mining threatens biodiversity and interferes with ecological processes through direct physical disturbance that degrades habitats and degrades water quality. With the rapid development of urbanization, the demand for sand mining will continue to increase, especially in Asia, Africa and Latin America. Many of the rivers and lakes in these areas, which are major sources of sand, are illegally exploited on a large scale. Some of these waters are also among the most biologically diverse and threatened ecosystems in the world. Alleviating the impact of sand mining and coordinating the contradiction between conservation and development are the key objectives of global biodiversity conservation, which requires a more comprehensive grasp of the scale and ways of sand mining threats to the ecological environment.
In view of the impact of sand mining on freshwater ecosystems, most of the current studies are descriptive or anecdotal warnings. For example, sand mining can interfere with macroinvertebrate movement, reduce the abundance and diversity of benthic fish and invertebrates, and lead to increases in exotic fish populations; and some of these effects have been identified as transient or specific to specific faunal groups; these findings are not sufficient to reveal indirect or long-term effects of sand mining. Therefore, how to make better use of existing technologies to monitor sand mining activities, assess the impact of sand mining on ecosystems, and provide targeted regulatory and protection recommendations is an urgent problem to be solved.
Remote sensing technology can overcome the limitations of data missing and based on field monitoring, and provide larger spatial and temporal scale data for the study of ecological impact caused by sand mining. The team led by Wang Kexiong, a researcher at the Institute of Hydrobiology, Chinese Academy of Sciences, presented the first case study of continuous monitoring of sand mining activities using remote sensing to assess the ecological impact of sand mining in Dongting Lake on the distribution of Yangtze finless porpoises over the past 14 years (2006-2019) (Figure 1, scope of study and identification of sand mining vessels).
Fig. 1 Spatial distribution of sand mining activities in Dongting Lake interpreted by remote sensing images. (A) Identification process of sand dredgers (B) Example: spatial overlap of 2006 Yangtze finless porpoise distribution (blue dots) and sand dredgers (red dots) for the time period corresponding to this survey & nbsp;
Dongting Lake is one of the most important sand mining areas in China. In 2011, the sand mining volume in Yueyang City alone was about 300 million tons, which is equivalent to 38% of the sand production in the United States in the same year. The research of the Institute of Aquatic Sciences shows that the sand mining activities in Dongting Lake show a consistent and extensive disturbance. Since 2007, the scope and intensity of sand mining have continued to increase; the period from 2008 to 2016 is a period of intensive sand mining with high mining intensity, and the sand mining area accounts for 40% -70% of the whole study area (Fig. 2).
Figure 2 The spatial distribution of sand mining activities from 2006 to 2017 (the orange color gradient represents the intensity of sand mining activities, and the percentage is the proportion of sand mining activities in the study area)
shows that large-scale sand mining activities have compressed the range of the Yangtze finless porpoise and limited its habitat use pattern in the lake. The Yangtze finless porpoise will strongly avoid sand mining areas, and there is a significant negative correlation between the probability of its occurrence and the intensity of sand mining in adjacent waters. During the period of intensive sand mining (2008-2016), there was a large blank area in the distribution of Yangtze finless porpoise (see Figure 3A). In the waters without sand mining, the Yangtze finless porpoise showed a continuous distribution, while all the waters with a distribution gap of more than 6 km had serious sand mining activities (see Figure 3C). Especially in 2009 and 2011, the distribution blank area of Yangtze finless porpoise reached 27 km and 20 km respectively, and the distribution area shrank most obviously.
