Vol.3 No.4 2011

37/72

Research paper : Investigation of the distribution of elements of the whole of Japan and their applications (N. Imai)−278−Synthesiology - English edition Vol.3 No.4 (2011) necessitating the cooperation of several geochemistry groups to produce the map collaboratively. Therefore, we harbored great expectations for its progress as a first project for the geochemistry groups. A unique scientific interest was also involved: to know the distribution and the movement of elements in the earth’s crust. However, the promotion of geochemical study by introduction of large-scale equipment such as neutron activation analysis and ICP emission analysis was another major purpose. I think everyone certainly appreciated the project after the nationwide geochemical map was completed.4 Similarity of the methodology between field research and laboratory experimentQuestion (Akira Ono)In viewpoint of the amount of data, the sampling points at a finer interval and the coverage of a wider area are in tradeoff. Which you should give priority to and how you harmonize them may be hard problems. In this work, it may have been an important point for you to assume first that even coarse sampling was scientifically meaningful if the coverage was wide enough, (which was excellently revealed later).Suppose a laboratory experiment where we measure a physical property of a sample changing the sample temperature in a range. It is recommended that measurements are made firstly over the whole range of temperature at a coarse temperature interval to see quickly the overall trend. Then measurements follow at a finer temperature interval in selected ranges of interest. I think that the technique of understanding the whole image first and proceeding toward detailed parts is a common approach, which is very effective even if the field of research is different. Unlike the laboratory experiment, because the field research cannot be repeated easily, such a technique is thought to be more important.Answer (Noboru Imai)I think that the technique of understanding the whole image first and proceeding toward detailed parts is important, as you have pointed out. As for the question about why we did not notice that point earlier, because similar research projects including those of foreign countries had adopted the mesh size of 1 km, we did not consider trying a more coarse mesh to cover the whole country. Considering that there are various types of mountains, valleys and plains, a mesh size of 10 km seemed to be too coarse to obtain useful data from geographical and geological viewpoints. I did not realize at that time that excellent geochemical maps could be obtained with such a coarse mesh size.We first thought that regional geochemical maps made by the local governments and universities in individual prefectures should be connected to cover the whole country. However, this did not progress very easily, and small-scale geochemical maps are now being made at a university to which the proposer of the first project moved, and at other universities which have an interest in compiling and contributing local geochemical maps.5 Representativeness of samplesQuestion (Akira Ono)In this research, the stream sediment at the root of a branch of a river is assumed to represent the area of watersheds of the branch. I think this is a very good idea. However, how did you check the assumption that the stream sediment fully represents the watersheds? Please tell us of any other thoughts concerning representativeness of analytical results, for example other conditions that might be needed.As you mentioned about the element distribution in soil in your manuscript, what is the difference of the definition between surface of the crust and soil? I imagine as an amateur that soil is mixed in the stream sediment at the root of a branch of a river. Is the mixing of soil in the sediment negligible?Although the element distribution in soil is not the main subject in this paper, can you tell us where you should sample the soil so that the sampled soil represents a certain area?Answer (Noboru Imai)It was confirmed in several places that the stream sediment at locations in the watersheds of the rivers represent its whole watershed. The examples of zinc and phosphorus concentrations in Sendai City are shown as follows. In Fig. a, the 39th sample, which is taken at the root of the Hirose River, is thought to be a representative point in the entire watershed of the Hirose River. Figure b shows that the averages of the concentrations of both zinc and phosphorus for all samples in the watershed agree well with the concentration of the 39th sample. Therefore, in this case, the entire watershed of the Hirose River is well represented by sample No. 39.To improve the representativeness, the sampling site is carefully selected to facilitate collection of samples that are as fine as possible. In addition, samples which are thought to be influenced by human activities such as industrial wastewater or enrichment of heavy minerals such as of iron sand should be avoided carefully.Regarding the difference of the definition between the earth’s crust surface and the soil, the thickness of the earth’s crust is several kilometers on land and several tens of kilometers in the sea. The definition of the word “surface crust” is ambiguous. Nevertheless, I think the thickness is within 1 km, from several tens to hundreds of meters. The soils are composed from the surface organic layer to A, B, C horizons in sequence proceeding to greater depths. The thickness is from a few centimeters to several tens of centimeters (several meters). The ratios of the soil in stream sediments differ greatly from place to place, but the ratio is not so large because the soil thickness is sufficiently small compared with the surface crust, although the surface materials are mainly incorporated into stream sediment. After all, because the soil is fundamentally the product of the surrounding rocks and sediments by erosion, the chemical composition of the soil does not differ much from that of rocks and sediments, although there are various additional anthropogenic influences from external contamination.Regarding the sampling method, the sampling point density is determined from the number of samples and the area. In this SendaiRepresentativeness of stream sediment39th sample at the root of the river is a mixed sample ofrocks and sediments distributed around the riverwatershed of 39th sample39th sample is a representative samplein the entire watershed8 ㎞642039Zn (ppm)01000Fig. a Zinc and phosphorus concentrations in Sendai City

※このページを正しく表示するにはFlashPlayer9以上が必要です