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Effects of wastewater treatment plant effluent inputs on planktonic metabolic rates and microbial community composition in the Baltic Sea

The Baltic Sea is the world's largest area suffering from eutrophication-driven hypoxia. Low oxygen levels are threatening its biodiversity and ecosystem functioning. The main causes for eutrophication-driven hypoxia are high nutrient loadings and global warming. Wastewater treatment plants (WWTP) contribute to eutrophication as they are important sources of nitrogen to coastal areas. Here, we evaluated the effects of wastewater treatment plant effluent inputs on Baltic Sea planktonic communities in four experiments. We tested for effects of effluent inputs on chlorophyll <i>a</i> content, bacterial community composition, and metabolic rates: gross primary production (GPP), net community production (NCP), community respiration (CR) and bacterial production (BP). Nitrogen-rich dissolved organic matter (DOM) inputs from effluents increased bacterial production and decreased primary production and community respiration. Nutrient amendments and seasonally variable environmental conditions lead to lower alpha-diversity and shifts in bacterial community composition (e.g. increased abundance of a few cyanobacterial populations in the summer experiment), concomitant with changes in metabolic rates. An increase in BP and decrease in CR could be caused by high lability of the DOM that can support secondary bacterial production, without an increase in respiration. Increases in bacterial production and simultaneous decreases of primary production lead to more carbon being consumed in the microbial loop, and may shift the ecosystem towards heterotrophy

Changes in dissolved oxygen due to anthropogenic disturbances and consequences for coastal marine life

[eng] Increased anthropogenic pressures to coastal ecosystems in the last Century are threatening coastal ecosystems, their biodiversity and ecosystems functioning. The two main stressors affecting coastal systems are increases in nutrients loadings and global warming. How coastal ecosystems will response to the combined effects of these two pressures remain uncertain. In this Ph.D. dissertation I explore the consequences of global warming on planktonic and benthic metabolism and on oxygen dynamics. I also explore the responses of benthic communities to the main consequence of eutrophication, oxygen depletion, and the environmental modulation of the responses of benthic organisms to hypoxia. Results confirm a steeper increase in respiration rates than in production rates with warming in experimental systems, whereas no differences were found between the responses of these metabolic rates to temperature, within the current thermal range, in a natural system. Results suggest an increase in the likelihood of hypoxia with warming. We also show that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O2/liter to designate waters as hypoxic is below the empirical sublethal and lethal oxygen thresholds for half of the species tested, and explore the environmental modulation of these thresholds. All studied processes and results obtained within this work reveal, in summary, that anthropogenic disturbances are significantly affecting coastal metabolism, and therefore, oxygen dynamics, leading to oxygen declines due to the combined effects of eutrophication and warming, threatening coastal biodiversity and ecosystems functioning.[cat] L'increment de les pressions antropogèniques als ecosistemes costaners durant el darrer segle estan posant en perill la seva biodiversitat i el seu funcionament. L'increment en l’aport de nutrients a les costes i l'escalfament global són les dues pressions més importants que afecten als sistemes costaners. Cóm respondran aquests sistemes a l'efecte combinat d'aquestes dues pressions és incert. En aquesta tesi doctoral exploro les conseqüències de l'escalfament global en el metabolisme de les comunitats planctòniques i bentòniques i en les dinàmiques d'oxigen. També exploro les respostes de les comunitats bentòniques a la major conseqüència de l'eutrofització, la disminució de la concentració d'oxigen dissolt, i la modulació ambiental de les respostes dels organismes bentònics a l hipòxia. Els resultats confirmen un major increment en les taxes respiratòries que en les de producció amb l’escalfament en sistemes experimentals, mentre no es troben diferències entre les respostes d'aquestes taxes metabòliques a la temperatura, dins el seu rang tèrmic actual, en sistemes naturals. Els resultats suggereixen que l'escalfament global augmentarà la probabilitat d'episodis hipòxics. També mostram que els llindars d'hipòxia varien àmpliament en els diferents organismes bentònics marins i que la definició tradicional d'hipòxia de 2 mg O2/litre per designar les aigües com hipòxiques està per davall dels llindars de les concentracions letals i subletals empíriques per a la meitat de les espècies testades. També exploram la modulació ambiental d'aquests llindars. Tots els processos estudiats i els resultats obtinguts en aquest treball revelen, en resum, que les pertorbacions antropogèniques afecten significativament el metabolisme de les comunitats costaneres i, per tant, les dinàmiques d'oxigen, produint una disminució en la concentració d'oxigen a causa dels efectes combinats de l'eutrofització i l'escalfament, posant en perill la biodiversitat costanera i el funcionament dels ecosistemes

