Protecting Surface Water Systems on Forest Sites Through Herbicide Use

Abstract

Sediment, nutrients, and pesticides are universally accepted as the greatest threats to surface water quality world-wide. Sedimentation in surface waters is a natural phenomenon, but is magnified by human activities. Intensive forest management practices, particularly road building, harvesting and planting site preparation, result in the greatest increases in erosion from forest sites. Significantly more sedimentation occurs on steeper slopes, finer-textured soils, and where episodic storms occur most frequently. Research has shown extreme events are more important than average events or streamflow levels in determining annual losses of sediment and other non-point pollutants. Factors important in reducing erosion and resultant sedimentation include percent groundcover and number of rooting stocks remaining intact to hold soil in place. Herbicides used in the Southern United States (South) in forest vegetation management programs typically kill residual vegetation leaving plant residues and root stocks in place. Use of these herbicides has been demonstrated to reduce erosion and when used in conjunction with streamside management zones greatly reduce sedimentation in streams. While stream contamination by forest herbicides is often cited as a threat to surface water systems, research in the South has demonstrated that these herbicides used according to label directions do not result in adverse impacts on aquatic ecosystems. Further, extensive monitoring of offsite movement of herbicides in stormflow and baseflow shows drinking water standards in the USA are not exceeded on the treated sites. Downstream dilution further reduces the potential for adverse impacts. Herbicide movement from treated sites to streams draining treated catchments can not be detected after 3-6 months. Thus herbicides, properly used in intensive forest management, have the potential to greatly reduce the sedimentation of streams and protect surface water.

Citation

Michael, J.L.; Gibbs, H.L.; Fischer, J.B.; Webber, E.C. 2000. Protecting Surface Water Systems on Forest Sites Through Herbicide Use. In. Xth World Water congress: Proceedings water the world''s most important resource, 12-17 March 2000; Melbourne, Australia.