Ephemeral lakes and shallow groundwaters in southern Western Australia are among the most extreme waters in the world in terms of both pH and salinity.
Extreme water compositions are up to 8x saltier than seawater and as acidic as stomach acid! Water temperatures range from ~0oC to ~49oC.
Lake Magic changes color with water composition. Here, in January, 2006, evaporation further enriched lake waters in Al, making the lake yellow.
Brenda Bowen holding orange acid saline groundwater.
Brenda Bowen removes a water sample from an XRF at Central Michigan University used to measure elements in waters without having to dilute them.
We measured pH, salinity, and temperature of waters in the field. In the lab, we used various instruments to analyze waters for major, minor, and trace elements,
major cations and anions, and stable isotopes.
(Bowen and Benison, 2008, Applied Geochemistry)
In the figure at right, note the blue diamond that represents the salinity and pH of typical seawater. Most waters in Western Australia are much more saline and acidic than seawater.
Although there is a large range of pH in lake water (teal circles), the regional groundwaters tend to be acidic (yellow triangles).
Some results show that acid lake and ground waters have unusually high concentrations of Al, Si, and Fe (a), Waters are Na-Cl-Mg-SO4-rich brines (b), and (c),
excess sulfur (S) relative to sulfate (SO4-2) suggests that other S-compounds besides SO4-2 exist at low pH, and that the main acid is sulfuric acid (H2SO4)
(Bowen and Benison, 2008, Applied Geochemistry)
Water Chemistry Controls Sediment Chemistry
At many lakes, we made measurements and collected samples along transects, such as this small one at Twin Lake West. GW1, GW2, and GW3, and LW are locations (~2 m apart)
where waters were measured for pH, salinity, and temperature in the field, samples, and samples were later analyzed in the lab. At these sample locations, shallow core
samples were taken and their sediments was later analyzed.
Left, selected measurements that correspond to each of the four locations. Right, photos of shallow cores samples and corresponding core sediment chemistry.
This shows: (1) the link between groundwater composition and sediment composition; and (2) the spatial and temporal variations in water chemistry.
Temporal Fluctuations and Spatial Heterogeneity in Water Chemistry
Benison et al., 2007, Journal of Sedimentary Research and Bowen and Benison, 2008, Applied Geochemistry.
Detailed measurements of water pH (top) and salinity in TDS (bottom) over four field seasons has allowed us to note the spatial and temporal changes in the water.
Two maps on left represent Lake Aerodrome during an evaporation stage in July 2001. The two maps on the right show Lake Aerodrome during a flooding stage.
Note that the groundwaters show great spatial diversity, but do not change much over time, but that lake waters are not so diverse spatially, but are fluctuate
over time due to flooding and evaporation.
White rafts with shadows below are halite rafts floating on the water surface
Halite and hematite are unusual partners in nature, but are characteristic of acid saline lakes and groundwaters. Finding these minerals together in ancient rocks
would be a clue that there were once waters that were rich in Na, Cl, and Fe.
