Lake Nakanuma Research Articles

Diel vertical migration patterns in two populations of Chaoborus flavicans larvae (Diptera: Chaoboridae) in response to fish kairomones

Diel vertical migration (DVM) of larvae of the phantom midge Chaoborus flavicans (Diptera: Chaoboridae) inhabiting a fishless pond and a fish-abundant lake (Lake Nakanuma) was studied in the field and in the laboratory. In the fishless pond, dissolved oxygen concentration and water temperature were homogeneously distributed in the vertical profiles and Chaoborus larvae did not show DVM. In contrast, there was thermal stratification and an anoxic layer in Lake Nakanuma, and 2nd, 3rd and 4th instar Chaoborus larvae exhibited DVM. Fourth instar Chaoborus larvae collected from the two populations were introduced into thermally stratified acrylic tubes containing 'fish water' (water conditioned by fish and containing only the fish 'smell') or control water free of fish smell after a two-day acclimatization, and the larval positions in the tubes were analysed during the day and at night. The two populations of Chaoborus larvae showed different DVM patterns in the control water: the larvae from Lake Nakanuma exhibited DVM, whereas those from the fishless pond did not. Chaoborus larvae from Lake Nakanuma responded to the fish kairomones, exhibiting marked DVM in the fish water, whereas little response to the fish smell was recognized in the larvae from the fishless pond. The presence of a difference in response between the two populations implies that they had genetically different patterns of expression of DVM and thus different behavioural responses to the fish smell. The fish smell tended to cause the Chaoborus larvae in the tubes to increase their depth, during both the day and night. The effects of the fish smell became ambiguous with time, suggesting microbial degradation of the fish kairomones.

The Seasonal Variation of Water Quality, Water Temperature and Water balance in Lake Ishi-numa and Lake Naka-numa on Mt. Yakeishi-dake, Iwate Prefecture

The Seasonal Variation of Water Quality, Water Temperature and Water balance in Lake Ishi-numa and Lake Naka-numa on Mt. Yakeishi-dake, Iwate Prefecture

Pesticide Residue Flux from Rainwater into Lake Nakanuma in the Rainy Season.

Pesticide residues in rainwater were investigated for the estimation of pesticide flux into a lake in Ibaraki Prefecture during the 1990 rainy season. The maximum concentration of oxiadiazon in the rainwater was 4.2μg l-1. The maximum concentrations of fenobucarb, fenitrothion and edifenphos in the rainwater were 0.58, 0.53 and 0.36μg l-1, respectively. The annual ratio of fenitrothion redeposition by rainfall was estimated at 1.5% of the total shipping amount in Ibaraki Prefecture. There was no significant difference between redepositions of pesticides by rainfall and shipping amounts in the prefecture (α= 0.05). Pesticide residues in lake water were investigated in Lake Nakanuma, Ibaraki Prefecture, from March to December 1990. The concentrations of molinate, simetryn, iprobenfos, and thiobencarb in irrigation canal water were in the high range (>1.2μg l-1). The concentrations of diazinon, malathion, and fenthion in the water were at a lower level (<0.2μg l-1). The maximum concentration of simetryn in the lake was 0.91μg l-1. Except for chlornitrofen, the maximum concentration of pesticide in the lake (<1.0μg l-1) was about one-tenths in that of irrigation canals. The amount of pesticide from rainfall was a major factor from the viewpoint of estimating the environmental viability of the lake.

Effects of nutrient addition on phytoplankton in Lake Nakanuma, Japan

We measured the uptake of carbon and inorganic nitrogen in nutrient-enriched water samples during 15-days incubation in summer in Lake Nakanuma, Japan. We calculated daily variations in neutral sugars and amino acids of the phytoplankton and estimated the efficiency of the increases in sugars and amino acids relative to photosynthetic activities. Only a small portion of carbon incorporated via photosynthesis was used for synthesis of sugars and amino acids during the incubation periods. The percentage increase in neutral sugars plus amino acids compared to photosynthetic rates ranged from 3.7 to 26.9% with an average of 12.8%. These findings suggest that large amounts of photosynthates were not used for the synthesis of cell components of phytoplankton and were lost through processes such as excretion and respiration.

Effects of nutrient addition on phytoplankton in Lake Nakanuma, Japan I. Changes in biochemical components

Effects of nutrient conditions on biochemical components (sugars and amino acids) of phytoplankton were examined in Lake Nakanuma in Japan. Phosphate, ammonium and silicate were added to water samples collected at 0 m, which were incubated for 15 days in situ. Chlorophyll a in phosphate-added samples increased much more than that in other samples. Total amino acids and total neutral sugars in phosphate-added samples also increased more than those in other samples. The increase of total amino acids and chlorophyll began faster than that of total neutral sugars during the first 5 days of incubation. Total neutral sugars in the phosphate-added samples increased rapidly after 8 days. The composition of amino acids did not change so much. However, the composition of neutral sugars changed according to the different nutrient addition. Phosphate-added samples changed greatly during the incubation. These changes were explained at least partly by changes in nutrient conditions. Addition of limiting nutrients decreased glucose content, whereas depletion of nutrients increased the content. This study indicates that measurements of the biochemical components contribute to the analysis of effects of nutrients on phytoplankton in natural waters.

