[MIS25-P08] Biogeochemistry and benthic community structure of volcanic stream ecosystems in northern Japan
Keywords:chemosynthetic ecosystem, sulfur-oxidizing bacteria, volcanic stream
Since the discovery of chemosynthetic ecosystems in deep-sea hydrothermal vents, benthic invertebrate communities sustained by organic matter derived from the chemoautotrophic bacteria have been found in many places of dark, deep-sea floor ecosystems. However, food webs sustained fully by chemoautotrophic primary productivity have never been reported from sunlit terrestrial ecosystems. In streams flowing through active volcanic regions, highly acidic hot-spring water often flows into the stream water, thereby making the stream ecosystems extreme environments. In such ecosystems, algal primary productivity, as well as the supply of terrestrial organic matter from surrounding arid environments, tends to be decreased. However, we found the high density of stream benthic macroinvertebrate community in volcanic streams around Mt. Akita-Yakeyama, where active volcanic activity influences the physicochemical characteristics of streams and rivers in the watershed. Here we report the biogeochemistry and benthic community structure of streams influenced by volcanic hot-spring water.
We performed a field survey in three volcanic streams where hot-spring water comes from geothermal environments of Mt. Akita-Yakeyama, and in a nearby reference stream, during June 6 and 8, 2019. In each study stream, we quantified the physico-chemical environments and the abundance of benthic stream communities. In addition, we conducted an in situ incubation experiment in a study stream to estimate the photoautotrophic and chemoautotrophic primary productivity in the stream ecosystem.
Our field study showed that water quality variables, such as pH and water temperature, differed greatly among the study streams. In particular, dissolved sulfide concentration was higher in the volcanic streams relative to the reference stream. Moreover, the standing crop of epiphytic algae and benthic particulate organic matter tend to be lower in the volcanic streams. Even in such environments with the decreased availability of basal resources of stream food webs, the density of benthic macroinvertebrates exhibited one to two orders of magnitude higher than that of the nearby reference stream. Moreover, specific taxa (e.g., a Nemourid stonefly larvae and Chironomid midge larvae) tend to predominate in the benthic community of the volcanic streams, suggesting that specific group adapted to extreme environments can be a dominant species in the stream communities under the predator- and competitor-less conditions. The in situ incubation experiment showed that the concentrations of dissolved sulfide and dissolved inorganic carbon (DIC) were significantly decreased in both light and dark chambers. In contrast, dissolved oxygen (DO) did not increased associated with the decrease of DIC, implying that oxygenic and anoxygenic photosynthesis was not responsible for the DIC consumption; chemoautotrophic production by sulfur-oxidizing bacteria is likely to play a primary role in organic matter production of the volcanic stream ecosystems. Based on the change in DIC and DO concentrations, we estimated the rate of chemoautotrophic primary productivity in the stream as 0.75 gC m-2 d-1. This organic matter productivity by chemoautotrophs is comparable to the gross photosynthetic production rate reported from the worldwide non-acidic stream and river ecosystems.
We performed a field survey in three volcanic streams where hot-spring water comes from geothermal environments of Mt. Akita-Yakeyama, and in a nearby reference stream, during June 6 and 8, 2019. In each study stream, we quantified the physico-chemical environments and the abundance of benthic stream communities. In addition, we conducted an in situ incubation experiment in a study stream to estimate the photoautotrophic and chemoautotrophic primary productivity in the stream ecosystem.
Our field study showed that water quality variables, such as pH and water temperature, differed greatly among the study streams. In particular, dissolved sulfide concentration was higher in the volcanic streams relative to the reference stream. Moreover, the standing crop of epiphytic algae and benthic particulate organic matter tend to be lower in the volcanic streams. Even in such environments with the decreased availability of basal resources of stream food webs, the density of benthic macroinvertebrates exhibited one to two orders of magnitude higher than that of the nearby reference stream. Moreover, specific taxa (e.g., a Nemourid stonefly larvae and Chironomid midge larvae) tend to predominate in the benthic community of the volcanic streams, suggesting that specific group adapted to extreme environments can be a dominant species in the stream communities under the predator- and competitor-less conditions. The in situ incubation experiment showed that the concentrations of dissolved sulfide and dissolved inorganic carbon (DIC) were significantly decreased in both light and dark chambers. In contrast, dissolved oxygen (DO) did not increased associated with the decrease of DIC, implying that oxygenic and anoxygenic photosynthesis was not responsible for the DIC consumption; chemoautotrophic production by sulfur-oxidizing bacteria is likely to play a primary role in organic matter production of the volcanic stream ecosystems. Based on the change in DIC and DO concentrations, we estimated the rate of chemoautotrophic primary productivity in the stream as 0.75 gC m-2 d-1. This organic matter productivity by chemoautotrophs is comparable to the gross photosynthetic production rate reported from the worldwide non-acidic stream and river ecosystems.