Eutrophic Lake In Japan Research Articles

Application of Orbitrap mass spectrometry to investigate seasonal variations of dissolved organic matter composition in a eutrophic lake in Japan

Orbitrap mass spectrometry can reveal the composition of DOM and the fraction responsible for CODMn in an eutrophic lake.

Characteristics of declining dissolved oxygen concentrations in Lakes Kasumigaura and Kitaura, two shallow polymictic eutrophic lakes in Japan

AbstractTo elucidate the patterns and characteristics of dissolved oxygen (DO) decline near bottom in shallow polymictic eutrophic lakes, we conducted a statistical analysis of monthly measurements for 12 years at 14 stations and hourly observation for 8 years at two stations in Lakes Kasumigaura and Kitaura. Results indicated that DO decline (hereafter, <2 mg/L) was negligible at stations with a depth of <5 m. Thus, we consider this depth to be critical depth for studying DO decline conditions in these lakes. The collected data revealed that DO decline events lasting more than 2 days occurred a few times a year. During these events, wind blew weakly (usually, <2 m/s), and diurnal stratification was formed by solar radiation. The averaged DO declining rate leading up to these events was 4.3 (±2.7) mg L−1 d−1, suggesting that within a few days, DO can fall into a declined state. The occurrence probability of DO declined events in the respective summer increased significantly with the proportion of weak wind hours (<2 m/s). Significant correlations between wind velocity and DO change rate (1 hr difference in DO) supported the importance of wind on DO changes in polymictic lakes. The influence of mean air temperature on DO decline events was insignificant.

Long-term observations of the vertical distributions of mineral elements and phosphorus dynamics in sediments in a shallow eutrophic lake in Japan

PurposeTo explore the mechanisms in the deposition and release of phosphorus (P) in the sediment of a shallow eutrophic lake using preserved samples, we investigated the vertical and temporal changes in P, manganese (Mn), sulfur (S), iron (Fe), aluminum (Al), calcium (Ca), and magnesium (Mg) in the sediment samples and the phosphate in the sediment pore water samples over a period of 6 years.Materials and methodsThe upper 15 cm of sediment from Lake Kasumigaura in Japan was collected monthly from 2003 to 2008 from the center of the lake. Sediment cores were divided into seven depth segments and were acid-digested for an elemental analysis via inductively coupled plasma atomic emission spectroscopy. Phosphate concentrations of the sediment pore water were determined using the molybdenum blue method. A multiple regression analysis was conducted by setting the P content as the response variable and Mn, S, Fe, Al, Ca, and Mg as explanatory variables.Results and discussionThe results of the multiple regression analysis demonstrated that P co-precipitates with Fe and Al oxides and accumulates on the sediment surface. The vertical distributions of Mn and S suggest that Mn reduction occurs within the 0–1-cm-depth layer of the sediment and that iron sulfide is actively formed in the 6–10-cm-depth layer of the sediment. These findings imply that the layer in which ferric oxides are reduced to ferrous ions is present near the 1–6-cm-depth layer of the sediment. This layer corresponds to the layer in which the maximum phosphate concentration of the sediment pore water often occurred (the 2–6-cm-depth layer). These results indicate that vertical distributions of mineral elements are useful for assessing P dynamics in sediments.ConclusionsThe lake sediments record the dynamics of P in the sediment. Our analytical approach using long-term observation data demonstrated that the accumulation and release of P associated with a change in the redox state can be assessed based on the vertical distributions of mineral elements in the lake sediments.

Seasonal changes in the biomass of floating leaved plant, Trapa spp., and its relation with a leaf beetle, Galerucella nipponensis, in Lake Inba, Japan

Trapa spp. dominate many shallow eutrophic lakes in Japan, which must affect the nutrient dynamics in lakes. Trapa spp. are utilized by several animals, in particular the leaf beetle, Galerucella. To quantify the trophic links and material transfers between Trapa spp. and G. nipponensis, their seasonal dynamics, the amount of leaves being consumed, and carbon and nitrogen stable isotope ratios (δ13C and δ15N) in Lake Inba were tracked. Trapa spp. began to increase in May, reached their highest biomass in September, and disappeared in October. G. nipponensis exhibited continuous reproduction from May until October. Grazing by G. nipponensis did not seem to affect the abundance of Trapa, as the average percentage of Trapa leaf consumed was 3%. Rather, G. nipponensis was influenced by Trapa, as δ13C and δ15N of Trapa spp. and G. nipponensis showed very similar seasonal fluctuations. The difference in δ15N was 3–4‰, which indicates that Trapa leaves were a main food source for G. nipponensis and a trophic linkage exists between them. The estimated nitrogen and phosphorus amounts in Trapa corresponded to 1% of nitrogen and 18% of phosphorus in the entire lake. If G. nipponensis migrate and die in a terrestrial environment, G. nipponensis can transport certain nutrients from lake to terrestrial environments. The nutrients from Trapa spp. are mostly regenerated, except for that biomass transported to terrestrial ecosystems by humans.

