Ecology and Civil Engineering
Online ISSN : 1882-5974
Print ISSN : 1344-3755
ISSN-L : 1344-3755
Current issue
Displaying 1-5 of 5 articles from this issue
ORIGINAL PAPER
  • Isao TAKAHASHI, Shizuo AINO
    2022 Volume 25 Issue 1 Pages 1-12
    Published: July 20, 2022
    Released on J-STAGE: October 05, 2022
    Advance online publication: July 21, 2022
    JOURNAL FREE ACCESS

    In order to clarify the riverine longitudinal distribution of native ayu, especially how the upper limit is determined, the density survey by underwater line transect was carried out at 12 fixed points for 9 years from 2013 to 2021 in the Syubuto River where are no structures which obstruct upstream migration of ayu and stocking is not performed. In 2014, ayu was collected from the downstream, midstream and upstream areas for otolith analysis. Otolith Sr/Ca ratio for ayu (n=52) was used to estimate the period of starting upstream migration in the river and relation between the period and settled position of ayu was examined. The estimated population of ayu in 9 years fluctuated from 46,000 to 1,320,000. The upper limit of the distribution and upper limit at density of 0.3 /m2 (density at which all individuals can feed sufficiently) varied between 21 and 37 km and 4 and 37 km from the river mouth, respectively. The distance from the river mouth to the upper limit of distribution and to the upper limit of the density of 0.3 /m2 extended with the increase in the estimated population of ayu. Estimating from the length of otolith after starting upstream migration, most of ayu which had been started upstream migration at early period settled in the upstream, but some of them also settled downstream. On the other hand, there were a lot of individuals which had been started upstream migration at late period in the downstream, but the individual who went upstream was admitted, too. These facts suggest that ayu is not simply moving upstream resulted from extrusion by the individuals recruited later in the season. In addition, the upper limit of distribution in 2018 when the population was the lowest was 10-15 km downstream compared to other years. It is presumed that ayu during upstream migration minimized the cost of migration if satisfactory feeding conditions were obtained.

    Download PDF (1590K)
CASE STUDY
  • Kota TAWA, Taishi HOSOURA, So TSUYUKI, Masami HASEGAWA, Motonari SAKUM ...
    2022 Volume 25 Issue 1 Pages 13-30
    Published: July 20, 2022
    Released on J-STAGE: October 05, 2022
    Advance online publication: July 21, 2022
    JOURNAL FREE ACCESS

    We studied the habitat status of fishes in a Tanaka retention pond (TRP) , which was expected to become a foraging site for oriental storks (Ciconia boyciana) in Japan. By comparing the distribution of a fish community in a lateral drainage channel (LDC) of a paddy field before (December 2018) and after (November and December 2019) flooding by Typhoon No. 19 (Hagibis) , we examined the problems and future policy considerations for fish habitats in the TRP during periods of normal water level. Before flooding, the numbers of taxa and individuals in the LDC were small, and some study sites were no fish. In the LDC, most fish species that have been observed in the main drainage channel (MDC) during the same season were not captured. After flooding, the number of fish taxa and individuals increased significantly in the LDC compared to those before flooding, and some fish species such as the Gnathopogon elongatus elongatus and the Oryzias sp., which were not observed before Hagibis, were captured. In addition, oriental weather loaches (Misgurnus anguillicaudatus) were captured from LDCs that were completely dry before the flood. According to the paddy field survey in May 2019 (before flooding) , only Misgurnus dabryanus, the invasive loach species, were observed to breed in the study paddy fields during the cropping season. Breeding abundance may have been impacted by low continuity to the LDC during baseflow conditions, as many fish species could not migrate to paddy fields during the cropping season nor overwinter sufficiently in the LDC during the non-cropping season. For improving the function of the TRP as a breeding and wintering habitat for fish during baseflow conditions, gaps between the MDC and the LDC and between the LDC and paddy fields must be connected, and a wintering habitat for fish must be secured by actively preserving the channel sections with soft mud and connecting them with the inter-levee floodplain water bodies. However, since these restorations may expand the distribution range of invasive species, our goal should be to conserve the continuity of healthy water bodies.

    Download PDF (28089K)
SHORT COMMUNICATION
  • Kazuaki TAKAHASHI
    2022 Volume 25 Issue 1 Pages 31-46
    Published: July 20, 2022
    Released on J-STAGE: October 05, 2022
    Advance online publication: July 21, 2022
    JOURNAL FREE ACCESS

    Bottom mud deposited in agricultural ponds has potential as a source of fertilizer for plants. I investigated associations of the vegetation area of the pond bank and water surface, the area of dry pond, and the river system with the hydrogen ion concentration (pH) and fertilizer components (nitrate nitrogen, water-soluble phosphate, and water-soluble potassium) of the bottom mud of 10 agricultural ponds by using simplified soil diagnosis kit. The study area was Shioda-daira plain, Ueda, Nagano Prefecture, central Japan, which has many agricultural ponds. The best generalized linear mixed models (GLMMs) revealed a significant associations of the river system with pH, a significant association of vegetation area with water-soluble phosphate content, a significant negative association of vegetation area with water-soluble potassium content, and no significant association of any factor with the nitrate nitrogen content. These results suggest that vegetation on the pond bank acts as a source of water-soluble phosphate, and as a sink absorbing water-soluble potassium. However, relative errors compared to conventional soil diagnosis methods were high for water-soluble phosphate and water-soluble potassium. Although the fertilizer component concentrations of bottom mud varied among the 10 ponds, they exceeded values suitable for plant growth (3 mg/L) in most of the ponds. The pH values were slightly lower than those suitable for plant growth (6.0-6.5) in all 10 ponds. Thus, the bottom mud deposited in agricultural ponds was a rich source of fertilizer characterized by weakly acidic soil. Adjustment of the relative proportions and concentrations of the fertilizer components would be required for use of the bottom mud as fertilizer.

    Download PDF (12864K)
BOOK REVIEW
MEMORIAL WRITING
feedback
Top