Dissolved organic matter cycling in a coastal upwelling system

289 páginasEsta tesis fue realizada durante el disfrute de una beca de Formación de Personal Investigador del Ministerio de Educación y Ciencia y una beca de postgrado del programa I3P del Consejo Superior de Investigaciones Científicas. Los trabajos que se recogen en esta memoria fueron financiados por los proyectos del Programa Nacional de Ciencias y Tecnologías Marinas: DYBAGA (CICYT-MAR99-1039-C02-01) y REMODA (CICYT-REN- 2000-0800-C02-01) Además, en el transcurso de la elaboración de esta tesis Doctoral, se realizó una estancia de dos meses en el Laboratoire de Microbiologie Marine (C.O.M.) en Marsella (Francia) financiada por el Ministerio de Educación y Ciencia.Peer reviewe

Vertical Niche Partitioning of Archaea and Bacteria Linked to Shifts in Dissolved Organic Matter Quality and Hydrography in North Atlantic Waters

Understanding the factors that modulate prokaryotic assemblages and their niche partitioning in marine environments is a longstanding challenge in marine microbial ecology. This study analyzes amplicon sequence variant (ASV) diversity and co-occurrence of prokaryotic (Archaea and Bacteria) communities through coastal-oceanic gradients in the NW Iberian upwelling system and adjacent open-ocean (Atlantic Ocean). Biogeographic patterns were investigated in relation with environmental conditions, mainly focusing on the optical signature of the dissolved organic matter (DOM). Alpha- and beta-diversity were horizontally homogeneous [with the only exception of Archaea (∼1700 m depth), attributed to the influence of Mediterranean water, MW], while beta-diversity was significantly vertically stratified. Prokaryotic communities were structured in four clusters (upper subsurface, lower subsurface, intermediate, and deep clusters). Deep (>2000 m) archaeal and bacterial assemblages, and intermediate (500-2000 m) Bacteria (mainly SAR202 and SAR406), were significantly related to humic-like DOM (FDOM-M), while intermediate Archaea were additionally related to biogeochemical attributes of the high-salinity signature of MW. Lower subsurface (100-500 m) Archaea (particularly one ASV belonging to the genus Candidatus Nitrosopelagicus) were mainly related to the imprint of high-salinity MW, while upper subsurface (≤100 m) archaeal assemblages (particularly some ASVs belonging to Marine Group II) were linked to protein-like DOM (aCDOM254). Conversely, both upper and lower subsurface bacterial assemblages were mainly linked to aCDOM254 (particularly ASVs belonging to Rhodobacteraceae, Cyanobacteria, and Flavobacteriaceae) and nitrite concentration (mainly members of Planctomycetes). Most importantly, our analysis unveiled depth-ecotypes, such as the ASVs MarG.II_1 belonging to the archaeal deep cluster (linked to FDOM-M) and MarG.II_2 belonging to the upper subsurface cluster (related to FDOM-T and aCDOM254). This result strongly suggests DOM-mediated vertical niche differentiation, with further implications for ecosystem functioning. Similarly, positive and negative co-occurrence relationships also suggested niche partitioning (e.g., between the closely related ASVs Thaum._Nit._Nit._Nit._1 and _2) and competitive exclusion (e.g., between Thaum._Nit._Nit._Nit._4 and _5), supporting the finding of non-randomly, vertically structured prokaryotic communities. Overall, differences between Archaea and Bacteria and among closely related ASVs were revealed in their preferential relationship with compositional changes in the DOM pool and environmental forcing. Our results provide new insights on the ecological processes shaping prokaryotic assembly and biogeography.Versión del edito

Microbial and photochemical reactivity of fluorescent dissolved organic matter in a coastal upwelling system

