Towards the outwelling hypothesis in a Patagonian estuary: First support from lipid markers and bacterial communities.

Biogeochemical markers in combination with bacterial community composition were studied at two contrasting stations at the Río Negro (RN) estuary to assess the outwelling hypothesis in the Argentinian Patagonia. Inorganic nutrients and dissolved organic matter were exported clearly during the last hours of the ebb at the station Wetland. Moreover, a considerable outwelling of polyunsaturated fatty acids (PUFA), particulates and microalgae was inferred by this combined approach. The exported 22:6(n-3) and 20:5(n-3) contributed very likely to sustain higher trophic levels in the coasts of the Southwest Atlantic. The stable isotopes did not evidence clearly the outwelling; nevertheless, the combination of δ13C with fatty acid bacterial markers indicated organic matter degradation in the sediments. The dominance of Desulfobacterales and Desulfuromonadales suggested sulphate reduction in the sediments, a key mechanism for nutrient outwelling in salt marshes. Marivivens and other Rhodobacterales (Alphaproteobacteria) in the suspended particulate matter were clear indicators of the nutrient outwelling. The colonization of particles according to the island biogeography theory was a good hypothesis to explain the lower bacterial biodiversity at the wetland. The copiotrophic conditions of the RN estuary and particularly at the wetland were deduced also by the dynamic of some Actinobacteria, Bacteroidia and Gammaproteobacteria. This high-resolution snapshot combining isotopic, lipid and bacterial markers offers key pioneer insights into biogeochemical and ecological processes of the RN estuary.

Chemically unidentified dissolved organic carbon: A pivotal piece for microbial activity in a productive area of the Northern Patagonian shelf.

The biochemical composition and fluorescence properties of DOM were assessed in relation to phytoplankton and major aquatic bacterial clades in a regenerative area of the Argentine Shelf. DOM was mainly of autochthonous biological origin, containing humic- and protein-like substances of medium degree of unsaturation and diagenesis. Biochemical-DOM accounted for 25% of total DOC, being dissolved combined amino acids (DCAA) the dominant fraction followed by free carbohydrates. Phytoplankton was the main source of serine, alanine, and valine, and particulate carbohydrates. Gammaproteobacteria abundance correlated negatively with ammonium and positively with DCAA, suggesting a coupling between ammonium consumption and refractory amino acid production. A preferential utilization of alanine, leucine and threonine as nitrogen source was inferred from the distribution of Cytophaga-Flavobacteria-Bacteroidete in relation with dissolved free amino acids (DFAA). Notably, Alpha- and Betaproteobacteria correlated with the large pool (75%) of chemically unidentified DOC and not with DCAA or dissolved combined carbohydrates. Particularly, Alphaproteobacteria (∼40% of EUB total heterotrophic bacteria) either significantly contribute to the production of the "humic", refractory fraction of marine DOM, or the latter impairs resource control on their abundance. Spatial heterogeneity inherent to coastal-shelf areas drives important regional variability in the biochemical properties of DOM.

Influence of microphytobenthos on the sedimentary organic matter composition in two contrasting estuarine microhabitats.

The influence of microphytobenthic community on the composition of sedimentary organic matter was evaluated in two Bahía Blanca estuary microhabitats contrasting in vegetation and hydrodynamic conditions; namely, S1 located in a Sarcocornia perennis saltmarsh with macroscopic microbial mats and S2 in a mudflat without macroscopic microbial mats or vegetation. Moisture, organic matter, chlorophyll a, phaeopigments, carbohydrates (CH), proteins (PRT), and abundance and structure of microphytobenthic community were evaluated in surface sediments. Higher moisture was observed at S2 and was related to the proximity of this site to the subtidal zone and the effect of the environmental variables temperature and rain. No significant differences were found in organic matter content between sites; however, at S1, a higher concentration was registered during winter and early spring associated to the period of higher microphytobenthic biomass. Chlorophyll a and phaeopigments were higher at S1, attributed to the higher microphytobenthos abundance at this site. Differences in microphytobenthos were observed not only in quantity but also in community structure since at S1 filamentous cyanobacteria dominated the community, whereas at S2, higher abundance of centric diatoms and the absence of cyanobacteria were observed during most of the study. S1 showed higher concentration of proteins and carbohydrates which could be attributed to the higher production of fresh organic matter by microphytobenthos. The total protein and carbohydrate concentrations allowed us to classify both microhabitats into the meso-oligotrophic category, contrasting with the classification made by other authors using water column proxies.

Vibrio and Bacterial Communities Across a Pollution Gradient in the Bay of Bengal: Unraveling Their Biogeochemical Drivers.