Phytoplankton species abundance in Lake Inba (Japan) from 1986 to 2016

AbstractLake Inba is one of the most eutrophic lakes in Japan. This data paper reports the abundance of phytoplankton species sampled biweekly from April 1986 to March 2016 at four stations in Lake Inba. Monitoring has been carried out by Chiba Prefectural Government, and phytoplankton count data have been collected since 1986. A total of 340 phytoplankton species were identified and enumerated by microscopy, as numbers of cells or colonies. The abundance of each species was expressed as cells per milliliter lake water. Total cell density ranged from 102 to 108 cells ml−1. The dominant cell class density was Cyanobacteria throughout the year. Cyanobacteria, such as Phormidium spp., Microcystis aeruginosa, and Anabaena spp. (Dolicospermum spp.), were the most dense in all months. The dominant cyanobacteria species reached concentrations of 107 cells ml−1. Diatoms, such as Aulacoseira granulata and A. ambigua, were also abundant, reaching 106 cells ml−1. These data can be used to appreciate how anthropogenic disturbances, such as eutrophication and global warming, affect density and community composition of phytoplankton.

Ontogenetic dietary shifts of largemouth bass do not increase trophic position in a shallow eutrophic lake in Japan

The trophic positions of top predators can provide useful information for estimating the length of food chains and for assessing the impacts of invasive species or the bioaccumulation of harmful compounds. In aquatic ecosystems, large carnivorous fishes may change their trophic positions ontogenetically. We used stable carbon and nitrogen isotope ratios to test the hypothesis that the trophic positions of largemouth bass, top predators in Lake Izunuma, Japan, would increase with total length (TL) as a result of ontogenetic shifts in diet. Results from a stable isotope analysis in R mixing model indicated that largemouth bass were a major food source for largemouth bass ≥200 mm TL. However, the trophic positions of largemouth bass did not increase with the dietary shift from zooplanktivory to piscivory, and actually decreased when larger fish shifted towards feeding on red swamp crayfish. In Lake Izunuma, the trophic positions of small omnivorous fishes and red swamp crayfish were not higher than those of zooplankton. This explains why the largest largemouth bass occupied lower trophic positions than smaller individuals. Our results suggest that the body size of carnivorous fishes should be taken into consideration when using their trophic positions as top predators to evaluate aquatic systems.

Spatial and temporal variations in nutrients in water and riverbed sediments at the mouths of rivers that enter Lake Hachiro, a shallow eutrophic lake in Japan

We evaluated the spatial and temporal variations in dissolved inorganic nitrogen (DIN=NO3−+NO2−+NH4+) and soluble reactive phosphorus (SRP) concentrations and the processes that control them in water and riverbed sediments at the mouths of five main rivers (MTN, BBM, IKW, TYK, and BFM) that enter Lake Hachiro, a shallow eutrophic lake in Japan. At the river mouths, we sampled water monthly and analyzed the nutrient concentrations and dissolved N2O and CH4 concentrations. We also sampled riverbed sediments to determine the SRP release potential, inorganic P fractions, and denitrification potential (dNp). Riverine SRP concentrations showed large spatial and temporal variations, with values increasing from summer to autumn in the three southernmost rivers (IKW, TYK, and BFM). High dissolved CH4 concentrations were observed in association with high SRP concentrations, indicating that SRP was released from the sediments under hypoxic conditions. In contrast, NO3− concentrations did not differ among the rivers and decreased during summer, likely owing to denitrification, thereby decreasing DIN/SRP ratios to a level suitable for the formation of summer algal or cyanobacterial blooms in the three southernmost rivers. Sediment incubation demonstrated high SRP release rates and high dNp values in the sediments of these rivers due to their higher iron (Fe)-bound P and organic matter contents. The riverine SRP concentration was significantly correlated with dissolved CH4 and sediment dNp in positive, and DIN/SRP in negative. In conclusion, differences in Fe-bound P and sediment organic matter content suggested to cause spatial and temporal variations in water quality, with high SRP release and denitrification under hypoxic summer conditions, resulting in lower DIN/SRP ratios that may trigger algal or cyanobacterial blooms in this shallow eutrophic lake.