Original research articleWe observed significant changes in the dissolved oxygen content and the fluorescence of humic substances anddissolved aromatic amino acids after 24 h light and dark incubations in the coastal upwelling system of the Rı´a deVigo under a wide variety of meteorologic and oceanographic conditions. Respiration rates were inverselycorrelated with the net production of humic fluorescence in the dark at a net rate of 20.027 6 0.003 mgequivalents of quinine sulphate per mmol of O2, suggesting that marine humics are a by-product of the bacterialrespiration of dissolved organic matter (DOM). On the contrary, humic fluorescence consumption in the lightminus dark incubations was positively correlated with the net production in the dark, indicating a rapidphotodegradation of recently produced marine humic substances. Parallel incubation experiments demonstratedthat daily photodegradation rates and residual humic fluorescence levels followed a seasonal pattern characterizedby a marked autumn maximum. Finally, a significant linear correlation between the gross primary production(Pg) and the net production of aromatic amino acids fluorescence in the light pointed to the rapid consumption ofdissolved protein-like materials at a net average rate of 21.4 6 0.2 ppb equivalents of tryptophan per day, whichaccumulates in the water column only when Pg exceeds 80 6 20 mmol kg21d21Financial support came from the Spanish Ministerio de Cienciay Tecnologı´a (MCyT) grant REN2000-0880-C02-01 and Xunta deGalicia grant PGIDT01MAR40201PN and a fellowship from theMCyT and the I3P-CSIC ProgramVersión del editor3,38

Local remineralization patterns in the mesopelagic zone of the Eastern North Atlantic, off the NW Iberian Peninsula

Original research articleThe short-time-scale variability of the remineralization patterns in the domain of Eastern North Atlantic Central Waters (ENACW) off the NW Iberian Peninsula is studied based on biogeochemical data (oxygen, nutrient salts, total alkalinity, pH, dissolved organic matter and fluorescence of dissolved humic substances) collected weekly between May 2001 and April 2002. The temporal variability of inorganic variables points to an intensification of remineralization during the summer and autumn, with an increase of nutrients, total inorganic carbon and fluorescence and a decrease of oxygen. During the subsequent winter mixing, there is a biogeochemical reset of the system, with lower nutrients, total inorganic carbon and fluorescence and higher oxygen. In contrast to inorganic variables, the levels of dissolved organic matter in the ENACW seem to respond to short-term events probably associated with fast sinking particles, where solubilisation of organic matter prevails over remineralization. Applying a previously published stoichiometric model, we observed a vertical fractionation of organic-matter remineralization. Although there is a preferential remineralization of proteins and P compounds in the entire domain of ENACW, the percentage was higher in the upper ENACW (σ80% for the upper ENACW and 63% for the lower. Likewise, the redissolution of calcareous structures contributes about 6% and 13% to the carbon regenerated in the upper and lower layers of ENACW, respectively.Financial support for this work came from CICYT project MAR99-1039-C02-01; a contract of the Ramón y Cajal programme of the Spanish MCYT and a fellowship from the Spanish MCYT.Versión del edito

SIZE-REACTIVITY OF DISSOLVED ORGANIC MATTER IN THE CAPE VERDE FRONTAL ZONE

Oral communicationDissolved organic matter (DOM) plays a major role in the recycling, export and sequestration of biogenic organic carbon, being a key component of ocean biogeochemical cycles and of the biological and microbial carbon pumps. Microbial degradation of DOM not only produces CO 2 but also generates dissolved molecules of decreasing bioavailability that can accumulate in the oceans for hundreds to thousands of years. The size-reactivity continuum (SRC) model is the conceptual framework to explain the DOM reactivity on a size basis, although field tests are still scarce and some of the pieces of this puzzle remain unclear. Taking advantage of the FLUXES-I cruise in the Cape Verde Frontal Zone (CVFZ), we have studied the size fractionated reactivity of the high (HMW; >1 KDa) and low (LMW; <1 KDa) molecular weight fractions of the DOM from surface down to 4000 m, using a high-efficiency and low-concentration-factor ultrafiltration cell. The wide ageing range covered by the water masses of the CVFZ makes it an excellent site to test the SRC model. Regarding the bulk C and N pools, the water masses with higher oxygen utilization were more depleted in HMW molecules, with a significant preference for the degradation of large N-containing compounds. Accordingly, preferential degradation of HMW fluorescent protein-like compounds was observed. In parallel, fluorescent humic-like compounds of both HMW and LMW were generated as by-product of the degradation of HMW organic compounds, and the remineralization of the DOM increases the aromaticy of both fractions, but especially the LMW one.ASL

Effect of dissolved organic matter (DOM) of contrasting origins on Cu and Pb speciation and toxicity to Paracentrotus lividus larvae

