The taxonomical and ecological study on the diatom vegetation of paddy fields was done by authors in July 1983 in the vicinity of Sakurai City, Nara Prefecture. From these peculiar inlandwaters were enumerated the 53 forms of diatom, belonging to 17 genera. The 16 forms among them seem to belong to the brackish species. The dominant or subdominant species of the community are represented by Navicula pupula, Nitzschia palea, and Surirella angustata.
Water quality charts were made on 28 rivers in Hokuriku District using the DAIpo values developed by WATANABE and others (1984). In these charts, sampling stations were established, considering pollution sources or tributaries, so as to obtain the present condition of water pollution exactly in each water system. These charts can be said to be numerical assessment charts. From these numerical assessment charts, the River Pollution Indecies (RPID) proposed by SumITA and WATANABE(1983) were already obtained. Judging from the values obtained, in the riv ers in this district the values of DAIpo even in polluted stations are lower and the values of RPID in the whole water systems are higher than those values in the rivers in Kinki District. It is true that those rivers have polluted water areas, but they are only limited to local spots no wide range of water pollution can be found in their water systems. The rivers of Tedori-gawa Water System and some tributaries of the River Kakehashi-gawa showed high values of RPID, because they either flow, in their upper and middle stream between mountains, or are mountain torrents. Even the rivers in Kuzuryfi-gawa Water System, the River A sano-gawa and the River Sai-gawa which flow near towns and cities in flat land show relatively high values of RPID comparable to the values in representive clean rivers in Kinki District. In the rivers of Noto peninsula contrary to the common expectation, the values of RPID were comparatively low except those in several rivers. And the present conditions of water pollution were compared with those of 1974 in two rivers e. g. the River Daishoji-gawa and the River Iburibashi-gawa using values of RPID.
The diatom appeard in attached algal communities on river bed were classified into saprophilous, eurysaprobic and saproxenous species groups, by the statistic analysis to the tolerance for organic water pollution. Diatom assemblage index to organic water pollution ( DAIpo ) can be calculated by the equation developed by us, using the relative frequencies of taxa belonging to the former two groups. Relative abundances of the three groups in diatom assemblage appeared in attached algal community show a remarkable regularity correlating with the change of DAIpo values. Consequently, it should be considered that DAIpo value is an index expressing the regularity in the numerical value, and an appropriate biological index to organic water pollution from the ecological viewpoint. In this paper, we will describe the method of the statistic analysis to the tolerance of diatom taxon for organic water pollution, and show the all taxa belonging to saprophilous and eurysaprobic species groups with microphotographs or drawing figures.
The investigation was carried out on attached algae collected from the River Takiya in Fukushima prefecture. This sample contained a mixed population belonging to Navicula radiosa. We can identify two taxa, N. radiosa f. nipponica and N. radiosa var. tenella, judging from their morphological differences. The differences are recognized in the length and the breadth of the valve, striae in 10μm and their appearance including puncta, and margin of the valve especially in their degree of obliquity.
Two rheophilic diatoms, Achnanthes convergens H. Kos. and A. japonica H. KOB. described in 1965 from the Ara-Kawa ( Ara River ) without type citation by one of the present authors, H. KOBAYASI, were re-examined in detail with SEM and TEM using original materials. In addition to the results obtained by careful comparison with the type slides of the related species, morphological differences of these species are confirmed and types are designated, thereby validating these previously invalid names.
Two diatoms previously reported by H. KOBAYASI from the Ara-kawa ( Ara River ), Japan, were re-examined in detail using scanning electron microscopy. A new species, Navicula pseudacceptata, is proposed for the diatom that was identified as N. acceptata HUST. The generic position of the second, Stauroneis japonica H. KOB., is confirmed and a type is designated, thereby validating this previously invalid name.
The diatom community of brackish water in the Kumano-gawa River Estuary ( Wakayama Prefecture ) was investigated. Examination of cleaned m aterial revealed a total of 75 forms, of which 29 forms seems to be allochthonous in origin. The diatom community was made up of 18-27 forms at each station. Species diversity ( SHANNON-WIENERD I ( bits ) ) was relatively low, and ranged from 2.01 to 2.18. The communities were predominated by Nitzschia frustulum, and significant diatoms were as follows;Achnanthes minutissima, Gomphonema pseudoaugur, Melosira varians, Navicula gregaria, N. mutica, N. neoventricosa, Nitzschia filiformis, N. palea, N. aff.romana, Synedra fasciculata var.truncata.
The diatom communities in the River Kinokawa, a less polluted river in Japan, were surveyed in summer 1985. In almost all stations, Homeothrix janthina was dominant in algal communities on river bed. In these co mmunities, we can find Achnanthes japonica or Nitzschia frustulum var. perpusilla with high abundancy. The former occured usualy in upper stream, the latter in downstream. From the data of diatom flora in each sampling station, water quality was estimated by using Diatom Assemblage Index to organic water pollution (DAIpo ), and water quality chart was made using the indices computed. River Pollution Index ( RPID ), of which value is able to be shown the general degree of pollution of river system, was 57. The value is comparatively higher than those of other rivers in Japan.
