Abstract
Water quality indices are suitable tools used for assessing water quality because of their capacity to reduce a large number of water quality indicators into one value which defines the water quality class. In this study, Water Quality Index (WQI), Water Pollution Index (WPI) and Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI) were applied in order to evaluate the seasonal and spatial variation of the water quality in the Romanian Lower Danube sector. Fourteen physico-chemical parameters, i.e., pH, DO, BOD5, COD, N-NH4+, N-NO3−, N-NO2−, N-total, P-total, SO42−, Cl−, Fe-total, Zn2+ and Cr-total, were monitored along the Danube course (on a distance of about 120 km), during the four seasons between the autumn of 2018 and the summer of 2019 in order to calculate the three indices mentioned above. Indices results showed that the water analysed was ranked into different water quality classes, although the same dataset was used. These differences were due to the contribution of each parameter taken into account in the calculation formula. Thus, the WQI scores were mostly influenced by those parameters whose maximum allowable concentration was low (e.g., heavy metals, N-NO2−), while the WPI and CCME-WQI scores were influenced by those parameters which exceeded the maximum allowable concentration (BOD5, DO, COD, N-NO3−, N-NO2−). Based on the WQI results, the water was ranked into quality classes II and III. WPI and CCME-WQI assessed water only in quality class II, with one exception in the case of CCME-WQI when water was ranked into quality class III. The temporal assessment identified the seasons in which the water quality was lower, namely summer and autumn. The variation of the indices values between the sampling stations demonstrates the existence of pollution sources in the study area. Moreover, the indices results illustrated the contribution of the main tributaries (Rivers Siret and Prut) to the Danube River water quality. The appropriate applicability of the three indices was also discussed in this study.
Highlights
Permanent water quality monitoring and assessment of surface water quality are indispensable for preserving the global ecosystem and human health [1]
Taking into account the aspects mentioned above, the present paper aims at testing and comparing the applicability of Water Quality Index, Water Pollution Index and of the Canadian Council of Ministers of the Environment Water Quality Index in order to obtain an accurate representation of water quality in the studied area, namely the Romanian Lower Danube sector bordering the cities of Galati, Braila and Tulcea
In terms of water quality seasonal variation, a lower quality was observed during summer and autumn, with this being due to flow variations and to the parameters which vary according to temperature
Summary
Permanent water quality monitoring and assessment of surface water quality are indispensable for preserving the global ecosystem and human health [1]. In order to assess water quality in the Danube River from a physico-chemical point of view, various indices have been calculated, such as Water Quality Index (WQI) [19], Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI), [20,21], Water Pollution Index (WPI) [22], Serbian Water Quality Index [23,24,25], Bascaron Water Quality Index (BWQI) [26] and Heavy. In order to reach this aim, a common dataset was used to calculate the three indices and, based on the results obtained, the water quality was included in the quality classes specific to each index. The area must be constantly monitored in order to create a habitat conducive to protected species
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