At-a-station diurnal variations in carbonate hydrochemistry were measured during four observation periods at Davys Creek, a tufa-depositing stream in central NSW, Australia. Major ion concentrations and continuously logged measurements of specific conductivity, pH and temperature showed that changes in the amount of CaCO 3 deposited upstream of the study reach were directly related to changes in diurnal water temperatures, which control the rate of CO 2 efflux to the atmosphere. The greatest upstream losses occured during the mid-afternoon water temperature peak, whereas the lowest upstream losses occured at sunrise, when water temperatures were at their lowest. Cloudy days at all times of the year produced small diurnal water temperatures ranges (c. 2-5°C) and, consequently, relatively small changes in upstream CaCO 3 loss (23-50 mg L -1) through the day. Clear sunny days, especially during summer months, produced large diurnal water temperature changes (up to c. 11°C), which in turn triggered diurnal changes in upstream CaCO 3 loss of up to 100 mg L -1. By implication, the active reach of tufa deposition must advance downstream and increase in length during the evening and vice versa during the day. Given that the temperature of Davys Creek waters are a function of insolation, changes in the reach of tufa deposition under baseflow conditions are a direct function of the prevailing weather. This has implications for the palaeoclimatic interpretation of fossil tufa deposits.
- CaCO 3 deposition
- Data logging