Oceanic iron fertilization: one of strategies for sequestration atmospheric CO_2

Carbon cycle is connected with the most important environmental issue of Global Change.As one of the major carbon reservoirs, oceans play an important part in the carbon cycle. In recent years, iron seems to give us a good news that oceanic iron fertilization could stimulate biological productivity as CO2 sink of human-produced CO2. Oceanic iron fertilization experiments have verified that adding iron into high nutrient low chlorophyll (HNLC) seawaters can increase phytoplankton production and export organic carbon, and hence increase carbon sink of anthropogenic CO2, to reduce global warming. In sixty days, the export organic carbon could reach 10 000 times for adding iron by model prediction and in situ experiment, i.e. the atmospheric CO2 uptake and inorganic carbon drawdown in upper seawaters also have the same magnitude. Therefore, oceanic iron fertilization is one of the strategies for increasing carbon sink of anthropogenic CO2. The paper is focused on the iron fertilization, especially in situ ocean iron experiments in order that the future research is more efficient.

Appropriate Location and Deployment Method for Successful Iron Fertilization

“High nutrient, low chlorophyll (HNLC)” regions were created by locking iron into sedimentary iron sulfides with hydrogen sulfide available from volcanic eruptions in surrounding oceans. Appropriate locations and deployment methods for the iron fertilization were far from volcanoes, earthquakes and boundaries of tectonic plates to reduce the chance of iron-locking by volcanic sulfur compounds. The appropriate locations for the large-scale iron fertilization are proposed as Shag Rocks in South Georgia and the Bransfield Strait in Drake Passage in the Southern Ocean due to their high momentum flux causing efficient iron deployment. The iron (Fe) replete compounds, consisting of natural clay, volcanic ash, agar, N2-fixing mucilaginous cyanobacteria, carbon black, biodegradable plastic foamed polylactic acid, fine wood chip, and iron-reducing marine bacterium, are deployed in the ocean to stay within a surface depth of 100 m for phytoplankton digestion. The deployment method of Fe-replete composite with a duration of at least several years for the successful iron fertilization, is configured to be on the streamline of the Antarctic Circumpolar Current (ACC). This will result in high momentum flux for its efficient dispersion on the ocean surface where diatom, copepods, krill and humpback whale stay together (~100 m). Humpback whales are proposed as a biomarker for the successful iron fertilization in large-scale since humpback whales feed on krill, which in turn feed on cockpods and diatoms. The successful large-scale iron fertilization may be indicated by the return of the humpback whales if they could not be found for a long period before the iron fertilization. On-line monitoring for the successful iron fertilization focuses on the simultaneous changes of the following two groups;the increase concentration group (chlorophyll, O2, Dissolved Oxygen (DO), Di Methyl Sulfide (DMS)) and the decrease concentration group (nitrate, phosphate, silicate, CO2, Dissolved CO2 (DCO2)). The monitoring of chlorophyll-a, nitrate phosphate, and silicate concentrations after deploying the Fe-replete complex is carried out throughout the day and night for the accurate measurement of algal blooms.

Effect of Ocean Iron Fertilization on the Phytoplankton Biological Carbon Pump

It has been proposed that photosynthetic plankton can be used as a biological carbon pump tp absorb and sequester carbon dioxide in the ocean.In this paper,plankton population dynamics are simulated in a single stratified water column to predict carbon dioxide sequestering due to surface iron fertilization in deep ocean.Using a predator-prey model and realistic parameter values,iron fertilization was found to only cause temporary blooms up to 5 months in duration,and relatively small increases in adsorption of atmospheric CO_(2).

Steel Slag as an Iron Fertilizer for Corn Growth and Soil Improvement in a Pot Experiment

The feasibility of steel slag used as an iron fertilizer was studied in a pot experiment with corn. Slag alone or acidified slag was added to two Fe-deficient calcareous soils at different rates. Results showed that moderate rates (10 and 20 g kg-1) of slag or acidified slag substantially increased corn dry matter yield and Fe uptake. Application of steel slag increased the residual concentration of ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA) extractable Fe in the soils. The increase of extractable Fe was usually proportional to the application rate, and enhanced by the acidification of slag. Steel slag appeared to be a promising and inexpensive source of Fe to alleviate crop Fe chlorosis in Fe-deficient calcareous soils.

