The pressures on coastal sea areas from industrial activity have been increasing in recent years, as have pressures from the use of the sea and sea bed as a site for the disposal of waste material In parallel with this increased usage of the sea has been an increase in concern for the health of the marine environment by both public and, in reaction, by their governments.

UK offshore oil operators are now obliged by law to carry out environmental monitoring in the vicinity of their production platforms Dredge spoil and sewage sludge disposal operations require monitoring programmes as a condition of licence to dump at sea Prior to this many companies and other users of the sea conducted monitoring programmes regardless of their legal obligatios.

The methods of monitoring the sea bed have changed little over the last 10 to 15 years There are usually two approaches one concerned with direct measurement of chemical contamination, the other with possible effects the particular operation is having on the biological environment.

Although the water column is sometimes sampled, the emphasis for offshore monitoring has invariably been the sea bed and its sediments This is not unreasonable since the sediments, and the particles that make it up, are likely to accumulate any contaminants by adsorption.

Being for the most part sedentary, the animals that live in the sediment are unable to move away from the area of effect and so can be used as biological indicators of stressful conditions, being particularly of value for monitoring intermittent insult to the environment.

SAMPLING PROGRAMMES

Most offshore sea bed monitoring programmes require the biological and chemical analysis of sediment samples acquired remotely from surface operated sampler systems Recently some attention has been turned to direct observation using underwater television However, whilst this approach is satisfactory for so called ‘skilled eye survey’ for the detection of gross effects, accurate quantification of chemical and biological parameters is essential if incipient environmental changes are to be detected.

The sedimentary environment is theoretically one of the easiest to sample quantitatively and has long been recognized as a potentially useful medium for sea bed environmental monitoring However, in practice the reliable acquisition of samples of suitable integrity for chemical and faunal analysis has proved extremely difficult This is largely a result of the design and mode of operation of existing equipment.

Most offshore monitoring surveys presently conducted by UK operators utilize a 0 1 m2 grab sampler as their central piece of sampling equipment These are used for both faunal samples, when the grab contents are retained in their entirety and then sieved to remove the biota from the sediment, and for chemical/physical samples, when a subsample is usually taken from the surface of the sediment obtained In both cases the sampling programme is reliant on the grab sampler's taking consistent and relatively undisturbed sediment samples.

CURRENT GRAB SAMPLER TECHNOLOGY

Although there are a great many designs for benthic samplers, three types of bottom grab sampler are used almost exclusively by UK

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