Seasonal changes in species composition and photosynthesis of the periphyton community were investigated in a copper (0.07-0.22 mg·l^-1) -and zinc (0.13-0.55 mg·l^-1) -polluted urban river (River Miyata, Japan). The pH, water temperature, concentrations of dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP), total copper and total zinc were measured. SRP was mostly below 0.01 mg·l^-1, whereas ammonium- and nitrate-nitrogen were high ranging from 0.1-2.0 mg·l^-1 and 0.9-4.0 mg·l^-1, respectively. The number of species in this river was restricted (only 7-10). The dominant species were Chamaesiphon subglobosus, Phormidium foveolarum, P. uncinatum, Achnanthes minutissima, Nitzschia palea, Stigeoclonium aestivale and Oocystis lacustris. The diatoms tended to be abundant with a lower temperature and Stigeoclonium tended to be dominant in a better illuminated condition in this river. The maximum photosynthetic rates were related closely to water temperature, and the values (0.0025-0.217 gC·gC^-1·hr^-1) were lower than those for unpolluted rivers in the literature. However, chlorophyll a in the periphyton was high, ranging from 31 to 1, 162 mg·m^-2. Therefore the primary production in this river was not low as compared with the reported unpolluted rivers. The unbalanced high algal biomass in contrast to low SRP concentrations may be due to low grazing pressure by the poorly developed aquatic insect community (HATAKEYAMA and SUGAYA unpublished).

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The N₂O production during nitrification was studied in Lake Kizaki by vertical observations and two incubation experiments. The apparent N₂O production (ΔN₂O), the difference between observed and atmospheric-equilibrium concentration, was highly correlated with apparent oxygen consumption (-ΔO₂), in situ NO₃^- concentration and the amount of NH₄⁺ decrease with time, indicating that N₂O was produced by the nitrification process. In a long-term in situ incubation, simultaneous accumulations of NO₃^- and N₂O were observed, the amounts of which were comparable to the in situ changes, suggesting their in situ productions. Both NO₃^- and N₂O productions were greatly enhanced by an NH₄⁺ enrichment after the emergence of nitrification activity.
From both vertical observations and long-term in situ incubations, the yield of N₂O relative to NO₃^- production was estimated to be about 0.1% during the active nitrification period. But thereafter, the obtained yields were appreciably higher. Another incubation experiment also showed that N₂O production was delayed several days compared to NO₃^- production, indicating that N₂O production was accelerated in the late phase of nitrification. The physiological state of nitrifiers was suggested to be of some importance for such phenomena. Nitrapyrin, a specific inhibitor of nitrification, was found not to be very effective for N₂O formations in contrast with NO₃^- productions completely inhibited, suggesting a possibility of some N₂O sources other than autotrophic nitrification.

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Production was estimated for the co-existing net-spinning caddisflies, Stenopsyche marmorata and S. sauteri, using the instantaneous growth method, in the Mamigasaki River in Yamagata, Tohoku District. S.marmorata was bivoltine, whereas S.sauteri was univoltine. Annual production for S.marmorata was calculated to be 15.47 g dry weight·m^-2 · yr^-1, which was the highest value of many reported for Trichoptera, excluding unusual conditions. Production for the overwintering generation of S.marmorata was roughly twice as large as that of the summer generation. Higher production was attained by the overwintering cohort because of heavier fifth instar body weights.
Annual production for S.sauteri was 1.08 g dry weight · m^-2·yr^-1, which was within the range of values reported for many species of Trichoptera.
Annual turnover ratio (P/B) was 8.99 for S.marmorata and 3.93 for S.sauteri. Cohort turnover ratios were 5.25 for the overwintering generation and 4.98 for the summer generation. Cohort turnover ratios for the two species were within the range observed for aquatic invertebrates.

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In the coastal region of Kamikoshiki Island in Kagoshima Prefecture of Japan, there are Lakes Namako-ike, Kai-ike, Kazaki-ike and Suguchi-ike. All four lakes are separated from the sea by a long gravel bar (Tomboro) called as “Nagamenohama.” Although these lakes are thought to be formed in the same geological period (5-10×10³yr BP), the ensuing geological succession has significantly differentiated their geochemical and biological situations. This study was undertaken to find out how these differences in ecological conditions reflect on the chemical composition of the underlying sediments. The sediment samples were collected with a grab sampler from the former three lakes. In Lake Kai-ike, particulates were collected from near the phototrophic “bacterial plate” peculiar to the lake. The stable carbon isotope ratio, δ¹³C, of the sedimentary organic matter was light (-25‰) for slightly saline Lake Kazaki-ike, while the values, around -22‰ for brackish Lake Kai-ike and Lake Namako-ike, were thought to indicate a higher contribution from authigenic marine biota. However, only slight differences were observed with regard to the major identifiable organic constituents examined, i. e., amino acids, carbohydrates and lipids (hydrocarbons, alcohols and fatty acids). The lipid compositions, influenced little by anthropogenic pollutants, were considered to represent a contribution primarily from the anaerobic bacterial community.

