C/N RATIO

The C/N ratio has been used as a representative proxy to reconstruct the depositional environment of freshwater lake sediments [5-10]. Carbon and Nitrogen in aquatic ecosystems are governed by the mixing of terrestrial and autochthonous organic matter [11-12,5,13-14,4]. C/N ratios of 5 to 6 are reported in phytoplankton and zooplankton, which have proteins, which are primarily nitrogen compounds [15,16]. Freshly-deposited OM, derived mainly from planktonic organisms, has a C/N ratio of 6 to 9 [15, 17-18]; Phycogenic C/N ratio was found to be between 4 and 10 [3]. This is contrary to C/N ratios 15 or higher with [16,19-23] in terrestrial vascular plants and their derivates in sediments, and greater than 20 [3] in terrestrial organic matter and about 39.4 [22] for macrophyte materials.

In this communication we analyze the distribution of OM and the variability in the C/N ratio under the prevailing seasonal oxic and anoxic conditions, and evaluate the sensitivity of the C/N ratio to changes in the proportions of planktonic and terrestrial OM. Variations in C:N ratio within sediment have been used to understand lake’s temporal depth profile apart from analyzing the period of high proportion of terrestrial OM input [24]. Conversely, lower C:N ratios help to identify periods when lake sediments have received a high proportion of algal OM [25]. C:N ratio to discern changes in organic matter sources has been the subject of discussion [26,27] as the C:N of terrestrial organic matter decreases during diagenesis, while that of algae increases [28]. In this backdrop, a study has been carried out to identify spatial and a short time temporal variability in nature and sources of organic matter to Lake Varthur, Bangalore (India) through the analysis of C:N of surficial sediments.