A glimpse into the littoral nutrient dynamics of a lake system connected to the sea

Authors

  • S Taljaard 1. Natural Resources and the Environment, Council for Scientific and Industrial Research (CSIR), Stellenbosch, South Africa; 2. Department of Botany, Nelson Mandela University, PO Box 77000, Port Elizabeth 6031, South Africa
  • L van Niekerk 1. Natural Resources and the Environment, Council for Scientific and Industrial Research (CSIR), Stellenbosch, South Africa; 2. Department of Botany, Nelson Mandela University, PO Box 77000, Port Elizabeth 6031, South Africa
  • DA Lemley Department of Botany, Nelson Mandela University, PO Box 77000, Port Elizabeth 6031, South Africa

DOI:

https://doi.org/10.4314/wsa.v44i1.08

Keywords:

Wilderness, estuarine lake, littoral zone, dissolved inorganic nutrients, catchment fluxes, in-situ processes

Abstract

In South Africa more than 80% of estuaries are small, dynamic and predominantly linear systems. Nutrient characteristics in these systems are mostly influenced by external catchment processes, except during extended periods of closure. However, a small percentage of the country’s estuaries (< 3%) comprise larger estuarine lakes mostly evolved from drowned river valleys. The physical properties of these systems suggest relatively low flushing rates, and the potentially stronger influence of in-situ processes on nutrient characteristics. This study investigates dissolved inorganic nutrient dynamics in the littoral zones of these estuarine lake systems, and potential influencing factors, using the Wilderness Lake System as a case study. Comparison of inter-annual and seasonal trends in dissolved inorganic nutrients (NOx-N, NH4-N and PO4-P) in river inflow and in the three lakes confirmed that external catchment fluxes are most likely not the sole, or even the dominant drivers of average long-term or seasonal dissolved inorganic nutrient patterns in the lake littoral zones. Relatively low NOx:NH4 ratios (mostly less than 1) in the lakes (especially in Eilandvlei and Langvlei) indicated a stronger influence of in-situ processes, such as bacteriological remineralisation, similar to observations in other lake type systems with low flushing rates. Low NO3:NH4 ratios are known to stimulate cyanobacteria, having the metabolic ability to potentially produce microcystins. Therefore, incremental dissolved inorganic nutrient and organic matter enrichment may cause these systems to tip into eutrophic, possibly toxic, aquatic states that will be difficult, if not impossible, to reverse given their weak flushing mechanisms. The findings from this study highlight the importance of appropriate water resource management, both in the catchments and within the floodplains of estuarine lake systems.

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Published

2018-01-31

How to Cite

Taljaard, S., van Niekerk, L., & Lemley, D. (2018). A glimpse into the littoral nutrient dynamics of a lake system connected to the sea. Water SA, 44(1 January). https://doi.org/10.4314/wsa.v44i1.08

Issue

Section

Research paper