Bárbara Úbeda

Plastic debris in the open ocean

Significance High concentrations of floating plastic debris have been reported in remote areas of the ocean, increasing concern about the accumulation of plastic litter on the ocean surface. Since the introduction of plastic materials in the 1950s, the global production of plastic has increased rapidly and will continue in the coming decades. However, the abundance and the distribution of plastic debris in the open ocean are still unknown, despite evidence of affects on organisms ranging from small invertebrates to whales. In this work, we synthetize data collected across the world to provide a global map and a first-order approximation of the magnitude of the plastic pollution in surface waters of the open ocean. There is a rising concern regarding the accumulation of floating plastic debris in the open ocean. However, the magnitude and the fate of this pollution are still open questions. Using data from the Malaspina 2010 circumnavigation, regional surveys, and previously published reports, we show a worldwide distribution of plastic on the surface of the open ocean, mostly accumulating in the convergence zones of each of the five subtropical gyres with comparable density. However, the global load of plastic on the open ocean surface was estimated to be on the order of tens of thousands of tons, far less than expected. Our observations of the size distribution of floating plastic debris point at important size-selective sinks removing millimeter-sized fragments of floating plastic on a large scale. This sink may involve a combination of fast nano-fragmentation of the microplastic into particles of microns or smaller, their transference to the ocean interior by food webs and ballasting processes, and processes yet to be discovered. Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean.

Plastic Accumulation in the Mediterranean Sea

Concentrations of floating plastic were measured throughout the Mediterranean Sea to assess whether this basin can be regarded as a great accumulation region of plastic debris. We found that the average density of plastic (1 item per 4 m2), as well as its frequency of occurrence (100% of the sites sampled), are comparable to the accumulation zones described for the five subtropical ocean gyres. Plastic debris in the Mediterranean surface waters was dominated by millimeter-sized fragments, but showed a higher proportion of large plastic objects than that present in oceanic gyres, reflecting the closer connection with pollution sources. The accumulation of floating plastic in the Mediterranean Sea (between 1,000 and 3,000 tons) is likely related to the high human pressure together with the hydrodynamics of this semi-enclosed basin, with outflow mainly occurring through a deep water layer. Given the biological richness and concentration of economic activities in the Mediterranean Sea, the affects of plastic pollution on marine and human life are expected to be particularly frequent in this plastic accumulation region.

Basin-scale control on the phytoplankton biomass in Lake Victoria, Africa.

The relative bio-optical variability within Lake Victoria was analyzed through the spatio-temporal decomposition of a 1997–2004 dataset of remotely-sensed reflectance ratios in the visible spectral range. Results show a regular seasonal pattern with a phase shift (around 2 months) between the south and north parts of the lake. Interannual trends suggested a teleconnection between the lake dynamics and El-Niño phenomena. Both seasonal and interannual patterns were associated to conditions of light limitation for phytoplankton growth and basin-scale hydrodynamics on phytoplankton access to light. Phytoplankton blooms developed during the periods of lake surface warming and water column stability. The temporal shift apparent in the bio-optical seasonal cycles was related to the differential cooling of the lake surface by southeastern monsoon winds. North-south differences in the exposure to trade winds are supported by the orography of the Eastern Great Rift Valley. The result is that surface layer warming begins in the northern part of the lake while the formation of cool and dense water continues in the southern part. The resulting buoyancy field is sufficient to induce a lake-wide convective circulation and the tilting of the isotherms along the north-south axis. Once surface warming spreads over the whole lake, the phytoplankton bloom dynamics are subjected to the internal seiche derived from the relaxation of thermocline tilting. In 1997–98, El-Niño phenomenon weakened the monsoon wind flow which led to an increase in water column stability and a higher phytoplankton optical signal throughout the lake. This suggests that phytoplankton response to expected climate scenarios will be opposite to that proposed for nutrient-limited great lakes. The present analysis of remotely-sensed bio-optical properties in combination with environmental data provides a novel basin-scale framework for research and management strategies in Lake Victoria.

Daily, biweekly, and seasonal temporal scales of pCO2 variability in two stratified Mediterranean reservoirs

Temporal scales of variability for the partial pressure of CO2 (pCO2) in the surface waters of two stratified Mediterranean reservoirs were examined through the temporal decomposition of 5 month time series with hourly sampling frequency. pCO2 time series included similar patterns of variability at daily, biweekly, and seasonal scales regardless of the difference in amplitude of the pCO2 variation in the two reservoirs studied. Daily variability was strongly related to the day-night cycles of metabolic activity, accounting for about one third of the total amplitude in pCO2 variation. At a biweekly scale, wind forcing led to higher rates of air-water CO2 exchange and subsequently temporary partial mixing events associated to relevant increase of CO2 concentration in surface waters. Seasonal variability accounted for one third of the amplitude of the pCO2 variability and was coupled to the seasonal dynamics of water temperature and thermal stratification of the water column. Our results provide evidence that CO2 emission from stratified water bodies shows significant variability at daily, biweekly, and seasonal scales; all of which should be taken into consideration in the analyses of the carbon fluxes. The wind-induced mixing events, operating at temporal scales between daily and seasonal cycles, may become a major factor controlling the pCO2 dynamics. Hence, some of the most common models for computing CO2 fluxes from pCO2 were not able to reproduce the biweekly response patterns of CO2 emissions to wind forcing.

