Stable isotope (δ13C and δ15N) values of sediment organic matter in subtropical lakes of different trophic status

Abstract

Lake sediments contain archives of past environmental conditions in and around water bodies and stable isotope analyses (d 13 C and d 15 N) of sediment cores have been used to infer past environmental changes in aquatic ecosystems. In this study, we analyzed organic matter (OM), carbon (C), nitrogen (N), phosphorus (P), and d 13 C and d 15 N values in sediment cores from three subtropical lakes that span a broad range of trophic state. Our principal objectives were to: (1) evaluate whether nutrient concentrations and stable isotope values in surface deposits reflect modern trophic state conditions in the lakes, and (2) assess whether stratigraphic changes in the measured variables yield information about shifts in trophic status through time, or alternatively, diagenetic changes in sediment OM. Three Florida (USA) lakes of very different trophic status were selected for this study. Results showed that both d 13 C and d 15 N values in surface sediments of the oligo-mesotrophic lake were relatively low compared to values in surface sediments of the other lakes, and were progressively lower with depth in the sediment core. Sediments of the eutrophic lake had d 13 C values that declined upcore, whereas d 15 N values increased toward the sediment surface. The eutrophic lake displayed d 13 C values intermediate between those in the oligo-mesotrophic and hypereutrophic lakes. Sediments of the hypereutrophic lake had relatively higher d 13 C and d 15 N values. In general, we found greater d 13 C and d 15 N values with increasing lake trophic state.

Sedimentary geochemical record of human-induced environmental changes in Huanggaihu Lake in the middle reach of the Yangtze River, China

“…However, after early 1970s the TP profile can track TOC, TN and Cd contents. C org of sediment organic matter (Torres et al, 2012;Woodward et al, 2012). The δ 13 C org signature of autochthonous organic matter is affected by the 13 C/ 12 C ratio of the dissolved inorganic carbon (DIC) in lake water that is used for photosynthesis.…”

Dissolved organic carbon, CO2, and CH4 concentrations and their stable isotope ratios in thermokarst lakes on the Qinghai-Tibetan Plateau

“…These values are much higher than boreal (-21‰ to -24‰) (Peters et al, 1978) and subtropical lakes (-25‰ to -26‰) (Torres et al, 2012). This result suggests that the OC in the thermokarst lake sediments was highly decomposed.…”

Historical changes in nutrient inputs from humans and anadromous fishes in New England's coastal watersheds

“…3e,f). Total d 13 C, which past studies have used as an indicator of allochthonous terrestrial inputs (Torres et al 2012), increased in Bride Lake and Rogers Lake around the time that watershed land use began to intensify, but later decreased in Linsley Pond as land use intensified (Fig. 3e).…”