CALCIUM CARBONATE PRECIPITATION WITHIN MISSOURI SPRINGS: CAUSES AND MECHANISMS

Colloidal white precipitates, suspected to be calcium carbonate (CaCO₃), are commonly observed in springs of Missouri as well as other regions. The waters that are expelled from Missouri springs are usually saturated in Ca and Mg due to dissolution of carbonate strata in the source area. The goal of my research project is to try and identify the mineralogy of the precipitate material, and the chemical mechanism(s) that causes its precipitation. Samples to be analyzed will be collected from Meramec Spring, located within Meramec State Park, St. James, Missouri.

Current hypothesizes regarding the precipitation of (CaCO₃) include a change in temperature, pressure, and/or the chemistry of the spring system (e.g., a change in dissolved CO₂ concentration). All of the measurements reported below were collected during eight separate visits to the site during the summer months, where five locations on the spring system were measured. Spring water temperatures measured at the point of upwelling were 13.9 ± .30 ^oC. Downstream water temperatures were 13.7 ± .30 (55 m from conduit), 13.8 ± .27 (85 m), 13.8 ± .38 (285 m), and 14.2 ± .23 ^oC (670 m). Eight rounds of pH measurements were also taken at the same dates and locations. At the point of upwelling the pH values averaged 7.01 ± .11. These values progressively increased downstream to: 7.09 ± .13 (55 m), 7.09 ± .20 (85 m), 7.24 ± .15 (285 m), and 7.31 ± .12 (670 m). The general trend displayed at this location is that the pH and temperature of the water both increase slightly downstream from the spring conduit. Conductivity measurements were only collected on the last four trips to the site. Unlike temperature and pH, conductivity measurements were relatively consistent throughout the sampling reach of the stream. These measurement values ranged from 196 to 309 micro-Siemens/cm and tended to be higher on days following local rain events. Eh values were measured only during the last sampling trip. Values decreased slightly, but progressively downstream, in correlation to the increasing pH values. The Eh values ranged from +3 (55 m), -5 (85 m), -10 (285 m), and -13 millivolts (670 m).

Future analyzes that will be conducted will include Ca and Mg hardness, cation analysis and alkalinity. The precipitate samples will also be analyzed by Scanning Electron Microscopy (SEM).