Origin of 13C-enriched methane in the crater lake Towada, Japan.

Nishimura, Rieko; Tsunogai, Urumu; Ishibashi, Jun-ichiro; Wakita, Hiroshi; Nojiri, Yukihiro

doi:10.2343/geochemj.33.277

Cited by 14 publications

(19 citation statements)

References 27 publications

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“…Recently, high CH 4 concentrations in the epilimnion and the bottom layer have been reported (Miyajima et al 1997). Though a maximum concentration of CH 4 in the epilimnion has been reported in some lakes and bays, its origin is not clear (Lamontagne et al 1973;Schmidt and Conrad 1993;Nakamura et al 1994;Nishimura et al 1999). It is necessary to investigate the distribution of CH 4 in Lake Biwa, to determine its source, and further clarify the mechanism of the decrease in the dissolved oxygen.…”

Section: Introductionmentioning

confidence: 95%

Distribution of CH 4 in the north basin of Lake Biwa and tributary rivers

et al. 2001

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To determine the origin of CH 4 , the vertical distribution of CH 4 around the thermocline in the north basin of Lake Biwa and the horizontal distribution in the Yasu and Ado rivers were measured. In 1995, CH 4 concentrations (ranging from 200 to 1000 nM) exceeding the saturation level were observed just above or in the thermocline in the pelagic region off the Yasu River. These values were higher than those just below the thermocline and in the hypolimnion. CH 4 concentrations in the mouths of the Yasu and Ado rivers were much higher than at other stations, around 2500 and 2000 nM, respectively. Due to the drought in 1994 when there was no water from the Yasu River flowing into the north basin, CH 4 concentration just above or in the thermocline in the pelagic region off the Yasu River ranged from 49 to 74 nM. It is thus concluded that the high level of CH 4 observed in the mouth of the Yasu River is one of the sources of the high CH 4 concentrations in the pelagic region off the Yasu River. On the other hand, the CH 4 concentration in the pelagic region off the Ado River was about 50 nM. It is thought that water flowing in from the Ado River diffused readily into the lake water because the depth of the lake in the region off the Ado River declines steeply. The maximum concentration of CH 4 in the river mouths indicates that these areas are important sites for clarifying the mechanism of the decrease in dissolved oxygen in Lake Biwa and the Yodo River watershed.

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Section: Introductionmentioning

confidence: 95%

Distribution of CH 4 in the north basin of Lake Biwa and tributary rivers

et al. 2001

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“…The increased buoyancy could allow the water to re-enter the lake. Nishimura et al (1999) had already attempted clarifying the origin of the deep waters in Lake Towada.…”

Section: Lake Towada 215mentioning

confidence: 99%

“…demonstrated by the appearance of hot springs at the bottom of Lake Kuttara, possibly connected to thermal springs in Gigokudani "Hell's Valley" of Noboribetsu (Chikita et al 1995). This heat however is felt in the lake only, if the heated groundwater can find its way 250 into the lake, as it is suspected for deep areas in Lake Towada (see also Nishimura et al, 1999).…”

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confidence: 99%

Geothermal heat flux into deep caldera lakes Shikotsu, Kuttara, Tazawa and Towada

Boehrer

Fukuyama²,

Chikita

2013

Limnology

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key words: physical limnology, heat flux, stratification, density, deep water running header: geothermal heat flux into deep caldera lakes for submission to "Limnology" -2 - AbstractGeothermal heat fluxes into the deepest waters of four caldera lakes were measured.Temperature profiles within the stratification period between July and November 2007 allowed a quantification of the acquired heat. Due to their enormous depth, heat input from 5 the lake bed was locally separated from heat fluxes at the surface. In conclusion, a direct measurement of geothermal heat input could be accomplished. Although enhanced geothermal activity could be suspected in all cases, two lakes showed a geothermal heat flux of 0.29 or 0.27 W/m² (Lake Shikotsu and Lake Tazawa), as found in other regions not affected by volcanism, while both other lakes (Lake Kuttara and Lake Towada) showed a 10 much enhanced heat input of 1 or 18.6 W/m², respectively. In conclusion within our investigated set, all lakes acquired more heat from the underground than the continental heat flux average. Hence, the heat flux into the lakes from the ground was not dominated by the temperature gradient implied by the inner heat of the Earth. Other effects like the general temperature difference of deep lake water and the groundwater or local sources of heat in the 15 underground deliver more important contributions. Obviously the flow of water in the underground can play a decisive role in the heat transport into the deep waters of lakes.-3 -

