Boehlert and Gill (2010) aimed to answer that question in their synthesis, which blends and summarizes previous research on the environmental effects of specific ocean renewable energy technologies. In their synthesis, the researchers focused on offshore wind, thermal gradient, wave, tidal, and ocean current technologies, through all stages of development—construction, operation, and decommissioning. To classify the results in an intuitive way, Boehlert and Gill grouped environmental effects as either stressors or receptors and by level, from effect to impact to cumulative impact. Although the authors created a very organized system for evaluating the environmental effects of ocean renewable energy development (ORED) projects, their synthesizing did not give rise to definitive conclusions. Rather, the authors acknowledged that there is little research on the environmental effects of ORED, and that existing research is clouded in uncertainty. Therefore, the authors ultimately advise that additional baseline data be collected and that longer, more continuous research studies be undertaken. —Juliet Archer
Boehlert, G., Gill, A., 2010. Environmental and ecological effects of ocean renewable energy development: A current synthesis. Oceanography 23, 68–81.
G. Boehlert and A. Gill from Oregon State University and Cranfield University, respectively, compiled, summarized, and synthesized current scholarly research on the environmental effects of different ocean renewable energy technologies. The authors chose to limit their synthesis to five technologies: wave, wind, thermal gradient, tidal, and current energy conversion. The authors created a framework with six levels for the classification of their results. The first level is the type of marine renewable energy technology. The second level contains environmental stressors. Stressors are aspects of the environment which may be altered during the installation, operation or decommissioning of marine renewable energy technologies. In their definition of stressors, the authors include device presence, chemical, acoustic, electromagnetic field, energy removal, and dynamic effects. Environmental receptors, defined as “ecosystem elements with [the] potential for some form of response to the stressor,” are the third level of their framework. Boehlert and Gill include animals, such as fish and marine mammals and birds, the food chain, ecosystem, and physical environment, including benthic and pelagic habitats. The fourth level of their framework contains four potential environmental effects. These are given as combinations of length, long or short term, and magnitude, single or multiple effects. Environmental impacts, such as population change, community change, biotic process alteration, and physical structure or process alteration, comprise the fifth level. The authors distinguish between an “impact” and an “effect.” Specifically, an impact indicates the severity, direction, and duration of an effect. Effects are relegated to level four while impacts included in levels five and six. Lastly, cumulative impacts are presented on the sixth level. These impacts are analyzed separately from level five impacts because level six impacts consider the collective impact of all stressors caused by human impacts. Cumulative impacts are considered on spatial and temporal scales. This framework is used throughout the paper to classify and evaluate the environmental effects of marine renewable energy development.
After outlining their entire framework, Boehlert and Gill go on to give detailed explanations of the environmental stressors found in level two. The first, and arguably most obvious, stressor is the physical presence of renewable energy structures in the marine environment. The presence of these devices can result in a range of changes above and/or below the water surface. For instance, ocean wind energy devices have the highest vertical presence above the water. In contrast, ocean thermal energy conversion (OTEC), with its extensive pipe system along the ocean bottom, will have a greater presence below the water. The authors also note that some wave energy devices, like the Pelamis or Sea Dragon, have a significant presence on the ocean surface.
The authors also consider the dynamic effects of a device, as a stressor independent of its physical presence. The moving parts of devices, located above and below the water may have effects on the marine environment. One of the most common effects is “blade strike,” which typically describes either a migratory bird or fish colliding with a wind or current energy device, respectively. A less apparent effect of moving parts is the removal of energy from the air, water or waves. In the water, this may result in changes to turbulence, stratification, sediment transport and even changes in currents and tidal range. These changes may result in further changes such as disturbing the foraging activities of shorebirds or changing the distribution of intertidal organisms. Moving large amounts of water, such as the movement of deep cold and shallow warm water in OTEC processes, may entrap mobile species and redistribute nutrients to colder waters. The above environmental effects of moving parts show the importance of studying both short and long term and near and far field effects.
The chemical effects of marine energy devices are not of paramount concern. As Boehlert and Gill explain, the effects of chemicals utilized in marine renewable energy development and operations will be similar to the effects of any other ocean construction projects. The small risk of chemical effects during installation, ordinary servicing, and decommissioning are expected to result from ocean vessel operations. However during ordinary operations, a risk of chemical spills exists, especially for devices which use hydraulic fluids. The effect of a spill from an OTEC could be very damaging because the working fluid would most likely be ammonia, which is extremely toxic to fish. Leaching of chemicals may also occur if anti-fouling paints are used to deter organisms which would foul the device. The authors advocate for more research on the toxic compounds used in marine renewable energy development. In addition, the natural chemistry of ocean systems must be examined to determine whether the potential for negative ecological effects, including the outgassing of carbon dioxide and acidification<!–[if supportFields]> XE “acidification” <![endif]–><!–[if supportFields]><![endif]–> of upwelled waters, are high.