4 tablas, 6 figurasWater samples of contrasting origin, including natural seawater, two sediment elutriates and sewage-influenced seawater, were collected and obtained to examine the effect of the dissolvedorganicmatter (DOM) present on metal bioavailability. The carbon content (DOC) and the optical properties (absorbance and fluorescence) of the coloured DOM fraction (CDOM) of these materials were determined. Cu and Pb complexation properties were measured by anodic stripping voltammetry (ASV) and the effect of DOM on Cu and Pb bioavailability was studied by means of the Paracentrotus lividus embryo-larval bioassay. Sediment elutriates and sewage-influenced water (1) were enriched 1.4–1.7 times in DOC; (2) absorbed and reemitted more light; and (3) presented higher Cu complexation capacities (LCu) than the natural seawater used for their preparation. LCu varied from 0.08 μM in natural seawater to 0.3 and 0.5 μM in sediment elutriates and sewage-influenced water, respectively. Differences in DOC, CDOM and Cu complexation capacities were reflected in Cu toxicity. DOM enriched samples presented a Cu EC50 of 0.64 μM, significantly higher than the Cu EC50 of natural and artificial seawater, which was 0.38 μM. The protecting effect of DOM on Cu toxicity greatly disappeared when the samples were irradiated with high intensity UV-light. Cu toxicity could be successfully predicted considering ASV-labile Cu concentrations in the samples. Pb complexation by DOM was only detected in the DOM-enriched samples and caused little effect on Pb EC50. This effect was contrary for both elutriates: one elutriate reduced Pb toxicity in comparison with the control artificial seawater, while the other increased it. UV irradiation of the samples caused a marked increase in Pb toxicity, which correlated with the remaining DOC concentration. DOM parameters were related to Cu speciation and toxicity: good correlations were found between DOC and Cu EC50, while LCu correlated better with the fluorescence of marine humic substances. The present results stress the importance of characterizing not only the amount but also the quality of seawater DOM to better predict ecological effects from total metal concentration dataP.S-M was granted with an FPU-fellowship from the Spanish Ministry of 15 Education and Science. J.S-E thanks the Basque Government for financial support (pre-doctoral grant). Research was partially funded by the project PGIDIT-05MA40201PR (Xunta de Galicia) and CTM2006-13880-C03-01/MAR (Spanish Ministry of Education and Science).Peer reviewe

Contrasting complexing capacity of dissolved organic matter produced during the onset, development and decay of a simulated bloom of the marine diatom Skeletonema costatum

Original research articleThe capacity of natural dissolved organic matter (DOM) produced during the onset, development and decay of a simulated bloom of the marine diatom Skeletonema costatum to complex free copper has been followed for a 2 week period. Copper binding capacity of the culture was measured by anodic stripping voltammetry (ASV) with a hanging mercury drop electrode (HMDE). The concentration of dissolved organic carbon (DOC) and two fluorophores, M (humic-like, Ex/Em: 320 nm/410 nm) and T (protein-like, Ex/Em: 280 nm/350 nm), were followed during the course of the incubation. Models using DOC concentrations alone could not accurately predict the complexing capacity of the culture, especially at the end of the bloom, and better predictions were obtained when fluorescence measurements were considered. They were helpful in characterising two types of copper ligands produced in the culture. The first type, traced by the fluorescence of peak T, was related to labile DOC directly exuded by phytoplankton. The second type, traced by the fluorescence of peak M, was the refractory humic-like material presumably produced in situ as a by-product of the bacterial degradation of phytogenic materials. During the onset and development of the bloom (days 0 to 7), the fluorescence of peak T explains 60–80% of the total complexing capacity of the culture, suggesting that exuded “protein-like” compounds among other exuded complexing agents efficiently complexed free copper. On the contrary, during the decay (days 8 to 13), these ligands were replaced by humic substances as the complexing agent for copper.Financial support for this work came from the Spanish ‘Ministerio de Educación y Ciencia’ (MEC), Grant Nos. REN2000-0880-C02-01 MAR and REN2003-00958 MAR and the ‘Xunta de Galicia’, Grant No. PGIDT01MAR40201PN.Versión del editor2,75

Bacterial activity and community composition response to the size-reactivity of dissolved organic matter

