??Efficacy of small-farm reservoirs (SFRs) was evaluated experimentally as supplemental irrigation of rainfed agriculture under a tropical monsoon climate. The experiment was conducted during two crop seasons from November 2013 to February 2014 in the rainy season and from March to June 2014 partly in the dry season. Five SFRs were constructed in Gondangrejo, Central Java, Indonesia, with the volumes designed to store runoff from the catchment area during the maximum daily rainfall in 2012 and 2013. SFRs harvested 10.4%-30.6% of total rainfall during the experiment, which was strongly influenced by the size and slope of the catchment area. In the first crop season, SFR1 irrigated an onion farm and other four SFRs irrigated paddy fields sufficiently for rice cultivation albeit four short droughts. In the second crop season, SFR1 was not used due to the labor shortage, and SFR2, SFR3, and SFR4 irrigated paddy fields sufficiently for rice cultivation. However, SFR5 could not irrigate the paddy field without a supplemental use of groundwater due to the larger irrigation area than the catchment area. The results indicated potential of SFRs for enabling cultivation of valuable crops such as rice during dry seasons under a tropical monsoon climate.
??The Sanriku coastal area suffered serious damage from the Great East Japan Earthquake that occurred on March 11, 2011. Four years have passed since the earthquake, and reconstruction of the aquaculture industry is progressing. In order to achieve sustainable development and promotion, it is necessary to correctly understand the environment of the Sanriku coastline. Sanriku Coast is a type of enclosed coastal sea which is called a rias coast; hence, substances such as nitrogen and phosphorus from rivers flow out and affect water quality. In this study, in order to consider outflow characteristics and nutrient load in two Sanriku rivers, we observed the outflows, water levels and water qualities of each by periodic field observation. As a result, the nutrient loads of the Sanriku rivers were estimated using the HQ curve and LQ equation. Additionally, we estimated the formula of the nutrient load using preceding rainfall. Although there was some variation in reliability due to the adopted period of preceding rainfall, it was successfully demonstrated that it is possible to estimate the substance load through a simple expression.
??When considering the aquatic environmental conservation of a closed water body in which organic contamination is ongoing, it is important to study the occurrence mechanism of anaerobic organic matter decomposition such as denitrification in addition to both iron and sulfate reduction due to increasingly anoxic conditions in the aquatic environment. From the perspective of oxidation-reduction potential (ORP), nitrate nitrogen (NO3-N), ammonia nitrogen (NH4-N), phosphate phosphorus (PO4-P), sulfides, and dissolved organic carbon (DOC), we herein present a quantitative evaluation of water quality dynamics near the water bottom under the anaerobic state in a laboratory environment. We modeled the ORP behavior at the bottom of the aquatic environment under anaerobic conditions by using a regression equation that applies a logistic curve and uses the number of days of continuous anoxic condition as the time axis. Specifically, the rate of ORP decrease was shown to be dependent on the concentration of NO3-N at the time of anoxic condition development. In addition, temporal changes in the decrease of NO3-N and increases of NH4-N, PO4-P, and sulfide were modeled with either linear or non-linear regressions. In particular, the properties of organic matter such as the ease and difficulty of degradation are shown to have a strong impact on the rate of PO4-P increase, whereas the production of sulfides increased with a higher concentration of TOC. Furthermore, the laboratory experiment showed that, in an actual aquatic environment with various coexisting redox reactions, the following reduction reactions take place under anaerobic conditions: denitrification, followed by iron reduction and then sulfate reduction. Each reaction is completed before the next one begins. In addition, when the concentration of DOC derived from humic acid is extremely high, even under an anoxic environment, ORP becomes positive and may lead to an oxidative state. Thus, we were able to incorporate the resultant measurements of PO4-P, sulfides and DOC to explain these mechanisms based on the experiment results.
??We examined the food webs in the main irrigation and drainage canals on the alluvial fan of the Tedori River (Ishikawa Prefecture, Japan) by measuring the carbon and nitrogen stable isotope ratios in food sources, aquatic insects, other benthic animals, and freshwater fishes in the upper, middle, and lower reaches. The results showed that the food webs in the canals mainly comprised aquatic insects, freshwater shellfish, and fish that originated from the canal bed sediment, and periphyton on the concrete-lined bed and side walls, and cobbles and boulders on the channel bed. The results also showed that the carbon and nitrogen stable isotope ratios of the periphyton increased in the lower reaches due to a decrease in flow velocity and an increase in the anthropogenic nitrogen load; the increases in the stable isotope ratios of the primary producers triggered increases in the stable isotope ratios of the entire food chain. The nitrogen of high stable isotope ratio conveyed by diadromous fish from a sea also might triggered the increase in the nitrogen stable isotope ratio of the entire food chain. Upstream migration of fishes and downstream migration of aquatic insects left gaps in the stable isotope ratios between predators and prey. Sustainable management of the cobbles and boulders will contribute to the conservation and rehabilitation of aquatic fauna and will promote water purification in the canals by increasing the number of aquatic insects that feed on periphyton and the number of fishes that feed on aquatic insects and periphyton.
??From the late-1980s until 1994, the coastal forest situated in the Fukiage sand dune, Kagoshima, Japan suffered catastrophic damage from pine wilt disease and wind damage, causing many of the trees to die. We studied the succession of vegetation, soil development and the water infiltration rate following severe damage of the coastal forest on the Fukiage sand dune. We placed two 250-m transects perpendicular to the shoreline from the top of the fore-dune to the inland area and conducted field investigations. The two transects were placed in contrasting areas of coastal forests; one in an area that had been severely damaged by pine wilt disease and wind damage, the other in an area that was almost undamaged. The number of trees and tree species, breast height cross-sectional area, Fisher-Williams index of diversity, forest soil thickness, and water infiltration rate all increased with distance from the top of the fore-dune. However, the pH and dry density of the forest soil surface layer decreased with distance from the top of the fore-dune. The severe environmental conditions in this coastal sand dune caused the coastal forest to become poorly developed. Specifically, the trees in this area had been severely damaged by pine wilt disease and wind damage causing it to be poorly developed when compared with an area of coastal forest that was almost undamaged and existed as climax forest.
??To evaluate the habitat and examine comprehensive conservation measures for the freshwater type of nine-spined stickleback (Pungitius sp.1) in the Oko River basin, Sika, Ishikawa, we developed a Habitat Suitability Index (HSI) model using weighted geometric mean formulas obtained by multiple linear regression analysis. The HSI values obtained by the model revealed that the habitat qualities in four of the watercourses were superior to those in other areas. The habitat unit (HU) values also showed that one watercourse and a pond were important habitats in terms of quality and quantity. The study showed that the HSI model is a practical tool in managing the habitat for this species. In the model test, significant regression formulas were obtained between the minimum values of population density and the minimum and averaged values of HSI for each water area in the study period.