Assessing variation in below-ground organic matter dynamics in the Ramsar-declared Nylsvley Wetland system, South Africa

ABSTRACT

Wetlands physical and biological processes are fundamental to the distribution and structuring of organic matter in sediments. This study investigated spatial and temporal changes in organic matter sources in sediments within the Nylsvley Wetland, South Africa across two seasons, five sites and three wetland zones and identified pertinent contributors to sediment organic matter. Results showed distributions were uneven throughout the wetlands, with the seasonal zone having slightly high sediment organic matter in the cool-dry season and the permanent zone had high sediment organic matter in the hot-wet season, whereas the temporary zone had low SOM concentrations. Significant differences in nutrient concentrations were observed across wetland zones and seasons for Phosphorous, Potassium, Calcium and Magnesium, with the seasonal zone tending to be the most nutrient-rich in the cool-dry season, and with permanent zone nutrient levels rising substantially in the hot-wet season. Sediment δ¹³C differed significantly among wetland zones, whereas δ¹⁵N was statistically similar. Autochthonous plants were the main sources of organic matter in sediments overall across sites and zones. This study’s findings help to better understand the distribution of organic matter in wetland ecosystems and the role wetland zones play in the seasonal provisioning of allochthonous inputs.

KEYWORDS:

• freshwaters
• stable isotopes
• allochthonous
• autochthonous
• nutrients

Acknowledgements

We thank Thendo Mutshekwa, Florence Murungweni, Mathaphelo Methi, Cyncinatia Malapane, Rotondwa Matshidze and Tshedza Murudi for assisting with fieldwork. Authors’ contributions: TD: Funding, conceptualisation, investigation, methodology, data curation, formal analysis, writing – original draft, review and editing; RNC: visualisation, methodology, writing – original draft, review and editing; LM: investigation, methodology, writing – review and editing; FD: investigation, methodology, visualisation, writing – review and editing; RJW: Funding, conceptualisation, investigation, methodology, data curation, visualisation, writing – review and editing.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical approval

We would also like to thank Limpopo Economic Development, Environment and Tourism (LEDET) for granting us permission to sample in the Nylsvley Nature Reserve. Ethical clearance was obtained from the University of Venda Research Ethics Committee (SES/18/ERM/10/1009).

Additional information

Funding

We greatly acknowledge the financial support of the University of Venda [grant number FSEA/21/GGES/02] and the National Research Foundation of South Africa [grant number 117700], [grant number 138206]. We acknowledge the use of infrastructure and equipment provided by the SAIAB - South African Institute for Aquatic Biodiversity and the funding channelled through the NRF–SAIAB Institutional Support system. TD and RNC acknowledge funding from the Wissenshaftskolleg zu Berlin Institute for Advance Study/Stellenbosch Institute for Advanced Study and Alexander von Humboldt Foundation, respectively.

Notes on contributors

Tatenda Dalu

Dr Tatenda Dalu is Lecturer in Water Management at the University of Mpumalanga, South Africa, an Iso Lomso and TWAS Young Affiliate Fellow and Honorary Research Associate at the South African Institute for Aquatic Biodiversity.

Ross N. Cuthbert

Dr Ross N. Cuthbert is Leverhulme Early Career Fellow specialising in aquatic ecology at Queen's University Belfast and Honorary Research Associate at the South African Institute for Aquatic Biodiversity.

Lufuno Makhuvha

Ms Lufuno Makhuvha is a former MSc student at the University of Venda, South Africa.

Farai Dondofema

Mr Farai Dondofema is the Chief Technician at the University of Venda and runs the GIS Resource Centre.

Ryan J. Wasserman

Prof Ryan J. Wasserman is an Associate Professor of aquatic ecology at Rhodes University, Honorary Research Associate at the South African.