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“…1) using a 2.0 L Niskin sampler (Nishimura et al, 1999) at depths of 0, 20, 50, 100, 150 and 200 m (Table 1). Each sample was transferred into 250 mL polyethylene bottles on the boat subsequent to being rinsed at least twice with the sample itself and then filtered through a pre-combusted Whatman GF/F filter (0.7 µm pore size) within a few hours of collection, after which the filtrate was stored in a refrigerator (4 • C) until analysis.…”

Section: Samplingmentioning

confidence: 99%

Quantifying nitrate dynamics in an oligotrophic lake using Δ<suP>17</sup>O

et al. 2011

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Abstract. The stable isotopic compositions of nitrate, including the 17 O anomalies ( 17 O), were determined twice in 1 yr (June and August 2007) in the oligotrophic water column of Lake Mashu, Japan. These data were then used to quantify the geochemical dynamics of nitrate in the lake, by using the deposition rate of the atmospheric nitrate onto the entire catchment area of the lake. The total amount of nitrate in the lake water decreased from 4.2 to 2.1 Mmol during the period between the observations, while the average 17 O values remained uniform at +2.5‰. The 17 O values corresponded to an small and uniform mixing ratio of atmospheric nitrate to total nitrate of 9.7 ± 0.8%. These results indicate that 0.52 ± 0.34 Mmol of the remineralized nitrate was fed into the water column through nitrification, while 2.6 ± 0.4 Mmol of nitrate was simultaneously removed from the water column by assimilation, during the period between the observations. The lake water dissolved nitrate was characterized by rapid removal through assimilation during summer until it was almost completely removed from the euphotic layer, as well as continuous feeding into the lake through nitrification (3.2 ± 0.3 Mmol a −1 ) and deposition (0.35 ± 0.2 Mmol a −1 ), regardless of the seasons. The 15 N-depleted nitrogen isotopic compositions of nitrate were as low as −6.5‰ in June, which also indicates that in-lake nitrification is the major source of nitrate in the lake and suggests that there is low potential for denitrification in and around the lake. Atmospheric nitrate deposited into the lake will be assimilated quickly, having a mean residence time of 1.2 ± 0.1 yr. In addition, more than 90% of the assimilated nitrate will be remineralized to nitrate and re-assimilated via active nitrogen cycling in the lake.

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Origin of 13C-enriched methane in the crater lake Towada, Japan.

Cited by 14 publications

References 27 publications

Distribution of CH 4 in the north basin of Lake Biwa and tributary rivers

Distribution of CH 4 in the north basin of Lake Biwa and tributary rivers

Geothermal heat flux into deep caldera lakes Shikotsu, Kuttara, Tazawa and Towada

Quantifying nitrate dynamics in an oligotrophic lake using Δ<suP>17</sup>O

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Origin of 13C-enriched methane in the crater lake Towada, Japan.

Cited by 14 publications

References 27 publications

Distribution of CH 4 in the north basin of Lake Biwa and tributary rivers

Distribution of CH 4 in the north basin of Lake Biwa and tributary rivers

Geothermal heat flux into deep caldera lakes Shikotsu, Kuttara, Tazawa and Towada

Quantifying nitrate dynamics in an oligotrophic lake using Δ&lt;suP&gt;17&lt;/sup&gt;O

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Quantifying nitrate dynamics in an oligotrophic lake using Δ<suP>17</sup>O