**3.1 Description of the study area**

value = 1.0, BPI value = 5.0. This means that there is no contamination in the reference lake. The data from one's samples would be compared with the reference lake. The ERI classification thresholds are modified for different assessments. For example, if there were eight substances analyzed in Håkanson's research and the

Moreover, Håkanson ignores the influence of BPI value on the *T<sup>i</sup>*

*<sup>r</sup>* values is 155, the thresholds of the first level could be 150.

*<sup>f</sup>* value is 1.0. Therefore, he regards the sum of *St<sup>i</sup>* value as the threshold.

This section illustrates the potential ecological risk index by using a case study.

1.Determine the substances of interest (As, Cd, Cr, Cu, Ni, Pb, and Zn) in the

2.Determine the accumulation areas for the river and collect the samples from

The data for the ERI values is taken from [11]. The main steps for creating a

potential ecological risk index to assess the Liaohe River system are:

4.Measure the IG value and N value to calculate the BPI and *T<sup>i</sup>*

*The location of sampling sites along the Liaohe River protected area [11].*

5.Calculate the potential ecological risk to assess the water quality.

*<sup>r</sup>* value because of

*<sup>r</sup>* value; and,

sum of all the *T<sup>i</sup>*

**3. Case application**

study area (the Liaohe River);

*Water Quality - Science, Assessments and Policy*

the 0–1 cm layer in the sediments;

3.Calculate or look up the *St<sup>i</sup>* value;

the *C <sup>i</sup>*

**Figure 2.**

**78**

The Liaohe River is located in the south of northeast China (**Figure 2**). It is one of the seven major rivers in China. As an important aquatic ecosystem, it plays an important role in the local economic and social development. Because of anthropogenic activities, the pollution of the Liaohe River is becoming a more serious problem. The Liaohe River has become one of the most polluted rivers in China. Therefore, it is significant to assess the quality of the Liaohe River [21].