Application of iron and silicon fertilizers reduces arsenic accumulation by two Ipomoea aquatica varities

A 45 d pot experiment was conducted to examine the effects of silicon fertilizer or iron fertilizer on the growth of two typical Ipomoea aquatica cultivars（Daye and Liuye） and arsenic（As） accumuation of Daye and Liuye grown in As-contaminated soils at different As dosage levels. The results showed that the application of these two fertilizers generally enhanced the growth of the plants, which may be partly attributable to the reduction in As toxicity. The addition of these two fertilizers also significantly reduced the uptake of As by the plants though the iron fertilizer was more effective, as compared to the silicon fertilizer. The accumulation of As in shoot portion was weaker for Daye than for Liuye. The research findings obtained from this study have implications for developing cost-effective management strategies to minimize human health impacts from consumption of As-containing I. aquatica.

Effects of Iron and Zinc Fertilizers on Antioxidant Activity of PearJujube in Loess Hilly Region

With eight-year-old pear-jujube trees with uniform and good growth as the research object,different concentrations of iron and zinc fertilizers were sprayed to the leaves,and the changes in the contents of vitamin C,total flavonoids,enzyme,as well as the removal rates of hydroxyl radicals,1,1-diphenyl-2-trinitrophenylhydrazine( DPPH) and hydrogen peroxide by polyphenols in pear-jujube were studied,so as to explore the effects of iron and zinc fertilizers on antioxidant activity of pear-jujube in loess hilly region. The results showed that different treatments affected the content of vitamin C and significantly increased the content of total flavonoids in pear-jujube. In the treatment of 0. 6%Fe SO_4+ 0. 3% Zn SO_4( L3),the contents of vitamin C and total flavonoids were both highest,2. 86 mg/g and 3. 02 mg/g,21. 8% and105. 4% higher than CK( P < 0. 05). Different fertilization treatments effectively reduced the activities of ascorbate oxidase and polyphenol oxidase in pear-jujube. The activity of ascorbate oxidase was lowest in the treatment of 0. 6% Fe SO_4+ 0. 3% Zn SO_4( oxidized ascorbic acid0. 069 mg/( g·min) FW,75. 1% lower than CK); and the activity of polyphenol oxidase was lowest in the L3 treatment( oxidized ascorbic acid 0. 146 mg/( g·min) FW,42. 0% lower than CK). Polyphenols of pear-jujube could effectively remove hydroxyl radicals,DPPH· and hydrogen peroxide. This was more significant in L3 treatment,of which the antioxidant activity was the best.

Global sources, emissions, transport and deposition of dust and sand and their effects on the climate and environment： a review

Dust and Sand Storms （DSS） originating in deserts in arid and semi-arid regions are events raising global public concern. An important component of atmospheric aerosols, dust aerosols play a key role in climatic and environmental changes at the regional and the global scale. Deserts and semi-deserts are the main source of dust and sand, but regions that undergo vegetation deterioration and desertification due to climate change and human activities also contribute significantly to DSS. Dust aerosols are mainly composed of dust particles with an average diameter of 2 l.tm, which can be transported over thousands of kilometers. Dust aerosols influence the radiation budget of the earth- atmosphere system by scattering solar short-wave radiation and absorbing surface long-wave radiation. They can also change albedo and rainfall patterns because they can act as cloud condensation nuclei （CCN） or ice nuclei （IN）. Dust deposition is an important source of both marine nutrients and contaminants. Dust aerosols that enter marine ecosystems after long-distance transport influence phytoplankton biomass in the oceans, and thus global climate by altering the amount of CO2 absorbed by phytoplankton. In addition, the carbonates carried by dust aerosols are an important source of carbon for the alkaline carbon pool, which can buffer atmospheric acidity and increase the alkalinity of seawater. DSS have both positive and negative impacts on human society： they can exert adverse impacts on human＇s living environment, but can also contribute to the mitigation of global warming and the reduction of atmospheric acidity.