3.6 References co-cited analysis in hydrological connectivity
research area
The co-cited analysis of references can obtain the scientific
development and intellectual structure of related topics. Clustering
analysis can aggregate literatures in related fields and identify the
clusters (Ouyang et al., 2018). As shown in Fig. 8, the larger cluster
means containing more terms, and the silhouette values of the top ten
clusters we obtained are all over 0.5, which indicates that the cluster
we generated is reasonable (Kaufman and Rousseeuw, 1990). The TF-IDF
(term frequency-inverse document frequency), a commonly used weighting
technique for information retrieval and data mining, is used to label
the clusters. It can be seen in Fig. 8 that “amphibians” is the
largest (#0) cluster, which also indicates that amphibians and
biodiversity as well as ecosystem are the most productive area about
hydrological connectivity. The second (#1) is the “channel network”,
which means that soil erosion, sediment dynamics and river-floodplain
interaction influenced by climate change and human activities also
attract many researchers’ attention. Moreover, the study of channel
network also provides better suggestions for the management of
hydrological connectivity. Followed is “transport” (#2), the research
of which is mainly focuses on the transport and utilization of water
resources, agriculture and Nitrogen source. The No. 4 - No.9 clusters
are “temporary rivers”, “hillslope scale”, “hyporheic zone”,
“downstream waters”, “giws (geographically isolated wetlands)” and
“soil”, respectively.
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Please Place Figures 8 here
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The timeline visualization displays the research time span of each
cluster, as well as recent research hotspots. It can be seen from Fig. 9
that “transport” (#2) is the earliest research topic relate to
hydrological connectivity and almost lasted from 1990 to nearly 2007,
followed by “amphibians” (#0) from 1992 to 2005. In addition,
“channel network” (#1) might have highly cited or citation bursts or
both due to much of them has large size nodes, and the primrose yellow
color means they attracted the most attention on the hydrological
connectivity research recently. Moreover, giws (#8 “geographically
isolated wetlands”) has the same primrose yellow as channel network,
which means it is also a new hot topic. Studies have often focused on
direct connectivity of water systems, ignoring the connectivity brought
by geographically isolated wetlands might be affected by climate
responses, such as rainfall and evapotranspiration. As an emerging
research direction, the
“geographically isolated wetlands” has attracted a lot of attention,
and since it started later than the channel network (as shown in Fig.
8), it might indicate that geographically isolated wetlands will be the
next research hotspot in the research of hydrological connectivity.