Metal Distribution and Sediment Quality Variation across Sediment Depths of a Subtropical Ramsar Declared Wetland

Tatenda Dalu,Ross N. Cuthbert,Florence M. Murungweni,Ryan J. Wasserman,Rolindela Tshivhase

doi:10.3390/w12102779

Abstract

The study of wetlands is particularly important as these systems act as natural water purifiers and thus can act as sinks for contaminated particles. Wetland sediments are important as they provide an indication of potential contamination across temporal and spatial scales. The current study aimed to investigate the distributions of selected metals and nutrients in different sites in relation to sediment depth, and identify relationships among sediment metals. Significant differences in nutrient (i.e., N, P) and metal (i.e., K, Mg, Na, Fe, Cu, B) concentrations were found across study sites, whereas nutrients (i.e., N, P) and metals (i.e., Ca, Mg, Fe, Cu, Zn) were significantly different with sediment depths. When compared against Canadian sediment standards, most of the assessed metals were within the “no effect” level across the different sites and depths. The K, Ca, and Mg concentration showed extreme contamination across all sites and depths. The enrichment factor values for K, Ca, and Mg showed extremely high enrichment levels for all sites and sediment depths. The Na, Mn, Fe, Cu, Zn, and B concentration showed mostly background enrichment levels. All sediments across the different sites and sediment depths indicated deterioration of sediment quality. Pearson correlations suggest that most metals might have originated in a similar source as that of Mn and B, owing to a lack of significant differences. These results provide baseline information for the general management of the Nylsvley Wetland in relation to sediment metal pollution. The specific sources of metal contaminants also require further elucidation to further inform management efforts.

Highlights

Wetlands are amongst the most productive ecosystems in the world, harboring high diversities of aquatic and semiaquatic biota [1,2,3,4]
The present study focuses on the Nylsvley Wetland, a protected Ramsar site of international conservation in South Africa [45], through analyses of sediment metal pollution across multiple study sites and sediment depths
The study results demonstrated a high degree of metal pollution in the wetland sediment across sites and sediment depths, as evidenced by the high Igeo and enrichment factor (EF) and pollution load index (PLI)

Summary

Introduction

Wetlands are amongst the most productive ecosystems in the world, harboring high diversities of aquatic and semiaquatic biota [1,2,3,4]. Despite the essential ecosystem services that wetlands provide, recent studies [2,9,10,11]. Sediments provide essential habitats for organisms and play an important role in maintaining environmental health [16,17,18] and carbon sequestration [19,20]. These habitats play a major role in the hydrological and ecological processes in wetland ecosystems, which are reliant on the health of sediment components [21]

Methods

Findings

Discussion

Conclusion