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Many of the traditionally sound cultural practices recommended for conventional agriculture are also employed in organic production. In fact, organic agriculture has been referred to as “good farming practice without using synthetic chemicals.”2 For example, planned crop rotations, which have multiple benefits in terms of soil building, plant health, pest management, and enhancing biodiversity, are required in annual organic cropping systems. Perennial cropping systems rely on alternative methods (such as intercropping, alley cropping, and hedgerows) to gain some of these benefits. Planting cover crops, cultivating, composting, irrigating, and using animal and green manures are also employed in organic. | Hydrological Chemical and Biological Processes of Transformation andTransport rf ContaminantsinAquatic Environments Proceedings of the Rostov-on-Don Symposium May 1993 . IAHS Publ. no. 219 1994. 21 Transport and fate of persistent toxic organic chemicals in aquatic ecosystems the Niagara River to St Lawrence River Estuary example R. J. ALLAN National Water Research Institute Canada Centre for Inland Waters Burlington Ontario L7R 4A6 Canada Abstract The transport and fate of persistent toxic organic chemicals in fresh-water ecosystems are controlled by many properties of the aquatic ecosystems themselves and of the specific chemicals. Predictions of the fate of specific chemicals can to some extent be modelled from chemical properties and laboratory tests but in real aquatic ecosystems accurate predictions of eventual sinks trends and concentrations in biota and response to remedial measures are site specific. This paper discusses the media involved in the aquatic transport of persistent toxic organic chemicals and the role of aquatic ecosystem media in the eventual fate of the chemicals. Specific examples are drawn from the last decade of research on the Niagara River to the St Lawrence River Estuary system. INTRODUCTION Detection of persistent toxic organic chemical PTOC contamination in the Great Lakes began in the early 1960s with pesticides such as DDT and dieldrin followed in the 1970s by other organochlorine pesticides and industrial organic chemicals such as PCBs. The insecticide mirex was then discovered in 1974 in fish in the Bay of Quinte chlorinated dioxins were detected in herring gull eggs from colonies in Saginaw Bay in 1979 and toxaphene was detected in fish from Lake Superior in 1982. Subsequent sampling has shown that many of these PTOCs can be detected in various media throughout the entire Great Lakes-St Lawrence River ecosystem. The available information on PTOC contamination of the Niagara River to St Lawrence Estuary system although far from .
