Impacts of salinity stress caused by ballast water discharge on freshwater ecosystems

Abstract

Global commodity trade and the transportation of goods rely heavily on shipping. But the discharge of large quantities of hypersaline ballast water carried by maritime vessels into freshwater ports, lakes, rivers and other water bodies cause salinity stress, which can be detrimental to native freshwater organisms. In this study, the effects of marine hypersaline ballast water discharge and the rate of discharge (abrupt vs. gradual) on inland freshwater lakes were assessed by observing changes in freshwater plankton communities under salinity stress. The findings indicate that increasing salinity has a negative impact on plankton community composition, density and biodiversity. Zooplankton were more sensitive to changes in salinity than phytoplankton through 10 consecutive days of experiments. Moreover, the plankton community showed some ability to recover itself at low salinities (S≤6.5 PSU). In terms of the rate of ballast water discharge, plankton were more likely to survive in aquatic environments with gradual changes in salinity than with abrupt changes. This research is of great significance for the scientific management of ballast water discharge in freshwater ports and the conservation of freshwater ecosystems.