Inducible defenses as factor determining trophic pathways in a food web

Understanding functional roles of prey defense in biological interactions remains a major task in food web ecology. We investigated the role of an inducible defense as a factor that influences the trophic pathway in an aquatic food web. Quantitative information on food web structure in Lake Suwa (a eutrophic lake in Japan) was provided by carbon and nitrogen stable isotope analyses using samples taken during summer and a structural equation model applied to annual monitoring data. As predicted, there was none or only a weak link detected between the prey with induced defenses (Bosmina fatalis) and its invertebrate predator (Leptodora kindtii). The effects of an inducible defense on the trophic links are based mainly on the mortality or population growth rate of organisms using predation, population (or community) level experiments, field data, and model estimates. However, there was no research linking these different data using stable isotope analyses. Our research provides new evidence supporting previous studies by suggesting the importance of the inducible defense in determining food web structure and function.

Silicon budget of eutrophic Lake Kasumigaura, Japan

Determining the dynamics of silicon in lakes, one of the essential nutrients for diatoms, is valuable for understanding aquatic environmental problems. The dissolved silicon (DSi) and biogenic silicon (BSi) budgets in Lake Kasumigaura, a shallow eutrophic lake in Japan, during the last three decades were assessed based on the analysis of dated sediment cores and a water quality database. Sediment cores (100 cm long) were taken at the center of Lake Kasumigaura in 2005, 2007, and 2009 and at two other sites in 2007. BSi contents of the dated sediments were determined by wet alkaline digestion. The net sedimentation rates of BSi were defined as the difference between the DSi load from inflowing rivers and the DSi and BSi loads from the outflow of the lake, calculated using DSi concentrations and diatom abundances in the lake from 1980 to 2007 and DSi concentrations of the inflowing rivers during 1994, 2007, and 2009. The gross sedimentation rates of BSi were estimated by multiplying BSi concentrations in lake water by the diatom sinking rate reported by previous studies. Budgetary calculations based on the database showed that 60–70 % of DSi inputs from the inflowing rivers during the 27 years could ultimately be accumulated as diatom frustules in bottom sediments in the lake. The sediment analysis revealed that the amount of BSi accumulated in the lake from 1980 to 2007 was 2.0–2.6 × 1011 g, similar to the amount based on the database of 1.3–2.4 × 1011 g. Although the gross sedimentation rates of BSi likely increased, the net sedimentation rates of BSi decreased significantly from 6–10 × 109 g year−1 in the 1980s to 2–6 × 109 g year−1 in the 2000s, suggesting a fast recycling of BSi in recent years caused by an increase in sediment resuspension and regeneration. The sediment core information and the water quality database can be used for calculating the long-term silicon budgets in Lake Kasumigaura. An increase in the DSi release rates was identified, which is consistent with recent sediment resuspension. Comparing the sediment core information with the database suggests the long-term dissolution of sediment BSi; however, analysis of the BSi content in sediment cores representing a much longer time period is needed to confirm this.

Phosphorus and nitrogen limitation of phytoplankton growth in eutrophic Lake Inba, Japan

Lake Inba is one of the most eutrophic lakes in Japan. In this study, field sampling and nutrient enrichment bioassays were conducted to determine the seasonal patterns of nutrient limitation for phytoplankton growth in this lake. Phytoplankton biomass increased significantly with the additions of phosphorus (P) on almost all sampling dates, indicating P limitation of phytoplankton growth from spring to autumn. However, nitrogen (N) limitation was also observed during summer (i.e., 19 August). On 10 August, a typhoon struck Lake Inba. After this event, dissolved inorganic nitrogen (DIN) and phosphorus concentrations increased, probably because of increased river discharge. At the same time, phytoplankton growth in the control treatment became relatively high, with the addition of neither P nor N stimulating the growth. However, 10 days after the typhoon, the phytoplankton growth rate in the control treatment decreased, with only the addition of N having a significant positive effect on phytoplankton growth. N limitation during summer is caused by the low concentrations of DIN, as well as changes in the N:P ratio due to allochthonous nutrient loads. These results indicate that a reduction of both P and N input is necessary to control phytoplankton blooms in Lake Inba.