Diel Changes in Biochemical Components of Particulate Matter, and Uptake Activities of Carbon and Nitrogen by Phytoplankton in August in Lake Nakanuma, Japan.

We measured diel changes in neutral sugars, amino acids and fatty acids of particulate matter in Lake Nakanuma in August 1988. We also measured uptake of carbon and nitrogen during the day and night. During the diel cycle, chlorophyll at 1 m varied little. Neutral sugars and glucose at 1 m increased during the day and decreased at night. Amino acids did not show such changes. Carbon uptake at 1 m was 2.06 μg-at C⋅l-1⋅h-1 during the day and almost zero at night. The uptake increase during the day corresponded to the diurnal increase of neutral sugars. Ammonium uptake under light conditions during the day at 1m was 1.84×10-1 μg-at N⋅l-1⋅h-1, whereas the night uptake was 59% of that. The change in ammonium uptake did not necessarily correspond to the amino acid changes. We discuss the. relationship between the biochemical components and uptake activities of phytoplankton.

Seasonal changes in neutral sugars and amino acids of particulate matter in Lake Nakanuma, Japan

Amino acids and neutral sugars in particulate matter were measured weekly from April in 1987 to March in 1988 in Lake Nakanuma, Japan. Changes in concentrations of total amino acids and total neutral sugars corresponded to those of chlorophylla. The composition of amino acids varied little seasonally and vertically. On the contrary, the composition of neutral sugars changed seasonally and vertically. We discuss the relationship between the changes in the biochemical components and environmental factors.

Daily changes of uptake of inorganic carbon and nitrogen, and their relation to phytoplankton blooms in late spring-early summer in Lake Nakanuma, Japan

Daily changes of inorganic carbon and nitrogen uptake were measured in May in 1986 in Lake Nakanuma, Japan. Uptake of inorganic carbon and ammonium in the light-bottle experiments in the 1 m layers, showed daily changes similar to chlorophyll a changes, though the uptake activities peaked before chlorophyll a peaks (phytoplankton blooms) appeared. Potential growth rates of phytoplankton and observed growth rates were calculated from the uptake rates and chlorophyll a changes. The potential growth rates did not always correspond to the observed growth rates. The potential growth rates did not correlate with the loss rates. The correlation between the observed growth rates and the loss rates was better. These results suggest that though the increase of uptake activities may be necessary for occurrence of phytoplankton blooms, loss processes may affect the occurrence of blooms.

Changes in activities of inorganic carbon and ammonium uptake by phytoplankton from May to August, and their relation to water temperature in Lake Nakanuma, Japan.

Daily and weekly sampling was carried out from May to August in 1986 in Lake Nakanuma to estimate the effects of environmental factors on the uptake of inorganic carbon and ammonium by phytoplankton. Rates of uptake of carbon and ammonium, on the whole, increased during the sampling period, though daily and weekly changes occurred. Water temperature among environmental factors examined affected most the uptake activities. Light and nutrients exerted only minor effects on the increases in the uptake activities. The changes in these activities did not correspond to those of chlorophyll a concentration. Active uptake did not necessarily increase phytoplankton biomass.

Net increase rates and dynamics of phytoplankton populations under hypereutrophic and eutrophic conditions.

The relationships between net increase rates of phytoplankton populations and ambient concentrations of nutrients were investigated in hypereutrophic Ilimonya Pond and eutrophic Lake Nakanuma, and were expressed by a hyperbolic function for Microcystis aeruginosa, Cvclotella kutzingiana and Scenedesmus quadricauda. M. aeruginosa increased faster than the other species in low concentrations of total inorganic nitrogen, whereas C. kittzingiana and S. quadricauda increased faster than M. aeruginosa in low concentrations of phosphate phosphorus.Using a mathematical model based on these relationships, the population dynamics of the planktonic algae were analyzed in hypereutrophic conditions and slightly eutrophic conditions. In hypereutrophic conditions, a large amount of phosphate phosphorus caused M. aeruginosa to develop into a large population, and then caused the phytoplankton diversity to drop to a low level. On the other hand, in slightly eutrophic conditions, phytoplankton did not develop into large populations, and thus the phytoplankton diversity remained at a high level. This was because low nutrient concentrations limited the population increase of each species. The results of the model analysis coincided with the patterns observed in the field surveys, and showed that the amount of nutrients available for phytoplankton played an important role in the regulation of phyto-plankton dynamics.

