Diatom species were classified as environmental indicators based on the species groups of benthic diatoms presented by KOSUGI (1987) and on planktonic diatoms from Tokyo Bay and Uraga Channel. All data on diatom ecology were obtained from living cells discriminated by the staining method (KOSUGI, 1985).
The species groups identified by KOSUGI (1987) were classified on the basis of similarities in adaptation to both salinity and substratum factors, so it can be said that they were classified from the biological viewpoint. In order to obtain indicators applicable to reconstruct paleoenvironments, it is necessary to clarify the relationship between the species groups and real environments. From this point of view, the environments specified by the salinity and substratum of each species group was examined.
The diatom environmental indicators were classified as follows;
A: Indicators of an outerbay
B: Indicators of an innerbay
C1: Indicators of an aquatic plant vegetation in saline water
C2: Indicators of an aquatic plant vegetation in brackish water
D1: Indicators of a sand flat in saline water
D2: Indicators of a sand flat in brackish water
E1: Indicators of a mud flat in saline water
E2: Indicators of a mud flat in brackish water
F: Benthic diatoms in fresh water
G: Planktonic diatoms in fresh water
H: Indicators of a river mouth
As an example of application to paleoenvironmental reconstruction, the Holocene fossil datom assemblages from the lower reach of the Murata River, Chiba prefecture, were analyzed using diatom environmental indicators. As a result, most fossil diatoms could be classified on the basis of each environmental indicator. And their vertical changes in fossil assemblages could be related to successive changes of paleoenvironments in the Murata River region.
It is an important part of this application that the paleoecological analysis using those indicators has the ability to reconstruct environments and their changes clearly. The main reason is that the indicators have been classified based on the data from living diatoms only, and that the relationships between them and both salinity and substratum as environmental factors have been clarified by the gradient analyses.
