11:15 AM - 11:30 AM
[MIS22-09] Chemosynthetic production supporting benthic food-web in a freshwater lake
★Invited Papers
Keywords:Benthic animals, Nutritional resource, Lake Biwa, sulfide
It is important to evaluate nutrient sources of benthic animals to understand material cycle and trophic structure in aquatic ecosystem. The major nutrient source of benthic animals in freshwater lakes is photosynthetic products, while microbial activities in sediment, such as methane-oxidizing bacteria are known to be one of the important nutrient sources. Recent studies showed that chemosynthetic products by sulfur-oxidizing bacteria in lake sediments may be a nutrient source for benthic animals. However, no studies have quantitatively investigated the contribution of the chemosynthetic products to benthic animal communities. For this study, we evaluated the contribution of chemosynthetic products to the nutrient sources of benthic communities in a large freshwater lake, Lake Biwa, using sulfur stable isotope ratios.
Sediment and animal samples were obtained from the central part of the northern basin in Lake Biwa (90 m water depth) and from the off Hikone (50 m water depth) in summer, when the thermal stratification was developing. Sulfur isotope ratio (δ34S) of acid volatile sulfide (AVS) in the sediments, sulfate in lake water, and animal tissues were measured to investigate contribution of sulfide-sulfur to sulfur source for the animals.
High concentrations and low δ34S values of AVS were detected in the sediments, indicating occurrence of microbial sulfate reduction. Using δ34S values of AVS, sulfate, and animals, the contribution of sulfide-derived sulfur to the sulfur source of the animals was calculated. The results showed a various contribution from 0% for amphipods to ~100% for oligochaetes with the largest biomass in the lake. These results indicate that even in freshwater environments, microbial sulfur cycling is significant during the stratification period when anoxic water masses are developed in the stagnant bottom water, affecting nutrient sources for the benthic animals.
Sediment and animal samples were obtained from the central part of the northern basin in Lake Biwa (90 m water depth) and from the off Hikone (50 m water depth) in summer, when the thermal stratification was developing. Sulfur isotope ratio (δ34S) of acid volatile sulfide (AVS) in the sediments, sulfate in lake water, and animal tissues were measured to investigate contribution of sulfide-sulfur to sulfur source for the animals.
High concentrations and low δ34S values of AVS were detected in the sediments, indicating occurrence of microbial sulfate reduction. Using δ34S values of AVS, sulfate, and animals, the contribution of sulfide-derived sulfur to the sulfur source of the animals was calculated. The results showed a various contribution from 0% for amphipods to ~100% for oligochaetes with the largest biomass in the lake. These results indicate that even in freshwater environments, microbial sulfur cycling is significant during the stratification period when anoxic water masses are developed in the stagnant bottom water, affecting nutrient sources for the benthic animals.