Parameterization of chlorophyll a-specific absorption coefficients and effects of their variations in a highly eutrophic lake: a case study at Lake Kasumigaura, Japan

The chlorophyll a-specific absorption coefficient (\( a_{\text{ph}}^{*} \left( \lambda \right) \)) in a highly eutrophic lake can show characteristics distinct from that in the ocean due to the differences in the structure and composition of phytoplankton. In this study, investigated the variation of \( a_{\text{ph}}^{*} \left( \lambda \right) \) in Lake Kasumigaura, a highly eutrophic lake in Japan, in association with the package effect and the effect of accessory pigments, and carried out the parameterization of \( a_{\text{ph}}^{*} \left( \lambda \right) \). Although \( a_{\text{ph}}^{*} \left( \lambda \right) \) did not vary spatially, it did show significant temporal variation, with a particularly high value after spring-bloom. This high \( a_{\text{ph}}^{*} \left( \lambda \right) \) in spring was attributed to a lower package effect and a higher proportion of carotenoid than the other samples. Although the value of \( a_{\text{ph}}^{*} \left( \lambda \right) \) was correlated with the concentration of chlorophyll-a (Chl-a), the correlation coefficient was lower than those reported in the ocean. Some lake-water samples showed variations of the package effect and the effect of accessory pigments that were independent of the concentration of Chl-a, and these independent variations resulted in the weak correlation between \( a_{\text{ph}}^{*} \left( \lambda \right) \) and the concentration of Chl-a. Together, these results suggest that the factors controlling \( a_{\text{ph}}^{*} \left( \lambda \right) \) in highly eutrophic lakes are distinct from that in ocean samples.

Historical change of phytoplankton in a eutrophic lake in Japan as determined by analysis of photosynthetic pigments in a lakebed sediment core

No pre-1977 quantitative data exist that describe phytoplankton biomass in the water column of Lake Suwa, a Japanese eutrophic lake, although several studies have been conducted since. To assess recent environmental changes with time in the lake, phytoplankton composition was determined from analysis of photosynthetic pigments in the sediment core. Specifically, the total chlorophyll a (TCh-a) concentration in the water column before 1977 was estimated for comparison with that of the water column and sediment deposited since 1977. The depth profile of zeaxanthin, a potential indicator of cyanobacteria activity, substantially increased from 1960 to 1973 (from 9.53 to 76.7 nmol g−1). Additionally, the concentration of fucoxanthin, diadinoxanthin and diatoxanthin, originating from diatoms and dinoflagellates, increased slightly during this period (from 1.64 to 4.90, 1.86 to 3.54, and 4.00 to 3.26 nmol g−1). Cyanobacteria have been the major algal species in the lake since 1949; however, the ratio of fucoxanthin versus total algal carotenoids has gradually increased since 1981 indicating diatoms have increased relative to cyanobacteria since 1979, and that organic matter inflow and nutrient concentrations have resulted in changes in the phytoplankton composition. Since 1977, the chlorophyll a concentration in water in the lake had a very similar pattern as the TCh-a concentration in the sediment. The concentration in the water column also corresponds to those in the sediment even before 1977. These results indicate that it might be possible to predict the phytoplankton biomass of the water column based on the TCh-a in the water and sediment in this lake.

Distribution and Diversity of Anaerobic Ammonium Oxidation (Anammox) Bacteria in the Sediment of a Eutrophic Freshwater Lake, Lake Kitaura, Japan

Although the emission of N(2) via anaerobic ammonium oxidation (anammox) is a key process in the elimination of nitrogenous compounds from aquatic environments, little information is available regarding its significance and the relevant microorganisms (anammox bacteria) in eutrophic freshwater lakes. In the present study, the anammox bacteria in the sediment of a eutrophic lake in Japan, Lake Kitaura, were examined using a (15)N-tracer technique to measure their potential anammox activity. Potential anammox activity was localized to the northern region of the lake where a stable supply of both NH(4)(+) and NO(3)(-) existed in the sediment. These results suggest the contribution of anammox bacteria to the total emission of N(2) from sediment in this eutrophic lake to not be negligible. Moreover, selective PCR successfully amplified anammox bacteria-related (Brocadiales-related) 16S rRNA genes from sediment samples in which potential anammox activity was observed. The clone libraries consisted of diverse phylotypes except the genus "Scalindua"-lineages, and the lineages of genus "Brocadia" were dominantly recovered, followed by the genus "Kuenenia"-lineages. Most of them, however, were novel and phylogenetically distinguishable from known Brocadiales species. A unique population of anammox bacteria inhabits and potentially contributes to the emission of N(2) from Lake Kitaura.

