On the Oxygen and Chlorophyll Maxima Found in the Metalimnion of a Mesotrophic Lake

Abstract

In Lake Haruna (mesotrophic lake) the oxygen and chlorophyll maxima were found in the metalimnion.Dominant species of phytoplankton in the low layer of the euphotic zone was Cry ptomonas sp. and it showed a characteristic shade type in the photosynthesis-light curve.The photosynthetic activity of Cry ptomonas sp. at low light intensities and low temperature was remarkably higher than that of other phytoplankters.From the photosynthesis-light curve of Cry ptomonas sp. obtained in the laboratory and depth-light profile observed in the lake, the depth-photosynthesis relation of the alga was calculated and it was found to be in good accordance with the relation measured in situ.It was thus concluded that the oxygen maximum in the metalimnion of Lake Haruna is due to the special photosynthetic characteristics of Cry ptomonas sp. living in that lake which is adapted to the environment of low light intensity and low temperature prevailing at the foot of the euphotic zone. The lake was found to show the chlorophyll maximum in the deeper layer. This was attributed to the intensive growth of Cryptomonas and not to the accumulation of the deteriorated phytoplankton sedimented from the surface layer.The majority of oligotrophic or mesotrophic lakes in Japan have a marked oxygen maximum in their middle layers'.In some situations, especially in mesotrophic lakes,, a supersaturation of oxygen appears occasionally in the upper layer of the metalimnion. These lakes are usually small and deep ones in the mountain districts and many of them are protected from the disturbance by strong wind. Yoshimura'> has propounded the opinion that the full development of metalimnetic oxygen maximum is due partly to warming of water in the epilimnion by solar radiation and partly to the photosynthetic activity of phytoplankton in the stable layer in question. Recently, a more detailed study was made by Eberly2'3> in plusheterograde lakes of northern Indiana.He measured the metalimnetic oxygen maximum greater than 12.7 ppm and also found an immense bloom of Oscillatoria agardhii in the metalimnion. The layer of oxygen maximum, however, did not always coincide with that of photosynthetic maximum found by the in situ experiments.Wetzel4> reported that in aa lake of Indiana the major portion of the primary productivity occurred in the metalimnion where oxygen maximum developed and the dominant phytoplankton of the metalimnion were Ceratium hirundinella and Oscillatoria agardhii.It has generally been said that in the stagnant layer of lakes the supersaturation

The origin of a metalimnetic chrysophyte peak

“…A similar argument was used by Ichimura et al (1968) to explain a peak of Cryptomonas erosa in a mesotrophic caldera lake of Japan. Their consecutive profiles of Chl a would also indicate a steady accumulation of chlorophyll in the metalimnion.…”

“…Subsurface chlorophyll maxima are common in many lakes (Eberly 1959;Ichimura et al 1968;Baker and Brook 197 1;Fee 1976) and oceans (Steele 1964;Anderson 1968;Cahet et al 1972;Vcnrick et al 1973). One hypothesis proposed to explain these chlorophyll maxima attributes the increase to the passive sinking of phytoplankton and subsequent accumulation in layers of increased density (Riley et al 1949;Jerlov 1959;Steele 1964;Steele and Yentsch 1960).…”

“…Another hypothesis invokes active in situ growth by algae adapted to low light (Eberly 1959(Eberly , 1964aAnderson 1968;Ichimura et al 1968;Cahet et al 1972;Fee 1976). This would mean that if such maxima were not included in estimates of lake productivity, the values obtained would be too low.…”

A 21-year record of vertically migrating subepilimnetic populations of Cryptomonas spp.

“…It has been known since the early studies of Yoshimura (1939) that deep chlorophyll maxima (DCM) tend to occur in lakes of low to moderate fertility when water column transparency allows light to penetrate into or below the thermocline. DCM have been reported in natural lakes worldwide, including Africa (Descy et al 2010), Asia (Ichimura et al 1968, Lohman et al 1988, Kim and Takamura 2002, Europe (Ilmavirta 1988, Jones 1991, all 5 of the Laurentian Great Lakes (Barbiero and Tuchman 2001), diverse natural lakes throughout North America (Pick et al 1984, deNoyelles and Likens 1985, Konopka 1989, Gross et al 1997, South America (de Matos Bicudo et al 2009), and Tasmania (Croome and Tyler 1984). DCM also have been reported in artificial freshwater impoundments where sufficient light is available in the upper metalimnion to allow in situ phytoplankton growth (e.g., Knowlton and Jones 1989).…”

Study of primary production magnitude under the thermocline (20-25 m) and the continuous supporting mechanism of production in Lake Pumayum Co, Tibetan Plateau

“…al., 1999)。これらの報告を基にすると，亜表層極大の形成 Kiefer and Holm-Hansen, 1972;Hino et. al., 1998)，もう一つは，生育条件に適合し Ichimura et. al., 1968;Fee, 1976;Davey and Heaney, 1989;Nakanishi et.…”