Blooms from above

Dianchi_lake_cyano_bloom

Saturday’s excursion saw us travelling to the southern end of the Kunming metro and joining a procession of locals trekking up the wooded slopes of the Xī Shān hills to the settlement of Lóng Mén (‘Dragon’s Gate’), which gave us some spectacular views over Diān Chí (Dian Lake) stretching away into the distance, After a lunch of fried noodles from one of the many takeaway stalls at Lóng Mén, we travelled back down to lake level by cable car, which gave us our second panoramic view of Cyanobacteria in three days.   The lake, China’s eighth largest, had a very conspicuous Cyanobacterial bloom that serves as the ‘yin’ to the Green Lake’s ‘yang’.

The environmental problems of Diān Chí are well known with an article in Newsweek describing it as the ‘ground zero of China’s toxic algae problem’.  The problems starts with Diān Chí’s location on a high plateau (1886 m above sea level) in Yunnan, which means that it has a relatively small catchment area relative to its size (40 km long, about 300 square kilometres area and with an average depth of 4.4 metres).   The city of Kunming sits at the north end of this lake and now has a population of over six million people.   For a long time, their untreated sewage was pumped directly into the lake, leading to high concentrations of phosphorus which, in turn, fertilised the lake water, allowing blooms of Microcystis aeruginosa to develop.   Many genera of Cyanobacteria, including Microcystis, produce potent toxins that attack the liver or nervous system, and which can cause skin rashes.

Unfortunately, the city of Kunming depended upon Diān Chí for its water supply in its past but now, due to this contamination, it has to rely upon reservoirs upstream of the city.  It has, according to the Newsweek article, invested $660 million dollars to reduce industrial pollutants, building sewage treatment works, intercepting polluted water and banning detergents containing phosphorus but that, as my photograph from the cable car shows, has had little effect.   There are two reasons for this.  The first of these is a reluctance to control fertiliser use in the productive agricultural areas to the west of the lake (China is not unique in this respect; a similar tardiness can be found in the West, where agriculture is a potent political lobby).  The second is that much of the phosphorus that was pumped into the lake in the past is still there, sitting in the sediments and being constantly recycled by the algae.  In small lakes it might be possible, albeit expensive, to dredge out this sediment but on a lake the size of Diān Chí this is an unimaginable prospect.

Another paper that I found online demonstrated a dramatic loss of higher plants and fish from Diān Chí. Since the 1950s, over half of all native higher plant species have been lost, along with 84 per cent of native fish.  Diān Chí also had a number of unique species, which evolved in this remote habitat, but 90 per cent of these, too, have been lost since the 1950s.  That is a catastrophe in biodiversity terms, but the collapse of the lake ecosystem also led to the loss of valuable commercial fisheries.  In the past, some of the fish and shellfish that we ate in local restaurants might have been bought from fishermen who worked the lake; now they have to be imported.

Dianchi_reaeration_equipment

A view from the cable car over Diān Chí, with yellow rafts bearing reaeration apparatus visible on the lake surface.  The picture at the top of the lake shows one edge of the Cyanobacteria bloom, with clearer water along a channel flushed by inflow from a lagoon.

We can see, in other words, another interesting case study in competing ecosystem services emerging. We might imagine a time in the far past when there was a balance between the use of the lake as a supply of resources (drinking water, fish and shellfish, irrigation water) was not compromised by the use of the lake’s natural biogeochemical cycles to break down any waste products that flowed in from the catchment.   More likely, human and animal wastes would have been recycled more directly as manure for local agriculture so, again, some sort of equilibrium would have pertained.   Now, we see the ‘provisioning’ services compromised due to the overuse of the ‘regulating’ services and, at the same time, opportunities for ‘cultural’ services such as recreation are also much reduced.

Thinking more widely, what about the ecosystem services lost due to the construction of the new water supply reservoirs around Kunming?   But then, rather than end on an overly sanctimonious tone, to what extent have we in the West, ‘solved’ some of our own environmental problems in recent decades through the contraction of our own manufacturing industries in the face of competition from countries such as China?  \

view_along_Dian_Chi

A view south along Diān Chí with the far shore, 40 km away, just visible in the distance.

References

Liu, J., Luo, X., Zhang, N. & Wu, Y. (2016).  Phosphorus released from sediment of Dianchi Lake and its effect on growth of Microcystis aeruginosaEnvironmental Science and Pollution Research23: 16321-16328.

Wang, S., Wang, J., Li, M., Du, F., Yang, Y., Lassoie, J.P. & Hassan, M.Z. (2013).  Six decades of changes in vascular hydrophyte and fish species in three plateau lakes in Yunnan, China.  Biodiversity and Conservation222: 3197-3221.

Zhu, L., Wu, Y., Song, L. & Gan, N. (2014).  Ecological dynamics of toxic Microcystis spp. and microcystin-degrading bacteria in Dianchi Lake, China.  Applied and Environmental Microbiology80: 1874-1881.

Notes:many authors, Western and Chinese, refer to ‘Dianchi Lake’.  However, as ‘chí’ means ‘lake’, I have just referred to ‘Diān Chí’ throughout.  See “Lake lakelake lake” for more about this. “La Grande Assiette de Lac Léman”  describes a similar conflict between ecosystem services in Lake Geneva, albeit with more positive outcomes.