Lake St Lucia system, iSimangaliso Wetland Park: A laboratory for understanding cumulative global change impacts?

Sue (SAEON) and Thandukwazi (Ezemvelo KZN Wildlife) clean one of the salinity loggers in the estuary

SAEON's Monique Nunes is driving the pilot programme on water quality sampling as part of her DST/NRF Internship programme

By Monique Nunes, Prof. Tim O'Connor, Sue J. van Rensburg and Dr Tommy Bornman, SAEON

SAEON is mandated with detecting and understanding the impacts of human-induced global change on ecosystems, which includes both land use change impacts and climate change. This is achieved through establishing long-term in situ monitoring platforms at key sentinel sites.

SAEON is currently exploring the Lake St Lucia system within iSimangaliso Wetland Park as a potential sentinel site. Estuarine ecosystems, and Lake St Lucia in particular, not only form the connection between terrestrial freshwater and marine water, they also provide a vast number of ecosystem goods and services, such as nursery grounds for fish populations.

SAEON scientists believe this site holds the potential to explore the cumulative impacts of both land use change and climate change on critical estuarine ecosystems.

A pilot approach

Before investing in long-term research programmes it is advisable to conduct pilot studies to inform the appropriate sampling design in relation to a system's variability. Scientists from SAEON's Grasslands-Forests-Wetlands and Elwandle Nodes are jointly conducting several such pilot studies in the Lake St Lucia system, addressing interlinking components of the water cycle. These include the in situ deployment of salinity loggers, periodic sampling of water quality and micro-algal assemblages in the lake as well as groundwater dynamics.

iSimangaliso must be the only place on the globe where the oldest land mammal (the rhinoceros) and the world's biggest terrestrial mammal (the elephant) share an ecosystem with the world's oldest fish (the coelacanth) and the world's biggest marine mammal (the whale). Nelson Mandela

As part of her DST/NRF Internship programme, Monique Nunes was tasked with driving the pilot programme on water quality sampling of the lake. The work she is undertaking forms part of an inclusive and collaborative effort between SAEON, the Department of Water and Sanitation (DWS), iSimangaliso Wetland Park Authority, Ezemvelo KwaZulu-Natal Wildlife (EKZNW) and a number of scientists from universities such as Nelson Mandela Metropolitan University and University of KwaZulu-Natal.

Why the Lake St Lucia system?

Lake St Lucia is the largest and most important estuarine system in South Africa. The ecological, scenic and economic value of this system is well known. Situated in the province of KwaZulu-Natal on the east coast of South Africa, it has RAMSAR Wetland status and forms part of the iSimangaliso Wetland Park, a UNESCO World Heritage site. iSimangaliso Authority is the mandated management authority of iSimangaliso Wetland Park.

Concern over the impact of human activities on the system has, through time, stimulated various active management interventions. These have been aimed at ensuring the health of the system. Efforts have been well documented and continue to evolve as understanding improves. A multidisciplinary study under the auspices of the iSimangaliso Authority is currently in progress and investigations are well underway to find a long-term solution to the hydrological and ecological issues facing this important estuary system.

There has been active research in the area since the 1950s. The net result is that there is a reasonable and growing conceptual understanding of the functioning of the system and a significant body of data and information available for the area. This presents a solid foundation on which to build long-term ecological research programmes. Much of the work has focused on conservation imperatives. SAEON, however, recognises the value in drawing and building on data sets and the understanding of the system, to test predictions of the impacts on system functioning within the broader global change context.

Why water quality?

The advantage of working in well-studied systems is that researchers can draw on available information to strategically inform monitoring efforts. It was Dr Ricky Taylor, a regional ecologist at Ezemvelo KZN, who first integrated the information gained by data collected through a long-term monitoring programme, the various independent studies conducted in the Lake St Lucia system and expert local knowledge. From this, he developed a conceptual model which helped to identify components of the system and potential priorities to facilitate an improved understanding of the Lake St Lucia estuarine ecosystem.

Lake St. Lucia is the largest and most important estuarine system in South Africa

Physico-chemical and water quality monitoring were identified as the priority for long-term ecological research. Monitoring these parameters will help refine the model on system functioning. These parameters have been reiterated as a priority by Whitfield (2014) and more recently the iSimangaliso Authority's scientific studies which have refined our understanding of the Lake. DWS also require the information for their estuaries health monitoring programme for the country and academics have indicated they need long-term baseline physico-chemical and water quality data to enable more discrete process-level research studies.

Although all these aspects assisted SAEON researchers in identifying what might be important to measure, they required further information on when and where to measure these parameters in relation to the spatial variability of the system, and hence the SAEON and DWS pilot study was initiated in 2014.

The aim of this pilot study is to:

refine a set of critical parameters to measure and collect baseline data;
determine the variability of these parameters within the Lake St Lucia system on a spatial and temporal scale over a one-year period; and
use the insights gained, also drawing on historic data sets and alternative data sets, and expert input, to inform a long-term ecological research approach to assess the Lake St Lucia system.

Study site

Lake St Lucia is characterised by wet dry cycles, shifting mouth states and stochastic events like cyclones, resulting in significant variability in the lake state and associated ecological processes. It is classified as an estuarine lake (Whitfield, 1992) and has four physically distinct regions that make up the estuary - False Bay, North Lake, South Lake and the Narrows.

