Spatial Variation of Sediment Physicochemical Characteristics of Lake Tana, Ethiopia

Abstract

The purpose of this study was to assess the physico-chemical properties of sediments of Lake Tana, Ethiopia. The parameters monitored include:  pH, conductivity, percentage of organic carbon, percentage of total nitrogen, available phosphorous and percentage of organic matter. Sediment sampling was done with the help of Eckman grap sediment sampler, from August 2011-July 2012 at 20 sampling sites. The physical properties of sediments of Lake Tana namely:  average pH and conductivity reported  between  5.81 to 7.02 with the overall mean value of 6.5 which is slightly acidic and 0.09 to 0.72 dS/m with the overall mean value of 0.27 dS/m  respectively. The sediment nutrients: percentage of total nitrogen and available phosphorous  of  Lake Tana revealed  average values 0.07 to 0.54% with overall mean value of 0.18% and 9.56 to 52.23 mg/kg with the overall mean value of 21.83 mg/kg respectively. There was a positive correlation between sediment  percentage of total nitrogen  and percentage of organic matter (r = 0.759) as well as between sediment available phosphorous and organic matter(r =0.630). Those correlation values revealed that  both nitrogen and phosphorous are originated from organic sources than inorganic sources. The correlation values between nitrogen and phosphorous(r=0.513)  indicated that they are generated from the same sources. The average organic carbon (%) was recorded between 0.82 to 5.03 % with the overall mean value of 1.99 while the average organic matter (%) of Lake sediment was recorded between 1.33 to 6.98 % with the overall mean value of 3.13%. In this study, the ratio of total organic carbon to total nitrogen(C:N ratio) for 20 sediments were between 7.5 to 16.3,which indicated that the source of organic matter could be related to aquatic sources  of Lake Tana. As it is the first time where monitoring physico-chemical properties of sediments of Lake Tana are presented, this study can be used as baseline data for comparison in future environmental assessment of the lake.

Keywords: Available phosphorous, eckman-grap, inverse distance weighting, lake sediments, organic carbon, organic matter, total nitrogen, available phosphorous.