The spatial and temporal variations in calcite ( @entity4959 ) solubility within the Dee basin of NE Scotland were assessed using water chemistry data gathered from a network of 59 sites monitored for water quality from June 1996 to May 1997. Calcite solubility, expressed in terms of a saturation index (SIcalcite), was determined from measured streamwater pH, Gran alkalinity and @entity460 concentrations and water temperature. In general, the waters of the Dee system are undersaturated with respect to calcite, though the saturation index is higher during the summer months indicating a dependency on flow conditions and biological activity. Under low-flow conditions, the streamwaters are dominated by water derived from the lower soil horizons and deeper groundwater stores and therefore, ions such as Gran alkalinity and @entity460 are at their highest concentrations as they are derived mainly from bedrock weathering. The influence of biological activity on the @entity6445 system is also evident as the observed pH and estimated EpCO2 values indicate strong seasonal patterns, with the highest pH and lowest EpCO2 values occurring during the summer low-flow periods. Only at three sites in the lowland region of the catchment, during the summer low-flow period, are the waters oversaturated. As such, the Dee system represents an extreme 'end-member' case when compared to many UK rivers that span both under- and oversaturated conditions during the year. Regression analysis highlights a systematic change in the SIcalcite-pH relationship in a broad east-west direction across the Dee system. At sites draining the relatively impermeable upland areas, the regression of SIcalcite against pH gives a straight line with a gradient in the range 1.6-2.4. Correspondingly, under the most extreme alkaline conditions found at sites draining lowland agricultural areas, a straight-line relationship exists but with a gradient of unity. It is concluded that these changes in the SIcalcite-pH relationship are due to variations in the @entity3157 system induced by the flow conditions and biological activity. Given the waters are undersaturated, then calcite precipitation and hence @entity3151 co-precipitation cannot occur within the water column.

XXXX saturation in the River Dee, NE Scotland.

@entity6445 :: ('CHEBI:41609', 'Chemical') :: ['carbonate'] @entity3157 :: ('CHEBI:17544', 'Chemical') :: ['bicarbonate'] @entity4959 :: ('MESH:D002119', 'Chemical') :: ['calcium carbonate'] @entity460 :: ('MESH:D002118', 'Chemical') :: ['calcium'] @entity3151 :: ('MESH:D010758', 'Chemical') :: ['phosphorus']
@entity4959 :: (MESH:D002119,Chemical) :: ['Calcite']
