ballastvattenexchange

Ballast water exchange is a ballast water management practice used on ships to reduce the transfer of aquatic organisms and pathogens by replacing ballast water drawn from one area with water from another, typically from the open ocean, during ballast operations. Ballast water is taken on to maintain stability and trim, and discharged at the destination; if the water contains non-native species, they can establish in new regions.

There are two common exchange methods. In sequential exchange, ballast tanks are partially or completely emptied and refilled several times with seawater, displacing the original water. In flow-through exchange, seawater is pumped in while ballast water is discharged in a one-way flow, gradually replacing the original contents. The aim is to minimize the survival of coastal organisms by diluting and changing salinity, temperature, and microbial communities. Exchange is typically conducted in offshore waters well away from shore and in water deep enough, though the exact offshore criteria vary by regulation and operational factors.

Regulatory context and practice: The International Maritime Organization’s Ballast Water Management Convention requires ships to manage ballast water to reduce invasions, either by approved exchange methods or by ballast water treatment systems, and to maintain a ballast water management plan and record. Many national regimes complement or tighten these requirements, sometimes mandating ballast water treatment systems (BWMS) in addition to, or instead of, exchange.

Effectiveness and limitations: BWE reduces, but does not guarantee, elimination of invasive organisms. Effectiveness depends on water conditions, timing, and adherence to procedures. It is commonly used in conjunction with ballast water treatment technologies to provide larger safeguards against biological introductions.