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Abstract This paper presents the hydrodynamic optimization study of CECO, a point absorber wave energy converter (WEC) with sloped motion. To maintain the overall costs, the characteristic dimensions of the optimized solution were not allowed to change significantly. Instead, different geometrical shapes have been generated and numerically investigated based on the exhaustive search method with a heuristic approach. The assessment of the different geometries was based on a new index - the hydrodynamic capacity for wave energy conversion - which considers that the theoretical maximum WEC's absorbed power from irregular waves is obtained assuming that for each individual wave component of the sea spectrum, the PTO system can operate with its optimum damping coefficient. The optimum geometry obtained is able to harvest twice as much wave energy than the original design of CECO. The numerical outcomes have been validated with the results of experimental tests with the new geometry. Unlike “pure” heaving WECs, a sloped-motion WEC can achieve natural oscillation periods within a broad range by controlling the inclination of the motion path, the submergence level or the shape of its floaters. Therefore, CECO can be tuned to any given sea state and avoid the need for active complex control strategies.

Abstract This paper presents the hydrodynamic optimization study of CECO, a point absorber wave energy converter (WEC) with sloped motion. To maintain the overall costs, the characteristic dimensions of the optimized solution were not allowed to change significantly. Instead, different geometrical shapes have been generated and numerically investigated based on the exhaustive search method with a heuristic approach. The assessment of the different geometries was based on a new index - the hydrodynamic capacity for wave energy conversion - which considers that the theoretical maximum WEC's absorbed power from irregular waves is obtained assuming that for each individual wave component of the sea spectrum, the PTO system can operate with its optimum damping coefficient. The optimum geometry obtained is able to harvest twice as much wave energy than the original design of CECO. The numerical outcomes have been validated with the results of experimental tests with the new geometry. Unlike “pure” heaving WECs, a sloped-motion WEC can achieve natural oscillation periods within a broad range by controlling the inclination of the motion path, the submergence level or the shape of its floaters. Therefore, CECO can be tuned to any given sea state and avoid the need for active complex control strategies.

Fish in northern European lakes must cope with climate change, including frequent extreme weather events, and eutrophication. In terrestrial vertebrates the disruption of local environmental stability can evoke a stress response, with potentially adverse outcomes for growth, reproduction and survival, but the effect of extreme weather events on aquatic vertebrates is not understood. As part of a mesocosm scale multiple-stressor study we investigated (i) whether three-spined sticklebacks (Gasterosteus aculeatus L.) exhibited an acute stress response (by measuring the steroid hormone cortisol) to simulated rainfall events, and (ii) whether any such response was modified by elevated temperature and nutrient concentrations. On two occasions, sticklebacks were sampled 1 h and 24 h following the simulated rainfall event. Cortisol levels were elevated within 1 h of the rainfall event in November in fish from heated tanks (with and without nutrient augmentation). In May, cortisol increased within 1 h of the rainfall event but only in fish from nutrient-enriched mesocosms (heated and unheated). Cortisol had declined to control levels within 24 h on both occasions. This outcome suggests that the acute effect on fish of transient stressors, such as extreme rainfall events, may be modified by other environmental factors, but that interactions between these variables may be difficult to predict.

Fish in northern European lakes must cope with climate change, including frequent extreme weather events, and eutrophication. In terrestrial vertebrates the disruption of local environmental stability can evoke a stress response, with potentially adverse outcomes for growth, reproduction and survival, but the effect of extreme weather events on aquatic vertebrates is not understood. As part of a mesocosm scale multiple-stressor study we investigated (i) whether three-spined sticklebacks (Gasterosteus aculeatus L.) exhibited an acute stress response (by measuring the steroid hormone cortisol) to simulated rainfall events, and (ii) whether any such response was modified by elevated temperature and nutrient concentrations. On two occasions, sticklebacks were sampled 1 h and 24 h following the simulated rainfall event. Cortisol levels were elevated within 1 h of the rainfall event in November in fish from heated tanks (with and without nutrient augmentation). In May, cortisol increased within 1 h of the rainfall event but only in fish from nutrient-enriched mesocosms (heated and unheated). Cortisol had declined to control levels within 24 h on both occasions. This outcome suggests that the acute effect on fish of transient stressors, such as extreme rainfall events, may be modified by other environmental factors, but that interactions between these variables may be difficult to predict.

