Environmental Engineering Reference
In-Depth Information
Because neither sand nor seawater has magnetic properties, burying a cable will
not affect the magnitude of the magnetic (B) field; that is, the B fields at the same
distance from the cable are identical, whether in water or sediment (CMACS, 2003).
On the other hand, due to the higher conductivity of seawater compared to sand, the
iE field associated with a buried cable is discontinuous across the sand/water bound-
ary; the iE field strength is greater in water than in sand at a given distance from the
cable. For example, for the three-phase AC cable modeled by CMACS (2003), the
estimated iE field strengths at 8 m from the cable were 10 µV/m and 1 to 2 µV/m in
water and sand, respectively.
The EMF generated by a multi-unit array of marine or hydrokinetic devices will
differ from EMFs associated with a single unit or from the single cable sources that
have been surveyed. Depending on the power generation device, a project may have
electrical cable running vertically through the water column in addition to multiple
cables running along the seabed or converging on a subsea pod. The EMF created by
a matrix of cables has not been predicted or quantified.
Effects of Electromagnetic Fields on Aquatic Organisms
Electrical Fields
Natural electric fields can occur in the aquatic environment as a result of biochemi-
cal, physiological, and neurological processes within an organism or as a result of an
organism swimming through a magnetic field (Gill et al., 2005). Some of the elas-
mobranchs (e.g., sharks, skates, rays) have specialized tissues that enable them to
detect electric fields (i.e., electroreception), an ability that allows them to detect prey
and potential predators and competitors. Two species of Asian sturgeon have been
reported to alter their behavior in changing electric fields (Basov, 1999, 2007). Other
fish species (e.g., eels, cod, Atlantic salmon, catfish, paddlefish) respond to induced
voltage gradients associated with water movement and geomagnetic emissions (Collin
and Whitehead, 2004; Wilkens and Hofmann, 2005), but their electrosensitivity does
not appear to be based on the same mechanism as sharks (Gill et al., 2005).
Balayev and Fursa (1980) observed the reaction of 23 species of marine fish to elec-
tric currents in the laboratory. Visible reactions occurred following exposure to electric
fields ranging from 0.6 to 7.2 V/m and varied depending on the species and orienta-
tion to the field. They noted that changes in the fishes' electrocardiograms occurred at
field strengths 20 times lower than those that elicited observable behavioral response.
Enger et al. (1976) found that European eels ( Anguilla anguilla ) exhibited a deceler-
ated heart rate when exposed to a direct current electrical field with a voltage gradient
of about 400 to 600 µV/cm. In contrast, Rommel and McCleave (1972) observed much
lower voltage thresholds of response (0.07 to 0.67 µV/cm) in American eels ( Anguilla
rostrata ). The eels' electrosensitivity measured by Rommel and McCleave is well
within the range of naturally occurring oceanic electric fields of at least 0.10 µV/cm in
many currents in the Atlantic Ocean and up to 0.46 µV/cm in the Gulf Stream.
Kalmijn (1982) described the extreme sensitivity of some elasmobranchs to elec-
tric fields. For example, the skate ( Raja clavata ) exhibited cardiac response to uni-
form square-wave fields of 5 Hz at voltage gradients as low as 0.01 µV/cm. Dogfish
( Mustelus canis ) initiated attacks on electrodes from distances in excess of 38 cm
and voltage gradients as small as 0.005 µV/cm.
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