Under open-mouth conditions, the South Lake will experience tidal influence from the mouth via the narrow estuarine channel, i.e. the narrows. South Lake is very shallow and forms the connection to the northern embayment. The latter includes False Bay and North Lake, which are both approximately 2 m in depth and experience limited tidal influence (Muir and Perissinotto, 2011).

The Mfolozi, Mzinene, Hluhluwe, Nyalazi and Mkhuze rivers are the five main tributaries of the system. The largest catchment of the Lake St Lucia system is the Mfolozi, which is severely impacted by human interventions and has for periods been artificially separated from the Lake St Lucia system (Stretch et al., 2013).

After two initial reconnaissance sampling events, a total of 26 sites have been incorporated into the pilot study. These include 14 historical sites as sampled by Pillay and Perissinotto (2008) and Perissinotto et al. (2010), the inlets of the five main tributaries and seven novelty sites (see map). The intention was to capture as much spatial variability as logistically feasible, given the constraints of access and sensitivity to wilderness zones which are difficult to access. A sampling interval of two months was selected to capture “fine scale” temporal variability.

Valuable data emerging

The exercise has so far been useful in streamlining logistics to feasible field operations. While it is too early to present comprehensive results, initial indications are that this pilot programme is yielding valuable information of both the spatial and temporal variability of the system. One example is salinity values extrapolated from real data (Figure 1).

Figure 1: Graphical representation of the spatial and temporal variability of salinity values recorded in:

a) November 2013	b) June 2014	c) August 2014

Hyper-salinity was a common occurrence in the lake region during the recent drought period as illustrated by a study conducted from February 2005 until May 2011 (Perissinotto et al. 2013). The drought broke at the end of 2011 and in 2012 the link between the Lake St Lucia system and the Umfolozi River was restored, boosting freshwater input into the lake.

SAEON's data indicates that the system is no longer hyper-saline, but more importantly, salinity was variable in space and time over three sampling events. These shifts can be attributed to rainfall and mouth state conditions, for example high salinity values are associated with the mouth being open to the sea via the link with the Umfolozi. Importantly, researchers are seeing short-term shifts in salinity patterns and well as extreme long-term shifts between wet and dry cycles, as could be expected.

Other basic parameters being collected include temperature and Ph levels (see Table 1). Work is underway analysing all the parameters collected as well as the micro-algal communities. There is already a promise of some interesting results.

Table 1: Data collected to date

Valuable spin-offs

Over and above the skills Monique has developed in running the programme (logistics, science and stakeholder engagement), the project has assisted in building the capacity of other DST-NRF interns that were exposed to various skills and experiences they would not ordinarily have had within their chosen field. This helps facilitate transdisciplinary thinking and encourages young scientists to engage in conceptual debates on the ecological function of different types of system. The value of diverse and intense field experience in building the skills (and character) of young scientists is considered a valuable spin-off of this work.

As part of the training experience, Monique presented an overview of the project at the recent EKZNW contemporary conservation symposium. Delegates expressed considerable interest in the presentation, the resolution of the data being generated and the patterns emerging.

What was confirmed by participants at the session following the presentation is that the type of data collected by SAEON is difficult for academic researchers to collect, but fundamental to their process-level research. SAEON's role in building long-term data sets to enable system function research was strongly validated by the research community present.

The way forward

Two more field trips will be conducted to complete the pilot study. All the data will be analysed and compared to historical and other data sources to refine the site selection for the long-term water quality monitoring programme. This will then be presented at a workshop during which stakeholders would be asked to provide input on the need and possible methods of taking long-term ecological research efforts forward.

References

iSimangaliso Authority. (2011). Lake St Lucia: understanding the problems and finding the solution. Background Information Document (2011/07). p 21
Perissinotto, R., Carrasco, N.K. and Taylor, R.H. 2013.Physico-chemical environment. In: Perissinotto, R., Stretch, D.D. and Taylor, R.H. (Eds.) Ecology and Conservation of Estuarine Ecosystems. Cambridge University Press, Cambridge. pp 168-185.
Perissinotto, R., Pillay,D., Bate, G.C. 2010. Microalgal biomass in the St. Lucia Estuary during the 2004-2007 drought period. Marine Ecology Progress Series, 405, 147-161.
Pillay, D., Perissinotto, R. 2008. The benthic macrofauna of the St. Lucia Estuarine Lake during the 2005 drought year. Estuarine,Coastal and Shelf Science, 77: 35-46.
Stretch, D., Chrystal, R. and Tirok, K. 2013. Theme 1: Catchment hydrology and hydrodynamic processes. In: Whitfield, A.K. (Eds.) Proceedings of the St. Lucia natural science workshop: Change, connectivity and conservation in a major wetland system. Water Research Commission Report: pp 9-15.
Whitfield AK. 1992. A characterisation of southern African estuarine systems. Southern African Journal of Aquatic Sciences 18: 89-103.
Whitfield, A.K. 2014. Proceedings of the St. Lucia natural science workshop: Change, connectivity and conservation in a major wetland system. Water Research Commission Report: p 101.