For being densely populated and urbanized, and for concentrating high-value economic activities, estuarine regions have an increased energy demand, which boosts the claim for new, efficient, renewable, and safe energy production. Among these technologies, hydrokinetic energy conversion systems are potentially well-suited for estuaries. However, in the actual context of climate change, it is important to know how changes in mean sea level may affect hydrokinetic energy production. This work proposes a methodology to assess the hydrokinetic energy potential for future scenarios using numerical hydrodynamic modeling techniques. Applied to the Douro estuary, several scenarios considering present conditions, as well as medium (2050) and long-term (2100) predictions under different Shared Socioeconomic Pathways are proposed. The results revealed that the studied region maintains a high dependence on freshwater discharge until 2100, although tidal oscillation is also significantly perceived in the entire estuary. Overall, hydrokinetic power potential will not increase with the mean sea level rise and will instead be considerably lower. Therefore, a decline in the kinetic energy available for exploitation is expected with increasing CO2 emissions, along with the associated intensification of sea level rise. Results reinforce the need to perform local studies to evaluate future trends in hydrokinetic energy production. This research was supported by the Strategic Funding UIDB/04423/2020 and UIDP/04423/2020 through national funds provided by FCT – Foundation for Science and Technology and European Regional Development Fund (ERDF), and by the project EsCo-Ensembles (PTDC/ECI-EGC/30877/2017), co-financed by NORTE 2020, Portugal 2020, and the European Union through the ERDF, and by FCT through national funds. The authors would like to thank the Instituto Hidrográfico, EDP Energias de Portugal and the projects ECOIS (POCTI/CTA/48461/2002), RAIA (0313-RAIA-1-E), RAIA. co (0520-RAIA CO-1-E), RAIA tec (0688-RAIA TEC-1-P), ECORISK (NORTE 07 0124-FEDER-000054) and INNOVMAR/ECOSERVICES (NORTE 01 0145-FEDER-000035) for the data provided.

For being densely populated and urbanized, and for concentrating high-value economic activities, estuarine regions have an increased energy demand, which boosts the claim for new, efficient, renewable, and safe energy production. Among these technologies, hydrokinetic energy conversion systems are potentially well-suited for estuaries. However, in the actual context of climate change, it is important to know how changes in mean sea level may affect hydrokinetic energy production. This work proposes a methodology to assess the hydrokinetic energy potential for future scenarios using numerical hydrodynamic modeling techniques. Applied to the Douro estuary, several scenarios considering present conditions, as well as medium (2050) and long-term (2100) predictions under different Shared Socioeconomic Pathways are proposed. The results revealed that the studied region maintains a high dependence on freshwater discharge until 2100, although tidal oscillation is also significantly perceived in the entire estuary. Overall, hydrokinetic power potential will not increase with the mean sea level rise and will instead be considerably lower. Therefore, a decline in the kinetic energy available for exploitation is expected with increasing CO2 emissions, along with the associated intensification of sea level rise. Results reinforce the need to perform local studies to evaluate future trends in hydrokinetic energy production. This research was supported by the Strategic Funding UIDB/04423/2020 and UIDP/04423/2020 through national funds provided by FCT – Foundation for Science and Technology and European Regional Development Fund (ERDF), and by the project EsCo-Ensembles (PTDC/ECI-EGC/30877/2017), co-financed by NORTE 2020, Portugal 2020, and the European Union through the ERDF, and by FCT through national funds. The authors would like to thank the Instituto Hidrográfico, EDP Energias de Portugal and the projects ECOIS (POCTI/CTA/48461/2002), RAIA (0313-RAIA-1-E), RAIA. co (0520-RAIA CO-1-E), RAIA tec (0688-RAIA TEC-1-P), ECORISK (NORTE 07 0124-FEDER-000054) and INNOVMAR/ECOSERVICES (NORTE 01 0145-FEDER-000035) for the data provided.

AbstractEcosystem functioning is simultaneously affected by changes in community composition and environmental change such as increasing atmospheric carbon dioxide (CO2) and subsequent ocean acidification. However, it largely remains uncertain how the effects of these factors compare to each other. Addressing this question, we experimentally tested the hypothesis that initial community composition and elevatedCO2are equally important to the regulation of phytoplankton biomass. We full‐factorially exposed three compositionally different marine phytoplankton communities to two differentCO2levels and examined the effects and relative importance (ω2) of the two factors and their interaction on phytoplankton biomass at bloom peak. The results showed that initial community composition had a significantly greater impact than elevatedCO2on phytoplankton biomass, which varied largely among communities. We suggest that the different initial ratios between cyanobacteria, diatoms, and dinoflagellates might be the key for the varying competitive and thus functional outcome among communities. Furthermore, the results showed that depending on initial community composition elevatedCO2selected for larger sized diatoms, which led to increased total phytoplankton biomass. This study highlights the relevance of initial community composition, which strongly drives the functional outcome, when assessing impacts of climate change on ecosystem functioning. In particular, the increase in phytoplankton biomass driven by the gain of larger sized diatoms in response to elevatedCO2potentially has strong implications for nutrient cycling and carbon export in future oceans.