The Benefits of Diver-Sampled Sediment in Shallow Coastal Locations

Minimizing the Disturbance for Accurate Read

One of the great benefits of diver-sampled samples is the fact that the structure of the sediments is, for the most part, undisturbed. Techniques that collect samples from the surface tend to create a high degree of perturbation during sampling and also have a tendency to disturb the natural stratification and biogeochemical properties of the sediments. Divers are capable of inserting and extracting core tubes with care and precision, so that the sediment-water interface is kept intact and the samples taken are more representative of existing conditions in situ.

Increased Accuracy and Reliability

The research identified that the samples collected through sediment cores by divers were very much within the range and close adherence to in situ measurements more than the values through techniques involving gravity coring. For example, levels of oxygen penetration depths (OPD) and total oxygen uptake (TOU) rates by diver samples were much closer to the actual conditions that existed in the environment. Particularly, the OPD was much shallow in the cases of Craib-cored samples (7.38 ± 0.26 mm) compared to the diver samples (7.88 ± 0.31 mm), and the in situ measurements identified the deepest OPD (8.0 ± 0.64 mm). This level of accuracy is very important for studies that rely on accurate biogeochemical data ([Mogg et al., 2017](https://www.researchgate.net/publication/320087255)).

Real-Time Observations and Adjustments

The third advantage of the use of divers is that it enables the taking of the in-situ observation of the sampling environment in real time. Real-time decisions can be taken on such observations, such as what to pull up, whether or not to reject the cores if they look like they were disturbed, and also on which sites to select that will be free of a visual disturbance. Real-time decision-making of that kind can help ensure that the samples are of high quality.

Tailored and Flexible Sampling for Surveys

Diver sampling is also more selective, allowing a targeting of collection and a selection of specific sites on the basis of direct observations. Such selectivity proves to be most useful in the case of complex or sensitive environments in which traditional coring techniques are sure to be impractical or too destructive to be implemented. Divers can also maneuver past obstacles and choose the best sampling sites, thereby ensuring representative and uncontaminated samples.

Reduced Equipment Footprint

The portability and relatively light weight of diver-operated sampling equipment is such that the physical disturbance to the sea floor is much less than that of heavier surface-deployed coring equipment. The lightness of impact is of special importance in sensitive or protected marine environments where disturbance is to be avoided.

Direct Observations and Holistic Insights

Having the divers on-site in the sampling environment allows them to give first-hand comments on the nature of the sediments as well as the progress of the sampling. Comments such as this, possibly having been born out of a first-hand observation of the context of the samples, may be of use in the course of making decisions and interpreting the study.

Technical Insights from the Research

1. Oxygen Penetration Depth (OPD) and Total Oxygen Uptake (TOU): - The study quantified the OPD and TOU in sediment samples obtained in two ways. Samples obtained by divers exhibited a greater OPD and a smaller TOU, suggesting less disturbance than in the Craib-obtained samples. The OPD was 7.38 ± 0.26 mm in Craib-cored samples, 7.88 ± 0.31 mm in diver-collected samples, and 8.0 ± 0.64 mm in in situ measurements. TOU was maximal in Craib samples (8.6 mmol m² d⁻¹) and diver-collected samples (5.8 mmol m² d⁻¹).