The highly populated coasts of the Bay of Bengal are particularly vulnerable to water-borne diseases, pollution and climatic extremes. The environmental factors behind bacterial community composition and Vibrio distribution were investigated in an estuarine system of a cholera-endemic region in the coastline of Bangladesh. Higher temperatures and sewage pollution were important drivers of the abundance of toxigenic Vibrio cholerae. A closer relation between non-culturable Vibrio and particulate organic matter (POM) was inferred during the post-monsoon. The distribution of operational taxonomic units (OTUs) of Vibrio genus was likely driven by salinity and temperature. The resuspension of sediments increased Vibrio abundance and organic nutrient concentrations. The δ13C dynamic in POM followed an increasing gradient from freshwater to marine stations; nevertheless, it was not a marker of sewage pollution. Bacteroidales and culturable coliforms were reliable indicators of untreated wastewater during pre and post-monsoon seasons. The presumptive incorporation of depleted-ammonium derived from ammonification processes under the hypoxic conditions, by some microorganisms such as Cloacibacterium and particularly by Arcobacter nearby the sewage discharge, contributed to the drastic 15N depletion in the POM. The likely capacity of extracellular polymeric substances production of these taxa may facilitate the colonization of POM from anthropogenic origin and may signify important properties for wastewater bioremediation. Genera of potential pathogens other than Vibrio associated with sewage pollution were Acinetobacter, Aeromonas, Arcobacter, and Bergeyella. The changing environmental conditions of the estuary favored the abundance of early colonizers and the island biogeography theory explained the distribution of some bacterial groups. This multidisciplinary study evidenced clearly the eutrophic conditions of the Karnaphuli estuary and assessed comprehensively its current bacterial baseline and potential risks. The prevailing conditions together with human overpopulation and frequent natural disasters, transform the region in one of the most vulnerable to climate change. Adaptive management strategies are urgently needed to enhance ecosystem health.

A protocol for the simultaneous identification of chitin-containing particles and their associated bacteria.

Chitin is the second most abundant polymer on Earth, playing a crucial role in the biogeochemical cycles. A core issue for studying its processing in aquatic systems is the identification and enumeration of chitin-containing particles and organisms, ideally in a manner that can be directly linked to bulk chitin quantification. The aim of this study was the development of such a technique. We successfully combined the methodology of bulk chitin determination using wheat germ agglutinin (FITC-WGA) for staining chitin-containing particles and organisms along with CARD-FISH staining of either chitin-containing eukaryotic cells or bacteria associated with them. Environmental chitin staining was successfully applied to natural water samples. Fungal hyphae, diatoms, and dinoflagellates, sestonic aggregates and chitin-containing structures derived from metazoa were observed. Also, hybridized bacteria attached to chitinaceous debris were clearly visualized. Finally, as proof of principle, cultured yeast cells were simultaneously-targeted by FITC-WGA and the EUK516 probe without exhibiting any interference between both stains. The presented approach appears as a powerful tool to evaluate the contribution of different size classes and organisms to chitin production and consumption, opening the possibility for application of single-cell approaches targeting the ecophysiology of chitin transformations in aquatic systems.

Biogeochemical and hydrological drivers of the dynamics of Vibrio species in two Patagonian estuaries.

The ecology of the most relevant Vibrio species for human health and their relation to water quality and biogeochemistry were studied in two estuaries in Argentinian Patagonia. Vibrio cholerae and Vibrio parahaemolyticus were reported in >29% of cases at the Río Colorado and Río Negro estuaries. Neither the pandemic serogroups of Vibrio cholerae O1, Vibrio cholerae O139 nor the cholera toxin gene were detected in this study. However, several strains of V. cholerae (not O1 or O139) are able to cause human disease or acquire pathogenic genes by horizontal transfer. Vibrio vulnificus was detected only in three instances in the microplankton fraction of the Río Negro estuary. The higher salinity in the Río Colorado estuary and in marine stations at both estuaries favours an abundance of culturable Vibrio. The extreme peaks for ammonium, heterotrophic bacteria and faecal coliforms in the Río Negro estuary supported a marked impact on sewage discharge. Generally, the more pathogenic strains of Vibrio have a faecal origin. Salinity, pH, ammonium, chlorophyll a, silicate and carbon/nitrogen ratio of suspended organic particulates were the primary factors explaining the distribution of culturable bacteria after distance-based linear models. Several effects of dissolved organic carbon on bacterial distribution are inferred. Global change is expected to increase the trophic state and the salinisation of Patagonian estuaries. Consequently, the distribution and abundance of Vibrio species is projected to increase under future changing baselines. Adaptation strategies should contribute to sustaining good water quality to buffer climate- and anthropogenic- driven impacts.

Global change effects on biogeochemical processes of Argentinian estuaries: an overview of vulnerabilities and ecohydrological adaptive outlooks.

