Testing the water

Zhu Jiang, deputy director of the prefecture's environmental monitoring station, joined an onboard water monitoring test out on the lake on Aug 22.

The weekly monitoring of 24 indexes takes place at 11 positions marked by geographic coordinates during the warm weather between July and November every year, to complement regular monthly monitoring sessions for 64 indexes.

At each position, Zhu and his colleagues take water samples, obtaining results for seven of the indexes at the scene, while leaving the rest to be analyzed at the laboratory.

That cloudy day, the water visibility at one of the intake points was 1.9 meters, about 0.2 to 0.3 meters better than same period two years previously, he says.

The 8 milligrams per liter of chlorophyll A, compared to over 15 mg/L in previous years during the summer months, together with an algal cell density of 17 million/L, suggest a relatively low algae concentration in the lake.

While there's not too much pressure to prevent cyanobacteria so far, a delayed rainy season and higher water temperatures this year will still raise alarm bells with Zhu.

The temperate weather in Daliwith its relatively cool summers and mild winters-encourages the growth of organisms, which explains the continuous threat of algae blooms despite the generally stable water quality.

"Erhai Lake is delicate," says Wang Xinze, a professor at Shanghai Jiaotong University's Dali Research Institute.

It's easily affected by exogenous pollution and changes to its ecosystem, making environmental protection work more difficult, Wang says, offering a response to critics who say the prefecture has devoted too much money, time and effort to a project that failed to produce a leapfrog effect in terms of improving water quality.

Water from 27 main rivers and the rainwater that empties into the lake usually remains in the lake for four years, leading to a longer reaction period for the prefecture's pollution abatement efforts, he says.