Approaching the tipping point?

Erhai_hu_panorama_Apr19

From Kunming we travelled by train 200 km to the east, to Dàlī, which sits between Ērhāi Hú (literally ‘ear-shaped lake’), another of Yúnnán’s plateau lakes, and the Cāng Shān mountains.  These rise to about 4000 metres and still, even at this time of year, have patches of snow near their summits.   Dàlī’s old city has escaped the ravages of modernisation that have blighted many Chinese cities and we spent hours wandering the narrow streets lined with the traditional Bai architecture, along with a very large number of Chinese tourists.

On one day we hired bicycles and cycled along quiet roads lined with market gardens to reach the lake, then turned north and followed the lake shore for about five kilometres.  There were many areas of semi-natural shoreline along this stretch, with a fringe of wetland, but the filamentous algae (mostly Cladophora) coating the rocks that had been piled up along the settled parts of the shoreline told their own story.  This lake is clearly in better health than Diān Chí but it, too, is nutrient-rich.

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A fringe of filamentous algae, along with floating leaves of Trapas natans(Eurasian water chestnut) growing on a jetty beside Ērhāi Hú.

Just after midday we pulled into a small family-run restaurant at the edge of a village.   A short conversation between the waitress and Ed (our only Mandarin-speaker) revealed that they specialised in serving fish from the lake so that seemed to be the obvious choice for our lunch.  The waitress disappeared, then reappeared with a net which she dunked into a tank behind our table and, with a couple of deft flicks, pulled it up with two carp wriggling inside.   These she quickly dispatched, cleaned and took into the kitchen.   About twenty minutes later she reappeared with a delicious stew comprising the whole fish cut into chunks, a generous seasoning of dried red chilli and tongue-numbing Sichuan pepper, lightly-pickled vegetables (white radish, celery and turnip) and some green leaves.   This, along with rice and endless green tea, and with Ērhāi Hú as a backdrop, created a perfect lunch for appetites whetted by our exercise.

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From tank to table in twenty minutes: our fish stew made from carp from Ērhāi Hú.

We had seen some locals fishing with poles, and there is also some commercial fishing using cormorants in the area. However, the abundance of fish on the menu confirmed my hunch that the many booms we could see across bays along the lakeshore were fish farms (maybe ‘fish ranches’ is a more appropriate term when the fish have, relatively speaking, plenty of space in which to roam and forage).   The nutrients pouring into the lake here are, at least, able to support a economically-viable industry rather than undermine the supply of resources, as is the case for Diān Chí.

Of course, the story is not that simple.   In the past, Ērhāi Hú, like Diān Chí, had some endemic species, found nowhere else, but these have not been recorded for about 20 years.   Pollution from surrounding cities is the most likely explanation and, if Ērhāi Hú is in a better state than Diān Chí, then this is partly because the lake is larger and deeper, the catchment area is bigger and the scale of urban development is smaller (Dàlī is about a twentieth of the size of Kunming).  That said, local scientists have identified a significant declining trend in water quality, particularly over the past 25 years.   Importantly, however, they also note that it is not too late to do something about the situation.

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Fishermen cleaning their nets beside Ērhāi Hú.  

In brief, nutrient concentrations in Ērhāi Hú are increasing. That leads to a more productive ecosystem which is, up to a point, good for commercial fishing but also means that oxygen concentrations drop, which is bad for the fish.   High nutrient concentrations also mean more algae but, at the present, these are not so high that cyanobacterial blooms develop as they have done in Diān Chí.  That means that the water in the lake can still be used as a drinking water supply for Dàlī and its environs.   However, if nutrient concentrations rise further then oxygen concentrations may pass a tipping point when it becomes almost impossible to manage lake phosphorus concentrations.

This is because phosphorus and other nutrients accumulate over time in lake sediments.  Phosphorus is not very soluble in the presence of oxygen, but becomes more soluble as conditions in the sediment and overlying water turn anoxic.   That means that when dissolved oxygen concentrations fall to the point where there is none at the sediment surface, the sediments are no longer a ‘sink’ for excess phosphorus, but become a ‘source’, releasing the stored nutrients back into the water.   From this point forwards, eutrophication in the lake becomes self-perpetuating and no amount of regulation alone will reverse this.

Better regulation now, on the other hand, might prevent the lake reaching this stage.  That, in turn, will protect the drinking water supply for the region, the economic benefits from the fishery and other ecosystem services. A survey of the local community revealed a willingness to pay an extra 27 Yuan a month for five years continuously in order to achieve this.  This is a small sum in absolute terms (27 Yuan is just over £3), but represents, on average, 1.7% of household income.   The economics of water quality improvement must look even more attractive to the regional government: if Ērhāi Hú crosses this tipping point then the investment in alternative water supplies, as was required in Kunming, will be equally expensive.  Looking at it from this perspective, applying a sensible ‘polluter pays’ policy now should be no more painful for the average resident than having to pay for new reservoirs to replace the resource on their doorstep.

The stretch of lakefront along which we cycled also had a steady trade in photographs, with photographers ready with diaphanous dresses for prospective models, and a number of ways for them to pose.  The girls in the photograph below posed, informally, on stones whilst friends photographed them using smartphones, but some photographers placed their models on the tops of jeeps or in hanging chairs, with an uninterrupted view of the lake behind. In their own way, they were valuing the broad scale panorama that the lake offered, just as we had enjoyed more local offerings during our lunch.  The challenge for the next decade, then, is to make the links between these valuations and the ecology of the lake, so that any price increases are recognised as sound investments in the future of Dàlī rather than as yet another form of negative taxation.

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Women posing for photographs with Ērhāi Hú as a backdrop

References

Wang, H., Shi, Y., Kim, Y. & Kamata, T. (2015).  Economic value of water quality improvement by one grade level in Erhai Lake: a willingness-to-pay survey and a benefit-transfer study.   Frontiers of Economics in China 10: 168-199.

Wang, S., Zhang, L., Ni, L., Zhao, H., Jiao, L., Yang, S., Guo, L. & Shen, J. (2015). Ecological degeneration of Erhai Lake and prevention measures.  Environmental Earth Sciences74: 3839-3847.

Zhang, K., Dong, X., Yang, X., Kattel, G., Zhao, Y. & Wang, R. (2018).  Ecological shift and resilience in China’s lake systems during the last two centuries.  Global and Planetary Change165: 147-159.