Insights into the hydrological functioning of RAMSAR listed Lake Clifton, southwest Australia, and the related threats to its Thrombolite community, via high-resolution hydrographic, geochemical and isotopic data.

Wednesday, 17 December 2014
Matthew Sean Forbes, Stanford Earth Sciences, Stanford, CA, United States and Ryan Vogwill, University of Western Australia, School of Earth and Environment, Crawley, Australia
High-resolution hydrographic data, hydro-geochemical and isotopic analysis are combined to investigate the current hydrological functioning of the RAMSAR listed Lake Clifton, Western Australia, and potential threats to the lakes Thrombolite deposits. Water level and electrical conductivity data for lake, sub-surface and deep ground waters imply continued contribution by both rainfall and sub-surface water to Lake Clifton’s water balance. Approximately two years of local daily rainfall totals and four-hourly lake level measurements, indicate a two-phase lake recharge process with immediate contributions by direct rainfall, followed by a combination of surface runoff and sub-surface infiltration. δ18O and δ18H stable isotope analysis also indicates recharge contributions by sub-surface and ground waters. Spatial uniformity and seasonal fluctuations in the isotope signatures promote a well-mixed lake system dominated by evaporative processes. Increases in ionic concentrations and salinity in adjacent groundwater are starting to mimic surface water trends identified over the last few decades. Thus, with groundwater, sub-surface water, and rainfall continuing to contribute to the composition of the lake water, it is possible that changing sub-surface water chemistry could be a driver in observed shifts in the lakes geochemical - hydrological balance. Such changes could be driven by over–extraction of groundwater causing saline water intrusion and/or reduction in rainfall and as such local recharge. Decreased rainfall and increasing temperature is also likely to have a direct effect on increases in salinity and TDS in Lake Clifton. These factors together are ultimately threatening the existence of the thrombolite reef in the north-east corner of the Lake.