Effect of phosphorus fluctuation caused by river water dilution in eutrophic lake on competition between blue-green alga Microcystis aeruginosa and diatom Cyclotella sp.

Tega-numa (Lake Tega) is one of the eutrophic lakes in Japan. For the improvement of water quality in Lake Tega, the North-chiba Water Conveyance Channel was constructed in 2000, which transfer water from Tone River into the lake. After 2000, the dominant species of diatoms, mainly Cyclotella sp., have been replacing blue-green algae, mainly Microcystis aeruginosa in Lake Tega. This transition of dominant species would be due to the dilution, but the detail mechanism has not been understood yet. This study examined the relationship between phosphorus fluctuation caused by river water dilution to Lake Tega and dominance of algal species, M. aeruginosa or Cyclotella sp. based on the single-species and the mixed-species culture experiments. The single-species culture experiment showed that the half-saturation constant and uptake rate of phosphorus were one order lower and seven times higher for M. aeruginosa than those for Cyclotella sp. These findings implied that M. aeruginosa would possess a potential for the growth and survival over Cyclotella sp. in the phosphorus limited condition. The superiority of M. aeruginosa was reflected in the outcome of the mixed-species culture experiment, i.e., dominance of M. aeruginosa, even phosphorus concentration was lowered to 0.01 mg-P/L. Therefore, it could be concluded that the decrease in phosphorus concentration due to the river water dilution to Lake Tega would be interpreted as a minor factor for the transition of dominant species from M. aeruginosa to Cyclotella sp.

Long-term changes in lake sediments and their infl uences on lake water quality in Japanese shallow lakes

In order to elucidate the nutrient dynamics in lakes with special reference to sediments, the changes in vertical distributions of sediment nutrients over 20 years were analyzed with the aid of sediment dating at the centers of two shallow, eutrophic lakes in Japan, i.e. Lakes Kasumigaura and Suwa. Peaks of 137 Cs and apparent density gave estimated sedimentation rates of around 1 and 2 kg m -2 y -1 in Lakes Kasumigaura and Suwa, respectively. Slight decreases of TP and TN contents (0.07 and 0.63 mg g -1 for TP and TN, respectively, in Lake Kasumigaura and 0.90 mg g -1 for TN in Lake Suwa) were observed by comparison between the cores obtained around 1980 and those of recent years except for a considerable decrease in TP in Lake Suwa (1.0 mg g -1 ). This decrease probably came from the higher percentage of easily releasable phosphorus in the past sediments of Lake Suwa. Using the TP and TN increases in lake waters during summer, the averaged nutrient release rates were estimated to be within the ranges of those observed by laboratory core experiments and by measuring the vertical profiles of interstitial concentrations except for a smaller estimation of TN in Lake Kasumigaura. On the other hand, the nutrient release rates were also determined using the long-term changes in sediment nutrient contents. The estimated rates were a little lower than the rates determined by the method using the increase in lake nutrient concentrations other than the higher ones for TP in Lake Suwa, which were originally based on the higher percentage of easily releasable phosphorus as mentioned above. Net sedimentation rates for 24 years in Lake Kasumigaura and those for 26 years in Lake Suwa calculated as the sum of new sedimentation and changes in old sediments during these periods were compared with the net input loads based on the per capita/exporting method. In the case ofTP, we observed a fairly good agreement because of its conservation, whereas the residuals were larger for TN due to denitrification in the overlying waters of sediments. The rates estimated from the imbalances in TN were in the ranges of the measured denitrification rates in laboratory tests with the sediments. Thus, the information on the long-term changes in sediment nutrients could provide the average rates of these fundamental processes in lake environments.

