Yansheng Gu

Lipid distributions in loess-paleosol sequences from northwest China

Molecular stratigraphic analyses using GC/MS have been performed on the top section of the Jiuzhoutai loess-paleosol sequences near Lanzhou in northwest China, with a record extending from the second-last interglacial through the present interglacial. The various molecular fossils identified from the second-order loess and paleosol layers include C14–C35n-alkanes, C8–C30n-alkanoic acids, C12–C30n-alkanols and C23–C33n-alkan-2-ones. The CPI (carbon preference index) values and the ratio of C29/C31n-alkan-2-ones display alternations between loess deposits and paleosols. They show a significant correlation with the loess magnetic susceptibility, an indicator of the East Asian summer monsoon. The observed variations of the ketone indices in relation to the change of lithology are proposed to result from microbial re-working of higher plant inputs in the paleosols.

Concordant monsoon-driven postglacial hydrological changes in peat and stalagmite records and their impacts on prehistoric cultures in central China

Asian monsoon records are widely documented, but specific proxies of monsoonal rainfall are limited. We present here two new independent proxy records from peatland and stalagmite archives that indicate a high degree of concordance between monsoon-driven hydrological changes occurring since the last deglaciation in a broad region of central China. The wet periods elevated the water table in the Dajiuhu peatland, as recorded by reduced mass accumulation rates of hopanoids, biomarkers for aerobic microbes, confirmed by molecular phylogenic analyses. The hopanoid-based reconstruction is supported by the first report of the environmental magnetism parameter ARM/SIRM (anhysteretic remanent magnetization / saturation isothermal remanent magnetization; ratio of fine magnetic particles to total ferrimagnetic particles) in a stalagmite from Heshang Cave in central China. Heavy rainfall resulted in the enhanced transport of coarse particles to the cave and thus low ARM/SIRM values in the stalagmite. The hydrological conditions inferred from the two records reveal three relatively long wet periods in central China: 13–11.5 k.y. ago, 9.5–7.0 k.y. ago, and 3.0–1.5 k.y. ago. Archaeological evidence for the hydrological impacts on regional populations comes from the observation that temporal shifts among six distinctive cultures of the Neolithic Period to the Iron Age in central China occurred during wet periods or flood episodes. Spatiotemporal distributions of >1600 prehistoric settlement sites correlate with the proxy-inferred fluctuating hydrological conditions, with enhanced flooding risk forcing major relocations of human settlements away from riparian zones.

Leaf wax n -alkane chemotaxonomy of bamboo from a tropical rain forest in Southwest China

The leaf waxes of 23 woody bamboo species of three subgenera, Dendrocalamus, Bambusa and Dendrocalamopsis, from the Xishuangbanna tropical rain forest in Southwest China were analyzed by gas chromatography and coupled gas chromatography–mass spectrometry. The waxes of the Dendrocalamus species are dominated by C27 and C29n-alkanes and their average chain length (ACL) has an average of 28.3. In marked contrast to the Dendrocalamus species, the wax composition of the Bambusa species is characterized by a broad distribution of major n-alkanes from C27 to C35, greater ACL values (>29) and an enhanced relative abundance (>30%) of n-alkanes with a carbon number greater than 30. Unlike the Dendrocalamus species and the Bambusa species, the Dendrocalamopsis species do not have a distinct n-alkane distribution; in some species the n-alkane distribution is comparable to that in the Bambusa species and in others to that in the Dendrocalamus species. The lipid data suggest that it might be reasonable to classify the controversial Dendrocalamopsis group as an independent genus separate from the Bambusa genus. On the basis of their smaller diversity of the dominant n-alkanes and their lower ACL values, the Dendrocalamus species might be more evolutionarily advanced than the Bambusa species, with the Dendrocalamopsis species being at an intermediate stage. The evolution and classification of the woody bamboos inferred from leaf wax n-alkanes are consistent with morphological investigations reported previously.

Molecular fossils in a Pleistocene river terrace in southern China related to paleoclimate variation

Abstract The red paleosols (Oxisols) in southern China provide a record of global climate oscillation during at least the last 0.80 Ma. Here we present a correlation between the marine oxygen isotope record (stage 11–21) and the paleosol molecular fossil signature in the fourth Xiushui river terrace in southern China. Temporal variations seen in two molecular ratios—C15–21/C22–33n-alkanes and pristane to phytane (Pr/Ph)—down the paleosol profile are postulated to have arisen from variations in biological input and subsequent pedogenesis in response to the changing strength of the East Asian summer monsoon climate. The preliminary findings suggest strong couplings among the soil, vegetation and climate, and provide a basis for a correlation between the terrestrial and oceanic records.

Diversity, distribution and biogeography of testate amoebae in China: Implications for ecological studies in Asia

Testate amoebae are a group of shelled protozoa that occur in high density populations in wet environments. More than 1900 testate amoebae species or subspecies have been reported in published literature over the last 200 years, from many regions of the world. Testate amoebae are classified as Lobosea or Filosea respectively, according to the presence of lobose or filiform pseudopodia. Testate amoebae have proved an interesting group of indicator organisms in palaeoenvironmental studies and have also been used as bioindicators of human impact on ecosystems. Until recently, the testate amoebae of China were unknown to most western scientists, but our knowledge has improved greatly over the past 20 years. This paper summarizes the testate amoebae research in China along with relevant data from other countries in Asia, and provides the necessary context for future research.

