Biogeochemical response of a secondary-salinised floodplain wetland to experimental freshening

ABSTRACT

An experimental flooding with freshwater was used to evaluate the biogeochemical impacts of freshening in a semi-arid floodplain wetland that had undergone severe secondary salinisation (Loveday Disposal Basin, Australia). Filling the wetland with freshwater lowered electrical conductivity (EC) from ~60 to 13 dS m^–1. This freshening was accompanied by substantial declines in total P (TP), filterable reactive P (FRP), dissolved organic C (DOC), total organic N (TON), dissolved organic N (DON), NH₄⁺ and molybdenum-reactive Si (MoR Si) concentrations. Owing to the semiarid climate, the water level receded and EC increased to pre-flooding conditions within seven months. During this drying phase, some chemical species maintained lower concentrations then pre-flooding (TP and FRP), others returned to within their original range (DOC, TON, DON), and others went above their original range (NH₄⁺ and MoR Si), the latter reflecting some bank discharge of groundwater. Unexpectedly low turbidity and P concentrations during the drying phase were promoted by the development of an extensive filamentous algal mat following flooding, which limited sediment resuspension as the water level receded. The transient response to freshening highlights that salinity is a key driver of biogeochemical cycles in semi-arid wetlands.

KEYWORDS:

• Salinity
• wetlands
• River Murray
• nutrient cycling

Acknowledgements

The Loveday Basin Adaptive Management Demonstration Site Project was developed by the Department of Water, Land and Biodiversity Conservation in partnership with the South Australian Murray-Darling Basin Natural Resources Management Board, Cooperative Research Centre for Landscape Environments and Mineral Exploration, Water for a Healthy Country National Research Flagship, and local communities. This project has been sponsored and funded from the Living Murray Environmental Works and Measures Program through the Murray-Darling Basin Commission and the CRC LEME (Project 3.18). Numerous volunteers contributed to field sampling trips, including Ian Jolly, Kris Broos, Evelyn Krull, John Dighton, John Gouzos, Kerryn McEwan, Julie Corriveau, and Michelle Caputo. We thank two anonymous reviewers and the Editor for many suggestions to improve the clarity of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This project has been sponsored and funded from the Living Murray Environmental Works and Measures Program through the Murray-Darling Basin Commission and the CRC LEME (Project 3.18).