Suchergebnisse

Abstract
Background
The International Maritime Organization (IMO) has set limits on sulphur content in fuels for marine transport. However, vessels continue to use these residual high-sulphur fuels in combination with exhaust gas cleaning systems (EGCS or scrubbers). Next to high sulphur, combustion of these fuels also results in higher emissions of contaminants including metals and PAHs. In scrubbers, exhaust gases are sprayed with water in order to remove SOx, resulting in acidic washwater with elevated contaminant concentrations discharged in the aquatic ecosystem. The number of vessels with scrubbers is increasing rapidly, but knowledge on washwater quality and impact are limited.

Results
The scrubber washwater is found to be acidic with elevated concentrations of, e.g. zinc, vanadium, copper, nickel, phenanthrene, naphthalene, fluorene and fluoranthene. Model calculations on the effects of scrubber discharge under scenario HIGH (20% of vessels, 90th percentile concentrations) on the water quality in harbour docks showed a decrease in pH of 0.015 units and an increase in surface water concentrations for e.g. naphthalene (189% increase) and vanadium (46% increase).

Conclusions
The IMO established sulphur regulations to mitigate the impact of high sulphur emissions of the maritime sector. However, the use of open-loop scrubbers as an abatement technology will not reduce their contribution to ocean acidification. In addition, different types of scrubbers discharge washwater that is acutely toxic for aquatic organisms. However, washwater is diluted and the compounds for which a large increase in surface water concentrations was calculated in the Antwerp (Belgium) harbour docks (naphthalene > phenanthrene > fluorene > acenaphthene > vanadium) were not the compounds that already exceed their respective Water Quality Standards (WQS). Nevertheless, the WQS of several 'priority hazardous substances' (Water Framework Directive) are already exceeded in the docks and the Scheldt estuary. Since these hazardous substances are also identified in the washwater, scrubber washwater discharge should be discouraged in coastal waters and estuaries with large ecological value.

International audience ; The Chinese mitten crab (Eriocheir sinensis) is a damaging invader which is designated as a species of Union Concern within the European Union. A negative impact of the crabs on macrophyte vegetation in lowland rivers is suspected but not yet proven or quantified. We have performed a mesocosm study that combines a density gradient of Chinese mitten crabs (0, 0.3, 1.0 and 2.5 ind. m−2) with chemical stress (2350 µg EDTA L−1 + 258 µg glyphosate L−1) or light limitation stress (− 70% irradiance compared to control) on water plants (Myriophyllum spicatum). The results clearly demonstrate that the crabs are capable of removing plant shoots effectively which can lead to a complete elimination of the vegetation. Generally, the higher the crab density, the sooner the plants started to disappear and the sooner the vegetation was completely removed. Additional light and chemical stress accelerated this process: plant disappearance at a crab density of 0.3 ind. m−2 compared to 1.0 ind. m−2 in the control treatments. Video recording, plant strength and crab pinch strength measurements and stable isotope signatures of δ13C and δ15N in the Chinese mitten crabs and their possible food sources showed that directly eating the plants is causing only minor damage to the plants. Most damage comes from the movement of the crabs and crab–crab interactions during which they use their chelae to grasp the shoots. We conclude that a decline of vegetation as a consequence of Chinese mitten crab behaviour can be a realistic scenario in freshwater ecosystems and warrants close attention and monitoring. Being primary producers and ecological engineers, macrophytes are key species in these ecosystems, whose services are lost when they disappear and are difficult to restore.

