Ballast Water Verification Project 

Project background 

Ballast tank  
                Container ship cross section in Busan Harbor, Korea

Ballast water is carried by ships to keep them upright during loading and offloading operations and to provide balance, stability, and trim during sailing. Ballast water is typically held in dedicated ballast tanks located around cargo holds and near the bow and stern of the ship. Since ballast water is loaded from the surrounding port or coastal waters, it can contain a diverse assembly of marine life. When released into a new port, organisms in the ballast water can sometimes establish non-native populations, resulting in "biological invasions". Some biological invasions have severe ecological or economic impacts. 

Foreign ships arriving to the USA are required by law to perform mid-ocean ballast water exchange (BWE) to reduce ther risk of biological invasions. During BWE, the vessel replaces its coastal ballast water with water from the open ocean. This process removes most of the coastal organisms from the ballast water, thereby reducing the likelihood that non-native species can establish when the ballast water is released in a coastal port.


    Tracer sampling on the MV Lily Fortune 

To assist in the enforcement of mandatory ballast water exchange regulations, reliable methods are needed to verify that BWE was performed by ships. SERC is investigating tracer methods for deducing ballast water sources. Several tracers have been identified that assist in identifying unexchanged ballast water, including salinity, optical characteristics of chromophoric dissolved organic matter (CDOM), and several trace elements. SERC has developed protocols for sampling ballast water for BWE verification purposes that are available online.

 Enforcement methods: Salinity as an indicator of ballast water exchange

Ballast water enforcement officers in the USA currently use several criteria to determine if a ship has complied with the mandatory ballast water management practices. These procedures are spelled out in the Navigation and Inspection Circular 07-04, Ch-1 published by the United States Coast Guard. The first step in the enforcement process is the careful examination of ballast water management records to determine if the ship has properly managed its ballast water. Samples of ballast water can also be collected if a vessel is suspected of discharging unexchanged ballast water.

Salinity can be an indicator of BWE, because the coasts are generally less salty than the open ocean due to freshwater inputs from rivers and runoff. The United States Coast Guard has laid out general guidelines for using salinity to verify exchange. Based on their criteria, ballast water with salinity below 30ppt or above 40ppt is determined to have been inadequately exchanged. However, salinity cannot be used as a stand alone measure of BWE compliance when the ballast water has salinity from 30-40 ppt, since many ports are as saline as the open ocean. 

New indicators of ballast water exchange

Following shipboard experiments and extensive ballast water sampling, SERC has identified several tracers that assist in distinguishing between high salinity coastal and oceanic ballast water. These tracers are naturally-occurring chemical constituents that differ in concentration between coastal and oceanic environments due to their differential proximity to terrestrial sources. Tracers with demonstrated utility for verifying high-salinity BWE include chromophoric dissolved organic matter (CDOM) and several trace elements (Murphy et al. 2006; Murphy et al. 2008).


                     Example of CDOM fluorescence EEM

Chromophoric dissolved organic matter (CDOM)

Chromophoric (or colored) dissolved organic matter (CDOM), is the colored fraction of dissolved organic carbon. CDOM is colored because it absorbs light within the visible spectrum, while also absorbing UV-A (315-400 nm) and UV-B (280-315 nm) light. CDOM is a primary factor affecting the absorption of sunlight in coastal and estuarine waters and consequently the ability of water to transmit sunlight for photosynthesis. In estuaries, CDOM concentrations change with salinity gradients and with changes in industrial effluents, agricultural and urban runoff, and biological activity. In coastal and ocean water, CDOM concentrations generally decrease with increased distance from shore and water depth. Since oceanic concentrations of CDOM are very low, high CDOM is a good indicator of coastal ballast water. CDOM concentrations are correlated with the intensity of fluorescence in the ballast water.

CDOM fluorescence can be measured by excitation emission matrix spectroscopy (EEMS). Each sample produces a three dimensional spectral image (an EEM) of CDOM fluorescence intensity from which various components can be distinguished. Natural fluorescence of certain proteins produced in estuarine, coastal and marine environments are often associated with plankton blooms, microbial activity, or inputs from underlying sediment. All three components occur in varying amounts according to the proximity and intensity of terrestrial and marine sources and sinks, and the mixing of marine and fresh water masses (Murphy et al. 2008). Our experiments on commercial vessels suggest that it is possible to distinguish between exchanged and unexchanged ballast water using simple thresholds of CDOM intensity at fixed positions within the EEM (Murphy et al. 2006)

Trace elements

Many trace elements occur in surface coastal waters at much higher or lower concentrations than in the open ocean and are potential tracers of unexchanged ballast water. Trace elements have been measured in >40 ballast tanks on eight ships to determine which elements can best distinguish between coastal and oceanic ballast water. Initial results indicate that concentrations of barium (Ba), phosphorus (P) and manganese (Mn) can be measured accurately in ballast tanks and are usually lowest in tanks that have undergone BWE (Murphy et al. 2008). Other elements such as iron, copper and zinc are sensitive indicators of terrestrial seawater but can not be measured accurately in ballast tanks due to contamination from the ship's structural materials.


               Tracer sampling on the MV Asahi Sunrise


Natural and artificially produced radioactive tracers can be used to monitor oceanic processes such as sediment deposit chronology and water mass mixing. Radium has four naturally occurring isotopes that have well studied and quantifiable source and sink functions. The four radium isotopes (223-Ra, 224-Ra, 228-Ra and 226-Ra) have a wide range of half-lives that correspond well with the duration of many coastal processes and are potential tracers of BWE.

Two of these isotopes, 223-Ra, 224-Ra, have been investigated as tracers of BWE (Murphy et al. 2004). Although a sensitive water tracer, radium offers less potential for BWE verification because sampling is relatively difficult and time consuming. Radium samples in our studies were collected by slow (1-2 L/min) filtration of 300 liters of ballast water (stored in two 150 litre bladders) through a manganese soaked fiber. This process required at least two hours for each sample. More practical methods for quantifying low concentrations of radium in seawater are needed, since BWE enforcement officers lack the time and space to conduct ballast water sampling by this method.


Radium sampling aboard the MV Ciclope