The diatom communities in the River Yamato-gawa, a most polluted diver in Japan, were surveyed in October 1985. In these communities, we can find Navicula minima, Navicula mutica, Nitzschia palea, Nitzschia amphibia or Nitzschia frustulum var. perpusilla ( the former three are Saprophilous taxa and the latter two are Eurysaprobic taxa ) without the most upperstream station. From the data of diatom flora in each sampling station, water qualities were estimated by using Diatom Assemblage Index to organic water pollution(DAIpo), and water quality chart was made using the indices compu ted. River Pollution Index ( RPID ), whose value is able to be shown the general degree of pollution of river system, was 29. The value is remarcably lower than those of other rivers in Japan.
Epilithic diatom assemblages on the river bed were collected in four seasons in the River Ina-gawa. From 16 sa mpling sites 144 diatom taxa occured in 57 samples obtained in this study. The representative dominant taxa were Achnanthes japonica in upper stream of the river ( sts.1-3 ), Nitzschia frustulum and Achnanthes minutissima in middle stream ( sts.4-7) and Navicula subminuscula, Nitzschia amphibia, Nitzschia palea in lower stream ( sts.8-9 ). The seasonal changes of the dominant taxa were found in 12 sites. The author was able to discover some trends in the change. However, the trends do not always correlate with the difference of sampling season. DAIpo ( Diatom Assemblage Index to organic water polltion ) values of the sampling sites decreased toward the lower stream throughout all seasons, and the water quality charts show the similar forms except two sites in lower streams (sts.8-9 ). From the result of the cluster analysis based on percentage similality among all assemblages, all assemblages were clasified into three groups. It is considered that each group has a special characterist ic addapted to the degree of water polltion. And, each group was able to be clasified into several groups whose difference of characteristics were caused by the seasonal change of environmental factors.
The Muroo Reservoir has been used as the source of water supply to Nara city and its neighbouring towns of the Yamato plains and the source of irrigation water. Since the River Uda-gawa being main inflow of the reservoir was polluted remarkably, the water of this lake has been eutrophicated. In this investigation, we applicated DAIpo value develo ped to assess the water quality of rivers by WATANABE and others (1986) based on the species components of epilithic diatom communities as the biological indicator to monitor the water quality of this reservoir. The following became clear after the investigation. The speed of self purification is high at the upper basin and low at the lower in the Muroo reservoir. The River Temma-g awa have a little flux and high polluted water quality, pollutes the water of this, reservoir again by it's inflow at St.3. So, we can make a synthetic judgement to the change of water qualities through the water system, e. g. inflow, lake and it's outflow, applicating of DAIpo to the lentic environment. Synthesizing the re sults of this study and those of WATANABEa nd other's study on several reservoirs, it will be able to classify the system into next three types. 1. W ater quality of the reservoir is nearly same to that of inflow. In these reservoirs, water from inflow stagnate for a short period in the reservoir. 2. Water quality of the reservoir is more inferior than that of in f low. In these reservoirs, water quality of inflow is comparatively clear, and stagnate for a long period in the reservoir. 3. Water quality of the reservoir is m ore clear than that of inflow. In these reservoir, water quality of inflow is high polluted and stagnate fo r a long period in the reservoir.
Samples of attached algae on the stone were collected several times from spring to summer or to autumn in four rivers of Japan and correlation between saprobic index and water temperature is surveyed. The values of the index vary in parallel with water temperature when the sampling is carried out after an interval of one month or more. While the interval is as short as one week, the lag is recognized between water temperature and saprobic index because it takes several days for algae to adapt to the change of water temperature. Its maximum time is considered to be one month. Positive correlation is found between water temperature and saprobic index in each river. This may be ralated to increase of decomposed organic matters and consequential decrease of dissolved oxygen, induced by high bacterial activity in higher water temperature. In addition, intolerant species to the water pollution has behaved mostly as cold-water species. Consequently, saprobic index in colder water temperature represent the water quality as clearer one than that in high water temperature.
Some fundamental problems on paleoecology of diatoms were picked out, and their present progresses were evaluated in the present condition where applied studies had remarkably increased. The fundamental problem s picked out in this paper were as follows; methods of ecological analysis for present diatom assemblages, processes of formation on fossil assemblages, development on new analysis methods and preservation of specimens. Significances of fundamental studies of paleoecology on diatoms become larger, as scientific and social demands for diatom analysis have greatly increased recently.
Fossil diatoms found in three samples, upper, middle, and lower stratum from Ohkui diatomite, Komoro city, Nagano Prefecture were investigated. In three samples,73 taxa belonging to the 23 genera and 8 families including unidentified 6 taxa were found. Species of the Genus Fragilaria ( middle part,5%; upper part,64% ), Genus Melosira ( lower part,62%; middle part,56%; upper part,4%) and Genus Stephanodiscus ( lower part,13%; middle part,24%; upper part,18% ) appeared to be dominant. The accumulation environment of this diatomite was assumed to be a lake or a marsh with stagnant water, based on the species component and dominant species of each part.