February 1st to 5th 2016
Olhão, Portugal
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Recovery of Seaweed at Barren Ground Using Steelmaking Steel Slag and Sediment on Bottom of Dam Reservoir in Japan

Oral Presentation
Natural Resources
Wednesday, February 3, 2016 -
16:30 to 16:45

Sakai, Y. 1 Nakamura, Y. 2 Onuma, Y. 3 Ono, S. 4 Yokoyama, K. 5 Nagamoto, H. 6 Toyoda, T. 7 Horiya, S. 8

1Kogakuin University
2Kogakuin University
3Kogakuin University
4Kogakuin University
5Kogakuin University
6Kogakuin University
7Previous President of JCOLD
8Shin Nihon Solar Solution

Barren ground develops when coastal areas are depleted of seaweed and has expanded to coastal areas in many countries. The increase of barren ground area leads to a significant reduction in fisheries production and biodiversity. Several reasons for barren grounds have been proposed, for instance, elevated seawater temperatures, grazing by herbivorous animals, and a shortage of dissolved iron (Fe). Phytoplankton growth and nitrogen fixation in the ocean are strongly influenced by Fe availability and Fe is an essential micronutrient for algal growth. Macroalgae need high concentrations of iron as well as nitrogen, phosphorus, and silicate. Therefore, the barren ground caused by the lack of dissolved Fe(?) in coastal water. The physicochemical speciation of dissolved Fe(?) is very important in the ocean. In addition, Humic substances (HS), and especially humic acids (HA) and fulvic acids (FA), are considered to exert a major control on metal mobility and bioavailability in the environment. Our group indicated that the iron-humate (Fe-HS) concentration in seawater of seaweed growth area was higher than that in barren ground area in Japan. And we demonstrated that Fe-HS was effective in recovering the vegetation on the areas of barren ground in the sea of Japan. The field experiments were performed at coast in Okushiri-cho, Hokkaido, Japan. Experimental test by using Fe-HS elution unit made with steelmaking slag and compost including much humic substances has been performed since 2006, and dam iron-humate (D-Fe-HS) elution unit made with sediment on bottom of dam reservoir has been performed since 2009. The Fe-HS, phosphoric acid, and silicic acid concentration in seawater at all experimental sites have been analyzed since 2006 and 2009, respectively. We investigated the relationship with the growth of seaweed. The growth areas of seaweed species growing at distance of 0, 5, 10, 20, and 30 m offshore were measured once a year. Consequently, the area of seaweed growth in all experimental sites using elution units (Fe-HS and D-Fe-HS) increased and was larger than that in control site. Moreover, from relationships between concentration of Fe-HS, P, and Si and the growth area of seaweed at all experimental sites, the concentration of Fe-HS was considered to be effective for the growth of seaweed.
keywords: 
Barren grounds, Dam reservoir, Iron-humate, Sediment, Steelmaking slag

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