A current synthesis on the effects of electric and magnetic fields emitted by submarine power cables on invertebrates

Abstract

The goal of clean renewable energy production has promoted the large-scale deployment of marine renewable energy devices, and their associated submarine cable network. Power cables produce both electric and magnetic fields that raise environmental concerns as many marine organisms have magneto and electroreception abilities used for vital purposes. Magnetic and electric fields’ intensities decrease with distance away from the cable. Accordingly, the benthic and the sedimentary compartments are exposed to the highest field values. Although marine invertebrate species are the major fauna of these potentially exposed areas, they have so far received little attention. We provide extensive background knowledge on natural and anthropogenic marine sources of magnetic and electric fields. We then compile evidence for magneto- and electro-sensitivity in marine invertebrates and further highlight what is currently known about their interactions with artificial sources of magnetic and electric fields. Finally we discuss the main gaps and future challenges that require further investigation.

Fig. 2. General distribution of some invertebrate species according to the theoretical values of magnetic fields emitted by 225 kV buried (1 m) and unburied single-conductor cables, energised with an intensity of 1000 A (diameter: 27 cm). Magnetic field intensities were calculated with the following formula: B = (µ.µ0)/(2πr) B is the magnetic induction (T), μ is the relative magnetic permeability of the medium, μ0 is the vacuum permeability (4π・10−7 V s A−1 m−1), I is the current intensity (A) and r is the distance from the centre of the wire (m) (formula from Otremba et al., 2019).

Highlights

 

  • Submarine power cables produce both magnetic and electric fields.
  • Marine invertebrate species inhabit the benthic or sediment compartment where cables are laid or buried.
  • Evidence shows magneto and electro-sensitivity in some invertebrates but their response to artificial fields is poorly known.
  • Invertebrate species are likely to experience the highest and longest exposures and should be prioritised in future studies.

 

References

Albert L., Deschamps F., Jolivet A., Olivier F., Chauvaud L., Chauvaud S. 2020. A current synthesis on the effects of electric and magnetic fields emitted by submarine power cables on invertebrates, Marine Environmental Research, Vol.159. https://doi.org/10.1016/j.marenvres.2020.104958

 

Bivalve δ15N isoscapes provide a baseline for urban nitrogen footprint at the edge of a World Heritage coral reef

Abstract

Eutrophication is a major threat to world’s coral reefs. Here, we mapped the distribution of the anthropogenic nitrogen footprint around Nouméa, a coastal city surrounded by 15,743 km2 of UNESCO listed reefs. We measured the δ15N signature of 348 long-lived benthic bivalves from 12 species at 27 sites and interpolated these to generate a δ15N isoscape. We evaluated the influence of water residence times on nitrogen enrichment and predicted an eutrophication risk at the UNESCO core area. Nitrogen isoscapes revealed a strong spatial gradient (4.3 to 11.7‰) from the outer lagoon to three highly exposed bays of Nouméa. Several protected reefs would benefit from an improved management of wastewater outputs, while one bay in the UNESCO core area may suffer a high eutrophication risk in the future. Our study reinforces the usefulness of using benthic animals to characterize the anthropogenic N-footprint and provide a necessary baseline for both  ecologists and policy makers.

Fig. 3. δ15N isoscape in 2012, estimated at 27 stations in the southwest lagoon of New Caledonia from muscle samples of 12 bivalve species.

 

Highlights

• Benthic filter-feeding bivalve communities are good bio monitors of spatial variations in anthropogenic-based eutrophication.

• The baseline δ15N value found in bivalves from the outer lagoon of New Caledonia was 4.7 ± 0.4‰.

• The δ15N signature of benthic bivalves reached 11.7‰ in the most exposed station.

• Isoscapes might be used both for long-term monitoring and to predict risks of at-sea anthropogenic pollution.

 

Reference

Thibault M., Duprey N., Gillikin D.P., Thébault J., Douillet P., Chauvaud L., Amice E., Munaron J.M., Lorrain A. 2020. Bivalve δ15N isoscapes provide a baseline for urban nitrogen footprint at the edge of a World Heritage coral reef. Marine Pollution Bulletin vol. 152. https://doi.org/10.1016/j.marpolbul.2019.110870

New guidelines for the application of Stokes’ models to the sinking velocity of marine aggregates

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Numerical simulations of ocean biogeochemical cycles need to adequately represent particle sinking velocities (SV). For decades, Stokes’ Law estimating particle SV from density and size has been widely used. But while Stokes’ Law holds for small, smooth, and rigid spheres settling at low Reynolds number, it fails when applied to marine aggregates complex in shape, structure, and composition. Minerals and zooplankton can alter phytoplankton aggregates in ways that change their SV, potentially improving the applicability of Stokes’ models. Using rolling cylinders, we experimentally produced diatom aggregates in the presence and absence of minerals and/or microzooplankton. Minerals and to a lesser extent microzooplankton decreased aggregate size and roughness and increased their sphericity and compactness. Stokes’ Law parameterized with a fractal porosity modeled adequately size‐SV relationships for mineral‐loaded aggregates. Phytoplankton‐only aggregates and those exposed to microzooplankton followed the general Navier‐Stokes drag equation suggesting an indiscernible effect of microzooplankton and a drag coefficient too complex to be calculated with a Stokes’ assumption. We compared our results with a larger data set of ballasted and nonballasted marine aggregates. This confirmed that the size‐SV relationships for ballasted aggregates can be simulated by Stokes’ models with an adequate fractal porosity parameterization. Given the importance of mineral ballasting in the ocean, our findings could ease biogeochemical model parameterization for a significant pool of particles in the ocean and especially in the mesopelagic zone where the particulate organic matter : mineral ratio decreases. Our results also reinforce the importance of accounting for porosity as a decisive predictor of marine aggregate SV.

