The production‐to‐respiration ratio and its implication in Lake Biwa, Japan

Abstract

Production-to-respiration (P:R) ratio was estimated at an offshore site of Lake Biwa in order to examine whether the plankton and benthic community is subsidized with allochthonous organic carbon, and to clarify the role of this lake as potential source or sink of carbon dioxide. The respiration rate of protozoan and metazoan plankton was calculated from their biomass and empirical equations of oxygen consumption rates, and that of bacterioplankton was derived from their production rate and growth efficiency. In addition, the carbon mineralization rate in the lake sediments was estimated from the accumulation rate of organic carbon, which was determined using a 210 Pb dating technique. On an annual basis, the sum of respiration rates of heterotrophic plankton was comparable to net primary production rate measured by the 13 C method. However, when the mineralization rate in the lake sediments was included, the areal P:R ratio was 0.89, suggesting that Lake Biwa is net heterotrophic at the offshore site with the community being subsidized with allochthonous organic carbon. Such a view was supported by the surface water pCO 2 that was on average higher than that of the atmosphere. However, the estimate of net CO 2 release rate was close to that of carbon burial rate in the sediments. The result suggests that the role of Lake Biwa in relation to atmospheric carbon is almost null at the offshore site, although the community is supported partially by organic carbon released from the surrounding areas.

Quantifying nitrate dynamics in a mesotrophic lake using triple oxygen isotopes as tracers

“…Similar seasonal variation in F assim + F denit of showing a maximum value in summer and a minimum value in winter was detected in Lake Mashu as well (Tsunogai et al ). Past observations on primary production rates in Lake Biwa ( F assim ) also displayed similar seasonal variation (Yoshimizu et al ; Urabe et al ; Ota et al ). Thus, the observed seasonal variation in F assim + F denit , showing a maximum in summer and a minimum in winter, is a highly reasonable estimate for this lake.…”

Abundance and nutrient limiting growth rate of heterotrophic bacterio‐plankton in Himalayan foot hill Lake Phewa, Nepal

“…Small lakes can depend on allochthonous DOC for metabolic activities (Wetzel 1984(Wetzel , 1995Urabe et al 2005;Wetzel & Tuchman 2005). Lake Phewa has a small volume relative to its catchment area, and the monsoondominated climate can deliver up to 4846 mm of rainfall per year (Paudel & Thapa 2001;Gurung et al 2006), causing lake water to be exchanged many times during summer (Ferro 1981(Ferro ⁄ 1982Lohman et al 1988).…”

“…Small lakes can depend on allochthonous DOC for metabolic activities (Wetzel 1984, 1995; Urabe et al. 2005; Wetzel & Tuchman 2005).…”

Toward the understanding of complex population dynamics: planktonic community as a model system

“…We speculate that organic matter resuspended by strong winter mixing of the water column may have supported zooplankton growth. Although such a hypothesis still remains to be tested, Urabe et al (2005) showed that an allochthonous source of organic carbon is not negligible in the support of the Lake Biwa pelagic system, especially in winter. Rotifers were abundant in late winter just before large zooplankton increased as in the PEG model, but they were scarce in summer since large zooplankton were abundant in contrast to the pattern in the PEG model, probably due to low fish predation in this lake.…”