Microalgae cultivation in urban wastewater: Coelastrum cf. pseudomicroporum as a novel carotenoid source and a potential microalgae harvesting tool

The aim of this work was to study the optimal growth and high value-added production of the microalgae Coelastrum cf. pseudomicroporum Korshikov cultivated in urban wastewater. It was observed that C. cf. pseudomicroporum grew ideally in this medium, acting as an efficient nutrient starver. Additionally, the obtained biomass increased carotenoid cell content after saltwater stress. The effects of light intensity and salt stress on its growth rate were analysed. The results showed that this alga can grow very fast using wastewater as culture medium, reaching maximum growth rates of 1.61±0.05day-1, and tolerating strong irradiances. It was also found that under salt-stress this species could accumulate carotenoids (range 1.73-91.2pgcell-1). Moreover, a good harvesting efficiency (96.84%) was observed using Coelastrum exudates as bioflocculant of Scenedesmus sp., so Coelastrum exudates could act as a potential bioflocculant for other species.

Potential effects of climate change on the water level, flora and macro-fauna of a large neotropical wetland.

Possible consequences of climate change in one of the world’s largest wetlands (Ibera, Argentina) were analysed using a multi-scale approach. Climate projections coupled to hydrological models were used to analyse variability in wetland water level throughout the current century. Two potential scenarios of greenhouse gas emissions were explored, both resulting in an increase in the inter-annual fluctuations of the water level. In the scenario with higher emissions, projections also showed a long-term negative trend in water-level. To explore the possible response of biota to such water-level changes, species-area relationships of flora and aerial censuses of macro-fauna were analysed during an extraordinary dry period. Plant species richness at the basin scale was found to be highly resistant to hydrological changes, as the large dimension of the wetland acts to buffer against the water-level variations. However, local diversity decreased significantly with low water levels, leading to the loss of ecosystem resilience to additional stressors. The analysis of macro-fauna populations suggested that wetland provides refuge, in low water periods, for the animals with high dispersal ability (aquatic and migratory birds). On the contrary, the abundance of animals with low dispersal ability (mainly herbivorous species) was negatively impacted in low water periods, probably because they are required to search for alternative resources beyond the wetland borders. This period of resource scarcity was also related to increased mortality of large mammals (e.g. marsh deer) around water bodies with high anthropogenic enrichment and cyanobacteria dominance. The synergy between recurrent climatic fluctuations and additional stressors (i.e. biological invasions, eutrophication) presents an important challenge to the conservation of neotropical wetlands in the coming decades.

Planktonic community metabolism in two stratified Mediterranean reservoirs with different trophic status

Community metabolism plays a crucial role in the carbon dynamics of continental aquatic ecosystems. In the present work, two Mediterranean reservoirs (Southern Spain) with different trophic status were monitored during the stratified phase over two consecutive years (2009 and 2010) to evaluate community metabolic dynamics and potential controlling factors. Dark and light incubations were performed in order to estimate the daily rates of gross production (GP), community respiration (CR) and net community production (NCP). Temperature, irradiance, chlorophyll, phosphorus and carbon concentration were also measured at different depths within the mixed layer. On average, results showed heterotrophic behavior (GP < CR) in both reservoirs, which was particularly evident in the more eutrophic reservoir. Interannual climate variability was high due to the exceptionally rainy winter of 2010. This resulted in a significant decrease in the magnitude of the heterotrophic balance in both reservoirs. The change in NCP was especially evident in the most eutrophic reservoir where high water renewal rates lead to a lower CR. In general, NCP was found to be directly related to the ratio between the euphotic layer depth and the mixed layer depth, and inversely related to the particulate phosphorus concentration. Autotrophic behavior was only found in conditions of high irradiance (mixed layer shallower than euphotic layer), relatively low concentrations of dissolved organic carbon (<6 mg L−1) and particulate phosphorus (<10 μg L−1), and moderate chlorophyll concentration (2–9 μg L−1), albeit these conditions did not always lead to a net autotrophic balance.

Organic carbon sedimentation dominates over CO2 emission in two net heterotrophic Mediterranean reservoirs during stratification

Freshwater reservoirs are significant components of the global carbon cycle. However, relatively few studies address the balance between the atmospheric carbon flux and sedimentation in these ecosystems. We performed a simultaneous analysis of the sedimentation fluxes of particulate organic carbon (SPOC) and atmospheric CO2 fluxes (

Daily, biweekly, and seasonal temporal scales ofpCO2variability in two stratified Mediterranean reservoirs: Temporal scales of pCO2

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