Insights of the food web in freshwater lake using radiocarbon measurements

Abstract

In this study, we conducted a food web analysis of aquatic organisms using radiocarbon in Lake Suwa, where deep-derived methane seeps into the lake. Lake Suwa is a fault lake located at the intersection of the Itoigawa-Shizuoka Tectonic Line and the Median Tectonic Line, and its sedimentary layers contain methane reserves. Previous studies have reported that this methane is depleted in radiocarbon, and that some of the methane is incorporated into the lake water as dissolved inorganic carbon (DIC). To assess the influence of deep methane on the entire lake, we performed radiocarbon analysis of DIC in the surface lake water, including major outflow and inflow rivers, and found that the radiocarbon values in the lake water were lower than those in the inflow rivers. While aquatic organisms, wakasagi and largemouth bass indicated radiocarbon values intermediate between those of lake water and river water. In this presentation, we will discuss multidimensional isotope systematics with stable carbon and radiocarbon dynamics in the entire hydrosphere, together with the results of ecosystem structure analysis using compound-specific isotope analysis for Amino acids.