocean biogeochemistry. Through the use of radium isotope methods, we are investigating groundwater flow and nutrient fluxes between iSimangaliso Wetland Park and the coastal ocean. Understanding the mechanisms of nutrient delivery and the composition of those nutrients is essential for elucidating how these estuarine and coastal ecosystems develop in response to local (direct increases in human population), regional (upstream development), and large scale climate change. The project dovetails with the international GEOTRACES program (http://www.geotraces.org).

Reconstructing relative sea-level change

reconstructing-relative-sea2

Recently there has been a growing interest in the relationship between climate and sea level change and a realization that human-induced global warming may accelerate the rate of sea-level rise. Understanding past patterns of sea-level change is important on local (e.g. for coastal management and engineering), regional to national (e.g. national future sea-level predictions) and global scales (e.g. for understanding polar ice sheet history). Relative sea-level curves have been constructed for a substantial portion of northern hemisphere coastline; however, to date, few curves have been presented for the southern hemisphere. Holocene sea-level records for the eastern and western coastlines are incomplete in extent and coarse in resolution. South African sea-level research has therefore relied largely on global records as a benchmark.

reconstructing-relative-sea

In the southern African context, the application of foraminifera as biological indicators has been restricted to studies of stratigraphy, temperature change, sedimentology and marine records. A successful a pilot study was conducted, whereby vertical zonation of salt-marsh foraminifera at a single site was established and relative sea-level form the past 1200 years reconstructed using transfer functions (Strachan et al., 2014). Here, an established sea-level proxy was introduced to determine proof of concept for South African sea-level research. This technique has the potential to contribute to our incomplete understanding of past sea-level change along the southern African coastline. Additional sites have been selected along the east and south coast of South Africa to apply and further develop this technique, including the Knysna Lagoon, the Keiskamma and Kei estuaries, and Lake St Lucia in Maputaland.