The Organic Pollution Indices and the Phytoplanktonic Index, Do They Allow to Assessing the Freshwater Quality, Case of Algeria

In Algeria, surface water resources are estimated at more than 11 billion m3, the vast majority concentrated on the coastal part (90.2%) of the overall flow, compared to the Saharan basins’ 0.5 billion m3 (4.1%), and the high plains’ only estimated 0.7 billion m3 (5.7%) of the total flow. Our goal was to monitor freshwater organic pollution status by adopting two indices, the Organic Pollution Index (OPI) and the LISEC index. The OPI assesses chemical quality of water that has been affected by actual organic pollution based on nutritional parameters such as orthophosphate, nitrite, biochemical demand for oxygen and ammonia. The second index is LISEC has the same principle as the OPI, but is based on calculating the sum of the values of the classes instead of the average, and the classes are numbered in reverse. In this case, the highest value of the index corresponds to severe pollution. The lake phytoplankton index was also used as a biological model (IPLAC). Water samples were taken from 63 Algerian lake ecosystems for physicochemical analysis. About 1406 observations were recorded during 3 years. In some dams, the pollution status was stabile during the 3 years, while other dams were marked by a pollution gradient. The OPI values varied between 1.67 and 4.82, for the LISEC, generally the values oscillated between 3.78 and 5.33, indicating the absence of organic pollution to a poor pollution. The highest value was found at the Hammam Boughrara dam (LISEC = 14.83). The application of the IPLAC index allowed us to assess the water quality at 13 dams. The values obtained were lower than 25, which revealed waters of very good quality. These indices variated between dams studied with 3.57 ± 0.69 and 6.40 ± 2.71 for OPI and LISEC index, respectively. The comparison of pollution classes is much less satisfactory, with large discrepancies observed between the three indices used. These discrepancies come from the choice of parameters and classes. In this case, the LISEC and IPLAC indices are certainly too optimistic compared to the OPI index, which indicates strong organic pollution. Although the latter is more realistic, it identifies the strongest pollution and the alteration by phosphates which announce eutrophication.