GROUNDWATER GEOCHEMISTRY OF A RIPARIAN WETLAND NEAR THE LITTLE TALLAPOOSA RIVER, GEORGIA, USA

This study examines groundwater chemistry of a riparian wetland adjacent to the Little Tallapoosa River in the Piedmont Physiographic Province, Carroll County, Georgia. Results show a complex spatial distribution of groundwater composition and relatively little temporal variation. We sampled groundwater from 20+ piezometers installed in three types of regolith: 1) organic-rich, predominantly fine-grained, contemporary floodplain alluvium, 2) pedogenically altered terrace alluvium, and 3) saprolite. Saprolite wells include one beneath contemporary floodplain alluvium and one in an upland position adjacent to the floodplain. Wells consist of 3.18 cm (1.25 in) PVC pipe completed at depths between 1.8 m (6.0 ft) and 4.8 m (16.0 ft). Samples were collected six times over a twelve-month period under conditions including drought and flood. Most waters are of a mixed-cation bicarbonate type; sodium chloride waters are also present. Approximate TDS ranges from 30 to 300 mg/L; pH ranges from 4.5 to 6.1. Concentrations of redox sensitive species (O₂, NO₃^-, Fe²⁺, Mn²⁺) vary considerably within the dataset and field-measured dissolved oxygen ranges from below detection limit to greater than 2.0 mg/L. Preliminary ICP analysis suggests As concentrations in some wells greater than 70 mg/L. Results show that hydrochemistry of this floodplain environment is heterogeneous over very small lateral distances and depths. At least some of the groundwater chemistry heterogeneity is explained by variable redox conditions due to unevenly distributed organic matter within sediment. Some heterogeneity may also be explained by diverse groundwater flowpaths into floodplain sediment.