The Nu River, known downstream as the Salween, represents the last of Southeast Asia’s great rivers with no dams in its mainstream.
The Nu is a critically important river in Asia. It represents a final refuge for many endemic fish species, and it also boasts riparian areas and forested slopes that support the region’s unique biodiversity. This region supports species including the now-famous sneezing snub-nosed monkey (Rhinopithecus strykeri), which was only described in 2011 and scientists agree that they likely have yet to describe a significant number of species.
Yet this fragile and unique region, like so many areas surrounding Asia’s great rivers, is under threat. A combination of land conversions, hunting, harvesting and mining has encroached on the region’s biodiversity scarring and degrading the land and filling the rivers with sediment.
Since the 1960s, the forests that once almost covered the Nu River’s banks have shrunk to a fraction of their former size, only 24%of the region. Only around half of these remaining forests fall within protected areas, and just a quarter of protected areas themselves still retain forest. With further developments and new roads planned, we expect these forests to decrease further, and with them their diverse and unique communities.
Asia as a whole has long been plagued by dams. Between 1950 and the present, China alone has built more dams (over 22,100) than existed in the entirety of Asia in 1982. In 1950, it contained just 30% of the world’s dams (1541 dams), but this increased to 65% of the global total by 1982 (22,701) (van der Leeden et al. 1990). Though these dams provide power for a rapidly growing population across Asia, they also come at a high cost to both humans and biodiversity.
A Sister River
Because the Nu has been so little studied, it may be useful to compare it to another major Asian river, the Mekong, to understand the implications of damming it.
Along the Mekong, over 58 million people rely on fish for 80% of their dietary protein. The 20% estimated reduction in migratory fish biomass resulting from the development of only a small portion of the planned dams means a loss of livelihoods for many of the people of the region. To try to make up this protein inevitably means more grazing, and the further encroachment of native forests in the regions of the river not directly inundated by water.
This represents the forgotten impacts of dams on local communities and economies. Once the dam is built and the construction jobs are over, many people may have lost homes, livelihoods and even their traditional diets. Once the jobs are gone and the power is exported, only the developers and government are likely to feel the ongoing benefits from the dam.
In these dammed regions, the small pockets of hilltop forests are left as islands that will slowly lose their species. Eventually, once-rich communities may be reduced to a single species, such as a close cousin to the ubiquitous rat (Rattus tiomenticus; Gibson et al., 2014), while mainlands may see increased hunting pressure from a population seeking an alternate source of protein after having lost such a large proportion of their diverse fish biota (over 1200 known species).
Though the Nu officially has no dams, a brief examination of its side streams tells a more complex tale. Many of the Nu’s tributaries have already been blocked by hundreds of small dams; as a result, the water temperature of the mainstream has risen, and the oxygen content has reduced considerably.
A team of researchers from the Kunming Institute of Zoology have been monitoring the mainstream for over a decade, and proudly boast of the many endemic species with suffixes of nujiangensis and gongshanensis. Yet that same team also indicates another critical column in their datasheet: the last time they recorded each of the species present. For many of these endemic species, that column indicates that many species have not been seen in the last eight years. The team fears these species are already extinct as a result of changing river conditions and overfishing.
To exacerbate this loss, a visit to the Nujiang last October uncovered a number of new non-native species that had never previously been recorded in the region. These newly imported species have been brought in to replace the declining native species in people’s diets, but their introduction may spell the end for many of the region’s already-threatened fish.
So what would the currently planned dams do to a region which has already seen the loss of so many of its former forests, the sedimentation and overfishing of its rivers, and the steady loss of endemic plants and animals through hunting and trade? These dams have been planned and surveyed, but their future – and with it the fate of the region’s biodiversity – is still under discussion.
Many species in the region are scarcely surviving at present, and for the majority of main river fish, it may already be too late to save these species. However, the development of dams on the main stream, and the resulting infrastructural development, would in all probability accelerate deforestation in the areas that still retain their forests.
Moreover, further damming of the smaller tributaries, especially further upstream, would undoubtedly spell disaster for many of the smaller species, and species which use these quiet streams as nurseries. The tributaries are crucial for the long-term survival of such species, and though further damming has recently been “banned”, the actual enforcement of such a policy in these small and remote tributaries may have little effect on the development of small dams on smaller streams and tributaries.
Damming the Nu or its tributaries would also inundate areas of forest, which are known refuges for a number of endemic species. The inundation of lower-altitude regions of the river would also push the people upslope, onto steeper and more marginal land. In addition to increasing the probability of landslides and destroying further forest, people would likely need more land to produce sufficient crops for their needs, and the increased development of infrastructure would likely open new, vulnerable areas to exploitation.
Currently the Nu represents the one last undammed great river in Southeast Asia. Yet it is already a fragile area that has lost much of its former diverse and endemic biota. A dam would likely ring the death knell for many of the species on the brink of extinction in on its banks or in its waters.
Alice C. Hughes is Principal Investigator Landscape Ecology, Xishuangbanna Tropical Botanic Garden, Chinese Academy of Sciences. She is also ATBC Asia-Pacific Secretary & ATBC Capacity Building Committee Chair.