Water Sources of Upland Swamps in Eastern Australia: Implications for System Integrity with Aquifer Interference and a Changing Climate

Kirsten L Cowley,Robert Chisari,Kirstie A Fryirs,Grant C Hose

doi:10.3390/w11010102

Abstract

Temperate Highland Peat Swamps on Sandstone (THPSS) in Eastern Australia are Groundwater Dependent Terrestrial Ecosystems that occur in the headwaters of streams on low relief plateaus. Like upland swamps and peatlands globally, they provide base flow to downstream catchments. However, these swamps are subject to aquifer interference from mining and groundwater extraction and are threatened by urbanization and climate change. We collected winter and summer water samples from swamps in two highland regions of Eastern Australia. Water from the swamps was analyzed for hydrogen (δ2H) and oxygen (δ18O) isotopes and compared with rainwater, surface water and groundwater samples from the surrounding bedrock aquifers to identify likely swamp water sources. Radon (222Rn) was used as an environmental tracer to determine whether the swamps were predominantly groundwater or rainwater fed. Four out of five swamps sampled in the Blue Mountains had greater than 30% of water derived from the surrounding bedrock aquifer, whereas swamps in the Southern Highlands received less than 15% of water from the surrounding aquifer. The water sources for swamps in both regions are controlled by catchment morphology, e.g., valley shape. Understanding water sources of these systems is critical for the determination of likely impacts on THPSS from aquifer interference activities and a changing climate.

Highlights

Temperate Highland Peat Swamps on Sandstone (THPSS) are a type of peat forming wetland located on plateaus in the headwaters of streams that feed into major drinking water catchments of eastern Australian cities
THPSS are low energy, sediment accumulation systems that terminate downslope at a bedrock constriction or step, discharging at the downstream end to small bedrock streams [3,4,5]. Like their Northern Hemisphere counterparts, THPSS are late-Pleistocene to Holocene features that began forming when increased rainfall and higher temperatures facilitated plant growth which led to organic matter accumulation within the sediment matrix, allowing for the formation of peat [6,7,8]
The connectivity of upland swamps and peatlands to aquifers has been well documented in the Northern Hemisphere [2,70,71] with slope and catchment morphology being key controls on water

Summary

Introduction

Temperate Highland Peat Swamps on Sandstone (THPSS) are a type of peat forming wetland located on plateaus in the headwaters of streams that feed into major drinking water catchments of eastern Australian cities. They are valley bottom swamps similar to the ‘fen’ classification of Northern. THPSS are low energy, sediment accumulation systems that terminate downslope at a bedrock constriction or step, discharging at the downstream end to small bedrock streams [3,4,5] Like their Northern Hemisphere counterparts, THPSS are late-Pleistocene to Holocene features that began forming when increased rainfall and higher temperatures facilitated plant growth which led to organic matter accumulation within the sediment matrix, allowing for the formation of peat [6,7,8].

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