Testate amoebae as indicators of 20th century environmental change in Lake Zhangdu, China

We investigated the response of lacustrine testate amoeba communities to 20 th century environmental changes in Lake Zhangdu, China. The lake and surrounding region have undergone dramatic changes in the past century, including the expansion of agricultural and industrial activities, and associated hydrological modifications that led to the isolation of the lake from Yangtze River. We assessed the potential effects of these activities on testate amoeba communities of the lake by examining subfossil assemblages in contiguous samples along a 35-cm long, 210 Pb dated sediment core. A total of 25 testate amoeba taxa belonging to 4 genera (Difflugia, Centropyxis, Neztelia, and Pentagonia) were encountered in the core. The largest change in the composition of testate amoeba communities occurred in the 1960s, coincident with the expansion of human activities in the watershed. Testate amoeba communities shifted from species characteristic of relatively oligotrophic lakes (e.g. Difflugia biwae, D. tuberspinifera and D. pristis) to species more common to mesotrophic and eutrophic systems (e.g. Difflugia oblonga, D. corona, D. smilion and D. lanceolata). Our results provide valuable baseline data on testate amoebae and water conditions before and after major 20 th century human impact on the lake ecosystem. Lake Zhangdu was recently reconnected with the Yangtze River as part of ongoing conservation efforts, and future monitoring of testate amoeba communities could be used to inform management and assess restoration success.

Moisture conditions during the Younger Dryas and the early Holocene in the middle reaches of the Yangtze River, central China

The last glacial–interglacial climate transition in East Asia was characterized by an intensified monsoon, but knowledge about hydrological responses at a regional scale during this transitional period is limited. Here we provide a novel lipid-based paleohydrological record for this period from the Dajiuhu peat deposit, central China. High water levels and persistent wet conditions during the Younger Dryas (12.5–11.6 ka) and the early Holocene (10.5–9.9 ka) were inferred on the basis of enrichments of sterenes, a group of unstable intermediate diagenetic products derived from biogenic sterols that are most likely preserved under a waterlogged peatland surface. These two wet intervals were accompanied by temperature decreases indicated by an increase in pollen abundance from cold favoring conifer trees and a decrease in total hardwood tree pollen. This cold and wet climate pattern, which is different from the concordant cold-dry pattern documented in north China, was probably caused by the regional influence of the western Pacific subtropical high on the residence time of the Meiyu rainband in the middle and lower reaches of the Yangtze River Valley.

Ecology of testate amoebae in Dajiuhu peatland of Shennongjia Mountains, China, in relation to hydrology

This study investigates the testate amoeba communities of a large peatland in Central China. The ecology and seasonal variability of testate amoeba communities were studied during 2009–2010. Investigation of environmental controls using ordination showed that the relationship between testate amoeba communities and depth to water table (DWT) and pH are extremely weak. The small proportion of variance explained by water table depth here (only 1.9% in the full data) shows that the hydrological control is weaker than we expected in this peatland, and weaker than any study we are aware of using a similar methodology. Attempts to develop species-environment (transfer function) models or identify indicator species for future palaeoecological studies were unsuccessful. Previous large-scale studies of peatland testate amoeba ecology have been largely restricted to Europe and North America and results have been relatively consistent among studies. Our results contrast with this consensus and suggest that at least in minerotrophic peatlands in China testate amoeba communities may be primarily controlled by different environmental variables. In China, testate amoebae have been relatively little studied but may prove to be valuable for a variety of applications in palaeoecology and biomonitoring and much further work is required.

Pentagonia zhangduensis nov. spec. (Lobosea, Arcellinida), a new freshwater species from China

The morphology of a new testate amoeba Pentagonia zhangduensis nov. spec. was investigated using light and scanning electron microscopy. The new species was discovered in the sediments of Lake Zhangdu, Hubei Province, China. The low coefficients of variation and normal size frequency distribution suggest that P. zhangduensis is a size-monomorphic species. P. zhangduensis differs from the one other species in this genus (P. maroccana), by its larger size and its quadrangular cross section with two parallel longitudinal ridges on each of the two flattened sides of the test.

Relationships between testate amoeba communities and water quality in Lake Donghu, a large alkaline lake in Wuhan, China

The middle Yangtze Reach is one of the most developed regions of China. As a result, most lakes in this area have suffered from eutrophication and serious environmental pollution during recent decades. The aquatic biodiversity in the lakes of the area is thus currently under significant threat from continuous human activities. Testate amoebae (TA) are benthic (rarely planktonic) microorganisms characterized by an agglutinated or autogenous shell. Owing to their high abundance, preservation potential in lacustrine sediments, and distinct response to environmental stress, they are increasingly used as indicators for monitoring water quality and reconstructing palaeoenvironmental changes. However this approach has not yet been developed in China. This study presents an initial assessment of benthic TA assemblages in eight lakes of Lake Donghu in the region of Wuhan, China. Testate amoeba community structure was most strongly correlated to water pH. In more alkaline conditions, communities were dominated by Centropyxis aculeata, Difflugia oblonga, Pontigulasia compressa, Pon. elisa and Lesquereusia modesta. These results are consistent with previous studies and show that TA could be useful for reconstructing past water pH fluctuations in China. To achieve this, the next step will be to expand the database and build transfer function models.