EFFECTS OF HYPOXIA ON MARINE BIODIVERSITY

participantHypoxia is a mounting problem affecting the world's coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O2/liter to designate waters as hypoxic is below the empirical sublethal and lethal O2 thresholds for half of the species tested. The effects of the presence of sulfide and warming were also tested to assess the responses of benthic organisms to hypoxia and these environmental stressors. Both environmental factors showed a negative impact on survival of marine benthic communities under hypoxia and suggest that the threats derived from hypoxia to marine biodiversity are greater than anticipated on the basis of the direct effects of low oxygen concentration alone. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated

Annual benthic metabolism and organic carbon fluxes in a semi-enclosed Mediterranean bay dominated by the macroalgae Caulerpa prolifera

Coastal areas play an important role on carbon cycling. Elucidating the dynamics on the production, transport, and fate of organic carbon (OC) is relevant to gain a better understanding on the role coastal areas play in the global carbon budget. Here, we assess the metabolic status and associated OC fluxes of a semi-enclosed Mediterranean bay supporting a meadow of Caulerpa prolifera. We test whether the EDOC pool is a significant component of the OC pool and associated fluxes in this ecosystem. The Bay of Portocolom was in net metabolic balance on a yearly basis, but heterotrophic during the summer months. Community respiration (CR) was positively correlated to C. prolifera biomass, while net community production (NCP) had a negative correlation. The benthic compartment represented, on average, 72.6 ± 5.2% of CR and 86.8 ± 4.5% of gross primary production (GPP). Dissolved organic carbon (DOC) production peaked in summer and was always positive, with the incubations performed in the dark almost doubling the flux of those performed in the light. Exchangeable dissolved organic carbon (EDOC), however, oscillated between production and uptake, being completely recycled within the system and representing around 14% of the DOC flux. The pools of bottom and surface DOC were high for an oligotrophic environment, and were positively correlated to the pool of EDOC. Thus, despite being in metabolic balance, this ecosystem acted as a conduit for OC, as it is able to export OC to adjacent areas derived from allochtonous inputs during heterotrophic conditions. These inputs likely come from groundwater discharge, human activity in the watershed, delivered to the sediments through the high capacity of C. prolifera to remove particles from the water column, and from the air-water exchange of EDOC, demonstrating that these communities are a major contributor to the cycling of OC in coastal embayments.This research was funded by project MEDEICG, funded by the Spanish Ministry of Science and Innovation (CTM2009-07013) and an intramural project funded by CSIC (ref. 200430E661).Peer reviewedPeer Reviewe

Experimental evaluation of the Response of coastal Mediterranean planktonic and benthic metabolic rates to warming

[eng] The Mediterranean Sea has been identified as one of the hotspots for climate change. Intense warming in the Mediterranean Sea may have strong implications for biological activity and ecosystem functioning. To elucidate the effects of warming on planktonic and benthic metabolism, we performed experiments under different increasing temperature regimes, ranging from three to six different temperatures. The lowest range of temperatures assessed was of 2.6 A degrees C and the maximum was 7.5 A degrees C. Our results suggest that a 6 A degrees C warming of the Mediterranean waters may yield a mean increment in planktonic respiration rates of coastal communities of 24 %, higher than the mean increase expected for planktonic gross primary production (9 %). These results confirm earlier theories, and agree with previous experiments, of a higher increase in respiration rates than in primary production with warming, with the subsequent consequences for the carbon cycle, resulting in a negative feedback to climate warming, as ocean communities will capture less CO2

Effects of global warming on thresholds of hypoxia for marine benthic organisms

Trabajo presentado en la EUR-OCEANS Conference - Ocean deoxygenation and implications for marine biogeochemical cycles and ecosystems, celebrada en Toulouse, Francia, del 24 al 26 de 2011Peer Reviewe

Sulfide exposure accelerates hypoxia-driven mortality

The effect of the presence of sulfide on the survival of benthic organisms under hypoxia was tested using a meta-analysis of published experimental results evaluating the effects of the presence of hydrogen sulfide on the median survival time of benthic macrofauna under hypoxia. The meta-analysis confirmed that survival times under hypoxia are reduced by an average of 30% in marine benthic communities exposed to hydrogen sulfide. The effect of sulfide on survival was higher for egg forms than for juvenile or adult stages. The aggravation of the negative effects of spreading hypoxia in the presence of sulfide suggests that the threats derived from hypoxia to marine biodiversity are greater than anticipated on the basis of the direct effects of low oxygen concentration alone. © 2010, by me American society of Limnology and Oceanography, Inc.This research is a contribution to the ‘‘Water bodies in Europe: Integrative Systems to assess Ecological status and Recovery (WISER)’’ project, funded by FP7 (contract 226273).Peer Reviewe