Underground, submarine and superconducting cables: Impact on the biosphere
Seabed ploughs, curious sharks and warmed sediment
What this tab covers Effects on human, animal, plant, fungal and microbial life and on whole ecosystems: in the short term (construction and early years), medium term (operating life) and long term (decommissioning and legacy).Cables avoid the visual impact and bird collisions of pylons, but building them digs a wide strip of land or seabed. In operation they give off a little heat and a magnetic field; the best-studied effects are on fish that sense electric fields and on seabed communities.
Plough trench footprint on the seabed about 2 to 8 m wide15 Cable footprint in UK coastal waters about 0.3 km², under 0.01% of the seabed15 Magnetic field near a 1,600 A cable about 320 µT at 1 m, close to Earth's natural 50 µT beyond about 6 m15 Effect of deeper burial Field at the seabed falls to about 25% of its initial value with 2 m burial, against about 60% with 1 m15Effects over time
| Life affected | Short term | Medium term | Long term |
|---|---|---|---|
| Humans3 | A 40 to 65 m working strip for 400 kV cables on land, with traffic and farm disruption. | Restrictions on building and deep cultivation over the route. Magnetic field directly over a buried 400 kV cable up to about 96 µT, typically 24 µT; in deep tunnels about 0.03 µT. | Long outages after faults; the easement remains for the cable's life. |
| Animals15 | Seabed ploughing noise up to about 178 dB re 1 µPa at 1 m; sediment plumes for hours to days. | Sharks and rays sense very weak electric fields and may be attracted or repelled; European eels slowed slightly crossing a 130 kV cable and American lobsters changed behaviour near a DC cable, with no population effects shown. | Little evidence of effect. |
| Plants315 | Seagrass beds cut by trenches can take several years to recolonise; hedges and trees removed on land. | No trees or hedges directly over or within 3 m of a GB cable trench. | Little evidence of effect. |
| Fungi and soil life15 | Soil and sediment layers are mixed during trenching. | Sediment about 50 cm below buried AC cables at Nysted was up to about 2.5 C warmer; effects on microbes are little studied. | Little evidence of effect. |
| Ecosystems15 | A Baltic study found no significant change in seabed diversity, abundance or biomass one year after laying. | Rock protection and exposed cables act as artificial reef; on artificial hard structures generally, non-native species can be about 2.5 times more numerous, though no spread caused by power cables has been documented. | Lead-sheathed cables contain about 12 kg of lead per metre and old oil-filled cables can leak tens of litres per hour if damaged, so removal or leaving in place is decided case by case. |
How the effects are reduced
Impacts are reduced by routing around seagrass, reefs and spawning grounds, burying deeper (which also protects against anchors), using horizontal directional drilling at shorelines so only small entry and exit pits are disturbed, timing works outside breeding seasons, and replacing oil-filled and lead-sheathed designs with XLPE. On land, separating and replacing topsoil and keeping deep-rooted planting off the route let most farmland return to use. Superconducting cables emit no external magnetic field and do not warm the ground, though they rely on nitrogen cooling plants.