[Research on the threshold of Chl-a in Lake Taihu based on microcystins].

Water samples were collected in Lake Taihu from June to October in 2013 in order to investigate the threshold of chlorophyll a (Chl-a). The concentrations of three microcystins isomers (MC-LR, MC-RR, MC-YR) were detected by means of solid phase extraction and high performance liquid chromatography-tandem mass spectrometry. The correlations between various MCs and eutrophication factors, for instance of total nitrogen (TN), total phosphorus (TP), chlorophyll a, permanganate index etc were analyzed. The threshold of Chl-a was studied based on the relationships between MC-LR, MCs and Chl-a. The results showed that Lake Taihu was severely polluted by MCs and its spatial distribution could be described as follows: the concentration in Meiliang Bay was the highest, followed by Gonghu Bay and Western Lake, and Lake Center; the least polluted areas were in Lake Xuhu and Southern Lake. The concentration of MC-LR was the highest among the 3 MCs. The correlation analysis indicated that MC-LR, MC-RR, MC-YR and MCs had very positive correlation with permanganate index, TN, TP and Chl-a (P < 0.01). The threshold value of Chl-a was 12.26 mg x m(-3) according to the standard thresholds of MC-LR and MCs in drinking water. The threshold value of Chl-a in Lake Taihu was very close to the standard in the State of North Carolina, which demonstrated that the threshold value provided in this study was reasonable.

Determining reference conditions for TN, TP, SD and Chl-a in eastern plain ecoregion lakes, China.

Establishing the nutrient reference condition (baseline environmental condition) of lakes in an ecoregion is a critical consideration in the development of scientifically defensible aquatic nutrient criteria. Three methods were applied to determine reference conditions in the Eastern plain ecoregion lakes with respect to total phosphorus (TP), total nitrogen (TN), planktonic chlorophyll a (Chl-a) and Secchi depth (SD). The reference condition value for the lakes in the Eastern plain ecoregion by the trisection method is TP of 0.029 mg/L, TN of 0.67 mg/L, Chl-a of 3.92 mg/m3, SD of 0.85 m, and the reference condition range by the lake population distribution approach is TP of 0.014-0.043 mg/L, TN of 0.360-0.785 mg/L, Chl-a of 1.78-4.73 mg/m3, SD of 0.68-1.21 m. Additionally, empirical models were developed for estimating the reference Chl-a concentration and SD successfully for lakes in the Eastern plain ecoregion. Overall, the data suggest that multiple methods can be used to determine reference conditions and that in Eastern plain ecoregion lakes the reference condition corresponds to a mesotrophic status.

Establishing eutrophication assessment standards for four lake regions, China.

The trophic status assessment of lakes in different lake regions may provide important and fundamental information for lake trophic state classification and eutrophication control. In this study, a region-specific lake eutrophication assessment standard was established through a frequency distribution method based on chlorophyll-a concentration. The assessment standards under the oligotrophic state for lakes in the Eastern plain, Yungui Plateau, Northeast Plain and Mountain Mongolia-Xinjiang regions are total phosphorus of 0.068, 0.005, 0.011, 0.005 mg/L; total nitrogen of 1.00, 0.16, 0.37, 0.60 mg/L; Secchi depth of 0.60, 8.00, 1.55, 3.00 m; and COD(Mn) of 2.24, 1.00, 5.11, 4.00 mg/L, respectively. Moreover, a region-specific comprehensive trophic level index was developed to provide an understandable assessment method for the public. The results indicated that the frequency distribution analysis based on chlorophyll-a combined with trophic level index provided a useful metric for the assessment of the lake trophic status. In addition, the difference of eutrophication assessment standards in different lake regions was analyzed, which suggested that the sensitivities of algae to nutrients and the assessment standard of trophic status possessed significant regional differences for the four lake ecoregions. Lake eutrophication assessment standards would contribute to maximizing the effectiveness of future management strategies, to control and minimize lake eutrophication problems.

A model to determine the lake nutrient standards for drinking water sources in Yunnan-Guizhou Plateau Ecoregion, China.

Lake eutrophication (LE) has become an increasingly severe environmental problem recently. However, there has been no nutrient standard established for LE control in many developing countries such as China. This study proposes a structural equation model to assist in the establishment of a lake nutrient standard for drinking water sources in Yunnan-Guizhou Plateau Ecoregion (Yungui Ecoregion), China. The modeling results indicate that the most predictive indicator for designated use-attainment is total phosphorus (TP) (total effect = -0.43), and chlorophyll a (Chl-a) is recommended as the second important indicator (total effect = -0.41). The model is further used for estimating the probability of use-attainment associated with lake water as a drinking water source and various levels of candidate criteria (based on the reference conditions and the current environmental quality standards for surface water). It is found that these candidate criteria cannot satisfy the designated 100% use-attainment. To achieve the short-term target (85% attainment of the designated use), TP and Chl-a values ought to be less than 0.02 mg/L and 1.4 microg/L, respectively. When used as a long-term target (90% or greater attainment of the designated use), the TP and Chl-a values are suggested to be less than 0.018 mg/L and 1 microg/L, respectively.