Sedimentary photosynthetic pigments of algae and phototrophic bacteria in Lake Hamana, Japan: temporal changes of anoxia in its five basins

Abstract

characteristics of anoxia are strongly influenced by the effects that various factors such as climate, river flow, tides, and geomorphology have on flushing, stratification, and temperature (Kelly 2001).Sedimentary organic indicators such as photosynthetic pigments originating from phototrophic sulfur bacteria and the ratio of algal chlorophyll derivatives to carotenoids have been used to assess the past development of anoxia in water bodies (Brown et al. Chen et al. 2001). These previous reports have dealt mostly with temporal changes deduced from the record of indicators in sediment cores. The spatial relationship between the sedimentary record and the status of anoxia in water has been rarely investigated.We previously reported that anoxia has long existed in the central basin of Lake Hamana, a brackish coastal lake in Japan, and that the characteristics of the anoxia have changed over the past 250 years (Itoh et al. 2003); this change was revealed by analyzing photosynthetic pigments of algae and bacteria, together with molybdenum, an indicator of sulfidic condition, in 210 Pb-dated cores. The sedimentary records and lake salinity data showed that significant changes in algal and bacterial compositions around 1955 were caused by increases in seawater intrusion resulting from the construction of training walls to direct tidal currents into the lake via the Imagire-guchi Channel, the sole inlet of seawater into the lake. Since Lake Hamana consists of a central basin and five outer basins, each outer basin having a freshwater supply and being connected to the central basin through narrow inlets, the lake is a suitable place to identify the differences and similarities in phototrophic activity among the basins and to examine the relationships between the redox condition in the water and the relevant residual indicators in the sediment cores.In this study, we describe the photosynthetic pigments of algae and bacteria in sediment cores collected from the central basin and four of the outer basins of Lake Hamana; these pigments record the historical changes in the phototrophic production in the oxic and anoxic zones. We Abstract We analyzed photosynthetic pigments of algae and bacteria (phototrophic sulfur bacteria: Chromatium and brown Chlorobium) in sediment cores and water samples obtained from five basins of Lake Hamana, a brackish, eutrophic, holomictic lake in Japan, and discussed our findings in relation to the distribution of the phototrophs. The four outer basins are connected to the central basin by narrow inlets. The prevalence of anoxia in Lake Hamana was demonstrated by the widespread presence of bacterial pigments in each core. The construction of training walls in 1954-1956 to direct tidal currents into the lake via Imagire-guchi Channel, the sole inlet for seawater, increased the lake water circulation, suppressed the development of anoxia, and caused Chromatium to disappear. Strong correlations (r 2 Ͼ 0.7) between total algal carotenoid (TAC) and total bacterial carotenoid (TBC) contents in each cor...

Algal pigments in Hornsund (Svalbard) sediments as biomarkers of Arctic productivity and environmental conditions

“…4). Fucoxanthin contains an epoxy group and is regarded as an unstable carotenoid (Itoh et al 2003;Patoine and Leavitt 2006), as it is highly degraded in sediments . Consequently, the high levels of fucoxanthin and undecomposed chlorophyll-a in the sediments at station H3 indicate that fresh organic matter was present there.…”

Seasonal and inter-annual sedimentation in meromictic Lake Shira (Siberia, Russia) during disturbance of meromixis

“…The subsequent decrease in okenone was interpreted by the authors as an indicator of a decrease in water transparency due to eutrophication (Dressler et al, 2007). In Lake Hamana (Japan), the disappearance of okenone in bottom sediments since 1955 coincided with an increase in circulation in the lake and deepening of the redox zone (Itoh et al, 2003). In Lake Montcortes (Spain), Vegas-Vilarrúbia et al ( 2018) assessed the evolution of the oxic/anoxic shifts over the last 500 years using several independent proxies and showed that periods of stable meromixis coincided with an increased content of isorenieratene and okenone -carotenoids of sulfur bacteria.…”

Hyperspectral imaging sediment core scanning tracks high-resolution Holocene variations in (an)oxygenic phototrophic communities at Lake Cadagno, Swiss Alps

“…Additionally, the spectrophotometer data track all bacteriopheopigments that absorb in the same band (745 nm in acetone), which is comparable to the in situ measurements of the HSI method. Finally, the carotenoid isorenieratene was identified in the HPLC chromatograms based on its retention time and spectral profile (Itoh et al, 2003;Fuciman et al, 2010). This carotenoid is produced by browncolored strains of GSB (Sinninghe Damsté and Schouten, 2006;Hopmans et al, 2005) and thus serves as a proxy for their abundance.…”