Principal Investigator: Richard Lowrance (University of Georgia)
Principal Investigator: Adel Shirmohammadi (University of Maryland)
Principal Investigator: Daniel L. Thomas (University of Georgia)
Sponsor: GWRI
Start Date: 1986-04-01; Completion Date: 1987-03-31;
Keywords: drainage, water quality, nitrates, ammonium, phosphates, pH, chlorides, electrical conductivity, drainage quality, water quality sampling, subirrigation.
Description:
Nitrate-N, Ammonium-N, Phosphate-P, pH, electrical conductivity, and chloride concentrations were measured from shallow subsurface wells and outlets of a drainage-subirrigation system in the Georgia flat woods. These data were compared to shallow subsurface water quality from adjacent forested and cleared areas using Duncan’s Multiple Range Test at the 0.05 level. A simulation of the nutrient movement from an area representative of the study site was also performed for a preliminary evaluation of the models applicability to the Georgia flat woods region.
Nitrate-N concentrations were significantly higher in the drained-subirrigated area than in the forested and cleared areas. Nitrate-N concentrations did not exceed 10 mg/l from any of the ouflow samples even though several infield samples did exceed this limit. Ammonium-N concentrations were not high and do not appear to be a problem in this drainage-subirrigation system based on the limited data available for this report. No significant differences were found between sites, but the sample size may not have been large enough to show a significant difference.
Phosphate-P concentrations were relatively low as compared to other water quality studies and only one site (cleared-unirrigated area) had significantly higher phosphate-P concentrations from all the other sites. The low phosphate-P concentrations of the outflow samples (less than 0.05 mg/l) indicates that the low clay content, sandy soils of this area have considerable ability for phosphate-P fixation and may not promote excessive leaching of phosphates.
The pH of all the shallow well sites were significantly lower then the inflow, outflow and surface water samples. However, the extremes in the pH measurements were not great enough to cause concern. The effect of the water supply on the outflow samples during the irrigation phase was evident in the pH results. The benefits of using alternative water supplies to reduce potential problems associated with the pH of outflow water needs further study.
The electrical conductivity and chloride concentrations from the drained-subirrigated areas indicates a potential problem if sufficient rainfall does not occur during the growing season to leach the salts. Significantly higher chloride concentrations were found in the drained-subirrigated field than in the cleared and forested areas. The drought period in 1986 showed a marked increase in chloride concentration under the drainage-subirrigation field, but the levels decreased after sufficient rainfall leached the salts from the soil.
Research is continuing on the evaluation of these water quality parameters to further verify the results presented in this report.
Preliminary simulations using CREAMS-WT (a derivative of the CREAMS model) on a field with similar characteristics to the drainage-subirrigation site, indicate that the potential nutrient losses in surface runoff were not severe. The model is not designed to simulate forested or cleared conditions so comparisons with existing conditions were not available