J. M. Santana-Casiano

Binding of Cu(II) to the surface and exudates of the alga Dunaliella tertiolecta in seawater

The adsorption process and the organic matter interaction between the marine phytoplankton specie Dunaliella tertiolecta and copper ions were investigated by differential pulse anodic stripping voltammetry. Suspensions of living algae in natural Gran Canaria (Islas Canarias) seawater were titrated with Cu(II) as a function of pH, temperature, and salinity. The acid-base properties of the surface of the alga in a 0.7 M NaCI solution were characterized and interpreted as if the surface contained carboxylic acid groups (pK a,1 = 4.92 ± 0.16) and amino groups (pK a,2 = 6.28 ± 0.09, pK a,3 = 10.06 ± 0.10). The binding constant for the weaker ligands of the Gran Canaria seawater increased from 8.60 ± 0.03 to 9.30 ± 0.12 when 2.2 x 10 7 cell L -1 was added to 0.45-μm filtered seawater. The rate of uptake was found to occur in two steps. The adsorption equilibrium data correlate well with a two-site model which considers the algal surface as one which possesses two major functional groups : high-affinity binding and low-affinity binding. The high-affinity constant was of the same order of magnitude as the complexing capacity of the exudates excreted by the algae, showing that extracellular ligands play an important role in decreasing the concentration of the free metal concentration. Changes in the temperature, salinity, and pH of the seawater solution modified both the adsorption of metal and the amount of complexed copper.

Reduction of Fe(III) with sulfite in natural waters

The Fe(III) in marine aerosols and rainwaters can be reduced to Fe(II) by photochemical processes and by reactions with sulfite. In this paper, measurements of the rates of reduction of nanomolar levels of Fe(III) with sulfite (without O2) have been determined in NaCl and seawater solutions as a function of temperature (0° to 40°C), pH (2 to 6.8), ionic strength (I = 0.1 to 6 M), and composition (Na+, Mg2+, Ca2+, F−, Cl−, Br−, HCO3−, SO42−). The overall rate constant (k, M−1 min−1) for the reaction, Fe(III)+S(IV)→k products, is given by d[Fe(III)]/dt = −k[Fe(III)] [S(IV)]. The reaction was found to be first order with respect to Fe(III) and S(IV). The rate constants as a function of pH increased from a pH = 2 to 4 and decreased at higher pH. The effect of temperature and ionic strength on the rates could be represented by log k = log k0 + AI0.5/(1 + I0.5), where A = −1.1 in NaCl and −2.2 in seawater and log k0 = 25.39 − 6,323/T. The energy of activation was found by 121±6 kJ mol−1. The measured rates in seawater as a function of salinity were lower than the rates in NaCl at the same ionic strength. Measurements in NaCl solutions with added sea-salt ions (Mg2+, Ca2+, F−, Br−, and SO42−) at pH = 3.5 indicate that the formation of inert FeF2+ may be responsible for the lower rates. The effect of changes in the composition on the rates was interpreted by examining the speciation of Fe(III) and S(IV). This analysis indicates that the rate-determining steps from a pH of 2.5 to 4.0 are FeOH2+ + HSO3− ↔ HOFeSO3H + and HOFeSO3H+⟶k1FeOH++HSO3· and at pH of 4 to 6, the reactions Fe(OH)2+ + HSO3− ↔ (HO)2FeSO3H and (HO)2FeSO3H⟶k2Fe(OH)2+HSO3· become important. The changes in the concentration of FeOH2+ and HSO3− as a function of pH and composition can account for most of the changes in the rates. These kinetic studies indicate that the rates of reduction of Fe(III) with S(IV) in acidic water droplets at natural levels of S(IV) may be an important source of Fe(II).

Oxidation of Fe(II) in natural waters at high nutrient concentrations.