Sinking velocities vs. ESD (equivalent spherical diameter) for aggregates formed in each tank of the four treatments and comparison with theoretical expectations from different parameterizations of Stokes’ Law and the general Navier‐Stokes’ drag equation. P: phytoplankton; PZ: phytoplankton + microzooplankton (rotifers); PM: phytoplankton + mineral (calcite); PMZ: phytoplankton + mineral + microzooplankton. (a) Model 1, Stokes’ Law with constant porosities of 0% (dashed lines) and 99% (solid lines). (b) Model 2, general Navier‐Stokes’ drag law with constant drags of 1 (dashed lines) and 5 (solid lines), and a constant porosity of 99%. (c) Model 3, Stokes’ Law with a porosity scaled on a fractal geometry with coefficient a = 0.03 and D3 = 1.4 (dashed lines) and D3 = 1.8 (solid lines). (d) Model 4, general Navier‐Stokes’ drag law with a porosity scaled on a fractal geometry with coefficient a = 0.03 and D3 = 1.4 (solid lines) and 1.8 (dashed lines). See the text for details on drag calculation

Reference

Laurenceau-Cornec, E.C., Le Moigne, F.A.C., Gallinari, M., Moriceau, B., Toullec, J., Iversen, M.H., Engel, A., and De La Rocha, C.L. 2020. New guidelines for the application of Stokes’ models to the sinking velocity of marine aggregates. Limnol. Oceanogr. doi:10.1002/lno.11388.
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Methanogenic and fertilizing potential of aquaculture waste :

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towards freshwater farms energy self‐sufficiency in the framework of blue growth

The fisheries sector, particularly aquaculture, is a fundamental source of nutrition for humans, particularly in developing countries. The modern development of fish farming requires energy for production systems. This study investigates the potential of using organic wastes derived from fish fattening to produce on-farm energy through the process of methanization. Oreochromis  niloticus faeces methanogen potential was determined with (IFF) and without (UIFF) methanizer microbial inoculum. At the end of the manure methanation trials, the resulting digestates were tested as organic fertilizers for agriculture. The tests showed that inoculated fish faeces had faster biogas kinetics production compared with uninoculated fish faeces. In both cases, the produced biogas contained more than 60% methane (CH4) from the second week of incubation, indicating that it was of good quality. Furthermore, the total CH4 volume was twice as larger in IFF compared with UIFF. Biofertilizer tests showed no significant differences for most of the growth parameters in onion and tomato when compared to the unfertilized control, except in one case for tomato plants, which significantly increased its aboveground biomass. The results show that fish faeces are good methanogenic substrates conducive to energy recovery that could facilitate farm autonomy; however, valorization of the digestates as biofertilizer still requires extensive agronomic optimization. Based on our results, we estimate that equivalents of energy need of almost ten millions of people could be covered using the aquaculture potential in freshwater fish faeces biogas worldwide or that at least aquaculture farm energy self-sufficiency could be fostered.

 

Biogas production of fish faeces

Biogas production of fish faeces was monitored using the standard BMP test. After 9 weeks, fish faeces produced more biogas with the inoculum (IFF = 1100 mL) than fish faeces without the inoculum (UIFF = 900 mL) (see figure). Biogas production from substrate only (UIFF) followed an almost constant rate (resulting in linear accumulation) during the nine weeks of incubation.

References

Ndiaye, N.A., Maiguizo-Diagne, H., Diadhiou, H.D., Ndiaye, W.N., Diedhiou, F., Cournac, L., Gaye, M.L., Fall, S., and Brehmer, P. (n.d.). Methanogenic and fertilizing potential of aquaculture waste: towards freshwater farms energy self-sufficiency in the framework of blue growth. Reviews in Aquaculture (Early view). doi:10.1111/raq.12390.

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Sponge skeletons as an important sink of silicon in the global oceans

Silicon (Si) is a pivotal element in the biogeochemical and ecological functioning of the ocean. The marine Si cycle is thought to be in internal equilibrium, but the recent discovery of Si entries through groundwater and glacial melting have increased the known Si inputs relative to the outputs in the global oceans. Known outputs are due to the burying of diatom skeletons or their conversion into authigenic clay by reverse weathering. Here we show that non-phototrophic organisms, such as sponges and radiolarians, also facilitate significant Si burial through their siliceous skeletons. Microscopic examination and digestion of sediments revealed that most burial occurs through sponge skeletons, which, being unusually resistant to dissolution, had passed unnoticed in the biogeochemical inventories of sediments. The preservation of sponge spicules in sediments was 45.2 ± 27.4%, but only 6.8 ± 10.1% for radiolarian testa and 8% for diatom frustules. Sponges lead to a global burial flux of 1.71 ± 1.61 TmolSi yr−1 and only 0.09 ± 0.05 TmolSi yr−1 occurs through radiolarians. Collectively, these two non-phototrophically produced silicas increase the Si output of the ocean to 12.8 TmolSi yr−1, which accounts for a previously ignored sink that is necessary to adequately assess the global balance of the marine Si cycle.

References

Maldonado, M., López-Acosta, M., Sitjà, C., García-Puig, M., Galobart, C., Ercilla, G., & Leynaert, A. (2019). Sponge skeletons as an important sink of silicon in the global oceans. Nature Geoscience. https://doi.org/10.1038/s41561-019-0430-7

 

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