Heterotrophic bacteria respond dynamically to variations in organic matter availability in the dark ocean. However, our knowledge on how the differences in sized and/or reactivity of dissolved organic matter (DOM) affect the bacterial community dynamics is still scarce. Our study aims to investigate the response of bacterial activity and community composition to the degradability of filtered and of size-fractionated DOM. A natural bacterial community isolated from Mediterrean Water (MW; at 1000 m depth) was inoculated in seawater from the same location subjected to three different treatments: 0.2µm-filtered seawater (control), low molecular weight fraction (LMW) obtained by ultrafiltration, and the combination of low and high molecular weight fractions at the original ratio (H+L). Bacterial abundance and activity was monitored every 24h over 6 days, while bacterial community composition and DOM characterization were assessed at the beginning (day 0), middle (day 4) and at the end of the experiment (day 6). Low (LNA) and high nucleic acid content (HNA) bacterial abundance, as well as leucine incorporation rates, were consistently higher in the H+L incubations than in the LMW treatments, indicating different reactivity of the two organic matter size fractions. Moreover, actively respiring cells, estimated as CTC-positive cells, highly correlated to humic-like substances (FDOM-M; R=0.7, P<0.05, n=9, Spearman Rank Order), particularly in the H+L incubations. Interestingly, LNA cell abundance was highly correlated with the slope ratio (SR) values (R=-0.8, P<0.05, n=9, Spearman Rank Order), indicating that bacteria belonging to the LNA population are tightly linked to the molecular weight or aromaticity of the DOM. Taken together, our results indicate differences in the bio-reactivity of the low and high molecular weight size classes of DOM associated to the phylogenetic composition of the bacterial communities

Fresh and saline submarine groundwater discharge in a large coastal inlet affected by seasonal upwelling

Original research paperSubmarine groundwater discharge is recognized as a major source of chemicals to the global ocean, exerting large control over coastal water composition. Radon and 226Ra are used to evaluate, for the first time, the occur rence and magnitude of submarine groundwater discharge in the Ría de Vigo, a large, highly productive embay ment affected by seasonal, wind-driven upwelling. The system is naturally enriched in 222Rn due to the regional granitic basement geology: high 222Rn activities (up to 106 Bq m−3 ) are detected in wells and boreholes in the drainage basin of the embayment. High 222Rn activities (>400 Bq m−3 ) are also measured in certain areas of the embayment. Comparatively lower 226Ra activities (<4 103 Bq m−3 ) were measured in the freshwater sources to the bay. Mass balances obtained with a box model are used to perform a volumetric estimate of fresh and saline submarine groundwater discharge in the Ría de Vigo under contrasting circulation patterns. Fresh groundwater is shown to be a relevant hydrological component of the Ria de Vigo water balance, equivalent to 9% 4% and 23% 9% of the volume discharged by tributary rivers during winter and summer, respectively. On the other hand, recirculation of seawater through permeable sediments is capable of filtering the entire upper volume of the Ria de Vigo through its seafloor in <100 days and might thus be a previously overlooked major source of regenerated solutes to the system.Irish Research Council and European Union Commission Horizon 2020 research and innovation programmeVersión del editor3,38

EFFECT OF DISSOLVED ORGANIC MATTER ON COPPER BIOAVAILABILITY TO A COASTAL DINOFLAGELLATE

Metal complexation by dissolved organic matter (DOM) is considered to decrease metal bioavailability by lowering the free metal ion concentration, therefore protecting organisms from the deleterious effects of metals (Campbell et al., 2002). In coastal lagoons like Mar Menor, with high terrestrial influence and low exchange with open sea, the levels of both DOM and metals are one or two orders of magnitude higher than in open-waters. In order to verify the free ion activity model (FIAM), copper internalization by Prorocentrum micans, a cosmopolitan dinoflagellate also present in the Mar Menor, was tested in the absence and presence of two types of DOM, commercially available fulvic acids from riverine origin (SRFA) and coastal DOM obtained by ultrafiltration (UF-DOM). The microalgae were exposed to artificial sea water enriched with increasing amounts of Cu65 isotope, at levels from 5 to 100 nM Cu, solely and in combination with DOM. After one-hour exposure, samples were centrifuged and washed and pellets were digested with nitric acid at 90ºC, following Sánchez-Marín et al (2010) and Croteau and Luoma (2005). In parallel, careful measurements of metal complexation by anodic stripping voltammetry (ASV) were performed and total Cu concentrations were measured by ICP-MS. Preliminary results show that copper internalization by the microalgae increases linearly as a function of labile Cu, both in the absence and presence of DOM, in agreement with FIAM and with labile Cu measurements performed by ASV. Future work might include testing the influence of competing metals, such as Pb or Zn, on Cu internalization, and to study Cu bioavailability in natural samples collected in the Mar Menor, in order to shed light into the factors that control Cu bioavailability in coastal lagoons