Comprehensive Analysis and Artificial Intelligent Simulation of Land Subsidence of Beijing, China

Mechanism and modeling of the land subsidence are complex because of the complicate geological background in Beijing, China. This paper analyzed the spatial relationship between land subsidence and three factors, including the change of groundwater level, the thickness of compressible sediments and the building area by using remote sensing and GIS tools in the upper-middle part of alluvial-proluvial plain fan of the Chaobai River in Beijing. Based on the spatial analysis of the land subsidence and three factors, there exist significant non-linear relationship between the vertical displacement and three factors. The Back Propagation Neural Network (BPN) model combined with Genetic Algorithm (GA) was used to simulate regional distribution of the land subsidence. Results showed that at field scale, the groundwater level and land subsidence showed a significant linear relationship. However, at regional scale, the spatial distribution of groundwater depletion funnel did not overlap with the land subsidence funnel. As to the factor of compressible strata, the places with the biggest compressible strata thickness did not have the largest vertical displacement. The distributions of building area and land subsidence have no obvious spatial relationships. The BPN-GA model simulation results illustrated that the accuracy of the trained model during fifty years is acceptable with an error of 51% of verification data less than 20 mm and the average of the absolute error about 32 mm. The BPN model could be utilized to simulate the general distribution of land subsidence in the study area. Overall, this work contributes to better understand the complex relationship between the land subsidence and three influencing factors. And the distribution of the land subsidence can be simulated by the trained BPN-GA model with the limited available dada and acceptable accuracy.

Sustainable utilization measures of groundwater resources in Beijing

Groundwater is the main source of water supply for Beijing. Through analysis of the water resources in Beijing from 1980 s up to now, this paper finds the major problems in the exploitation and utilization of groundwater in Beijing lie in the over-exploitation and pollution in groundwater, which are primarily caused by the rapid growth of population, enduring imbalance between exploitation and replenishing of groundwater and the contamination of groundwater. Thus based on this, this paper puts forward proposals and opinions to exploit groundwater in a scientific and moderate way, and to comprehensively protect the groundwater resources and environment in Beijing.

Impacts of Human Activities on the Occurrence of Groundwater Nitrate in an Alluvial Plain: A Multiple Isotopic Tracers Approach

Nitrate pollution is a severe problem in areas with intensive agricultural activities. This study focuses on nitrate occurrence and its constraints in a selected alluvial fan using chemical data combined with environmental isotopic tracers （180, 3H, and lSN）. Results show that groundwater nitrate in the study area is as high as 258.0 mg/L （hereafter NO3） with an average of 86.8 mg/L against national drinking water limit of 45 mg/L and a regional baseline value of 14.4 mg/L. Outside of the riparian zone, nitrate occurrence is closely related to groundwater circulation and application of chemical fertilizer.High groundwater nitrate is found in the re- charge area, where nitrate enters into ground- water through vertical infiltration, correspond- ing to high 3H and enriched 1SO in the water. In the riparian zone, on the contrary, the fate of groundwater nitrate is strongly affected by groundwater level. Based on two sampling tran- sects perpendicular to the riverbank, we found that the high level of nitrate corresponds to the deeper water table （25 m） near the urban center, where groundwater is heavily extracted.Groundwater nitrate is much lower （〈12.4 mg/L） at localities with a shallow water table （5 m）, which is likely caused by denitrification in the aquifer.