Carla V. Spetter

Dissolved Nutrient Availability during Winter Diatom Bloom in a Turbid and Shallow Estuary (Bahía Blanca, Argentina)

Abstract The inner zone of Bahía Blanca Estuary is a shallow, well-mixed, highly turbid, and nutrient-rich temperate ecosystem. The phytoplankton annual cycle is characterized by a recurrent winter/early-spring diatom bloom. From May to August 2002 a research program aimed to describe the potential relations between the dynamics of phytoplankton and nutrients was carried out. Phytoplankton composition, abundance, chlorophyll a (Chl a), and dissolved inorganic nutrients (nitrate, nitrite, ammonium, phosphate, and silicate) were measured. The species involved were classified in blooming (including Thalassiosira spp. and Chaetoceros spp.) and nonblooming species (including other diatoms and dinoflagellates). The results show: (1) a prebloom period, which includes low biomass values and a strong decrease of NO3−; (2) an initial bloom period characterized by high diatom abundance and Chl a, a marked dominance of Thalassiosira curviseriata, and a strong decrease of NH4+; (3) an intermediate bloom period of high abundance, codominance of blooming species, and a strong decrease of PO43−; and (4) a final bloom period with a decrease in abundance of blooming species and a general nutrient recovery. Thalassiosira curviseriata seems to be a species associated with high nutrient stock and low light intensity. Its growth, mainly concurrent with DIN decrease, was related to new production in this area. The obtained data suggest that low phosphate concentrations, more than DIN and silicates, contributed to the diatom bloom collapse. According to our results, this high production during winter can be explained as a net growth of phytoplankton because of a successful low light- and temperature-acclimated species, possibly favored by low predation and high nutrient availability.

Role of Nutrients in Phytoplankton Development during a Winter Diatom Bloom in a Eutrophic South American Estuary (Bah´ õa Blanca, Argentina)

ABSTRACT Spetter, C.A.; Popovich, C.A.; Arias, A.; Asteasuain, R.O.; Freije, R.H., and Marcovecchio, J.E., 2015. Role of nutrients in the phytoplankton development during a winter diatom bloom in a eutrophic South American estuary (Bahía Blanca, Argentina). The Bahía Blanca Estuary is considered highly eutrophic. Long-term studies have shown that the winter–early spring bloom can be considered the development of a diatom assemblage with Thalassiosira curviseriata as the dominant species. Since 2003, several changes have been observed in the annual pattern of nutrients and phytoplankton. To assess the availability of nutrients and their relationship with phytoplankton development, nutrient variability was studied during a winter bloom in 2003 (April 22–September 4). Nitrite, nitrate, ammonium, phosphate, silicates, chlorophyll-a, phytoplankton abundance, particulate organic matter, and physicochemical parameters were measured in surface water at Cuatreros Port. In the Sauce Chico River mouth, we determined the concentration of nutrients to estimate the input of this river. The results of this study were compared with those of a previous usual diatom bloom from 2002. In 2003, the bloom was dominated by the Cyclotella sp. with high chlorophyll-a concentrations (26.5–40.4 μg L−1). Thalassiosira curviseriata was present only at three sampling dates, reaching up to 19% of the total abundance. Mean values of dissolved oxygen, nitrate, oxygen saturation percentage, and salinity were significantly higher in 2003 than in 2002, while N:P ratios were significantly lower. Si was never limiting. A shift in the limiting nutrient between the years (N in 2003 and P in 2002) could have lead to a change in species dominance during the blooms. Results suggest that the nutrients levels in the coastal ecosystems at Cuatreros Port play an important role in the control of phytoplankton dynamics during the productive period and partially explain its interannual variability. RESUMEN El estuario de Bahía Blanca es considerado altamente eutrófico. Los estudios anteriores han demostrado que la floración invernal del fitoplancton se caracteriza por el desarrollo de una asociación de diatomeas con Thalassiosira curviseriata como la especie dominante. Desde el 2003, se han observado cambios en el patrón anual de nutrientes y fitoplancton. La variabilidad de los nutrientes fue estudiada en Puerto Cuatreros durante una floración invernal (22 Abril–4 Septiembre 2003) con el fin de evaluar la disponibilidad de nutrientes y su relación con el desarrollo del fitoplancton. Se determinó la concentración de nitrito, nitrato, amonio, fosfato, silicatos, clorofila a, materia orgánica particulada, la abundancia del fitoplancton y los parámetros fisicoquímicos en agua superficial. Para estimar el aporte del Río Sauce Chico se determinaron las concentraciones de los nutrientes en su desembocadura. Los resultados de este estudio se compararon con los de una floración típica previamente estudiada durante el 2002. En 2003, la floración estuvo dominada por Cyclotella sp. presentando altas concentraciones de clorofila a (26.5–40.4 μg L−1). Thalassiosira curviseriata alcanzó el 19% de la abundancia total y se detectó solo en tres fechas del muestreo. Los valores promedios de oxígeno disuelto, nitrato, porcentaje de saturación de oxígeno, y salinidad fueron significativamente mayores en 2003 que en 2002, mientras que la relación N:P fue significativamente menor. El Si nunca fue limitante. Se sugiere que un cambio en el nutriente limitante (N en 2003 y P en 2002) puede haber conducido a un cambio en la dominancia de la especies durante la floración invernal. Los resultados evidencian que los niveles de nutrientes en sistemas costeros como Puerto Cuatreros cumplen un rol importante en el control de la dinámica del fitoplancton durante un período productivo y podrían explicar en parte su variabilidad interanual.

