The hydrological function of a large chain-of-ponds: a wetland system with intermittent surface flows

Rory T. Williams, Kirstie A. Fryirs*, Grant C. Hose

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Like many wetlands globally, the Mulwaree River chain-of-ponds system exists in two dichotomous states characterised by the presence or absence of surface flow connecting large, deep, permanently inundated ponds. We develop a conceptual model of hydrological function of this chain-of-ponds system combining surface and subsurface water levels, 2H and 18O stable isotopes and 222Rn as a groundwater tracer over a period of time that incorporated extended dry periods and large rainfall events. During high-flow or flood events, ponds are connected by flow along connecting channels and preferential flow paths. The water column is fully mixed to depths of up to 7 m. During high-flow, water level in the ponds can be greater than the water level in the surrounding floodplain aquifer, producing a hydraulic gradient away from the ponds, reflecting a losing wetland system. During no-flow periods, connecting channels and preferential flow paths are dry. A thermocline develops within the ponds and surface waters become enriched in 2H and 18O with evaporation losses. During periods of no-flow, increases in water level beyond atmospheric flux often occur during winter. Only small groundwater inflows enter the ponds from the floodplain aquifer. The hydrological function of this chain-of-ponds system is delicately balanced making it potentially sensitive to changes in climate that alter rainfall and evaporation rates, and any local-scale groundwater interference activities. Efforts to conserve and protect this system, and the aquatic ecosystems it supports, will be critical into the future.

Original languageEnglish
Article number61
Pages (from-to)1-18
Number of pages18
JournalAquatic Sciences
Volume82
Issue number3
DOIs
Publication statusPublished - Jul 2020

Keywords

  • Mulwaree
  • Discontinuous watercourse
  • Temporary wetland
  • Hydrological function
  • Groundwater
  • Geographically isolated wetland

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