Stable isotope compositions of sedimentary organic carbon and nitrogen recovered from East African crater lake

Variation in the contents of organic carbon and nitrogen and stable isotopes composition of organic carbon for two cores (EMP LIV 2b and EMP LIV 4) recovered from the Empakai crater lake are used to deduce variability in sources of organic matter in the lake in relation to climatic changes. Also the stable isotopes of sedimentary nitrogen are used to assess effect of acid treatment on nitrogen stable isotopes. Cores EMP LIV 2b and EMP LIV 4 are 1 and 2 m long, and were recovered from water depths of 11 and 20 m respectively. This study also assessed impact of sample treatment on the stable isotope compositions of nitrogen. Generally acidification processes cause isotope fractionation where treated particulate materials are depleted in 15N relative to untreated fraction. The difference in the stable isotope composition between treated and untreated samples is as high as 7 per mille. This could be attributed to hydrolysis effect where nitrogen rich compounds are removed. Thus, for the determination on nitrogen stable isotopes, untreated sedimentary materials are preferred over treated sediments