Tidal time-scale variation of inorganic nutrients and organic matter in Bahía Blanca mesotidal estuary, Argentina

Land-derived materials are regulated by coastal and shelf environmental conditions before being transported to the open sea. It is of great concern to understand the processes and to establish the extent in which they modify terrestrial compound fluxes, such as nutrients, that end up in the oceans. At present, one of the topics that arouses the highest interest within environmental coastal studies is the direction and magnitude of inorganic nutrients and the exchange fluxes of organic matter between the water column and the associated tidal plains during the daily tidal cycle. These processes, together with the local hydrographic conditions, define the key role of this type of environment: its function as a nutrient and organic matter reservoir and/or as a source. A research programme directed to understand this mechanism within mesotidal estuaries was developed in the Bahía Blanca estuary, on the coast of Buenos Aires (Argentina). On a tidal time-scale basis, levels of DIN (nitrate + nitrite + ammonium), DIP, DISi, and organic matter were measured in the estuarine water column and tidal plain porewater, for two years. Results showed no significant variations during the tidal cycle, even though the temporal variation of these compounds was clearly identified. In addition, the biological production of the estuary was considered and taken into account, so as to understand the organic matter cycle within the system. Particular conditions of the environment (sediment characteristics, porewater chemical environment, hydrodynamics, anthropogenic sources, etc.) were also considered to help fully understand the results.

The role of Sarcocornia perennis and tidal flooding on sediment biogeochemistry in a South American wetland

Abstract The roles of Sarcocornia perennis and tidal flooding on sediment biogeochemistry were evaluated within a wetland in the Bahía Blanca estuary. pH and Eh were measured in sediments while particulate organic carbon (POC) and dissolved inorganic nutrient concentrations were determined in porewater, at three sites with different conditions according to vegetation and flooding. Grain size was also analysed. pH varied in a narrow range (7–8.2) and was lower in the vegetated site. Eh values (50–250 mV) imply that sediment conditions were moderately reduced, in agreement with the relatively high percentage of sand; it was influenced by both factors. POC concentration was high (26.24±1.62 mg/l), especially at the vegetated site. The concentrations of ammonium and nitrate were similar (21.30±1.83 and 18.77±3.06 µmol/l, respectively) and not affected by flooding; only nitrate was affected by vegetation. Phosphate was rather constant (13.43±1.19 µmol/l) and affected mainly by flooding. Silicate was high (566.45±76.06 µmol/l) and not affected by either factor. These results suggest that the sediment biogeochemistry of this environment is significantly influenced by flooding and, especially, by S. perennis, as vegetation affected a higher number of parameters.

Ionic conductivity in montmorillonite-doped silver iodide

Abstract The ionic conductivity of AgI–montmorillonite composites was studied at a temperature ranging from 35 to 520 °C. Composites with montmorillonite as small as 0.89 w/o exhibited a maximum of about eight times the conductivity of the pure β-AgI at low temperatures. These results, which can be ascribed to the large surface area of the clay, may be qualitatively explained on the basis of a stabilisation of the low-temperature, higher-conducting metastable γ-phase of AgI.