The Fe(II) oxidation kinetic was studied in seawater enriched with nutrients as a function of pH (7.2-8.2), temperature (5-35 °C), and salinity (10-36.72) and compared with the same parameters in seawater media. The effect of nitrate (0-1.77 × 10(-3) M), phosphate (0-5.80 × 10(-5) M) and silicate (0-2.84 × 10(-4) M) was studied at pH 8.0 and 25 °C. The experimental results demonstrated that Fe(II) oxidation was faster in high nutrient concentrations affecting the lifetime of Fe(II) in nutrient rich waters. Silicate displayed the most significant effects on the Fe(II) oxidation rate with values similar to those determined in seawater enriched with all the nutrients. A kinetic model was applied to the experimental results in order to account for changes in the speciation and to compute the fractional contribution of each Fe(II) species to the total rate constant as a function of pH. FeH(3)SiO(4)(+) played a key role in the Fe(II) speciation, dominating the process at pH over 8.4. At pH 8.0, FeH(3)SiO(4)(+) represented 18% of the total Fe(II) species. Model results show that when the concentration of silicate is 3 × 10(-5) M as in high nutrient low chlorophyll areas, FeH(3)SiO(4)(+) contributed at pH 8.0 by 4% increasing the rate to 11% at 1.4 × 10(-4) M. The effect of nutrients, especially silicate, must be considered in any further study in seawater media cultures and eutrophic oceanic areas.

Effect of Dunaliella tertiolecta organic exudates on the Fe(II) oxidation kinetics in seawater.

The role played by the natural organic ligands excreted by the green algae Dunaliella tertiolecta on the Fe(II) oxidation rate constants was studied at different stages of growth. The concentration of dissolved organic carbon increased from 2.1 to 7.1 mg L(-1) over time of culture. The oxidation kinetics of Fe(II) was studied at nanomolar levels and under different physicochemical conditions of pH (7.2-8.2), temperature (5-35 °C), salinity (10-37), and dissolved organic carbon produced by cells (2.1-7.1 mg L(-1)). The experimental rate always decreased in the presence of organic exudates with respect to that in the control seawater. The Fe(II) oxidation rate constant was also studied in the context of Marcus theory, where ΔG° was 39.31-51.48 kJ mol(-1). A kinetic modeling approach was applied for computing the equilibrium and rate constants for Fe(II) and exudates present in solution, the Fe(II) speciation, and the contribution of each Fe(II) species to the overall oxidation rate constant. The best fit model took into account two acidity equilibrium constants for the Fe(II) complexing ligands with pKa,1=9.45 and pKa,2=4.9. The Fe(II) complexing constants were KFe(II)-LH=3×10(10) and KFe(II)-L=10(7), and the corresponding computed oxidation rates were 68±2 and 36±8 M(-1) min(-1), respectively.

Partitioning of hydrochlorinated pesticides to chitin in seawater: Use of a radial-diffusion model to describe apparent desorption hysteresis

Abstract Desorption hysteresis has been reported frequently in the literature, with several theories advanced to explain the cause of this phenomenon. Batch experiments were performed to observe sorption-desorption behaviour of endrin and heptachlor epoxide onto chitin in seawater as a function of chitin concentration, temperature and salinity. For full range of solids concentrations, sorption was described by a single linear partition coefficient. Desorption hysteresis was found at low chitin concentrations for endrin, increasing both at low temperatures and high salinity values. Results of these experiments were interpreted with a radial-diffusion sorption rate model. Model predictions of the desorption experiments showed that slow desorption rates explained most of the apparent hysteresis. The “salting effect” in marine systems makes partition coefficients ∼ 0.2 log unit higher than comparable partition coefficents measured in freshwater.