International audience ; The Chinese mitten crab (Eriocheir sinensis) is a damaging invader which is designated as a species of Union Concern within the European Union. A negative impact of the crabs on macrophyte vegetation in lowland rivers is suspected but not yet proven or quantified. We have performed a mesocosm study that combines a density gradient of Chinese mitten crabs (0, 0.3, 1.0 and 2.5 ind. m−2) with chemical stress (2350 µg EDTA L−1 + 258 µg glyphosate L−1) or light limitation stress (− 70% irradiance compared to control) on water plants (Myriophyllum spicatum). The results clearly demonstrate that the crabs are capable of removing plant shoots effectively which can lead to a complete elimination of the vegetation. Generally, the higher the crab density, the sooner the plants started to disappear and the sooner the vegetation was completely removed. Additional light and chemical stress accelerated this process: plant disappearance at a crab density of 0.3 ind. m−2 compared to 1.0 ind. m−2 in the control treatments. Video recording, plant strength and crab pinch strength measurements and stable isotope signatures of δ13C and δ15N in the Chinese mitten crabs and their possible food sources showed that directly eating the plants is causing only minor damage to the plants. Most damage comes from the movement of the crabs and crab–crab interactions during which they use their chelae to grasp the shoots. We conclude that a decline of vegetation as a consequence of Chinese mitten crab behaviour can be a realistic scenario in freshwater ecosystems and warrants close attention and monitoring. Being primary producers and ecological engineers, macrophytes are key species in these ecosystems, whose services are lost when they disappear and are difficult to restore.

International audience ; The Chinese mitten crab (Eriocheir sinensis) is a damaging invader which is designated as a species of Union Concern within the European Union. A negative impact of the crabs on macrophyte vegetation in lowland rivers is suspected but not yet proven or quantified. We have performed a mesocosm study that combines a density gradient of Chinese mitten crabs (0, 0.3, 1.0 and 2.5 ind. m−2) with chemical stress (2350 µg EDTA L−1 + 258 µg glyphosate L−1) or light limitation stress (− 70% irradiance compared to control) on water plants (Myriophyllum spicatum). The results clearly demonstrate that the crabs are capable of removing plant shoots effectively which can lead to a complete elimination of the vegetation. Generally, the higher the crab density, the sooner the plants started to disappear and the sooner the vegetation was completely removed. Additional light and chemical stress accelerated this process: plant disappearance at a crab density of 0.3 ind. m−2 compared to 1.0 ind. m−2 in the control treatments. Video recording, plant strength and crab pinch strength measurements and stable isotope signatures of δ13C and δ15N in the Chinese mitten crabs and their possible food sources showed that directly eating the plants is causing only minor damage to the plants. Most damage comes from the movement of the crabs and crab–crab interactions during which they use their chelae to grasp the shoots. We conclude that a decline of vegetation as a consequence of Chinese mitten crab behaviour can be a realistic scenario in freshwater ecosystems and warrants close attention and monitoring. Being primary producers and ecological engineers, macrophytes are key species in these ecosystems, whose services are lost when they disappear and are difficult to restore.

International audience The Chinese mitten crab (Eriocheir sinensis) is a damaging invader which is designated as a species of Union Concern within the European Union. A negative impact of the crabs on macrophyte vegetation in lowland rivers is suspected but not yet proven or quantified. We have performed a mesocosm study that combines a density gradient of Chinese mitten crabs (0, 0.3, 1.0 and 2.5 ind. m−2) with chemical stress (2350 µg EDTA L−1 + 258 µg glyphosate L−1) or light limitation stress (− 70% irradiance compared to control) on water plants (Myriophyllum spicatum). The results clearly demonstrate that the crabs are capable of removing plant shoots effectively which can lead to a complete elimination of the vegetation. Generally, the higher the crab density, the sooner the plants started to disappear and the sooner the vegetation was completely removed. Additional light and chemical stress accelerated this process: plant disappearance at a crab density of 0.3 ind. m−2 compared to 1.0 ind. m−2 in the control treatments. Video recording, plant strength and crab pinch strength measurements and stable isotope signatures of δ13C and δ15N in the Chinese mitten crabs and their possible food sources showed that directly eating the plants is causing only minor damage to the plants. Most damage comes from the movement of the crabs and crab–crab interactions during which they use their chelae to grasp the shoots. We conclude that a decline of vegetation as a consequence of Chinese mitten crab behaviour can be a realistic scenario in freshwater ecosystems and warrants close attention and monitoring. Being primary producers and ecological engineers, macrophytes are key species in these ecosystems, whose services are lost when they disappear and are difficult to restore.