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Persistent eutrophication and hypoxia in the coastal ocean
- Minhan Dai, Yangyang Zhao, Fei Chai, Mingru Chen, Nengwang Chen, Yimin Chen, Danyang Cheng, Jianping Gan, Dabo Guan, Yuanyuan Hong, Jialu Huang, Yanting Lee, Kenneth Mei Yee Leung, Phaik Eem Lim, Senjie Lin, Xin Lin, Xin Liu, Zhiqiang Liu, Ya-Wei Luo, Feifei Meng, Chalermrat Sangmanee, Yuan Shen, Khanittha Uthaipan, Wan Izatul Asma Wan Talaat, Xianhui Sean Wan, Cong Wang, Dazhi Wang, Guizhi Wang, Shanlin Wang, Yanmin Wang, Yuntao Wang, Zhe Wang, Zhixuan Wang, Yanping Xu, Jin-Yu Terence Yang, Yan Yang, Moriaki Yasuhara, Dan Yu, Jianmin Yu, Liuqian Yu, Zengkai Zhang, Zhouling Zhang
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- Journal:
- Cambridge Prisms: Coastal Futures / Volume 1 / 2023
- Published online by Cambridge University Press:
- 23 February 2023, e19
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- Article
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Coastal eutrophication and hypoxia remain a persistent environmental crisis despite the great efforts to reduce nutrient loading and mitigate associated environmental damages. Symptoms of this crisis have appeared to spread rapidly, reaching developing countries in Asia with emergences in Southern America and Africa. The pace of changes and the underlying drivers remain not so clear. To address the gap, we review the up-to-date status and mechanisms of eutrophication and hypoxia in global coastal oceans, upon which we examine the trajectories of changes over the 40 years or longer in six model coastal systems with varying socio-economic development statuses and different levels and histories of eutrophication. Although these coastal systems share common features of eutrophication, site-specific characteristics are also substantial, depending on the regional environmental setting and level of social-economic development along with policy implementation and management. Nevertheless, ecosystem recovery generally needs greater reduction in pressures compared to that initiated degradation and becomes less feasible to achieve past norms with a longer time anthropogenic pressures on the ecosystems. While the qualitative causality between drivers and consequences is well established, quantitative attribution of these drivers to eutrophication and hypoxia remains difficult especially when we consider the social economic drivers because the changes in coastal ecosystems are subject to multiple influences and the cause–effect relationship is often non-linear. Such relationships are further complicated by climate changes that have been accelerating over the past few decades. The knowledge gaps that limit our quantitative and mechanistic understanding of the human-coastal ocean nexus are identified, which is essential for science-based policy making. Recognizing lessons from past management practices, we advocate for a better, more efficient indexing system of coastal eutrophication and an advanced regional earth system modeling framework with optimal modules of human dimensions to facilitate the development and evaluation of effective policy and restoration actions.
Natural fractures in tight gas sandstones: a case study of the Upper Triassic Xujiahe Formation in Xinchang gas field, Western Sichuan Basin, China
- Yunzhao Zhang, Lianbo Zeng, Wenya Lyu, Dongsheng Sun, Shuangquan Chen, Cong Guan, Lei Tang, Jinxiong Shi, Junhui Zhang
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- Journal:
- Geological Magazine / Volume 158 / Issue 9 / September 2021
- Published online by Cambridge University Press:
- 18 March 2021, pp. 1543-1560
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The Upper Triassic Xujiahe Formation is a typical tight gas reservoir in which natural fractures determine the migration, accumulation and production capacity of tight gas. In this study, we focused on the influences of natural fractures on the tight gas migration and production. We clarified characteristics and attributes (i.e. dips, apertures, filling degree and cross-cutting relationships) of the fractures based on image logging interpretations and core descriptions. Previous studies of electron spin resonance, carbon and oxygen isotopes, homogenization temperature of fluid inclusions analysis and basin simulation were considered. This study also analysed the fracture sequences, source of fracture fillings, diagenetic sequences and tight gas enrichment stages. We obtained insight into the relationship between fracture evolution and hydrocarbon charging, particularly the effect of the apertures and intensity of natural fractures on tight gas production. We reveal that the bedding fractures are short horizontal migration channels of tight gas. The tectonic fractures with middle, high and nearly vertical angles are beneficial to tight gas vertical migration. The apertures of fractures are controlled by the direction of maximum principal stress and fracture angle. The initial gas production of the vertical wells presents a positive correlation with the fracture abundance, and the intensity and aperture of fractures are the fundamental factors that determine the tight gas production. With these findings, this study is expected to guide the future exploration and development of tight gas with similar geological backgrounds.