We study small stump transplantation for the regeneration of the reed bed in the Kitakami river mouth that was destroyed by the Great East Japan Earthquake, taking workability into consideration. We experimentally examined the optimal suitable submergence factors (water depth, submergence time and salinity) for small reed stumps harvested with and without above-ground organs. Consequently, a suitable water depth and submergence time for transplanting a small reed stump harvested with above-ground organs were concluded to be less than 20 cm and less than 12 h d^-1 (2 cycles d^-1, 6 h cycle^-1) , respectively. Also, even with a submergence time of 12 h d^-1 and water depth of 10 cm, a salt concentration of 1.5-2.0% was inferred to be inadequate for transplanting a small stump harvested with above-ground organs. In contrast, when reed harvested without above-ground organs was submerged 24 h d^-1 at water depths of 10, 20, 30 and 40 cm, early growth was not inhibited. From the above results, for the transplantation of small reed stump harvested without above-ground organs, continuous submergence at water depths of 10-40 cm was inferred to cause no problems.

View full abstract

The application of anammox for nitrogen removal from domestic wastewater was investigated in this study. In order to increase the treatment efficiency, polyurethane foam was used as an attached growth medium, and the organic loading rate was reduced by the high-efficiency solid-liquid separation device. Design and operational parameters such as the volumetric nitrogen loading rate to both the attached growth medium and the reactor, the substrate concentration, and agitation conditions were examined with actual sewage using a pilot-scale experimental apparatus. The main results obtained in this study were as follows; 1) the Kj-N loading rate should be kept less than 100 mg-N L-medium^-1 h^-1 from the viewpoint of sufficient nitrogen removal by anammox; 2) the T-N removal rate was approximately proportional to the square root of NH₄-N concentration, therefore, the plug-flow style in the bioreactor was considered to be desirable for increasing the treatment efficiency; 3) it was also founded that aeration control based on the NO₂-N concentration in the reactor was effective for simultaneous reaction of both nitritation and anammox; 4) the minimum agitation condition was required to avoid the suppression of the reaction rate. Operation under the minimum agitation condition should be adopted from the viewpoint of energy saving.

View full abstract

The concentrations of emerging pesticides in the Sagami River, its tributaries and tap water in the basin were investigated throughout the year of 2014. We investigated six neonicotinoids, tebuconazole, bromacil, tefuryltrione and 2-chloro-4-mesyl-3-［ (tetrahydrofurane-2-il-methoxy) methyl］benzoate (CMTBA) which is one of the products of tefuryltrione degradation. Nine pesticides were detected in river water. Imidacloprid and tefuryltrione were detected during the periods of their application to fields. Tebuconazole and bromacil, which are commonly used as herbicides in urban areas, were mainly detected in winter. We compared the concentrations of pesticides with the Predicted Environmental Concentrations (PEC) that were calculated by the Ministry of the Environment. The maximum concentrations of tebuconazole and bromacil exceeded the PEC for aquatic animals and plants. The concentrations of imidacloprid and clothianidin in tap water varied in accordance with their concentrations in the river water. CMTBA was detected in tap water samples at concentrations almost comparable to the concentrations of tefuryltrione in river water on a molar basis.

View full abstract

After the recovery of natural gas and iodine from the brine pumped up from a gas reservoir layer 500–2,000 m below the ground surface, waste brine containing a high concentration of ammonium (about 200 mg L^-1 NH₄-N) is drained into the Isumi River in the Kujukuri district in Chiba Prefecture. In this study, the fate of NH₄ in the Isumi River was investigated. The nitrification rates in the investigated river section from the discharge point to Shiodome Weir ranged from 0.000 to 0.360 mg L^-1 d^-1, and the transformation efficiency of NH₄-N to NO₂-N and NO₃-N was 6.9％ on average. These extant nitrification rates positively correlated with those obtained in a laboratory test using river water samples. The estimated nitrification rates based on the number of ammonia oxidizing bacteria (AOB) present in the river bottom sediment and their biokinetic parameter values available from references were in the range from 0.044 to 0.104 mg L^-1 d^-1, which are of the same order of magnitude as the extant nitrification rates. Furthermore, the nitrification rates determined by a ¹⁵N dilution technique ranged from 0.00 to 0.19 mg L^-1 d^-1, supporting the extant nitrification rates in the investigated river section.

View full abstract

We investigated temporal changes in ¹³⁷Cs concentrations in the surface soil of flood channels at a primary tributary (site name, Sakai) and a secondary tributary (site name, Nekoya) of Abukuma River from 2012 to 2014. In this study, we employed a real-time kinematic global positioning system (RTK-GPS) to collect samples from pinpoint locations, and to survey the microtopographical change at the monitoring sites. The flood channel of Nekoya was considered to have been completely inundated about 11 times, while Sakai had been partially inundated a few times during the survey period. ¹³⁷Cs concentrations in the surface sediments (0–5 cm) were decreased faster than those in the watershed by inundation (s) . Specifically, ¹³⁷Cs concentrations (Bq m^-2) decreased by 72 ± 21％ at Nekoya from 2012 to 2014, and by 59 ± 34％ at Sakai from 2013 to 2014. However, ¹³⁷Cs concentrations in the flood channel of Nekoya increased at a deeper horizon up to 30 cm. This result suggested that sediment with higher ¹³⁷Cs concentration was buried by that with lower ¹³⁷Cs concentration eroded during flood events.

View full abstract

The volume of treated sewage effluent (TSE) in public water bodies in Japan has increased over time. Therefore, it is critical that we understand the effect of TSE on water cycling, freshwater ecosystems, and conservation. However, it is difficult and expensive to implement studies and conservation activities on the large scales required using only researchers and government agency staff. Citizen science (i.e., engaging the public in scientific research) is increasingly being used to solve the challenge of large-scale environmental monitoring, especially in the United States and Europe. Citizen science is used less frequently in Japan. In 2014, we started a citizen science project to investigate the influence of different sewage treatment methods on the water quality of three rivers in the Sakai River basin in Yokohama City. The project involved the collaboration of citizens, universities, federal and local governments, and local communities. The project revealed that ammonium (NH₄-N) and nitrate (NO₃-N) concentrations and nitrogenous biochemical oxygen demand (N-BOD) differ among the effluents of the sewage treatment plants, suggesting different impacts on the water quality and BOD of each river.

View full abstract