**1. Introduction**

The water and sediments are the main storage medium for pollutants in lake environments. The sediments adsorb various kinds of pollutants which could accumulate in sediments for a long time. When external conditions change, pollutants adsorbed in sediments may be released back into the water and taken up by organisms. Eventually, these pollutants may affect human health through the food chain. Therefore, how to assess the risk of the water system with contaminated sediments has become an important issue. If ecological risk assessment can be used as a diagnostic tool to evaluate the potential risks accurately, it is of great significance to pollution control [1, 2].

Until now, various approaches, which are based on the different perspectives of the chemical, biological and toxicological indices, have been proposed to assess the water quality ecological risk of the environment. For example, the enriched factor (EF) can evaluate the accumulation of elements in the sediment. It is calculated by comparing the concentration of the sample with the background value [3]. The geoaccumulation index (Igeo) assesses the risk by comparing the total concentration,

the background value, and the background matrix correction factor of lithogenic effects is considered in it [4]. The pollution load index (PLI) is defined as the nth root of the product of the ratios between the concentration of each metal to the background values [5]. The sediment quality guidelines (SQGs) include threshold effect concentrations (TECs) and probable effect concentrations (PECs). Bioavailability is taken into account in this approach [6]. It is not adequate to assess the ecological risk by using only concentrations without factors of toxicity. The potential ecological risk index (ERI) posed by Swedish geochemist Lars Håkanson (The National Swedish Environment Protection Board, Water Quality Laboratory Uppsala) is based on the "abundance principle", "sink-effect", and "sensitivity factor" [7]. As a diagnostic tool for pollution control, the potential ecological risk index has been widely used since its development in the 1980s [8–10].

where *C<sup>i</sup>*

where *Ei*

**Figure 1.**

**73**

*The ETA-diagram [12].*

**2.3 The parameters**

value of the substance i, *C<sup>i</sup>*

risk index for the basin/lake.

*2.3.1 The contamination factor C<sup>i</sup>*

ence value of substance i (*C<sup>i</sup>*

and *Cd* is the degree of contamination.

*DOI: http://dx.doi.org/10.5772/intechopen.88594*

*<sup>f</sup>* is the contamination factor of the substance i, *Ci*

*Ei <sup>r</sup>* <sup>¼</sup> *<sup>T</sup><sup>i</sup>*

*i*¼1 *Ei*

*ERI* <sup>¼</sup> <sup>X</sup>*<sup>n</sup>*

*Water Quality Ecological Risk Assessment with Sedimentological Approach*

*f*

To get the value of the contamination factor (*C <sup>i</sup>*

may mean the sediments are from an accumulation area.

known about the measured value of substance i (*C<sup>i</sup>*

*<sup>r</sup>* � *<sup>C</sup> <sup>i</sup>*

*Ti <sup>r</sup>* � *<sup>C</sup> <sup>i</sup>*

*<sup>r</sup>* <sup>¼</sup> <sup>X</sup>*<sup>n</sup> i*¼1

*<sup>r</sup>* is the potential ecological risk factor for the given substance i, *T<sup>i</sup>*

"toxic-response" factor for the given substance i, and ERI is the potential ecological

Håkanson proposed that "undisturbed" samples should be collected from accumulation areas in the lake targeting the 0–1 cm layer. Håkanson provides two methods to determine the accumulation areas for a given lake. The first method, the ETAdiagram (**Figure 1**), uses only the water depth and the effective fetch. The second method uses the water content of sediments (*W*<sup>0</sup>�1). In this second method, researchers have to collect and analyze sediments to determine the bottom dynamic condition. The method requires 5 g wet sediment dried for 6 h at 105°C, then expressed as the water content as wet sediment. Accordingly, if the *W*<sup>0</sup>�<sup>1</sup>>75%, it

In addition, Håkanson gives the types of contaminants that could be included in this contamination factor index. These contaminants include PCB, Hg, Cd, As, Cu, Pb, Cr, and Zn. Of course, it is possible to study other pollutants

<sup>0</sup>�<sup>1</sup> is the measured

*<sup>f</sup>* (3)

*<sup>f</sup>* (4)

*<sup>f</sup>* Þ, more information needs to be

<sup>0</sup>�1) and the preindustrial refer-

*<sup>r</sup>* is the

*<sup>n</sup>* is the preindustrial reference value of the substance i,

*<sup>n</sup>*). In order to reflect the risk of the lake accurately,

This chapter describes an approach to assess water quality risks using its basic theory, calculation formula, evaluation criteria, and parameters calculation. This approach combines environmental chemistry with ecotoxicology in order to assess the potential risks accurately. The approach integrates the concentration of substances with ecological effects, environmental effects, and toxicity. Furthermore, the model is used to explain in detail a water quality case study of the Liaohe River, China [11].
