Nutrients adsorption from seawater by new porous carrier made from zeolitized fly ash and slag

This study investigated the adsorption and precipitation of phosphate by blast furnace slag (BFS) separately.

In order to evaluate the adsorption capacity of BFS, BFS was treated before its use by acid. The authors aim to develop a new porous carrier to adsorb simultaneously ammonium and phosphate from seawater under eutrophic conditions. The current paper deals with a promising new approach to improve the utilization of some industrial solid wastes such as BFS and zeolite synthesized from fly ash [ZFA(Fe)] by their solidification to cylindrical porous carriers using a hydrothermal hot-pressing (HHP) method.

Attempts to produce porous carriers using an arranged HHP method with different porosities (24%, 40% and 52% (v/v)) were carried out. Physical properties of carriers such as porosity, compressive strength and height have been investigated. Laboratory studies showed strong evidence that the porous carrier was very selective towards phosphate and ammonium. The results demonstrated the role of porosity in enhancing phosphate and ammonium adsorption by the increase of the surface area per weight. The estimates of the parameters and the correlation coefficients according to the Freundlich equations revealed that adsorption was related to the porosity of carriers and phosphate and ammonium were adsorbed well on the carriers having large porosity.

The results suggested that developing carrier with high porosity was a promising way to enhance nutrients adsorption.     

Growth stimulation and inhibition of natural phytoplankton communities by model organic ligands in the western subarctic Pacific

The influence of organic ligands on natural phytoplankton growth was investigated in high-nitrate low-chlorophyll (HNLC) waters and during a phytoplankton bloom induced by a mesoscale iron enrichment experiment (SEEDS II) in the western subarctic Pacific. The growth responses of the phytoplankton in the treatments with iron complexed with model ligand were compared with those with inorganic iron or a control. Desferrioxamine B and protoporphyrin IX were used as models for hydroxamate-type siderophore and tetrapyrrole-type cell breakdown ligand, respectively. In the HNLC water, iron associated with protoporphyrin IX especially stimulated smaller phytoplankton (<10 μm) growth, 1.5-fold more than did inorganic iron. Surprisingly, only the addition of protoporphyrin IX stimulated small phytoplankton growth, suggesting that these cell breakdown ligands might be more bioavailable for them. The protoporphyrin IX’s stimulatory effect on small phytoplankton was not observed during bloom decline phase. The growth of phytoplankton was inhibited in the treatment with desferrioxamine B-complexed iron, suggesting its low bioavailability for the natural phytoplankton community. Its inhibitory effects were particularly pronounced in pico-eukaryotic phytoplankton. During the iron-induced bloom, the phytoplankton’s iron-stress response gradually increased with the desferrioxamine B concentration, suggesting that the competition for iron complexation between natural ligands and desferrioxamine B affected phytoplankton growth. However, the pico-eukaryotes did seem better able to utilize the desferrioxamine B-complexed iron during the bloom-developing phase. These results indicate that the iron bioavailability for phytoplankton differs between bloom-developing and bloom-decline phases.     

Physical behavior of the SEEDS iron-fertilized patch by sulphur hexafluoride tracer release

The first iron (Fe) – fertilization experiment in the western North Pacific was carried out using SF₆ to trace the Fe-fertilized water mass. A solution in 10,800 liters of seawater of 350 kg of Fe and 0.48 M of SF₆ tracer was released into the mixed layer over a 8 × 10 km area. On the first underway transects through the patch after the Fe release, we observed a significant increase of dissolved Fe (ave. 2.89 nM). The fertilized patch was traced for 14 days by on-board SF₆ analysis. A Lagrangian frame of reference was maintained by the use of a drogued GPS buoy released at the center of the patch. The patch moved westward at a rate of 6.8 km d⁻¹. Mixed layer depth increased from 8.5 to 15 m during the experiment. Horizontal diffusivity was determined by the change of SF₆ concentration in the patch. The horizontal diffusivity increased during the experiment. We evaluate here the fate of Fe in a Fe-fertilized patch using the dilution rate determined from sulphur hexafluoride (SF₆) concentration. Dissolved Fe concentrations subsequently decreased rapidly to 0.15 nM on Day 13. However, the dissolved Fe half-life of 43 h was relatively longer than in previous Fe-enrichment studies, and we observed a larger increase of the centric diatom standing stock and corresponding drawdown of macro-nutrients and carbon dioxide than in the previous studies. The most important reason for the larger response was the phytoplankton species in the western North Pacific. In addition, the smaller diffusivity and shallower mixed layer were effective to sustain the higher dissolved Fe concentration compared to previous experiments. This might be one reason for the larger response of diatoms in SEEDS.     