Application of spectral decomposition algorithm for mapping water quality in a turbid lake (Lake Kasumigaura, Japan) from Landsat TM data

The remote sensing of Case 2 water has been far less successful than that of Case 1 water, due mainly to the complex interactions among optically active substances (e.g., phytoplankton, suspended sediments, colored dissolved organic matter, and water) in the former. To address this problem, we developed a spectral decomposition algorithm (SDA), based on a spectral linear mixture modeling approach. Through a tank experiment, we found that the SDA-based models were superior to conventional empirical models (e.g. using single band, band ratio, or arithmetic calculation of band) for accurate estimates of water quality parameters. In this paper, we develop a method for applying the SDA to Landsat-5 TM data on Lake Kasumigaura, a eutrophic lake in Japan characterized by high concentrations of suspended sediment, for mapping chlorophyll-a (Chl-a) and non-phytoplankton suspended sediment (NPSS) distributions. The results show that the SDA-based estimation model can be obtained by a tank experiment. Moreover, by combining this estimation model with satellite-SRSs (standard reflectance spectra: i.e., spectral end-members) derived from bio-optical modeling, we can directly apply the model to a satellite image. The same SDA-based estimation model for Chl-a concentration was applied to two Landsat-5 TM images, one acquired in April 1994 and the other in February 2006. The average Chl-a estimation error between the two was 9.9%, a result that indicates the potential robustness of the SDA-based estimation model. The average estimation error of NPSS concentration from the 2006 Landsat-5 TM image was 15.9%. The key point for successfully applying the SDA-based estimation model to satellite data is the method used to obtain a suitable satellite-SRS for each end-member.

佐鳴湖底泥からの窒素・リン・ＣＯＤ負荷量の評価

To evaluate the loads of nitrogen, phosphorus and COD constituents from the bottom sediment in Lake Sanaru, one of the most eutrophic lakes in Japan, their release fluxes from the sediment were measured in a laboratory experiment using sediment cores. The cores were collected from two sites in August 2005. The release flux of nitrogen was underestimated due to the volatilization of ammonia in water during the experiment. The estimated release fluxes of phosphorus and COD constituents of the entire lake corresponded to approximately 6- and 0.6-fold their respective inflow fluxes. In addition, the nutrients are transferred from the sediment in dissolved forms that phytoplankton can use. Owing to the shallowness of the lake (mean depth:∼2 m), the nutrients are used by phytoplankton immediately after their release from the sediment. These suggest that nutrient release from sediment has a large contribution to primary production in Lake Sanaru. This nutrients release is probably due to the rapid decomposition of large amounts of dead phytoplankton deposited at the lake's bottom.

The discrimination of the response pattern of inter-phylum phytoplankton diversity to long-term eutrophication trends in Lake Kasumigaura, Japan

To study the response pattern of phytoplankton to eutrophication, the long-term water chemistry and biological data spanning three phytoplankton phyla and 19 genera were investigated in Lake Kasumigaura, a eutrophic lake in Japan. Fisher' s linear discrimination functions in combination with ecological indexes and a similarity index were used to analyze the relationship between the eutrophic levels (representing with dissolved inorganic nitrogen and total dissolved phosphorus) and the response of the inter-phylum phytoplankton diversity. The algal similarity index was found to characterize the change of eutrophication levels well. Almost 80 percent of eutrophic lake water samples can be correctly discriminated based on the logarithmic cells of phytoplankton genera. However, the ecological indices (number of genera, Margalef' s index, Menhinick' s index, McNaughton' s index, as well as the Shannon' s index and evenness index) failed to predict the change of eutrophic state.

Zoobenthos effects on the gaseous metabolism in lake sediments

The sediments which were used in the following experiments were taken from the center of Lake Suwa, an eutrophic lake in Japan, in August. Three kinds of experimental systems were constructed as fo...

Polymorphic hemoglobin from a midge larva ( Tokunagayusurika akamusi) can be divided into two different types

The hemoglobin from the 4th-instar larva of Tokunagayusurika akamusi, a common midge found in eutrophic lakes in Japan, was composed of as many as 11 separable components (IA, IB, II, III, IV, V, VIA, VIB, VII, VII, IX) on a DEAE-cellulose column. However, we found that these components can be divided into two groups on the basis of their spectroscopic properties, one being named as the normal type (N-type) and the other being referred to as low type (L-type). Since the major difference between them seemed to be the presence or absence of the distal (E7) histidine residue, which plays an important role in the stability properties of the bound dioxygen, the complete amino acid sequence was then determined for each typical component, namely, VII (N-type) and V(L-type): the former hemoglobin contained the usual distal histidine residue at position 64, whereas the latter one replaced it by isoleucine at position 66. The homology test for 40 N-terminal amino acid residues of all components also demonstrates that T. akamusi hemoglobin is composed of two different clusters showing a very early separation in the phylogenetic tree.