Figure 3 Impact of sand mining on the distribution of Yangtze finless porpoise. (A) The spatial relationship between the distribution sites (blue dots) of the Yangtze finless porpoise and the sand mining area. The base map is the vector map of the water area during the survey of the Yangtze finless porpoise in the corresponding year. (B) The relationship between the distribution probability of the Yangtze finless porpoise and the relative sand mining intensity of the nearest sand mining zone. (C) The length
of the distribution gap of the Yangtze finless porpoise in the presence/absence of sand mining. In addition, the study found that sand mining activities also introduced a large number of sand carriers, which further hindered the migration of the Yangtze finless porpoise between rivers and lakes and affected the connectivity of the population (see Figure 4). In 2006 and 2007, the Yangtze finless porpoise was observed to enter the mainstream of the Yangtze River through the Dongting Lake Bridge. However, since 2009, no river-lake migration behavior has been found. Remote sensing results show that the disorderly operation and berthing of sand carriers cover almost the entire water surface (see Figure 4A), and the number of ships continues to grow from 2007 to 2016 (see Figure 4B), which is the main reason for the blockage of river and lake migration. Since the cessation of sand mining in the middle of 2017, at the suggestion of the research team of the Institute of Aquatic Sciences, the management department has dispatched these sand dredgers to set aside the Yangtze finless porpoise migration channel in the open water (see Figure 4A), which provides the possibility to promote the migration of rivers and lakes.
Figure 4 Number and distribution of sand dredgers on the Tongjiang waterway in Chenglingji, Dongting Lake (a) Image of the largest number of sand dredgers in the year. The blue dotted line is the Yangtze finless porpoise passage reserved since the cessation of sand mining in mid-2017. (B) Estimation
of the number of sand carriers The results of the study also show that from 2006 to 2017, sand mining resulted in the loss of nearshore habitats in about 70% of the study area (38.6 km2, dark red area in Figure 5), which are important feeding and breeding sites for aquatic organisms such as the Yangtze finless porpoise. Comparing 2006 and 2019, the water area in the study area increased by 75% during the dry season, and the meandering channel became wider and straighter.
Fig. 5 Status of habitat loss in the study area from 2006 to 2019 (dark red area)
The above study shows that the 14-year sand mining activities in Dongting Lake show a continuous and extensive disturbance, which affects the Yangtze finless porpoise through different temporal and spatial scales and different ways. Large-scale sand mining activities have compressed the range of the Yangtze finless porpoise and limited its habitat use pattern in the lake. Sand carriers further hinder the migration of the Yangtze finless porpoise and affect the connectivity of the population. In addition, nearshore habitat loss caused by sand mining occurred in about 70% of the waterways in the study area, and the nearshore habitat is an important feeding and breeding habitat for aquatic organisms such as the Yangtze finless porpoise, and its impact needs long-term attention.
Sand has become the world's second most mined resource after freshwater, with the United Nations Environmental Programme stating: "Fundamentally, improving the environmental impact of global sand mining requires an increased willingness to act". This study provides the first empirical evidence of the impact of unregulated sand mining on species distribution, and deepens the understanding of the impact of sand mining on freshwater ecosystems. The research methods can support the regulation of sand mining and species protection, and the results can provide a reference for sustainable sand mining worldwide.
The study was supported by the Strategic Key Research Program of the Chinese Academy of Sciences, the Key Research and Development Program of the Ministry of Science and Technology, the National Natural Science Foundation of China and the Ocean Park Conservation Foundation of Hong Kong. The result of the study is "Ecological impacts of unsustainable sand mining: urgent lessons learned from a critically endangered fresh water". "Cetacean" was published in Proceedings of the Royal Society B: Biological Sciences. Dr. Han Yi of the Institute of Aquatic Sciences is the first author of the paper, researcher Wang Ding and associate researcher Mei Zhigang are the corresponding authors, and researcher Wang Kexiong gives important guidance to the work. The co-authors also include Dr. Xu Wenjing of the University of California, Berkeley, and Liu Jiajia, a researcher at Fudan University. Dr. Zhang Xinqiao also contributed to this study by conducting the Yangtze finless porpoise expedition in Dongting Lake from 2006 to 2010 during his postgraduate study in the Institute of Aquatic Sciences.
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