Significant discharge of CO2 from hydrothermalism associated with the submarine volcano of El Hierro island

The residual hydrothermalism associated with submarine volcanoes, following an eruption event, plays an important role in the supply of CO2 to the ocean. The emitted CO2 increases the acidity of seawater. The submarine volcano of El Hierro, in its degasification stage, provided an excellent opportunity to study the effect of volcanic CO2 on the seawater carbonate system, the global carbon flux, and local ocean acidification. A detailed survey of the volcanic edifice was carried out using seven CTD-pH-ORP tow-yo studies, localizing the redox and acidic changes, which were used to obtain surface maps of anomalies. In order to investigate the temporal variability of the system, two CTD-pH-ORP yo-yo studies were conducted that included discrete sampling for carbonate system parameters. Meridional tow-yos were used to calculate the amount of volcanic CO2 added to the water column for each surveyed section. The inputs of CO2 along multiple sections combined with measurements of oceanic currents produced an estimated volcanic CO2 flux = 6.0 105 ± 1.1 105 kg d−1 which is ~0.1% of global volcanic CO2 flux. Finally, the CO2 emitted by El Hierro increases the acidity above the volcano by ~20%.

pH Decrease and Effects on the Chemistry of Seawater

Variation in seawater pH is just one response to the increased CO2concentration in the atmosphere due to anthropogenic activities. The decrease in pH has a significant effect on the carbonate chemistry of the ocean and causes a decrease in the calcium carbonate saturation state (Ω). Ten years of experimental pH measurements at the ESTOC station show a progressive reduction on pH in the ocean (-0.0017 ± 0.0002 year–1) and its effects on its carbonate chemistry. The calcium carbonate saturation state decreases by 0.018 ± 0.006 unit year–1for calcite and 0.012 ± 0.004 unit year–1for aragonite. The direct consequences of the pH decrease are a decrease in the buffer capacity (-1.99 ± 0.25 µmol kg–1year–1) and an increase in the Revelle factor (0.02 ± 0.002 year–1) of the surface seawater.

Lindane adsorption-desorption on chitin in seawater

Abstract The adsorption and desorption processes by solid materials are important in determining the movement and fate of pesticide compounds in aquatic systems. Chitin is one of the constituents of natural organic matter and may serve as a model organic phase for studying the pesticide adsorption-desorption in marine systems. The lindane adsorption-desorption to chitin has been studied as a function of chitin concentration (2.5 gl−1 to 12.5 gl−1), temperature (5 to 45°C), pH (1.5 to 8) and salinity (15‰ to 36‰). Both, Freundlich and linear isotherms for the adsorption and desorption processes were used to represent the experimental data. Two-site Langmuir isotherm can describe well the measured sorption isotherm. The adsorbent-concentration effect and the adsorption-desorption hysteresis show the existence of different classes of site with different accessibility. Thus, the adsorption-desorption reaction of lindane is the result of more than a single mechanism. An increase in temperature (ΔH = −4.0 ± 0.7...

The natural ocean acidification and fertilization event caused by the submarine eruption of El Hierro

The shallow submarine eruption which took place in October 10th 2011, 1.8 km south of the island of El Hierro (Canary Islands) allowed the study of the abrupt changes in the physical-chemical properties of seawater caused by volcanic discharges. In order to monitor the evolution of these changes, seven oceanographic surveys were carried out over six months (November 2011-April 2012) from the beginning of the eruptive stage to the post-eruptive phase. Here, we present dramatic changes in the water column chemistry including large decreases in pH, striking effects on the carbonate system, decreases in the oxygen concentrations and enrichment of Fe(II) and nutrients. Our findings highlight that the same volcano which was responsible for the creation of a highly corrosive environment, affecting marine biota, has also provided the nutrients required for the rapid recuperation of the marine ecosystem.

The submarine volcano eruption at the island of El Hierro: physical-chemical perturbation and biological response

On October 10 2011 an underwater eruption gave rise to a novel shallow submarine volcano south of the island of El Hierro, Canary Islands, Spain. During the eruption large quantities of mantle-derived gases, solutes and heat were released into the surrounding waters. In order to monitor the impact of the eruption on the marine ecosystem, periodic multidisciplinary cruises were carried out. Here, we present an initial report of the extreme physical-chemical perturbations caused by this event, comprising thermal changes, water acidification, deoxygenation and metal-enrichment, which resulted in significant alterations to the activity and composition of local plankton communities. Our findings highlight the potential role of this eruptive process as a natural ecosystem-scale experiment for the study of extreme effects of global change stressors on marine environments.