Abstract:When evaluating forest functions and their responses to climate change, it is important to clarify carbon dynamics in forested basins. Carbon fluxes in litter fall, throughfall, soil solution, groundwater and stream water were determined from November 1997 to October 1998 for a forest stream ecosystem in a cool-temperate forested basin in the Tomakomai Experimental Forest, Hokkaido University, northern Japan. The annual carbon input to the stream by litter fall was 0Ð23 gC m 2 year 1 , with the greatest flux in the autumn. Owing to biological decomposition of litter in the stream, the carbon concentration in stream particulate organic matter (>0Ð45 µm) decreased as particle size decreased. The upstream carbon flux was 1Ð9 gC m 2 year 1 , and the annual carbon output in stream water was 7Ð6 gC m 2 year 1 , mainly as dissolved inorganic carbon (DIC), resulting in net carbon output in stream water of 5Ð7 gC m 2 year 1 . The mean dissolved organic carbon (DOC) concentration in soil solution was higher than that in throughfall and stream water. The estimated annual carbon flux from soil in deep (about 1Ð5 m) soil solution was 4Ð4 gC m 2 year 1 . About 40% of DOC in soil solution was decomposed and converted to DIC in groundwater. These results indicate that carbon dynamics in the forest stream were affected strongly by decomposition of organic matter in the soil-groundwater-stream continuum and by the hydraulic conditions, which are characterized by a large pool of groundwater and high soil permeability.
Conventional morphology-based identification is commonly used for routine assessment of freshwater ecosystems. However, cost and time efficient techniques such as high-throughput sequencing (HTS) based approaches may resolve the constraints encountered in conducting morphology-based surveys. Here, we characterized stream macroinvertebrate species diversity and community composition via metabarcoding and morphological analysis from environmental samples collected from the Shigenobu River Basin in Ehime Prefecture, Japan. We compared diversity metrics and assessed both approaches' ability to evaluate the relationship between macroinvertebrate community and environmental variables. In total, we morphologically identified 45 taxa (3 families, six subfamilies, 31 genera, and five species) from 8,276 collected individuals from ten study sites. We detected 44 species by metabarcoding, with 35 species collapsed into 11 groups matching the morphologically identified taxa. A significant positive correlation between logged depth (number of HTS reads) and abundance of morphological taxa was observed, which implied that quantitative data can be used for subsequent analyses. Relatively higher estimates of alpha diversity were calculated from the metabarcoding data in comparison to morphology-based data. However, beta diversity estimates between metabarcoding and morphology data based on both incidence and abundance-based matrices were correlated proving that community differences between sampling sites were preserved in the molecular data.Also, both models were significant, but metabarcoding data (93%) explained a relatively higher percentage of variation in the relationship between community composition and the environmental variables than morphological data (91%). Overall, we present both the feasibility and limitations of HTS-driven estimations of taxonomic richness, community composition, and diversity metrics, and that metabarcoding was proven comparable and more sensitive against morphology-based analysis for stream macroinvertebrate biodiversity assessment and environmental monitoring.
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