Salinity and pH related microbial nitrogen removal in the largest coastal lagoon of Chinese mainland (Pinqing Lagoon).

Coastal lagoon is critical habitat for human and provides a wide range of ecosystem services. These vital habitats are now threatened by waste discharge and eutrophication. Previous studies suggest that the pollution mitigation of coastal lagoon relies on the water exchange with open sea, and the role of microbial processes inside the lagoon is overlooked. This study takes the Pinqing Lagoon which is the largest coastal lagoon in Chinese mainland as example. The distribution of nutrients, microbial activity of nitrogen removal and community structure of denitrifying bacteria in sediment are analyzed. The results showed that the nutrient in sediment represented by DIN (1.65-12.78 mg kg-1), TOM (0.59-8.72 %) and TN (0.14-1.93 mg g-1) are at high levels and are enriched at the terrestrial impacted zone (TZ). The microbial nitrogen removal is active at 0.27-19.76 µmol N kg-1 h-1 in sediment and denitrification is the dominate pathway taking 51.44-98.71 % of total N removal. The composition of the denitrifying microbial community in marine impacted zone (MZ) is close to that of ocean and estuary, but differs considerably with those of TZ and transition zone (TM). The denitrification activity is mainly controlled by salinity and pH, and the denitrifying bacterial community composition related to the nutrient parameters of TN, TOM, etc. Our study suggested that the distribution of nutrients, microbial activity of nitrogen removal and community structure in Lagoon are the combined effects of terrestrial input and exchange with open sea. The microbial processes play important role in the nitrogen removal of coastal lagoon.

Reservoirs as high-efficacy sentinels of regional atmospheric pollution and precipitation: magnetic and chemical evidence from a typical subtropical reservoir in South China.

While there is a general sense that reservoirs can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. Here multiple-proxy analyses including 210Pb, grain size, heavy metals, magnetic parameters, and spheroidal carbonaceous particles (SCPs) were conducted for a sediment core from a typical subtropical reservoir in South China (Huangkeng Reservoir). 210Pb dating revealed that the core spans from ~ 1964 to 2019, with the sedimentary rate increasing during recent years. The sedimentary environment was mainly influenced by natural process (especially precipitation), along with the accumulation of Cr, Ni, Cu, V, As, Sb, and Co and most magnetic particles. However, four heave metals (Cd, Pb, Tl, and Zn) were found mainly from atmospheric deposition from industrial/agricultural activities in Huizhou City, which was also indicated by SCPs, S-ratio, and χARM/SIRM. According to temporal variation of SCPs, the atmospheric pollution history of nearby city (Huizhou City as the most close one) from 1964 was reconstructed. The study shows that reservoir sediments, especially in areas with few or no natural lakes, are high-efficacy and high-resolution achieves for research on environmental evolution in the Anthropocene related to global change and intensifying human activities.

Secular change of true polar wander over the past billion years.

The rate of movement of Earth's solid shell relative to its spin axis, or true polar wander, depends on variations in mantle convection and viscosity. We report paleomagnetic and geochronologic data from South China that constrain the rate of rapid true polar wander (>5° per million years) between 832 million years and 821 million years ago. Analysis of the paleomagnetic database demonstrates secular change of true polar wander related to mantle cooling and thermal structure across supercontinent cycles. True polar wander rates are relatively muted with a partially insulated mantle during supercontinent assembly and accelerate as mantle thermal mixing reestablishes with supercontinent breakup. Decreasing true polar wander rate through the Neoproterozoic was succeeded by overall smaller variations in the Phanerozoic. We propose that Neoproterozoic extensive plate tectonic activities enhanced mantle cooling, giving rise to a reduction in mantle convective forcing, an increase in mantle viscosity, and a decrease in true polar wander rates into the Phanerozoic.

Geochemical baseline establishment and pollution assessment of heavy metals in the largest coastal lagoon (Pinqing Lagoon) in China mainland.

Establishing geochemical baselines and assessment of heavy metal pollution in lagoon sediments are critical for providing guidance to coastal zone environmental management. We analyzed heavy metals in high-resolution sediment cores from Pinqing Lagoon in South China, and defined the baselines of common pollution elements with a significant anthropogenic contribution. With these baselines, a spatiotemporal pollution assessment revealed Cu and Cd as the predominant pollution metals in both core and surface sediments, although the ecological risk level in the interior lagoon remained low during the past ~170 years. Surface sediment pollution status indicate a significant spatial difference. The findings from this typical coastal lagoon evidence a strong self-clean capacity attributable to the frequent water-mass-energy exchange between the lagoon and the sea. Furthermore, despite the significant impact by the sea, the geochemical baselines are close to the catchment soil backgrounds that can be defined using a paleolimnological approach.

High-resolution reconstruction of typhoon events since ~1850 CE based on multi-proxy sediment records in a coastal lagoon, South China.

Coastal lagoon sediments provide continuous and high-resolution records of the activity of past typhoons. In this study, multiple proxies were analyzed with a core taken from Pinqing Lagoon located on the northeast margin of the South China Sea. Based on 210Pb dating, grain sizes and other geophysical/geochemical analyses, a total of seven typhoon-induced layers covering the past ~170 years were identified and compared with observational and historical records of typhoons. The layers were characterized by a higher sand fraction, lower loss-on-ignition, decreased magnetic susceptibility, and increased element ratios of Sr/Fe, Sr/Ba, Ca/Ti, and Ca/K. We found reduced sensitivity of the sedimentary response to typhoons due to the coastal geomorphological evolution, such as sand spit growth, which emphasizes the value of using a multiple-proxy approach. The typhoon activity revealed by both sedimentary proxies and observational/historical records in Shanwei was closely related to the variations of the El Niño/Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and to sunspot activity, providing useful clues for reconstructing the long-term typhoon history in the lagoon in order to decipher the patterns and mechanisms of typhoons in South China.