Riverbank soil ecosystems are important zones in terms of transforming inorganic nitrogen (N), particularly nitrate (NO3−-N), in soils to nitrous oxide (N2O) gases. Thus, the gasification of N in the riverbank soil ecosystems may produce a greenhouse gas, N2O, when the condition is favourable for N2O-producing microbes. One of the major N2O-producing pathways is denitrification. Thus, we investigated the denitrification potentials along Shibetsu River, Hokkaido, Japan. We sampled riverbank soils from eight sites along the Shibetsu River. Their denitrification potentials with added glucose-carbon (C) and NO3−-N varied from 4.73 to 181 μg·N·kg−1·h−1. The increase of the denitrification after the addition of C and N was negatively controlled by soil pH and positively controlled by soil NH4+-N levels. Then, we investigated the changes in 16S rRNA bacterial community structures before and after an anaerobic incubation with added C and N. We investigated the changes in bacterial community structures, aiming to identify specific microbial species related to high denitrification potentials. The genus Gammaproteobacteria Aeromonadaceae Tolumonas was markedly increased, from 0.0 ± 0.0% to 16 ± 17%, before and after the anaerobic incubation with the excess substrates, when averaged across all the sites. Although we could not find a significant interaction between the denitrification potential and the increase rate of G. Aeromonadaceae Tolumonas, our study suggested that along the Shibetsu River, bacterial response to added excess substrates was similar at the genus level. Further studies are needed to investigate whether this is a universal phenomenon even in other rivers.
Nitrification and denitrification are important processes of the nitrogen (N) cycle in soils because of their relations to N availability for plants and to environmental risks. However, paddock scale heterogeneity of these processes is not well understood in pasture ecosystems. Thus, we focused on the variability of nitrification and denitrification potentials within one pasture paddock. Twelve soil samples were taken from various places within a 2.3 ha paddock in September and were analyzed for nitrification and denitrification potentials, inorganic‐N, total carbon (C) and N, C/N ratio, soil pH and moisture contents. The variability of the denitrification potentials was smaller than that of the nitrification potentials. We found that inorganic‐N, total C and N, and soil pH were positively correlated to the nitrification potential. We also identified a “hot‐area” with 3.3‐fold higher nitrification potentials than other areas. A better understanding of this paddock scale nitrification variability may help to decrease environmental risks, such as nitrate leaching and/or nitrous oxide emissions, and to improve N use efficiencies.
The Geospatial Information Authority of Japan (GSI) is the national organization that has jurisdiction over the Survey Act, and develops geospatial information. We are also promoting utilization of them based on the Basic Act on the Advancement of Utilizing Geospatial Information. In addition, the Japanese government is promoting the Open Data initiative, in which the government widely discloses public data in machine-readable formats and allows secondary use of them. In accordance with these laws and initiative, we aim to realize a society where geospatial information can be widely and highly utilized by the disclosure of geospatial information. In order to achieve our mission, we are working on providing map data using "GSI Maps" (https://maps.gsi.go.jp/) which is a web map developed by using open source software (OSS) as the basis (Figure 1a). In this paper, we introduce "Three Open Policies" to promote utilizing geospatial information provided via GSI Maps.
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