Diatom-based water-table reconstruction in Sphagnum peatlands of northeastern China

Diatom cell-size composition as a novel tool for quantitative estimates of the water table in peatlands

Diatom cell-size composition is an indicator of aquatic environmental changes but has been rarely investigated, especially in semi-terrestrial peatlands. In this study, both taxonomic composition and cell-size composition of diatoms were analysed in 41 samples from two montane peatlands, northeastern China. Redundancy analyses revealed that diatom taxonomic composition was significantly related to the depth to the water table (DWT) and Ca2+, while cell-size composition was significantly associated with DWT and Si. DWT was the most important factor and its sole effect explained 26.2% and 17.9% of the total variance in taxonomic composition and cell-size composition, respectively. Accordingly, diatom-based water-table transfer functions were developed based on taxonomic composition and cell-size composition, respectively. The maximum-likelihood (ML) model based on diatom taxonomic composition had the best performance, with a correlation coefficient value (R2) of 0.78 and the root mean squared error of prediction (RMSEP) of 6.66 cm. The ML model based on cell-size composition had similar performance, with an R2 of 0.78 and the RMSEP of 6.87 cm, suggesting that diatom cell-size composition can be a new quantitative means to track past water-table changes. This method requires further appraisal with palaeoecological data but offers a new option that deserves exploration.

Ecological distribution of modern diatom in peatlands in the northern Greater Khingan Mountains and its environmental implications

Relationships between diatom assemblages and environmental variables in peatlands of the northern Greater Khingan Mountains are helpful for understanding the indicative significance of diatoms to environment changes, and potentially provide a reference for environmental monitoring and paleoenvironment reconstruction in the edge of monsoon region. In this study, we analyzed modern diatom assemblages and their relationships with environment factors in 30 surface samples from shrubby-herbaceous and herbaceous peatlands based on ordination analysis. Benthic and epiphytic Pennatae diatoms are mainly ecological types, whereas planktonic Centricae diatoms are relatively fewer. The most diverse genera are Pinnularia and Eunotia. Eunotia paludosa and Achnanthidium minutissimum dominated in shrubby-herbaceous peatlands, while Navicula minima and Fragilaria capucina dominated in herbaceous peatlands. The diatom community structures are different in different vegetation types and the diatom species diversity in herbaceous peatlands is higher than that in shrubby-herbaceous peatlands. COD_Mn and pH are the most important environmental factors affecting diatom species composition and diversity. Eunotia bilunaris, Eunotia mucophila, and Eunotia paludosa can be used as indicators of acidic water environments. Caloneis silicula, Fragilaria capucina, Hantzschia amphioxys, and Navicula radiosa can be applied to indicate the weak alkaline conditions. Eunotia bilunaris and Eunotia paludosa can indicate low conductivity, while Sellaphora pupula indicates the medium-high conductivity. Fragilaria capucina and Navicula radiosa can indicate oligotrophic habitats.

Biology, Genetic Diversity, and Ecology of Nitzschia acidoclinata Lange-Bertalot (Bacillariophyta)

The diatom Nitzschia acidoclinata is a widespread eurybiontic alga. There is little information on its life cycle properties and cardinal points. To fill this gap, we analyzed six N. acidoclinata clones from a range of habitats in Asiatic Russia regarding their genetic diversity, morphology, morphometry, geography, and ecology. A comparison of 15 N. acidoclinata rbcL sequences sampled across its relatively wide distribution area and contrasting habitats revealed no distinct genotypes in the species. We demonstrated that the valve morphology, their length, and the sexual activity of the investigated clones varied depending on the phase of their life cycle. In this species, abrupt size reduction was observed. It was revealed that N. acidoclinata reproduced by pedogamy, and its auxosporulation was season-dependent and observed in spring and autumn only. The mating activity in our clones was detected only when the cell size was reduced to 9–22 µm in length. The available data on sexual reproduction in the genus Nitzschia suggest that neither clades nor subclades comprise pedogamous or anisogamous taxa at the same time. However, isogamy could occur in the same clade with either pedogamy or anisogamy. These data provide a fundamental basis for the development of N. acidoclinata mass cultivation and long-term maintenance in culture technologies.

Diatom evidence for mid-Holocene peatland water-table variations and their possible link to solar forcing

Peatlands located at the northern edge of the East Asian monsoon (EAM) are well placed to provide a terrestrial record of past climate and hydrological changes for this globally sensitive region. Here we present a middle to late Holocene, diatom-derived water-table records from a peatland in the Greater Hinggan Mountains, northeastern China. An age-depth model was achieved through AMS¹⁴C dating and Bayesian piece-wise linear accumulation modelling. The diatom-based water-table reconstructions show that the peatland water-table rose from 5100 to 3500 cal. yr BP, but fell approximately 3500 cal. yr BP. From about 2800 to 1500 cal. yr BP, the peatland water-table stabilized. After about 1500 cal. yr BP, several rapid hydrological shifts, which correspond with global climate anomalies such as ice-rafted debris (IRD) events, were registered in the reconstructed water-tables. Compared with other paleoclimate records in East Asia, the general trend of peatland water-table fluctuations follows the variations in the East Asian summer monsoon (EASM) intensity. Spectrum analysis of the water-table profile yielded a statistically significant periodicity of 470-year that may be related to the "~500-year" inherent solar irradiation cycles. In addition, positive correlation between the peatland water-table levels and cosmic-isotope-reconstructed sunspot numbers underscores the role of the sun in regulating hydrological processes in the EASM margin area. The data suggest that the regional climate and hydrological variations at the EASM margin were first triggered by changes in solar output, but may have been amplified by interactions with oceanic and atmospheric circulations.