The impact of anthropogenically induced degradation on the vegetation and biochemistry of South African palmiet wetlands

Abstract

There are many different anthropogenic causes of wetland degradation, such as disturbances which affect the physical structure of wetlands, resulting in erosion (altered fire regimes, road and railway building through wetlands, channelization of wetlands), pollution, land-cover change, and climate change. These different types of degradation have various impacts, depending on the type of wetland, soils, biochemistry and other factors. We researched a poorly-studied South African valley-bottom peatland that is dominated by the ecosystem engineer Palmiet: Prionium serratum. We ask the question: what is the impact of degradation by gully erosion, pollution and alien tree invasion on biochemistry and plant community composition of palmiet wetlands? In 39 plots from three palmiet wetlands situated approximately 200 km apart we found that channel erosion, through a loss of alluvium, has probably resulted in leached soils with lower soil organic matter and water content, less able to retain nutrients and cations. Soil leaching is a possible explanation for the groundwater of degraded wetlands having higher electrical conductivity and pH than that of pristine wetlands and a lower soil cation exchange capacity (21.3 ± 5.80–7.7 ± 4.91 meq/100 g). The loss of alluvium typically resulted in a completely new plant community, composed mostly of pioneer species and several alien species. The increase in base saturation (17.5 ± 8.46–30.2 ± 17.85%) and soil pH (4.8 ± 0.51–5.1 ± 0.50) with degradation was hypothesized to be the result of liming practices. Once extremely degraded, i.e. all the alluvium is lost, it is unlikely that these sensitive palmiet wetlands will recover original vegetation communities and lost functions, except on long timescales. We recommend conservation of the few pristine wetlands that remain, and rehabilitation of those that still retain some of their original function.

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Acknowledgements

A.J.R. gratefully acknowledges the following organizations for funding: The Erasmus Mundus Programme (European Commission), Research Fund of the University of Antwerp (Belgium), the National Research Foundation (South Africa) and a Consolidoc Grant (Stellenbosch University). Thank you to Byron-Mahieu van der Linde for assistance in the field and Tom van der Spiet for lab assistance. We also wish to thank two anonymous reviewers for helpful suggestions which improved the manuscript. Research was conducted under permit number: 0052-AAA008-00019 (Cape Nature).

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AJR conceived the study, performed data analysis, wrote the manuscript and KJE, PM, WE, contributed and edited it.

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Correspondence to Alanna J. Rebelo.

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Rebelo, A.J., Emsens, WJ., Meire, P. et al. The impact of anthropogenically induced degradation on the vegetation and biochemistry of South African palmiet wetlands. Wetlands Ecol Manage 26, 1157–1171 (2018). https://doi.org/10.1007/s11273-018-9638-3

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Keywords

  • Fen
  • Gully
  • Anthropogenic activities
  • Peatland
  • Liming
  • Ecological infrastructure