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Vertical profiles of dissolved manganese were examined in the interstitial water of a monomictic Lake Fukami-ike from October 1987 to June 1988. The speciation of dissolved manganese in the interstitial water was conducted by ultrafiltration (Mn (UF)) and by adsorption on XAD-2 resin (Mn (XAD-2)). On passing the ultrafiltrates through an XAD-2 column, the percentage of Mn (XAD-2) at neutral pH were 0.3 to 8.0 % (molecular weight fraction less than 1, 000 ; M. W. <1, 000), 14.8 to 50.9 % (1, 000< M. W. <50, 000), 3.7 to 20.0% (50, 000< M. W. <200, 000) and 7.0 to 19.6 % (M. W. >200, 000) of the total manganese in interstitial waters. The amounts of Mn (XAD-2) at neutral pH in interstitial waters were 82 to 95 % of Mn (UF) fractionated into three high molecular weights. About 41 to 77 % of the total dissolved manganese in the interstitial water was present in organic forms associated mainly with a molecular weight of 1, 000 to 50, 000. Regression plots of dissolved organic manganese vs. dissolved organic carbon in the two high molecular weight fractions, 50, 000 to 200, 000 and 1, 000 to 50, 000, showed good linear correlations (γ = 0.54 and 0.85) with slopes of 0.045 and 0.070, respectively. This suggests that manganese is mainly associated with dissolved organic matter having a molecular weight of 1, 000 to 50, 000 and 50, 000 to 200, 000, and the average molar ratios of dissolved organic carbon to dissolved organic manganese are 60 : 1 and 75 : 1, respectively.

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Organically bound iron in the interstitial water of a lagoon sediment was fractionated successively by ultrafiltration, cation exchange column, and gel-filtration. Each fraction was bioassayed for iron availability to a fresh water red tide Chrysophyceae, Uroglena americana. Iron bound to anionically charged ninhydrin reactive organic compounds (molecular weight around 300-600 dalton) promoted the growth of U. americana. Iron-complexing capacity of interstitial water was estimated at ca. 14 μM as an equivalent concentration of iron available to U. americana.

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Seasonal fluctuation of phytoplankton with special reference to chrysophytes was studied in four ponds and lakes, Doro - ike, Hoshino - ike, Sengari Reservoir and Yasuba- ike, which are situated in the southern part of Hyogo Prefecture, Japan, and are in different stages of eutrophication. The chrysophytes increased in cell number from autumn to spring. The maximum density of the chrysophytes was recorded in March in all the ponds and lakes ; 5, 900 cells·ml^-1 in Doro-ike Pond, 13, 000 cells·ml^-1in Hoshino - ike Pond, 190 cells·ml^-1 in Sengari Reservoir and 6, 900 cells·ml^-1 in Yasuba- ike Pond. The chrysophytes were an abundant algal group in the low temperature period and Mallomonas akrokomos, Synura mammillosa, Chrysococcus rufescens and Dinobryon sociale were dominant in the freezing time.
Many chrysophyte species occurred not only in oligotrophic waters but also in eutrophic ones, and the number of species increased with eutrophication. The chrysophytes appeared all the year round in oligotrophic waters, whereas, in eutrophic waters, they appeared in the low temperature period with higher density than in oligotrophic waters. But in heavily polluted waters where water blooms of the cyanophytes occurred, the number of species and the density were very low. Based on these, the chrysophytes are regarded as representatives of eutrophic waters as well as of oligotrophic ones.

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The seasonal maximum biomass of Nymphoides peltata growing on sandy sediment at the littoral zone of Edosaki-iri Bay in Lake Kasumigaura was only 47.6 g dry weight·m^-2 in late September. Leaf life span was 28 days and thus biomass turnover rate was estimated as 3.4 for 200 days, comparable with those reported for floating-leaved plants and much higher than other herbaceous plants. The yearly net production per unit ground area was estimated at 182 g dry weight·m^-2. This value is smaller than that reported for phytoplankton at the same site and for floating-leaved plants growing at other regions of this lake.

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