The aims of this work are to provide an overview of the current stresses of estuaries in Argentina and to propose adaptation strategies from an ecohydrological approach. Several Argentinian estuaries are impacted by pollutants, derived mainly from sewage discharge and agricultural or industrial activities. Anthropogenic impacts are expected to rise with increasing human population. Climate-driven warmer temperature and hydrological changes will alter stratification, residence time, oxygen content, salinity, pollutant distribution, organism physiology and ecology, and nutrient dynamics. Good water quality is essential in enhancing estuarine ecological resilience to disturbances brought on by global change. The preservation, restoration, and creation of wetlands will help to protect the coast from erosion, increase sediment accretion rates, and improve water quality by removing excess nutrients and pollutants. The capacity of hydrologic basin ecosystems to absorb human and natural impacts can be improved through holistic management, which should consider social vulnerability in complex human-natural systems.

Seasonal dynamics of Vibrio cholerae and its phages in riverine ecosystem of Gangetic West Bengal: cholera paradigm.

The Gangetic delta is a century-old cholera endemic belt where the role of riverine-estuarine ecosystem in cholera transmission has never been elucidated. Seasonality, distribution, and abundance of environmental Vibrio cholerae O1/O139 and vibriophage in Hooghly riverine-estuarine environment and their correlation with cholera incidence pattern in West Bengal, India, have been analyzed for the first time across summer, monsoon, and winter months. A total of 146 water samples collected from two sites of the Hooghly River (Howrah and Diamond Harbour) were analyzed physicochemically along with cultivable Vibrio count (CVC), V. cholerae O1/O139, and vibriophages. V. cholerae O1 was detected in 56 (38.3%) samples, while 66 (45.2%) were positive for V. cholerae O1 phages. Flood tide, water temperature (31 ± 1.6 °C), and turbidity (≥250 nephelometric turbidity unit (NTU)) significantly stimulated V. cholerae and vibriophage abundance in riverine ecosystem. Solitary existence of V. cholerae O1 and phages (p < 0.0001) in aquatic environment divulges the dominance of either of the entity (V. cholerae O1 or V. cholerae O1 Φ) on the other. Significant association (p < 0.05) between Kolkata cholera cases and V. cholerae O1 in aquatic environment implies the role of riverine-estuarine ecosystem in cholera transmission. A "biomonitoring tool" of physicochemical stimulants, tidal, and climatic variants has been proposed collating V. cholerae and phage dynamics that can forewarn any impending cholera outbreak.

Seasonal baseline of nutrients and stable isotopes in a saline lake of Argentina: biogeochemical processes and river runoff effects.

The seasonal variability of inorganic and organic nutrients and stable isotopes and their relations with plankton and environmental conditions were monitored in Lake Chasicó. Principal component analysis evidenced the strong influence of the river runoff on several biogeochemical variables. Silicate concentrations were controlled by diatom biomass and river discharge. Higher values of nitrate and soluble reactive phosphorus (SRP) indicated agricultural uses in the river basin. Elevated pH values (∼ 9) inhibiting nitrification in the lake explained partially the dominance of ammonium: ∼ 83 % of dissolved inorganic nitrogen (DIN). The low DIN/SRP ratio inferred nitrogen limitation, although the hypotheses of iron and CO2 limitation are relevant in alkaline lakes. Particulate organic matter (POM) and dissolved organic matter (DOM) were mainly of autochthonous origin. The main allochthonous input was imported by the river as POM owning to the arid conditions. Dissolved organic carbon was likely top-down regulated by the bacterioplankton grazer Brachionus plicatilis. The δ(13)C signature was a good indicator of primary production and its values were influenced probably by CO2 limitation. The δ(15)N did not evidence nitrogen fixation and suggested the effects of anthropogenic activities. The preservation of a good water quality in the lake is crucial for resource management.

Influence of hydrologic and anthropogenic factors on the abundance variability of enteropathogens in the Ganges estuary, a cholera endemic region.

This study deals with the influence of water physico-chemical properties, tides, rainfall and fecal pollution on the abundance of enteropathogens in a main distributary of the Ganges, in the endemic cholera belt of West Bengal. Between January and June 2011, water and sediments were sampled from two sites of the Hooghly River by Kolkata and Diamond Harbour. Counts of cultivable Vibrio (CVC, from~10(2) to~10(5)CFU/L) and total bacteria (TBC, from~10(5) to~10(9)CFU/L) increased with water temperature (17°C to 37°C). A combination of variations in tidal height, salinity and turbidity had a distinct influence on CVC, TBC and coliform counts. At Diamond Harbour, a salinity increase from 0.6 to 7.9 was accompanied by a 1000-fold amplification of initial CVC~10(2)CFU/L, whereas higher prevalence of coliforms in Kolkata was related to greater disposal of untreated sewage into the river. Turbidity-dependent variation of CVC was noteworthy, particularly at Diamond Harbour, where CVC in intertidal surface sediments showed an analogous trend as in surface waters, suggesting bentho-pelagic coupling of Vibrio dynamics. Besides the influence of salinity variation with tidal cycles, sediment re-suspension from tidal flats can play a role on Vibrio abundance in aquatic ecosystems.

