Analysis of Overseas Vessel Transits into the Great Lakes and Resultant Distribution of Ballast Water

Abstract

The introduction of nonindigenous species into the Great Lakes has caused grave economic and ecological damages to the entire region. It is thought that a primary vector for release of threatening species arises from the ballast discharges of vessels originating from overseas ports, and to a lesser degree, vessels which originate from the North American seaboard. Of particular concern are those vessels entering fully loaded, with no ballast on board (NOBOB), which through normal operations mix and discharge Great Lakes freshwater with unpumpable residuals left in empty tanks. In this study, a model of vessel ballasting operations is applied to all overseas vessel transits of the 1995 shipping season in order to quantify the amount and location of ballast transfers taking place within the Great Lakes. Results for 1995 are also aggregated to overseas and domestic traffic data over the past several years. The model demonstrates that although a large portion of ballast discharges are made in the major grain ports, significant risks for foreign species introduction exist throughout the Great Lakes.