Time-varying environmental control of phytoplankton in a changing estuarine system

Estuaries are among the most valuable aquatic systems by their services to human welfare. However, increasing human activities at the watershed along with the pressure of climate change are fostering the co-occurrence of multiple environmental drivers, and warn of potential negative impacts on estuaries resources. At present, no clear understanding of how coastal ecosystems will respond to the non-stationary effect of multiple drivers. Here we analysed the temporal interaction among multiple environmental drivers and their changing priority on shaping phytoplankton response in the Bahía Blanca Estuary, SW Atlantic Ocean. The interaction among environmental drivers and the number of significant direct and indirect effects on chlorophyll concentration increased over time in concurrence with enhanced anthropogenic stress, changing winter climate and wind patterns. Over the period 1978-1993, proximal variables such as nutrients, water temperature and salinity, showed a dominant effect on chlorophyll, whereas in more recent years (1993-2009) climate signals (SAM and ENSO) boosted indirect effects through its influence on precipitation, wind, water temperature and turbidity. Turbidity emerged as the dominant driver of chlorophyll while in recent years acted synergistically with the concentration of dissolved nitrogen. As a result, chlorophyll concentration showed a significant negative trend and a loss of seasonal peaks reflecting a pronounced reorganisation of the phytoplankton community. We stress the need to account for the changing priority of drivers to understand, and eventually forecast, biological responses under projected scenarios of global anthropogenic change.

Phenological Changes of Blooming Diatoms Promoted by Compound Bottom-Up and Top-Down Controls

Understanding phytoplankton species-specific responses to multiple biotic and abiotic stressors is fundamental to assess phenological and structural shifts at the community level. Here, we present the case of Thalassiosira curviseriata, a winter-blooming diatom in the Bahía Blanca Estuary, Argentina, which displayed a noticeable decrease in the past decade along with conspicuous changes in phenology. We compiled interannual field data to assess compound effects of environmental variations and grazing by the invasive copepod Eurytemora americana. The two species displayed opposite trends over the period examined. The diatom decreased toward the last years, mainly during the winters, and remained relatively constant over the other seasons, while the copepod increased toward the last years, with an occurrence restricted to winter and early spring. A quantitative assessment by structural equation modeling unveiled that the observed long-term trend of T. curviseriata resulted from the synergistic effects of environmental changes driven by water temperature, salinity, and grazing. These results suggest that the shift in the abundance distribution of T. curviseriata toward higher annual ranges of temperature and salinity—as displayed by habitat association curves—constitutes a functional response to avoid seasonal overlapping with its predator in late winters. The observed changes in the timing and abundance of the blooming species resulted in conspicuous shifts in primary production pulses. Our results provide insights on mechanistic processes shaping the phenology and structure of phytoplankton blooms.

Magnetic nanotechnological devices as efficient tools to improve the quality of water: analysis on a real case

Magnetic nanoparticles (MNPs), based on iron oxide (magnetite) and ferrogel of gelatin and MNPs, were employed as efficient tools for the removal of heavy metals and nutrients from water samples from Bahia Blanca estuarine (BBE). An exhaustive adsorption performance of Cu, NO3−, and NO2− was conducted in batch using model solutions aiming to adjust the adsorption conditions. Adsorption studies using water simulating the real samples were also performed. Both kinds of nanomaterials demonstrated an efficiency between 60 and 80%, and 85% for the removal of heavy metals and NO3− and NO2−, respectively. Similar adsorption assays were performed using BBE water samples, employing the experimental conditions explored with model and simulated water. The reached efficiency was 30 and 45% for heavy metal and nutrient removal, respectively, using nanoparticles; meanwhile, ferrogels displayed a removal capacity around 50–60%. The nanoparticles showed structural instability by the leaching of iron to the medium after the adsorption processes. Ferrogels remained almost inalterable in terms of their integrity during the adsorption time. These materials showed satisfactory perspectives regarding their reuse possibilities. They were used for almost five repeated cycles of adsorption without losing efficiency on the adsorption. The results of this study suggest that MNPs and FGs appear as versatile and promising materials that may be considered as valid alternatives to the actual tools for the remediation of real water samples.