Model of wetland development of the Amapá coast during the late Holocene

The modern vegetation types, sedimentary sequences, pollen records and radiocarbon dating obtained from three sediment cores from Calçoene Coastal Plain were used to provide a palaeoecological history during the late Holocene of Amapá coastal wetland according to flood regime, sea-level and climatic changes. Based on these records, four phases of vegetation development are presented and they probably reflect the interaction between the flow energy to the sediment accumulation and the brackish/freshwater influence in the vegetation. This work suggests interchanges among time periods characterized by marine and fluvial influence. The longitudinal profile did not reveal the occurrence of mangrove in the sediment deposited around 2100 yr B.P. During the second phase, the mud progressively filled the depressions and tidal channels. The mangrove probably started its development on the channel edge, and the herbaceous field on the elevated sectors. The third phase is characterized by the interruption of mangrove development and the increase of "várzea" vegetation that may be due to the decrease in porewater salinity related to a decrease in marine water influence. The last phase is represented by the mangrove and "várzea" increase. The correlation between current patterns of geobotanical unit distribution and palaeovegetation indicates that mangrove and "várzea" forests are migrating over the herbaceous field on the topographically highest part of the studied coast, which can be related to a relative sea-level rise.

Os tipos de vegetação atual, sequências sedimentares, dados de pólen e datações por radiocarbono obtidas em três testemunhos de sedimento da planície costeira de Calçoene foram utilizados para estabelecer uma história paleoecológica durante o Holoceno superior das zonas úmidas costeiras do Amapá conforme as mudanças no regime de inundação, nível do mar e clima. Baseado nestes três registros, quatro fases de desenvolvimento da vegetação são apresentadas e provavelmente refletem a interação entre o fluxo de energia na acumulação do sedimento e a influência das águas salobras e doces na vegetação. Este trabalho sugere alternâncias entre períodos caracterizados por influências marinha e fluvial. O perfil longitudinal não revelou a ocorrência de manguezais nos sedimentos depositados por volta de 2100 anos A.P. Durante a segunda fase, a lama preencheu progressivamente as depressões e canais de maré. Provavelmente, os manguezais iniciaram seu desenvolvimento nas margens dos canais, e os campos herbáceos nos setores elevados. A terceira fase é caracterizada por uma interrupção no desenvolvimento dos manguezais e a expansão da vegetação de várzea devido a uma diminuição na influência das águas marinhas. A última fase é representada pela expansão de manguezais e várzeas. A correlação entre os padrões atuais de distribuição das unidades geobotânicas e a paleovegetação indica que os manguezais e as florestas de várzea estão migrando sobre os campos herbáceos nos setores topograficamente mais elevados do litoral em estudo, o que pode estar relacionado a um aumento do nível relativo do mar.

Influence of catastrophic climatic events and human waste on Vibrio distribution in the Karnaphuli estuary, Bangladesh.

Vibrios are bacteria of marine and estuarine origin that can cause human diseases, such as cholera, and also affect aquatic organisms. The impact of storm-driven changes in salinity and suspended particulate matter (SPM) on cultivable Vibrio counts (CVC) and distribution in Karnaphuli estuary, Bangladesh, was compared before and after a strong cyclone in mid May 2007 and after a monsoon landslide a month later. CVC were higher (approximately 10(3) colony forming units-cfu/ml) at estuary's mouth (salinity 20-15 parts per thousand, ppt) and steeply declined landwards. CVC and their proportion of total aerobic bacteria were highest after the cyclone and also increased after the landslide, likely due to higher SPM loads. The cyclone did not significantly change previous fecal coliform abundance, contrasting with the ten times increase after the landslide. Sewage input enhanced CVC near the point sources. CVC and salinity correlated highly significantly at salinities <10 ppt; however, at higher values dispersion increased, probably due to the effect of sediment resuspension on CVC. Cyclone or heavy rainfall-mediated turbidity changes jointly with salinity gradients can significantly influence abundance and distribution of estuarine vibrios. Extended salt intrusion and higher turbidities in tropical estuaries by stronger and more frequent storms and deforestation-derived erosion could favor Vibrio growth, with increasing risks for aquatic resources and human health in the coastal zone.