3.2 Aquatic life protection index (ALPI)

The Aquatic Life Protection Index (ALPI) is one of the most complete indexes for the assessment of the quality of aquatic ecosystems. It allows analyzing the water quality differently from other indexes, taking into account the presence and concentration of contaminants and their effects (toxicity), comprising two indexes: IMPAC (Index of Minimum Parameters for the Protection of Aquatic Communities) and TSI (Trophic State Index), which provide information on water quality and degree of trophy [32].

The IMPAC, proposed by Zagatto et al. [17] is composed of two groups of parameters: toxic substances (copper, zinc, lead, chromium, mercury, nickel, cadmium, surfactants, and phenols) and essential parameters (dissolved oxygen, pH and toxicity analyzes). For each parameter, three different levels were set, with numerical weightings of 1, 2, and 3. Weighting 1 corresponds to the water quality standards established by the Brazilian legislation [30] and weightings 2 and 3 consider the American and French legislations [33, 34], respectively, which establish maximum permissible limits of chemical substances in water to avoid chronic and acute effects on the aquatic biota.

Environmentally speaking, these weightings mean the following:


The IMPAC is calculated as follows (Eq. (1)):

$$\mathbf{IMPAC} = \mathbf{PE} \times \mathbf{ST} \tag{1}$$

where PE = value of the highest weighting in the group of essential parameters; ST = average value of the three highest weightings in the group of toxic substances.

If the value of the toxic substances is an integer, the following rounding criterion is considered: values smaller than 0.5 will be rounded down and values greater than or equal to 0.5 will be rounded up. Using this methodology, the value of the index can vary from 1 to 9. For the water classification, the IMPAC was subdivided into four levels (Table 2).

Toxicity tests followed the regulation ABNT/NBR 15088 [35] adapted for the euryhaline species Poecilia sphenops [36], considering salinity variation between sampling sites in the Jansen lagoon.

#### Table 2.

Water quality according to the index of minimum parameters for the protection of aquatic communities (IMPAC) by Zagatto et al. [17].

The TSI, used to determine the trophic levels of the Jansen lagoon, followed the standards proposed by Carlson [37], modified by Toledo et al. [38], who updated the original formula using the water parameter transparency, phosphate, orthophosphate, and chlorophyll a for tropical environments.

In this study, the calculation of the ALPI considered the Trophic State Index for phosphorus-TSI (TP) and the Trophic State Index for chlorophyll a-TSI (Chl), modified by Lamparelli [18], established for lotic environments, according to the equations (Eqs. (2) and (3)):

$$\text{TSI}\left(\text{TP}\right) = \mathbf{10} \times \left(\mathbf{6} - \left(\left(\mathbf{0.42 - \mathbf{0.36} \times (\ln \text{TP})\right) / \ln 2\right)\right) - \mathbf{20} \tag{2}$$

$$\text{TSI} \,(\text{Chl}) = \mathbf{10} \times (\mathbf{6} - ((-\mathbf{0}.7 - \mathbf{0}.6 \times (\ln \text{Chl}))/\ln 2)) - \mathbf{20} \tag{3}$$

where TP: total phosphorus concentration measured at the water surface (μg L�<sup>1</sup> ); Chl: chlorophyll a concentration measured at the water surface (μg L�<sup>1</sup> ) ln: natural logarithm.

Regarding the TSI, the result shown in the tables is the simple arithmetic mean of the indexes related to the total phosphorus and chlorophyll a, expressed in the following equation (Eq. (4)):

$$\text{TSI} = [\text{TSI}\,\text{TP} + \text{TSI}\,\text{Chl}]/2 \tag{4}$$

According to Lamparelli [18], the different values of TSI lead to the following water classification (Table 3):

Based on the data obtained and associated by IMPAC [17] and the Trophic State Index (TSI) as shown in Table 4, the ALPI (Aquatic Life Protection Index) was calculated according to the following equation (Eq. (5)):

$$\text{ALPI} = (\text{IMPAC} \times \text{1.2}) + \text{TSI} \tag{5}$$


Table 3.

Water quality according to the state trophic index (TSI) by Carlson [37] modified by Toledo et al. [38].


#### Table 4.

Calculation of the ALPI integrating the values of the TSI and IMPAC. Where: excellent (blue), good (green), regular (yellow), bad (red), and very bad (purple).

Phytoplankton Biomass and Environmental Descriptors of Water Quality of an Urban Lagoon DOI: http://dx.doi.org/10.5772/intechopen.87955


#### Table 5.

Water quality according to the aquatic life protection index (ALPI) by Zagatto et al. [17] modified by CETESB [32].

The classification of the waters can be represented according to the ALPI index values, being divided into five categories as described below (Table 5):

Phytoplankton was analyzed in terms of chlorophyll a. Water samples for chlorophyll a (μg L<sup>1</sup> ) determinations were filtered through Whatman GF/F glass fiber filters, and a pigment extraction was performed with 90% acetone. To obtain the fractional values of chlorophyll, sub-samples were passed through a 20 μm mesh and then filtered. Pigment concentration was measured by spectrophotometry [39, 40] and the calculations were done according to Strickland and Parsons [41].
