Drought altered trophic dynamics of an important natural saline lake: A stable isotope approach

Lizaan de Necker; Luc Brendonck; Ruan Gerber; Pieter Lemmens; David X Soto; Yoshinori Ikenaka; Mayumi Ishizuka; Victor Wepener; Nico J Smit

doi:10.1016/j.scitotenv.2022.155338

Drought altered trophic dynamics of an important natural saline lake: A stable isotope approach

Sci Total Environ. 2022 Aug 15:834:155338. doi: 10.1016/j.scitotenv.2022.155338. Epub 2022 Apr 19.

Authors

Lizaan de Necker¹, Luc Brendonck², Ruan Gerber³, Pieter Lemmens⁴, David X Soto⁵, Yoshinori Ikenaka⁶, Mayumi Ishizuka⁷, Victor Wepener⁸, Nico J Smit⁹

Affiliations

¹ Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa; South African Institute for Aquatic Biodiversity (NRF-SAIAB), Makhanda 6139, South Africa. Electronic address: l.denecker@saiab.nrf.ac.za.
² Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa; Animal Ecology, Global Change and Sustainable Development, Department of Biology, University of Leuven, 32 Charles Deberiotstraat, Leuven 3000, Belgium. Electronic address: luc.brendonck@kuleuven.be.
³ Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa.
⁴ Laboratory of Aquatic Ecology, Evolution and Conservation, KU Leuven, Ch. Deberiotstraat 32, 3000 Leuven, Belgium; Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany. Electronic address: pieter.lemmens@kuleuven.be.
⁵ Department of Nuclear Sciences and Applications, Division of Physical and Chemical Sciences, Isotope Hydrology Section, International Atomic Energy Agency, Vienna, Austria. Electronic address: D.Soto-Arrojo@iaea.org.
⁶ Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa; Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo 060-0818, Japan; Translational Research Unit, Veterinary Teaching Hospital, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo 060-0818, Japan; One Health Research Center, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo 060-0818, Japan. Electronic address: y_ikenaka@vetmed.hokudai.ac.jp.
⁷ Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo 060-0818, Japan. Electronic address: ishizum@vetmed.hokudai.ac.jp.
⁸ Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa. Electronic address: victor.wepener@nwu.ac.za.
⁹ Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa. Electronic address: nico.smit@nwu.ac.za.

PMID: 35452726
DOI: 10.1016/j.scitotenv.2022.155338

Abstract

Climate change and associated droughts threaten the ecology and resilience of natural saline lakes globally. There is a distinct lack of research regarding their ecological response to climatic events in the Global South. This region is predicted to experience climatic events such as El Niño-Southern Oscillation (ENSO) more often and with greater severity with the potential to alter the structure and functioning of aquatic ecosystems significantly. From 2015 to 2016 South Africa experienced one of the most severe country-wide droughts as a result of a strong ENSO event. Our study aimed to investigate the effect of this supra-seasonal drought on the trophic structure of fish communities in a naturally saline shallow lake of a Ramsar wetland using stable isotope techniques. Fishes and potential basal sources were collected from the lake, during predrought conditions in 2010 and after severe drought (recovery phase; 2017). The δ¹³C and δ¹⁵N values of food web elements were determined and analysed using Bayesian mixing models and Bayesian Laymen metrics to establish the proportional contribution of C₃ and C₄ basal sources to the fish (consumer) diets, and examine the fish community in terms of isotopic niche and trophic structure, respectively. Fish consumers relied predominantly on C₃ basal sources in the predrought and shifted to greater reliance on C₄ basal sources, decreased isotopic niche space use and a reduction in trophic length in the recovery phase. Drought altered the type and abundance of the basal sources available by limiting sources to those that are more drought-tolerant, reducing the trophic pathways of the food web with no significant alterations in the fish community. These results demonstrate the resilience and biological plasticity of Lake Nyamithi and its aquatic fauna, highlighting the importance of freshwater inflow to saline lakes with alterations thereof posing a significant threat to their continued functioning.

Keywords: Climate change; Ecosystem resilience; Endorheic lake; Salinity; Southern Africa; Stable isotope analysis.

MeSH terms

Animals
Bayes Theorem
Droughts*
Ecosystem
Fishes / physiology
Food Chain
Isotopes
Lakes* / chemistry

Substances

Isotopes