Mesozooplankton responses to iron-fertilization in the western subarctic Pacific (SEEDS2001)

A mesoscale iron-fertilization experiment was carried out in the western subarctic Pacific during summer 2001. The iron-patch was traced for 14 days after the fertilization, and the abundance and behavior of mesozooplankton were compared with those outside of the patch. The phytoplankton biomass in the patch rapidly increased to over 15 times the initial level by the later half of the observation period, and was composed of large-sized (>10 mm), centric diatoms. Dominant zooplankton species in the upper 200-m depth were large copepods: Neocalanus plumchrus, Neocalanus cristatus, Eucalanus bungii and Metridia pacifica. Mesozoplankton biomass as well as species composition did not change significantly in the patch over the observation period. Furthermore, no changes of vertical distribution or diel vertical migration were observed for any species or stages of mesozooplankton throughout the observation period. However, the abundance of the first copepodite stages of N. plumchrus and E. bungii increased several fold in the patch after the diatom bloom formation compared to the densities outside the patch. The increases of both species are considered to be due to lowered mortality during the egg and nauplius stages. Spawning of N. plumchrus takes place at depth using lipid storage, while spawning of E. bungii takes place in the surface layer supported by grazing. These facts suggest that the relative importance of nauplii in the diets of the large copepods was decreased in the patch by the diatom bloom. Gut-pigment contents of dominant copepods in the patch increased 4–18 times, and the maximum values were observed during the bloom peak. However, the grazing impact on phytoplankton was low throughout the experiment, especially during the bloom period (<6% of the primary production).     

Impacts of elevated CO2 on particulate and dissolved organic matter production: microcosm experiments using iron-deficient plankton communities in open subarctic waters

Response of phytoplankton to increasing CO₂ in seawater in terms of physiology and ecology is key to predicting changes in marine ecosystems. However, responses of natural plankton communities especially in the open ocean to higher CO₂ levels have not been fully examined. We conducted CO₂ manipulation experiments in the Bering Sea and the central subarctic Pacific, known as high nutrient and low chlorophyll regions, in summer 2007 to investigate the response of organic matter production in iron-deficient plankton communities to CO₂ increases. During the 14-day incubations of surface waters with natural plankton assemblages in microcosms under multiple pCO₂ levels, the dynamics of particulate organic carbon (POC) and nitrogen (PN), and dissolved organic carbon (DOC) and phosphorus (DOP) were examined with the plankton community compositions. In the Bering site, net production of POC, PN, and DOP relative to net chlorophyll-a production decreased with increasing pCO₂. While net produced POC:PN did not show any CO₂-related variations, net produced DOC:DOP increased with increasing pCO₂. On the other hand, no apparent trends for these parameters were observed in the Pacific site. The contrasting results observed were probably due to the different plankton community compositions between the two sites, with plankton biomass dominated by large-sized diatoms in the Bering Sea versus ultra-eukaryotes in the Pacific Ocean. We conclude that the quantity and quality of the production of particulate and dissolved organic matter may be altered under future elevated CO₂ environments in some iron-deficient ecosystems, while the impacts may be negligible in some systems.     

Dissolved iron and zinc in Sagami Bay and the Izu-Ogasawara Trench

Using a clean seawater sampling system for trace metals onboard the R. V. Shinsei-Maru, newly launched in 2013, we investigated the vertical distributions of dissolved iron and zinc in Sagami Bay and the Izu-Ogasawara Trench. We applied appropriate clean sampling and filtering processes for trace metals, so that uncontaminated seawater samples were successfully collected. The distribution of zinc in the trench area was similar to that of silicate and the same as that previously reported in the subtropical North Pacific. There were spatial variations in the iron (Fe) distribution in the trench areas. We used previously reported information about biogeochemical cycling in the trench area, and found that Fe has a residence time of 29 years in the water column. The short residence time of Fe (29 years) corresponds to the vertical variations of dissolved Fe in the water column.     

Iron nutritional status of the phytoplankton assemblage in the Okhotsk Sea during summer

To clarify the iron (Fe) nutritional status of the phytoplankton assemblage in the Okhotsk Sea, we conducted incubation experiments in summer 2006. Replicate surface seawater samples with the natural plankton community were incubated with three treatments: Fe enrichment; addition of the strong Fe chelator siderophore desferriferrioxime B (DFB) which strips Fe from the biologically accessible pool; and as a control, no addition. To prevent macronutrient limitation, we added surplus nutrients to all treatments. At all 4 stations in Sakhalin Bay near the mouth of the Amur River and around the east of Sakhalin Island, net specific growth rate showed no significant difference between the control and +Fe treatment, and was repressed in +DFB treatment both in large- and small-sized phytoplankton. These findings indicate that these waters contain sufficient bioavailable Fe and that the Amur River plume which is transported by the east Sakhalin current is a major source of the Fe. In the Bussol’ Strait, net specific growth rate in the control was significantly higher than +DFB treatment, suggesting a supply of bioavailable Fe through intense vertical mixing at this site. Iron enrichment treatment stimulated the net specific growth rate of large-sized phytoplankton, indicating that Fe still limits the growth for the large-sized phytoplankton assemblage, but not for small-sized phytoplankton, in this area. An index of Fe availability was defined to quantify the degree of ambient Fe availability in each station, and it revealed the spatial variability of ambient Fe availabilities among the sites.