Peatlands are important ecosystems for biodiversity conservation, global carbon cycling and water storage. Hydrological changes due to climate variability have accelerated the degradation of global and regional ecosystem services of peatlands.Diatoms are important producers and bioindicators in wetlands, but comprehensive diatom-based inference models for palaeoenvironmental reconstruction in peatlands are scarce. To explore the use of diatoms for investigating peatland hydrological change, this study established a training set consisting of diatom composition and twelve environmental factors from 105 surface samples collected from five Sphagnum peatlands in northeastern China. Diatom communities were dominated by Eunotia species. Ordination analyses showed that depth to the water table (DWT) was the most important factor influencing diatom distribution, independently accounting for 4.99% of total variance in diatom data. Accordingly, a diatom-based DWT transfer function was developed and thoroughly tested. The results revealed that the best-performing model was based on weighted averaging with inverse deshrinking (R 2 = 0.66, RMSEP = 8.8 cm with leave-one-out cross validation). Quantitative reconstruction of DWT on a short peat core collected from the Aershan Peatland (Inner Mongolia) recorded climate-mediated hydrological changes over the last two centuries. This study presents the first diatom-water table transfer function in Sphagnum peatlands, and highlights the potential of diatoms as a powerful tool to assess the magnitude of past hydrological changes in peatlands of northeastern China, as well as similar peat environments worldwide.

Accurate chronologies for recent sediments of shallow lakes in the Yangtze floodplain are critical to calibrate proxy records for reconstructing environmental changes during the past century. This study presents the results of detailed 210 Pb analysis from eight lake sediment cores collected from the middle Yangtze reaches, southeast China. Unsupported 210 Pb activities generally declined exponentially with mass depth in the eight cores. The chronologies and sedimentation rates for the sediment cores were calculated using different 210 Pb-based mathematical models. The 137 Cs chronomarker (i.e. the 1963 fallout peak) and the spheroidal carbonaceous particle (SCP) chronomarker (i.e. the start of the rapid increase in 1970 AD) were selected to validate the 210 Pb dating. Sedimentation rates derived from different models were validated using historical data including lake area, arable land area, sediment discharge and reservoir volume in the Yangtze basin. The SCP-corrected CRS (constant rate of supply) model performs better than other models, based on validation using historical documents in the Yangtze basin. The 137 Cs chronomarker might be erroneous due to catchment-driven 137 Cs inputs from soil erosion and post-depositional diffusion. Both SCPs and 137 Cs are susceptible to inputs from catchment soil erosion, but SCPs showno apparent degradation and post-depositional changes in lake sediments. The SCP profile provides a relatively reliable chronomarker, which can be used for validating 210 Pb chronologies in these floodplain lakes. Generally, sedimentation rates in the eight lakes were less than 0.2 g cm -2 yr -1 before the 1930s, and then increased to a peak in the 1960s. Afterwards, sedimentation rates decreased and remained low after the 1980s.

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Urbanization is altering water quality and biotic communities of lake ecosystems worldwide, especially in developing regions. In this study, the diatom community structure and water quality of the epilimnion were analyzed in 38 lakes (40 sampling sites) in Wuhan City (central China) to assess the impacts of urbanization on lake ecosystems. Diatom communities displayed clear variation along the urban-to-rural gradient, with blooms of eutrophic species found in urban lakes in contrast to higher abundances of mesotrophic or oligotrophic taxa in rural lakes. Redundancy analyses revealed that the diatom community recognition to species, genus, and ecological guild level were all significantly correlated with Chl a, Si, and secchi depth, indicating that the changes in diatom communities were mainly explained by differences in nutrient concentrations and light condition. Considering the rapid urbanization and population expansion, it is important to carry out effective measures for the protection of these lake ecosystems, especially by reducing sewage discharge. The high consistency found between diatom community classification and water quality status highlights the applicability of diatoms for bioindication of shallow urban lakes, especially in rapidly developing cities. Even the taxonomic determination at the level of genera or ecological guilds can enable rapid water-quality assessment. K E Y W O R D S diatoms, ecological guild, redundancy analysis, the Yangtze floodplain, urban lakes, Wuhan City