[Spatial-temporal Variation in Water Quality of Rain-source Rivers in Shenzhen from 2015 to 2021 and Its Response to Rainfall].

Rain-source urban rivers have the characteristics of small water capacity， lack of dynamic water supply， and being easily polluted. This study analyzed the spatial and temporal distribution characteristics of river water quality and the response of characteristic pollutants to rainfall based on daily rainfall data and 21 water quality indicators of nine major river basins in Shenzhen （excluding Shenzhen-Shantou） from 2015 to 2021 by using the single-factor assessment method， comprehensive pollution index method， hierarchical cluster analysis， and Pearson correlation. The results showed that： ① in 2015， the water quality of most sections in the whole region was inferior Class V water. After October 2018， the overall water quality of rivers was greatly improved， which was consistent with the background of Shenzhen's special water control activities in 2018. By 2021， the water quality of approximately 62% of sections reached Class Ⅰ-Ⅲ water standards. ② The water pollution in the densely populated western part of Shenzhen was more serious than that in the eastern part， and the water pollution in the lower reaches of the estuaries and tributaries was more serious than that in the upper reaches. ③ The water quality of the Pingshan River， Guanlan River， Longgang River， and Maozhou River was significantly affected by rainfall. ④ The main characteristic pollution indexes of the Shenzhen River were DO， permanganate index， COD， BOD5， NH4+-N， TP， petroleum， and anionic surfactant. For the Pingshan River and Longgang River， rainfall increased the concentrations of TP and NH4+-N. For the Maozhou River， rainfall increased the concentrations of TP and COD. For the Shenzhen River， rainfall increased the concentrations of COD， TP， and NH4+-N. The above results reveal the spatio-temporal variation in rain-source river water quality in Shenzhen and its response to non-point source pollution caused by rainfall events and provide a scientific reference for building a higher quality water environment in Shenzhen.

Seawater intrusion on the west coast of Shenzhen during 1980-2020 due to the influence of anthropogenic activities.

Anthropogenic activities are considered key factors to affect the evolution of seawater intrusion (SWI) status. Understanding the relationships between anthropogenic factors and SWI development is crucial to formulate strategies that are used to mitigate groundwater salinization in coastal areas. In this study, we analyzed changes in land use on the west coast of Shenzhen, Guangdong province, China, over the recent four decades based on remote sensing data, and evaluated the SWI degrees in three historical stages during 1980-2020 based on the hydrochemistry data. Then, combining the timelines of groundwater exploitation, land use, land reclamation, and groundwater salinization, we presented the evolution of SWI affected by anthropogenic activities on the west coast of Shenzhen. It is found that the SWI can be divided into three stages: 1988-1999, a fully developing period; 2000-2009, a partly degrading period; and 2018-2020, a fully degrading period. The interface of saline and fresh groundwater paralleling with the coastline advanced 2 km inland in 20 years and took the next 20 years to retreat about 1 km. The interface advancing and retreating correspond to the excess and the prohibition of groundwater exploitation, respectively. Meanwhile, the construction and demolishment of high-position saltwater aquaculture areas, respectively, corresponded to the increase and decrease of Cl- concentrations in these areas. Besides, the correlation between seawater mixing index (SMI) values and Na+ concentrations became much lower during the desalination of groundwater, which can be considered direct evidence for the SWI retreat.

Salt precipitation and associated pressure buildup during CO2 storage in heterogeneous anisotropy aquifers.

CO2 can be injected into deep saline aquifers for storage, thereby reducing the concentration of CO2 in the atmosphere. When CO2 is injected into the aquifer, salt precipitation may occur, which may impair the injectivity and affect storage safety. In this study, numerical simulation was used to study salt precipitation in heterogeneous anisotropic sandstone aquifers, the feedback effect of salt precipitation on the flow was considered, and the additional pressure increase caused by salt precipitation was evaluated. The results showed that the maximum decrease in formation permeability and the maximum additional pressure buildup caused by salt precipitation reached 88% and 4.91 MPa, respectively. The salinity of the formation water and the maximum additional pressure buildup is approximately proportional when the salinity is low. Once the salinity exceeds a certain value (approximately 20% in this study), the maximum additional pressure buildup increases sharply. As the permeability increases, the additional pressure buildup decreases. When permeability reaches a certain threshold (approximately 5×10-14 m2 in this study), the maximum additional pressure buildup decreases rapidly and changes only slightly as permeability increases. The CO2 injection rate is basically proportional to the maximum additional pressure buildup. When the vertical permeability increases, the additional pressure buildup due to salt precipitation shows a downward trend. The low-permeability interbeds above the CO2 injection well will cause more local salt precipitation near it, which will further cause a greater and wider pressure buildup. The heterogeneity of the formation will greatly enhance salt precipitation, thereby promoting the formation pressure buildup. The formation heterogeneity must be considered in the study of the salt precipitation and its effect on CO2 injection, especially when the formation permeability is low, the CO2 injection rate is high, and the salinity of the formation water is high.

Wingspan stenting with modified predilation for symptomatic middle cerebral artery stenosis.

OBJECTIVES: Our purpose was to assess the feasibility, safety, and effectiveness of a modified predilation for middle cerebral artery (MCA) stenosis. BACKGROUND: Wingspan stenting of MCA remains a technical challenge, and rates of residual stenosis and restenosis must be lowered. METHODS: A series of 48 patients with symptomatic MCA stenosis greater than 50% and refractory to medical therapy underwent Wingspan stenting with different balloon/artery ratios before (group 1, Boston guidelines predilation) or after (group 2, modified predilation) July of 2008. Technical success, periprocedural complications, recurrent symptoms, and restenosis were assessed retrospectively, and risk factors for restenosis were analyzed using logistic regression. RESULTS: Successful stenting occurred in 48 of 49 (98%) lesions. Primary endpoints within 30 days included one (2.12%) minor stroke and two (4.26%) transient ischemic attacks. Stenoses were reduced from 77.11% ± 10.09% to 27.50% ± 6.91% in group 1 versus from 72.56% ± 10.46% to 8.20% ± 5.41% in group 2. A total of 43 patients were followed up for 12.92 ± 5.08 months, and recurrent stroke or transient ischemic attack occurred in two (4.65%) patients. Vessels were followed with transcranial Doppler (43 vessels), angiography (23 vessels), or computed tomographic angiography (one vessel). The restenosis rate was 8 of 18 (44%) in group 1 and 3 of 25 (12%) in group 2. Restenosis was associated with residual stenosis and diabetes. CONCLUSIONS: Wingspan stenting for symptomatic MCA stenosis can be performed with high success and low complication rates, and modified predilation with the Gateway balloon can reduce the rates of residual stenosis and restenosis.