Marine Pollution Monitoring via Coastal Surveys

As everybody knows, environmental pollution has been a topic of growing concern over recent years. Pollution can detrimentally effect both human life and other living systems that form part of our biosphere and upon which we are ultimately inextricably dependent.

Concern about pollution extends to the damage it may do to the marine environment, particularly in the near-shore coastal environment which plays a key role as a hatchery for much of the marine biota. For this reason, many coastal states have established marine monitoring programmes which are designed to evaluate the status of the marine environment with respect to heavy metals pollution or petrochemical pollution amongst other sources. Monitoring campaigns usually take one of two formats: trend monitoring or hot-spot monitoring.

 

The purpose of Hot-Spot monitoring is to evaluate the pollution at a specific location where it is believed a pollution event may have occurred (an example of this might be in the vicinity of a new wreck where concerns exist over spillage of cargo or fuel oil, for instance). Hot-spot monitoring may also be conducted in the vicinity of shore based construction activities, such as harbour extensions, or following dredging activities. In this latter case, baseline measurements should ideally have been made of the pollution levels in the vicinity before the construction or dredging activities began such that their impact can be assessed. When this is not possible, comparison samples may be taken from a nearby location which is believed to be unaffected by these activities.

Trend Monitoring, as the name implies, is a longer term activity where designated coastal measuring stations are monitored at regular intervals, perhaps across a season or over several years. The intention is to look at the history of a particular type of pollution over time and at various locations. Is the pollution increasing, declining or staying roughly constant. Are the sources of pollution changing over time?

One programme that I was involved with has been monitoring designated sites within the Gulf region since the aftermath of the first Gulf war in 1990. That campaign now has trend data that stretches back for almost 20 years.

Typically, in this type of marine pollution survey, surface sediment samples are collected using a Van Veen grab sampler and are specifically collected either for metals or organic contaminants. The grab sampler is dropped to the seabed and the jaws of the device shut, trapping a sample of the surface sediment for subsequent analysis in the laboratory. The sample is carefully hauled back aboard the survey vessel, excess sea and pore water is allowed to run off and then the sediment is transferred to an appropriate, properly labelled and coded sample container.

In both types of monitoring activity, the sample station location position is accurately determined using a GPS device and the depth of water at which the sample was taken is recorded (either by sonar, if available, or crudely, by noting the length of rope that had to be deployed to get the sampler to the seabed).

In some coastal surveys, divers are sent down to collect marine biota specimens such as mussels or rock and pearl oysters. The divers are usually local people who will have the knowledge to find suitable locations to collect appropriate specimens. Usually,the same team will conduct regular surveys and the diver will be able to ensure that samples are collected from the same area each time it is surveyed. These marine molluscs feed on marine sediments and consequently, their tissues provide valuable information about marine pollution levels. It may also be the case that fish can be included in a coastal survey (typically a predatory fish and a grazer would be collected), but unless these can be caught on station, care needs to be taken in interpreting the data. Fish obtained from a market can be used, but then it is best to take samples from markets well dispersed along the coast that is being studied, such that they will better reflect the pollution in the local regions where they lived, fed and were caught.