Seasonal dynamics of carbon stable isotope ratios of particulate organic matter and benthic diatoms in strongly acidic Lake Katanuma

Abstract

Lake Katanuma is a strongly acidic volcanic lake (average pH 2.2) located in NE Japan in which only 2 algal species are found: Pinnularia acidojaponica, a benthic diatom, and Chlamydomonas acidophila, a phytoplankton species. Although the δ 13 C of phytoplankton generally varies seasonally in lake ecosystems, in Lake Katanuma the mean δ 13 C of particulate organic matter (POM, mainly phytoplankton) is constrained to a narrow range from -26.4 to -23.7 ‰. A major reason for this is the continuous supply of dissolved CO 2 gas available to C. acidophila from fumaroles at the lake bottom. The δ 13 C of P. acidojaponica in Lake Katanuma varied seasonally and was positively correlated with P. acidojaponica abundance at 1 and 4 m depths. This suggests that the higher P. acidojaponica biomass at 1 and 4 m produced the 13 C-enrichment in the high-density algal mats because of the limited dissolved CO 2 gas. The mean δ 13 C of benthic diatoms was higher than that of phytoplankton in Lake Katanuma, although the diatoms seemed to assimilate the same carbon source (CO 2 gas) in the lake water. KEY WORDS: Carbon stable isotope · POM · Phytoplankton · Benthic diatoms · Inorganic carbon · Seasonal variation · Acidic conditions Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 33: [87][88][89][90][91][92][93][94] 2003 phytoplankton species Chlamydomonas acidophila and the benthic diatom species Pinnularia acidojaponica are found in the lake.Usually, the phytoplankton and benthic algal communities in lake ecosystems are composed of many species. The complexity of the species composition may make it difficult to analyze the relationships between the carbon isotope ratios of algae and their physiological and environmental conditions in situ, since the isotope ratios of microalgae are mainly measured for an entire algal community (Yoshioka et al. 1989, Takahashi et al. 1990b). The seasonal variation in the δ 13 C of planktonic and benthic microalgal communities is inevitably influenced by changes in species composition (Fry 1996). Only few studies have reported seasonal variation in the carbon isotope ratio at the species level (Zohary et al. 1994).This study examines the seasonal changes in the δ 13 C of phytoplankton and benthic diatoms in a strongly acidic lake and compares the difference in the δ 13 C between the 2 algal species that dominate it. In Lake Katanuma, because of its limited phytoplankton and benthic algal species, we could analyze the relationships between the carbon isotope ratios of the phytoplankton and benthic diatoms and physiological and environmental factors more accurately than in an environment with a greater variety of species. Moreover, we could determine the difference in the δ 13 C of benthic diatoms and phytoplankton in the same natural environment. MATERIALS AND METHODSStudy area. Lake Katanuma is a volcanic lake located in NE Japan (38°44' N, 140°43' E) and is situated 306 m above sea level. Lake Katanuma is strongly acidic, with an average pH...

Complementary ecophysiological strategies combine to facilitate survival in the hostile conditions of a deep chlorophyll maximum

“…8b), for example, may supplement acclimation by providing a flexible spatial and temporal strategy by which to avoid the harshest of environmental conditions. For the first time (although postulated in the field: Doi et al 2003), laboratory experiments discovered and characterised a light-dependent behavioural response in C. acidophila ( Fig. 4; Table 2), showing a controlled phototactic orientation towards a preference of around 50 lmol photons m -2 s -1 , maintained by photophobic reactions.…”

Differences in nitrogen and carbon stable isotopes between planktonic and benthic microalgae

“…To determine the d 15 N values of the benthic diatom P. acidojaponica, cells were separated from the sediment by making use of its phototactic movements (Couch 1989;Doi et al 2003). Sediment samples for P. acidojaponica separation were collected from 1-m depths in the lake (three replicates) using an Ekman-Birge grab from April to December in 2001.…”

“…Lake Katanuma is a strongly acidic lake (annual average pH of 2.2). The microalgal community in the lake is very simple, with only two dominant microalgal species, Pinnularia acidojaponica (Pennales, Naviculaceae) as benthic diatoms and Chlamydomonas acidophila (Chlorophyceae) as planktonic green algae (Doi et al 2003). In general, lake microalgal communities are composed of many species, and this complicates the determination of relationships between stable isotope values of individual microalgal species and the prevailing physiological and environmental conditions.…”

“…Carbon and nitrogen isotope ratios of phytoplankton and benthic microalgae vary widely among seasons as well as species, especially in lentic systems (Zohary et al 1994;France 1995;Takai et al 2002;Doi et al 2003). However, in lentic systems, detailed studies of the nitrogen and carbon isotope dynamics in microalgae are somewhat limited, especially of the nitrogen isotope dynamics, though seasonal variations in the carbon and nitrogen of phytoplankton and benthic microalgae have been observed in several systems (Takahashi et al 1990;Zohary et al 1994;Takai et al 2002;Doi et al 2003). Moreover, very little is known about the primary factors controlling the nitrogen isotope values of microalgae.…”

Phosphorus limitation of algae living in iron-rich, acidic lakes

“…C. acidophila is found in a number of very acidic lakes (e.g. Gyure et al 1987, Doi et al 2003, Gerloff-Elias et al 2005, and in the German mining lakes it is the main photoautotrophic phytoplankter (Kamjunke et al 2004). Although species diversity in the acidic lakes is low, taxa from a number of algal classes are present, including several diatom species, chrysophytes, euglenophytes and chlorophytes (Lessmann et al 2000).…”