Organics and Nutrients Loading to The 23rd of July Man-Made Lake in Benghazi City, NE Libya

The 23 of July lake in Benghazi City is a Man-made lake or lagoon. It was established in 1982. The lake has a surface area of about 93 hectares and the water depth ranges from 5 m  near its landward edge to about 2.5 m  in the seaward direction. The lake receives inputs from various outlets, however, the discharge of untreated sewage remains the major environmental problem for the neighboring residential area as well as the commercial and recreational places. The current study was carried out in order to estimate the organic and nutrient loading into the lake and determine the pollution status of the lake. The result obtained showed a very high concentration of almost all pollution indicators parameters and showed levels above those reported for the non-polluted body. For instance, the parameters for the water characteristics such as the total dissolved solutes were found to range from 18468.2-23233 mg/l. The level of dissolved oxygen was found to range from 1.97-3.07 mg/l, while the pH showed no significant differences ranging from 7.35-7.94. The results also indicated a massive enrichment of organics as the BOD values were found to range from 117.5–148.33 mg/l while the COD values ranged from 235.0-296.7 mg/l and the total suspended solids were 60.50-86.50 mg/l, all of which reflecting on an environment highly polluted by organic material. The ranges for the nutrient NO3- and PO4-3 were found to be ranging from 1.68-3.43 mg/l for nitrate and 0.95-2.22 mg/l for phosphorus, revealing the possibility of stimulating algal growth in the lake if the environmental condition needed exist. The levels of ammonia (NH3 and nitrite (NO2) were found to be in the range of 0.01-0.03 mg/l and 3.60-11.20 mg/l  respectively.  In general, the results showed large variations both between samples and among zones. This could be attributed to the variety of input sources. The exceptionally high level of BOD at zone (D) could be attributed to the initial entrance of the major sewage input point and low dilution.