Diel changes of uptake of inorganic carbon and nitrogen by phytoplankton, and the relationship between inorganic carbon and nitrogen uptake in Lake Nakanuma, Japan

Diel changes of uptake of inorganic carbon and nitrogen by phytoplankton, and the relationship between inorganic carbon and nitrogen uptake in Lake Nakanuma, Japan

Uptake of inorganic carbon and nitrogen by phytoplankton during the winter mixing period in a freshwater lake, Lake Nakanuma, Japan

Uptake of inorganic carbon and nitrogen by phytoplankton during the winter mixing period in a freshwater lake, Lake Nakanuma, Japan

Fatty Acids in Lipids from Particulate Organic Matter in a Eutrophic Lake, Lake Nakanuma, Japan

AbstractThe depth profiles and seasonal abundance of fatty acids in lipids from the particulate organic matter in the eutrophic Lake Nakanuma, Japan, were closely related to both photosynthetic activity and the distribution of phytoplankton. The changes in the relative proportions of the fatty acids suggest that their synthesis is directly related to the photosynthetic activity of phytoplankton.

Uptake of carbon and inorganic nitrogen in a eutrophic lake, Lake Nakanuma, Japan, from spring through summer

Uptake of carbon and inorganic nitrogen in a eutrophic lake, Lake Nakanuma, Japan, from spring through summer

Applicability of the stable isotope method using 13C and 15N simultaneously to the estimation of carbon and nitrogen assimilation in a eutrophic, freshwater lake, Lake Nakanuma, Japan

Applicability of the stable isotope method using 13C and 15N simultaneously to the estimation of carbon and nitrogen assimilation in a eutrophic, freshwater lake, Lake Nakanuma, Japan

Distribution of denitrifying bacteria and its controlling factors in freshwater environments.

Distribution of denitrifying bacteria and its controlling factors were investigated in freshwater environments. Denitrifying bacteria were counted by use of PY-Nitrate liquid medium and the most probable number method. The population (100-103 cells·ml-1) fluctuated more remarkably than that of aerobic heterotrophic bacteria in eutrophic pond and lakes. The ratio of the number of denitrifying bacteria to that of aerobic heterotrophic bacteria (D/Aeh) was between 0.0001 and 0.1 in those environments. In non-stratified eutrophic pond and lakes, the number of denitrifying bacteria tended to increase as the concentration of total nitrogen increased. In a stratified eutrophic lake, the D/Aeh ratio tended to increase as the concentration of dissolved oxygen decreased. Denitrifying bacteria in both water and attached substances in a polluted river tended to increase in number with the increase in BOD. The D/Aeh ratio in water and attached substances was higher than 0.01. Almost all denitrifying bacteria detected in the Himon-ya Pond, Lake Nakanuma and the River Tamagawa were gram-negative. Pseudomonas was the genus most frequently isolated from every type of water and attached substance.

Seasonal variations of dissolved organic constituents in Lake Nakanuma during March and November 1979

(1981). Seasonal variations of dissolved organic constituents in Lake Nakanuma during March and November 1979. SIL Proceedings, 1922-2010: Vol. 21, No. 1, pp. 682-687.

In situ Growth and Photosynthetic Characteristics of Oscillatoria mougeotii in the Metalimnetic Layer of the Small Eutrophic Lake Nakanuma

In situ growth and photosynthetic characteristics of Oscillatoria mougeotii were studied in the metalimnetic layer of a small eutrophic lake. Population growth of O.maugeotii showed a logistic curve and the mean increase rate of population was 0.086 (day-1). Photosynthesis of individual species in the natural phytoplankton community was measured by grain density autoradiography. The photosynthetic nature of O.mougeotii represented by the light-photosynthesis curve was a shade type with a steeper initial slope and a low maximum photosynthetic rate.The growth curve of O. mougeotii estimated by a model using the light-photosynthesis curve and light conditions coincided fairly well with the observed curve. Thus it was concluded that the population development of O. mougeotii in the metalimnion would be mainly due to the in situ photosynthetic growth.

A Study of the Excretion and Extracellular Products of Natural Phytoplankton in Lake Nakanuma, Japan

AbstractExcretion of photosynthetic products by phytoplankton in Lake Nakanuma ranged from 8 to 54% of the total carbon assimilated. Percentage of excretion increased under the conditions of high and very low light intensity, low temperature and nutrient deficiency. Estimated daily production of extracellular products in the lake was about 150 mg C/m2 in the summer season and the major components of it were glycolic acid, polysaccharides and polypeptides.

中沼における溶存有機物の季節変化

Seasonal fluctuation of dissolved organic matter and chlorophyll-a was measured in Lake Nakanuma, a small eutrophic lake in Ibaragi Prefecture during the period from spring turnover to summer stratification. The maximum concentrations of dissolved organic carbon (DOC) and dissolved carbohydrates (DCHO) were observed four and two weeks after that of chlorophyll-a, respectively. Dissolved organic matters rich in amino acids were accumulated in deep water under anaerobic conditions. Throughout the experimental period, only about 20% of DOC could be attributed to DCHO and DAA carbon, but a larger fraction remained to be identified.