# A Vulnerable Environment Study in Karst Regions between 1991 and 2017: A Bibliometric Analysis
## 3 Results and Discussion  
### Author Keywords Analysis  
The co-occurrence relation of the keywords of SCI/SSCI journal articles about \"vulnerable karst environment\" (Figure 4) was analyzed and the result showed that the research interests were focused  
Figure 3: Publishing trend in the area of “vulnerable karst environment”. on the following areas: (1) The frequent occurrence of the keywords related to karst water environment, such as \"groundwater\", \"karst aquifer\", and \"spring\", indicated that karst water environment had attracted more attention. (2) The frequent occurrence of cave environment related keywords, such as \"cave\", \"sinkhole\", \"speleothem\", and \"speleogenesis\" implicated that cave environment study was an important research focus. (3) Those keywords such as \"hydrochemistry\", \"geochemistry\", \"geomorphology\", and \"hydrogeology\", suggested the branches of vulnerable karst environment study. (4) The nation identity related keywords such as \"China\", \"Italy\", and \"Spain\" suggested the increasing influence of these countries in the field of vulnerable karst environment research. In addition, the stable isotope method, technology of geographic information system (GIS), conservation of karst ecosystem, and climate change are also important issues. Karsh hydrology and cave environment study received stable and continued attention; stable isotope and GIS technologies rapidly progressed, yet they still account for a small proportion in the research field. The results of our study revealed the inevitable trend of conducting comprehensive studies, which 3-dimentionally combine the above and underground elements, for the purpose of securing ecological safety. By investigating the burst terms in vulnerable karst environment researches (Figure 5), the keyword \"karst\" was found at the top of the list with intensity of 7.761. Its impact duration was from 1991 to 1996. Keyword \"hydrology\" with intensity of 4.3264 ranked the second and its impact duration was from 1994 to 2008. Keyword \"biogeography\" with its intensity of 3.4869 and impact duration from 1994 to 2009 took the third position. Then there was a surging of keywords including \"Slovenia\" (intensity: 5.9329; impact duration: 2002-2009), \"karst hydrology\" (8.6885; 2003-2009), and \"speleogenesis\" (6.3853; 2009-2011). The burst terms appeared recently included \"carbon isotope\" (5.7482; 2010-2012), \"new specy\" (4.8023; 2010-2014), \"Croatia\" (4.4348; 2010-2014), \"Dinaric karst\" (4.348; 2010-2012), \"karst groundwater\" (4.1339; 2010-2013), and \"modeling\" (3.4386; 2010-2014). Those keywords have clearly depicted the flowchart of vulnerable karst environment research progress, which is from process and mechanism research to application and modeling research. Figure 4: The co-occurrence relation of keywords about “vulnerable karst environment” in SCI/SSCI journal articles published from 1991 to 2017. Figure 6 shows the clustering graph of keywords about \"vulnerable karst environment\" appeared in SCI/SSCI journal articles from 1991 to 2017, from which several clusters formed in the past 27 years in the field can be detected. (1) The karst water environment related keywords, such as \"k karst\", \"groundwater\", \"hydroology\", \"contamination\", and their interrelation indicated that karst water environment had drawn more attention. (2) The fact that keywords \"speleothem\", \"organic matter\", \"stable isotope\", and \"carbonate\" were clustered implicated that it was common to study the changes in karst ecosystem based on sediments in the karst region. (3) Keywords \"vegetation\", \"cosystem\", \"biodiversity\", \"flow\" and \"land use\", \"precipitation\", \"climate change\" were grouped respectively, which suggested that ecosystem study and climate and land use research were both major directions of vulnerable karst environment researches.