The effect of organic pollution on the seasonal dynamics of water quality of Hammam Boughrara Dam that is located in a semi-arid zone in the northwestern city of Tlemcen (Algeria)

Abstract

Abstract The present study aims to assess the impact of human activities on the water quality of Hammam Boughrara Dam, while highlighting the importance of seasonal variations of the organic pollution indicator parameters. The COD/BOD5 Ratio (CBR) values, over the period mentioned above, revealed the dominance of two categories, namely Moderately Biodegradable Effluent (MBE) and Difficult to Biodegrade Effluents (DBE) or Non-Biodegradable Effluents (NBE), with significant seasonal variations. The MBE category showed a maximum frequency in autumn (29 occurrences) and a minimum frequency in spring (20 occurrences), while the DBE or NBE category had a maximum frequency of 26 during winter and a minimum frequency of 21 during the autumn season. The analysis of Organic Pollution Index (OPI) revealed that the water of the dam under study is strongly impacted by organic pollution, with significant seasonal variations. This is confirmed by the predominance of the Organic Pollution (OP) category, with a maximum frequency in autumn and summer seasons (25 occurrences) and minimum in spring (21 occurrences), as well as by the Very Strong Organic Pollution (VSOP) category, with a maximum frequency in winter (23 occurrences) and minimum in summer (11 occurrences). The box-plot graphs showed positive skew, while others exhibited a negative one, with significant seasonal variations in the InterQuartile Range (IQR). It should also be mentioned that the correlation of the Organic Pollution Index (OPI) with the concentrations of NH₄⁺ and PO₄³⁻ ions is higher than that of the OPI with BOD5 and NO₂⁻. However, it must be recognized that the correlation between the OPI and BOD5 as well as NO₂⁻ remains significant at 1% threshold level. Moreover, the correlation coefficients showed significant seasonal variations. It is worth noting that the OPI showed a positive correlation with the dam’s water volume, during all four seasons, with correlation coefficients varying significantly for each season. On the other hand, the OPI exhibited negative correlation with COD, TDS and \({NO}_{3}^{-}\) concentrations in some seasons. In addition, positive correlations were observed between the concentrations of \({NH}_{4}^{+}\)and \({PO}_{4}^{3-}\) ions, as well as between the concentrations of \({NH}_{4}^{+}\) and \({NO}_{2}^{-}\) ions, throughout the four seasons.