Gabrielle Mawby, from Xodus, gives the practitioner's view on benthic surveys and their importance for marine environmental impact assessment (EIA)
The development and execution of a sound survey strategy is very important to EIA. The initial steps for any EIA should look to kick off the screening process with an evaluative environmental issues identification (ENVID) workshop. The ENVID examines the issues that may affect the project. Following this the EIA can be scoped.
For most marine developments it becomes clear that the seabed will experience some level of impact due to the nature of inshore and offshore ventures. Benthic surveying will, therefore, be compulsory. The benthic zone is the ecological region at the lowest level of a body of water (be it a sea, ocean or lake), including the sediment surface and some sub-surface layers. Organisms living in this zone are called the benthos.
A pre-installation survey will usually be required depending on the existing data available. Data collected during this survey will inform the assessment of impacts to the benthic community. The robustness of this assessment will be significantly affected by the quantity and quality of information available.
Benthic ecology
Benthic ecology is an important component in consideration of how significant an environmental impact a marine development will have. Benthic communities vary in complexity level and it is this complexity that helps determine the environmental significance of the area, the sensitivity of the flora and fauna and the overall feasibility of the development.
The important aspects of a benthic survey include the assessment of:
- the substrate – incorporating studies of sediment consistency and chemistry, where relevant;
- the geography of the seabed; and
- the site’s proximity to areas of high sensitivity – ultimately the fauna and flora (benthos) inhabiting the area at different levels within the column and seabed.
Pre- and post-installation surveys
A pre-installation benthic survey establishes the initial baseline for the EIA highlighting the sensitivities of the benthos so as to ensure protection occurs where necessary. This is often valuable to allow for further comparison later on in the EIA when consequences will have had time to develop.
After the project installation it is good practice to undertake a survey to judge if the impacts were as predicted in the EIA. It is a way of validating the assessment and this validation will be more robust if the pre-installation survey is of a high standard.
Other surveys post-installation include decommissioning surveys. Following a well-developed decommissioning strategy is invaluable as it encourages a thoroughly holistic EIA.
Benthic surveys in the field
Xodus has recently completed an EIA including benthic surveys for a marine renewables project using a wave power device attached to the seabed.
Due to licence conditions it was required to conduct benthic surveys for the EIA. A pre-installation survey was carried out to establish a baseline for impact assessment.
The wave regime at the project’s location is of fluctuating turbulence. This makes the area potentially sensitive to strong currents and it was in reasonable proximity to the coastline where biodiversity is often rich.
The pre-installation seabed survey followed the European Marine Energy Centre guidelines to ensure a robust analysis of the seabed. Remotely operated vehicles were used in numerous locations to gain clear footage and stills of the area to see whether the zone contained any sensitive or protected species or habitats before the foundations could be inserted.
Results of the surveys showed the seabed in the vicinity played host to kelp parks and forests which would require clearing. The clearing would, of course, impact the kelp species and their ecosystem, and the discharge of drill cuttings from pile installation also had the potential to result in seabed impacts. However, the area of the seabed affected was very small and only represented a tiny percentage of the locally present habitat, with the species concerned showing widespread abundance in the area.
The recovery rate of the organisms was expected to be rapid and the overall negative impact imposed on the benthic environment was assessed to be not significant. For this development it was vital to carry out the seabed surveys to prove the impact was low and allow for a comparison to be made post-installation.
This project was one of the first of its kind, leaving a window for the unknown and so a post-installation survey is important. This was also a requirement of the projects license and will assist both in the development of mitigation measures that might be appropriate for future projects. Without the EIA’s inclusion of benthic surveying, mitigation measures could not be developed for further progression in this new area of energy generation.
This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.
Gabrielle Mawby is an assistant environmental consultant at Xodus
