Posted 12 May 2015
Lead author, Monica Markowska.
University of New South Wales (UNSW), Australian Nuclear Science and Technology Organisation (ANSTO) and National Parks and Wildlife Service (NPWS) researchers working at Yarrangobilly Caves in the Australian Snowy Mountains have found new information from cave deposits that will help reconstruct past climates and groundwater recharge processes.
Given the importance of water in Australia, surprisingly little information is available about the variability of rainfall on this continent in the past. Although there is a good annual record dating back 100 years in Australia, there is nothing much before that period and no known cave deposit records exist for New South Wales.
The newly published research is investigating how to retrieve Australian rainfall records from the past 2000 years from cave deposits. Certain types of cave deposits, including stalagmites, are formed by mineral-rich water in underground caverns. They are important because they can be used to establish a record of past environmental changes, such as rainfall variability.
Understanding past climate can help predict the availability of water resources in the future.
Located in Kosciuszko National Park, the study site is in an important area because it is a source of water for the Murrumbidgee and Murray River systems, two major waterways in southeast Australia. The 440 million year old limestone deposits there contain a system of about 400 caves managed by the NPWS.
Lead author, UNSW Connected Waters Intiative (CWI) and Institute for Environmental Research scientist Monika Markowska and colleagues, have been monitoring dripping water in the cave system, from which stalagmites form, for fifteen months.
“Monitoring the water movement from the surface into the cave is important because this water carries the majority of information about climatic and environmental conditions at the surface,” said Professor Andy Baker of the UNSW CWI, a co-author on the paper.
The research identified the significance of the role of soil moisture content in the formation of stalagmites and the climatic records they contain.
“While rainfall is an essential source of the drip-water that forms stalagmites, at Harrie Wood Cave it was the degree to which soil was saturated with moisture that controlled whether water from individual rainfall events reached the cave system where they could be recorded by the formation of stalagmites” said Markowska.
The research team came to this conclusion after a detailed analysis of drip-waters recorded at 15-minute intervals within the Harrie Wood Cave, along with weather data from the surface above the cave. By monitoring drip rates, researchers determined how long it took the water to get into the cave. They also monitored precipitation, temperature, barometric pressure and soil moisture.
In the cave, dripping water was automatically recorded using Stalagmate® drip logger devices. Drips are recorded by measuring the vibration caused each time a water droplet hit the surface of the miniature drum-like detectors. The data reported in the paper are from 14 sites forming part of a network of fifty devices throughout the cave, one of the largest such studies in the world. Interpreting the data provided by the Stalagmate® loggers provided a unique way to understand water flow from the surface to the cave.
The researchers identified five different types of drip water responses to surface conditions and were surprised to see different flow patterns in drips in close proximity to each other.
The five types of response are due to the many possible flow paths of water from the surface to the cave. Before reaching the cave, water may be stored in the soil, as well as in fractures and solution pockets in the limestone.
Most importantly, the research demonstrates that cave deposits can have very individual relationships to the surface climate due to the specific water flow route.
This information has allowed researchers to identify which speleothems can be used to obtain a rainfall record for the past 2000 years.
The research has been published in the Journal of Hydrology.
Source: ANSTO.
Professor Andy Baker features in American Water Resources Association ‘Water Resources Impact’, September 2020 edition.
The Connected Waters Initiative (CWI) is pleased to welcome Taylor Coyne to its network as a postgraduate researcher. If you’re engaged in research at a postgraduate level, and you’re interested in joining the CWI network, get in touch! The CWI network includes multidisciplinary researchers across the Schools of Engineering, Sciences, Humanities and Languages and Law.
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