||Fettweis M1, Toorman E2, Verney Romaric3, Chapalain Marion3, Legrand S1, Lurton Xavier4, Montereale-Gavazzi G1, Roche M5, Shen X2, Van Den Eynde Dries1, Van Lancker Vera1
||1 : Royal Belgian Institute of Natural Sciences, ODNature, Rue Vautier 29, 1000 Brussels, Belgium
2 : Hydraulics Laboratory, Department of Civil Engineering, KU Leuven, Kasteelpark Arenberg 40, 3001 Leuven, Belgium
3 : IFREMER, Laboratoire DHYSED, CS10070, 29280 Plouzané, France
4 : IFREMER, Underwater Acoustics Laboratory, IMN/NSE/AS, CS 10070, 29280 Plouzané, France
5 : Federal Public Service Economies, Continental Shelf Service, Boulevard du Roi Albert II 16, 1000 Brussels, Belgium
To protect the marine environment more effectively, the European Union adopted the Marine Strategy Framework Directive (MSFD) in 2008, aiming to achieve the Good Environmental Status (GES) of the EU's marine waters by 2020 and to protect the resource base upon which marine-related economic and social activities depend. A major challenge in the implementation of the MSFD is to achieve the necessary scientific knowledge on the marine environment, its processes and the methods to monitor them. The focus of INDI67 is on the evaluation and development of indicators to monitor GES of descriptor 6 and 7. Seafloor integrity (descriptor 6) refers to the structure and functions of the benthic ecosystems. It relates to the comprises physical, chemical and biological properties as well as to spatial and temporal connectedness, avoiding artificial fragmentation of habitats or temporal sealing due to ephemeral sediment deposits or armouring. Hydrographic conditions (descriptor 7) imply that the nature and scale of any long-term changes to the prevailing hydrographical conditions resulting from anthropogenic activities (individual and cumulative), do not lead to significant negative impacts on the benthic and pelagic habitats, functioning or on hydro-geomorphological impacts on the seabed.
The overall objective of INDI67 is to develop and evaluate tools and methods to support the monitoring of MSFD descriptors 6 and 7. The subject is the monitoring of seafloor integrity and hydrography using both modelling and measurements of hydro- and sediment dynamic processes and seabed characteristics. Three parameters have been selected as key indicator, i.e. turbidity, bottom shear stress and seabed/habitat type. These parameters are all related to sea floor dynamics and are strongly linked as changes in seafloor integrity and turbidity occur as a result of the combined force that waves and currents exert on the sea floor. Furthermore, they are witnesses of changes induced by human activities (dredging/disposal, aggregate extraction, constructions, fishery). Turbidity (used both in terms of suspended particulate matter(SPM) concentration and light availability) and bottom shear stress are currently measured and modelled. Bottom shear stress and seabed/habitat type are included in the Belgian MSFD monitoring programme, while turbidity is not yet included as GES indicator.
The major conclusion with respect to the measuring and modelling of the key indicators turbidity/SPMC, bottom shear stress and seabed/habitat type are:
1) Despite calibration to a reference solution and the use of ISO-normed optical turbidity sensors, model calibration may vary considerably in recorded turbidity for a same SPMC solution across different instruments resulting in instrument-specific turbidity-SPMC relation. Turbidity (or dB for acoustic sensors) should therefore not be used as it is not standardized and will diminish the comparability of the data. Instead, the optical and acoustic sensor output should be transformed into a mass concentration, a unit that is comparable in time and between regions. Monitoring in situ SPMC should follow common guidance and protocols to restrict their measurement uncertainties. The main challenge is now to evaluate model results uncertainty and improve the formulation of natural processes, such as flocculation and bottom shear stress, together with the effects of pressures in the models.