7 EXISTING CONDITIONS IN THE PROJECT AREA
7.1 Environmental baseline surveys
The environmental baseline description has been prepared on the basis of peer-reviewed scientific literature, relevant EIAs (e.g. the national EIA report for NSP, which provided a valuable source of empirical data for the area), as well as other relevant technical reports and data for the area. This has been supplemented by a number of surveys that have been conducted in Danish waters in order to inform route development as well as to ensure a solid basis for the baseline description and subsequent impact assessment. A number of these surveys were undertaken to inform route de-velopment and are therefore discussed in section 6.
Environmental baseline surveys were undertaken in Danish waters from several vessels in the pe-riod November 2017-January 2018. These surveys are described in general terms below, whilst further details can be found in the survey report /80/.
Water column
A water column survey was undertaken in November-December 2017 along the proposed NSP2 route in Danish waters (see Figure 7-1).
Figure 7-1 Survey stations for water column sampling.
The survey included the following sampling activities:
• Measurements of physical-chemical properties of the water column carried out with a conduc-tivity, temperature, depth and oxygen (CTDO) recording unit;
• Niskin water sampler for calibration and verification of oxygen content at 1 m above the
sea-Figure 7-2 CTDO profiler and Niskin water sampler.
The key results of the survey are presented in section 7.5.
Seabed conditions
Seabed conditions were surveyed in November-December 2017. Sampling of surface sediment and deeper sediment was undertaken at the stations shown in Figure 7-3.
Figure 7-3 Survey stations for surface sediment (HAPS) and deeper sediment (vibrocore).
The survey included the following sampling activities:
• Before sampling, a ROV video sequence was recorded, covering the sediment surface at and around each sampling station;
• Sampling of surface sediment was undertaken with HAPS sampler (samples from 0-0.02 m depth for chemical analysis and from 0-0.05 m depth for physical analysis);
• Sampling of deeper sediment undertaken with a vibrocore (divided into subsamples/intervals of 0-0.5 m; 0.5-1.5 m and 1.5-3.0 m);
• Photography and description of each sample, including sediment composition, oxidised layer, colour and odour.
The sediment samples were analysed for standard physical and chemical conditions (such as dry weight, loss on ignition (organic content), grain size distribution) and concentrations of heavy metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlo-rine pesticides, organotins and nutrients.
The equipment used in the survey is shown in Figure 7-4.
Figure 7-4 HAPS core sampler for surface sediment sampling (left) and Vibrocore sampler for deeper sed-iment samples (right).
The key results of the survey are presented in section 7.3.
Chemical warfare agents in seabed sediments
CWA were sampled in November-December 2017, see Figure 7-5. Sampling was performed at 22 stations with the same HAPS core sampler used for sampling surface sediment (see section 7.1.2).
Figure 7-5 Stations for CWA samples.
The survey included the following sampling activities:
• Surface sediment for chemical analysis taken from 0-5 cm depth;
• At some stations, samples for CWA were also taken from deeper sediment (10-40 cm).
Figure 7-6 Sample for analysis of CWA.
The key results of the survey are presented in section 7.17.
Infauna
Infauna sampling was undertaken in November-December 2017. Sampling stations are shown in Figure 7-7.
Figure 7-7 Stations for infauna sampling.
The survey included the following sampling activities:
• Quantitative sampling of infauna performed with a Van Veen sampler;
• Photographic documentation of the sediment samples used for infauna analysis;
• Analysis of infauna.
The equipment used in the survey is shown in Figure 7-8.
Figure 7-8 Sampling of infauna was undertaken with a Van Veen sampler (left). An example of an infauna sample (right).
The key results of the survey are presented in section 7.8.
Habitat mapping
Habitat mapping was undertaken in the Natura 2000 site “Adler Grund og Rønne Banke” in Janu-ary 2018. The survey was undertaken with ROV along survey lines, see Figure 7-9.
Figure 7-9 Survey transects for ROV habitat mapping in the Natura 2000 site “Adler Grund og Rønne Banke”.
The survey consisted of:
• Video-recordings, depth and position measured simultaneously on the ROV by use of a mounted camera, pressure sensor and echosounder;
• Description and mapping of the different sediment types and biotopes;
• Identification of flora and fauna communities, including a species list for the different habitat types along the survey lines;
• Coverage (%) of flora/fauna species inside the different habitat types;
• Mapping of the Natura 2000 habitat types “reef” and “sandbank”.
The equipment used in the survey is shown in Figure 7-10.
Figure 7-10 ROV on board the vessel.
The key results of the survey are presented in section 10.
7.2 Bathymetry
The Baltic Sea is characterised by its deep basins and shallow sills that, together with meteorological conditions, control the exchange of saltwater with the North Sea. As will be described in this section, this influences the conditions for life both in the water column and on the seabed. The depth of the seabed is also a defining factor for marine life. The bathymetry of the Baltic Sea is therefore con-sidered an important receptor.
The Baltic Sea is one of the largest brackish water bodies in the world. It is located between 53°
and 66° N and between 10° and 26° E and is bordered by the Scandinavian Peninsula, the mainlands of northern, eastern and central Europe and the Danish islands. The sea covers an area of 415,000 km2, and its total volume is approximately 21,700 km3. The catchment basin is approximately 1.7 million km2, stretching from densely populated temperate areas in the south to subarctic rural areas in the north. The average depth is 52 m, and the maximum depth is 459 m /81//82/. The topogra-phy of the seabed is characterised by several basins separated by sills at different depths /83/. The names of the major basins of the Baltic Sea are shown in Figure 7-11, and the bathymetry is shown in Figure 7-12.
The Baltic Sea is connected to the North Sea through the shallow and narrow Danish straits Little Belt, Great Belt and Oresund (0.8 km, 16 km and 4 km wide, respectively). Two sills in this transition zone (the Dars Sill in Femern Belt, with a water depth of 18 m, and the Drogden Sill in Oresund, with a water depth of 8 m) effectively limit the inflow of saline, oxygen-rich water to the Baltic Sea to rare occurrences of storms from the west.
Figure 7-11 Major basins in the Baltic Sea.
The Danish waters around Bornholm include the Arkona Basin (maximum depth of 55 m) and the Bornholm Basin (maximum depth of 106 m, within the Swedish EEZ). The maximum depth of the Bornholm Strait, which separates the Arkona Basin from the Bornholm Basin, is 45 m. The inflow to the Arkona Basin is controlled by the sills at Dars and Drogden. The outflow of the Bornholm Basin is controlled by the Stolpe Channel, which separates the Bornholm Basin and the Gotland Deep and reaches depths of approximately 60 m /84/. The bathymetry of the Danish waters around Bornholm and the areas mentioned above is shown in Figure 7-12.
Figure 7-12 Bathymetry in the Danish sector of the Baltic Sea.
A geophysical reconnaissance survey was performed along the proposed NSP2 route through Danish waters in November-December 2017 to determine the seabed morphology, sediment types and the presence of wrecks, munitions or other features on the seabed. The survey corridor covered a nominal width of 500-1,000 m along the proposed NSP2 route /77/.
The bathymetry along the proposed NSP2 route is illustrated in Figure 7-13 and shows that the seabed within the northern part of the Danish EEZ (KP 0 to 70) is generally deep and featureless.
The depth decreases gradually and the profile becomes more rugged as the route enters the strait between Sweden and Bornholm. In the last part of the route west and south-west of Bornholm, the depth is relatively shallow, with a minimum of approximately 18 m as the route crosses the area at Rønne Banke.
Figure 7-13 Water depth along the proposed NSP2 route in Danish waters.