The North China Plain (NCP) has been suffering from groundwater storage (GWS) depletion and land subsidence for a long period. This paper collects data on GWS changes and land subsidence from in situ groundwater-level measurements, literature, and satellite observations to provide an overview of the evolution of the aquifer system during 1971–2015 with a focus on the sub-regional variations. It is found that the GWS showed a prolonged declining rate of ?17.8?±?0.1 mm/yr during 1971–2015, with a negative correlation to groundwater abstraction before year ~2000 and a positive correlation after ~2000. Statistical correlations between subsidence rate and the GWS anomaly (GWSA), groundwater abstraction, and annual precipitation show that the land subsidence in three sub-regions (Beijing, Tianjin, and Hebei) represents different temporal variations due to varying driver factors. Continuous drought caused intensive GWS depletion (?76.1?±?6.5 mm/yr) and land subsidence in Beijing during 1999–2012. Negative correlations between total groundwater abstraction and land subsidence exhibited after the 1980s indicate that it may be questionable to infer subsidence from regional abstraction data. Instead, the GWSA generally provides a reliable correlation with subsidence. This study highlights the spatio-temporal variabilities of GWS depletion and land subsidence in the NCP under natural and anthropogenic impacts, and the importance of GWS changes for understanding land subsidence development. 相似文献
Alpine timberline is a proper indicator of climate change and has received much attention in ecological research during the past decades. In this study, variations of alpine timberlines and their biogeographic characteristics were investigated by a combination of field surveys, climate indices, and soil nutrient analyses in the northern Tianshan Mountains (NTM) of northwest China. The timberline altitudes were probed to range from 2,530 to 2,800 m a.s.l. in the NTM, gradually descending from west to east along the V-shaped Ili valley (from Zhaosu to Xinyuan), and ascending from west to east across the northernmost range of the study area (from Bole to Balikun). The vertical widths between the upper and lower limits of the timberlines were widest in the middle NTM (Kuytun to Changji) and the Ili valley (Zhaosu to Xinyuan). Interactions between the terrain and air currents resulted in variant climates within the NTM, which contributed to significant timberline distribution differences. Although vertical width was positively correlated to soil nutrient (especially organic matter, r = 0.78), and timberline altitudes were positively related to the soil pH values, the temperature during the growing season primarily determines both altitude and vertical width. In conclusion, timberline altitudes were dominated by the combined effects of local topography, soil nutrient properties, water, and thermal conditions. Identifying the dominating influencing factors of NTM timberlines provided potential insights to better understand the effects of climate change on the alpine ecosystem over central Asia. 相似文献
Sediment samples were collected at 17 stations in the central Bohai Sea, China, and the diversity and community structure of eukaryotic microalgae were assessed by metabarcoding the V4 region of 18S rDNA. A total of 930 operational taxonomic units (OTUs) were detected for microeukaryotes, including 98 algal OTUs. The algal communities comprised 42 genera belonging to 19 classes of six phyla, and they were dominated by chrysophytes and dinoflagellates. Dinoflagellates were also the most diverse microalgal group. The nano-sized dinoflagellates Biecheleria halophila and Azadinium trinitatum occurred abundantly in the study area; however, they have not been reported previously, as they may be overlooked or misidentified in light microscopy. Many pico-sized chlorophytes were detected in the sediment samples. Sixteen of the detected OTUs were assigned to potentially harmful and/or bloom-forming microalgae, suggesting some potential risks of harmful algal blooms in the central Bohai Sea. The capacity of metabarcoding to detect morphologically cryptic and small species makes this method a sufficiently sensitive means of detection for assessing eukaryotic microalgae in sediments.