DRAINAGE-SUBIRRIGATION EFFECT ON WATER-QUALITY IN GEORGIA FLATWOODS

The effects of controlled-drainage-subirrigation (CD-SI) systems on subsurface and outflow water quality must be evaluated before these systems can be promoted for use in the Georgia flatwoods region of the eastern Coastal Plain. In this paper, Nitrate-nitrogen (N), ammonium-N, and orthophosphorous (P) concentrations are measured from shallow subsurface wells and outlets of a CD-SI system in the Georgia flatwoods for comparison to adjacent forested and grassland areas (the most common current land uses). Nitrate-N concentrations did not exceed 10 mg/L from any of the outflow samples although almost 6% of the well samples taken from the CD-SI area had concentrations exceeding 10 mg/L. Nitrate-N concentrations in most of the wells in the CD-SI area were significantly higher than in the forested and cleared areas. Ammonium-N and ortho-P concentrations were relatively low and do not appear to be a problem based on this limited data. No significant differences in ammonium-N and ortho-P concentrations were shown between any of the sites. Ammonium-N concentrations did exceed 2 mg/L from at least one sample of the scrub forest, one of the CD-SI blueberry sites, an open ditch (1.8 m depth), and one of the cleared unirrigated sites. Ortho-P concentrations ranged from 0 to 1.94 mg/L, with average concentrations from all sites near 0.1 mg/L.