Title: Role of Riparian Buffer Systems in Filtering Agricultural Effluents

Cooperators: R.K. Hubbard, R.R. Lowrance, G.L. Newton

Problem:

Excess nutrients from animal wastes pose a serious threat to soils, surface water and groundwater. Contamination of surface waters may result in fish and invertebrate kills and eutrophication. Contamination of groundwater may render it unsuitable for drinking. Methods are needed to treat and utilize the nutrients contained within lagoon wastewater.

Approach:

Studies have shown that riparian buffer systems are effective in filtering sediment and nutrients entering from upslope agricultural fields. The mechanisms involved are both physical and biological, including deposition, uptake by vegetation, and loss by microbiological processes such as denitrification. Research using small plots is evaluating overland flow-riparian buffer systems for assimilation of nutrients contained within swine lagoon wastewater. The wastewater is applied through slotted pipes to the top end of plots which are 4 m wide and 30 m long. The buffer systems being tested are 10 m grass draining into 20 m natural riparian forest, 20 m grass draining into 10 m natural riparian forest, and 10 m grass draining into 20 m of the recommended wetland species maidencane. In addition to this study, which started in 1993, two new studies using this same concept are currently in progress. A larger scale study on a commercial hog producer=s land is evaluating this same system where the application areas are 60 m wide. The vegetation for this study is 10 m grass buffer draining into 20 m of natural riparian forest. A study with a commercial alligator producer is using overland flow application to areas which are either grassed or in forest.

Results:

The plot scale study has shown that these systems are effective in assimilating N. While nitrate concentrations in shallow groundwater have increased at the top ends of the plots, concentrations at the bottom ends after 3 years of wastewater application are still at background levels. Phosphorus is also being assimilated in these systems, although levels in shallow groundwater increased over time. As with upland areas, it appears that wastewater application rates will have to be based on P content of the wastewater rather than N content. Insufficient data have been collected so far from the larger scale swine and alligator lagoon wastewater studies to draw any conclusions.