Acoustic effects of ORED may interfere with the natural acoustic environment, causing a disturbance to animal communication, orientation, reproduction and/or predator and prey sensing. For instance, it is widely known that acoustic changes impact fish and marine mammals. However, new research has shown that lobster and crab larvae may also be impacted. Therefore, acoustic effects must be examined during all phases of development, and on various temporal and spatial scales. For instance, the construction phase is usually considered noisiest and “most acoustically diverse.” These different noises may result from increased shipping surrounding the area, seismic surveys, pile driving and/or other construction activities. Currently, data to quantify the noise of ORED are deficient and therefore, hypotheses, such as that devices with underwater moving parts will be the nosiest, cannot be tested. Boehlert and Gill recommend that future research focus on determining the intensity, propagation, and acoustic profile of sounds emitted from various forms of ORED.
Since ORED are required to transmit electricity, all except shore-based OTEC or pressurized water pumps create electromagnetic effects in the marine environment. Industry standards currently require shielding on all cables that transmit electricity, to confine “directly emitted electric fields.” However, shielding does not restrict the magnetic part of an electromagnetic field (EMF). This can pose a problem for magneto-sensitive organisms, especially those which migrate long distances or orient using natural geomagnetic fields. Similarly, organisms which are electroreceptive, and use bioelectrical impulses to orient, feed, or mate may be severely impacted by the electromagnetic effects of ORED. However, scientists are uncertain as to the response of marine creatures to EMFs because the data needed to assess an impact does not exist. The authors suggest that “before-and-after baseline assessments” be completed and that the biological significance of effects as wells as possible thermal effects be examined.
The authors also list the possible impacts on the environmental receptors. The first receptors considered are the physical environment, and pelagic and benthic habitat. The physical environment may be changed by the removal of kinetic energy from the water, resulting in local acceleration, scouring, or altered sediment transport, deposition, or thermal regimes. Pelagic habitats will be most impacted by the creation of structures in previously vacant areas. This may increase fish populations which will probably attract more predators to the area. Pelagic organisms may also be impacted through impingement, collisions, or entanglement with ORED. Benthic habits will probably be the most impacted by ORED because of structural modifications and changes to water circulation and currents. Greater biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–> may result as devices create an “artificial reef,” but some species may benefit while others are negatively impacted. Other impacts have similar mixed effects. For instance, “shell mounds” may accrue on the ocean bottom as growth on lines, buoys, and anchors are sloughed off. This will alter the habitat but it may also create a productive habitat for fish. Therefore, research shows, albeit with much uncertainty, that ORED may have both positive and negative effects on the physical environment and various habitats.
Another important group of receptors includes organisms within the broad categories of fish, seabirds, and marine mammals. One surprisingly positive effect on fish is the creation of de facto reserves in areas where ORED are located, if fishing is banned. However, these reserves may result in increased mortality of resident fishes as new species and additional predators are attracted to the area. Migrating fishes, such as salmon<!–[if supportFields]> XE “salmon” <![endif]–><!–[if supportFields]><![endif]–>, elasmobranchs, and sturgeons, may also be affected by individual EMF, chemical, and acoustic stressors, or a combination of these stressors. Seabirds, on the other hand, will be primarily impacted by the above surface effects of ORED. For example, birds that are attracted to lights may collide with the above-water structures such as wind turbines. Furthermore, even if most seabirds are able to steer clear of turbines, the extra energy required to do so may have a negative impact, especially on local, diurnal migratory species. Since studies show that the impact of additional energy required intensifies as the time period of avoidance lengthens, cumulative impacts should be considered in future research. Seabirds may also be impacted by below surface structures to the extent that such devices increase fish populations, or present collision, entanglement, or blade strike risks for diving birds. Boehlert and Gill recommend that the effects on crucial areas of bird activity, migration patterns, and seabird prey be studied in the future.
Marine mammals receive a disproportionate amount of attention among marine receptors in studies of the environmental effects of ORED. This is not surprising since the group is usually protected, captures more public interest and is more visible than other receptors. Concerns for cetaceans are similar to those for diving seabirds, and include risks of entanglement, collision, and blade strike, especially if fish populations increase near ORED. In addition, marine mammals may be attracted to or repelled by the acoustic emissions of ORED. Also, like fish, there is a potential that EMFs may disturb marine mammals’ natural orientation systems. The authors recommend more monitoring of cetaceans and pinnipeds, beginning at that same time as pilot and demonstration projects are launched. In addition, baseline data are needed for marine mammals and their prey species. Lastly, the authors urge that “special attention” be given to the migratory routes and important feeding grounds of marine mammals.
Although the number of studies on ORED has increased, the number that focuses on the environmental effects of these devices is relatively small. Currently, the development of devices and deployment of pilot projects and demonstrations outpaces the understanding of their effects. Thus, the need for more research is urgent and great. Boehlert and Gill advocate for simultaneous environmental research as these new technologies are deployed, in order to identify impacts for receptor and stressor groups and decrease uncertainty. Environmental standards for ORED are also needed, but stringent standards may inhibit new development. In contrast, lenient standards may lead to tremendous environmental damage. In light of these undesirable consequences, the authors recommend that balanced environmental standards be developed. At the end of their synthesis, Boehlert and Gill remind readers that the ultimate goal of ORED is to decrease our dependence on fossil fuels.