Calcite saturation in the River Dee, NE Scotland

Area of Science:

• Geochemistry
• Environmental Science
• Hydrology

Background:

• Calcite (calcium carbonate) solubility is crucial for aquatic ecosystems.
• Understanding spatial and temporal variations in riverine calcite saturation is key to biogeochemical cycling.
• The Dee basin in NE Scotland provides a unique case study for riverine carbonate system dynamics.

Purpose of the Study:

• To assess spatial and temporal variations in calcite solubility within the Dee basin.
• To determine the factors influencing calcite saturation index (SIcalcite) in streamwaters.
• To compare the Dee system's calcite saturation characteristics with other UK rivers.

Main Methods:

• Water chemistry data from 59 sites (June 1996-May 1997) were analyzed.
• Calcite saturation index (SIcalcite) was calculated using pH, Gran alkalinity, calcium, and temperature.
• Regression analysis was employed to examine SIcalcite-pH relationships across the catchment.

Main Results:

• Dee basin waters are predominantly undersaturated with respect to calcite.
• Calcite saturation index (SIcalcite) is higher during summer low-flow periods, influenced by flow and biological activity.
• Waters are oversaturated only at three lowland sites during summer; the system is an 'end-member' case compared to other UK rivers.

Conclusions:

• Variations in the SIcalcite-pH relationship are linked to bicarbonate system changes driven by flow and biological activity.
• The general undersaturation of Dee basin waters prevents calcite precipitation.
• Consequently, phosphorus co-precipitation within the water column is inhibited.