In Japan, the WET method for assessing the ecological effects of wastewater in a short-term chronic toxicity test employing aquatic creatures is now being explored for development. On the other hand, there is a johkasou, which is an individual decentralized wastewater treatment facility in Japan. However, the ecological impact of this johkasou treated water, has yet to be determined. Therefore, in this study, the tandoku-syori and gappei-syori johkasou treated water and greywater were collected from 120 sites in Saitama, and the algae growth inhibition effect of the johkasou treated water was evaluated in the algae growth inhibition test. As a result, tandoku-syori johkasou treated water had a stronger growth-inhibiting effect than gappei-syori johkasou treated water on algae. It was also confirmed that the effects of algae growth inhibition on greywater vary greatly from site to site. Differences were observed in water quality of the treated water between winter and summer, but no significant difference was observed in the inhibition of algae growth. The correlation between each sample’s water quality concentration and the inhibition of algae development in the sample water was confirmed to be low.

Large nitrate (NO₃⁻) leaching from forests is undesirable. Along the Japan-sea side, stream NO₃⁻ concentrations are low level in Japan despite the high level of nitrogen (N) deposition. Here, the causal relationships between stream NO₃⁻ concentrations and key regulating factors were investigated using structural equation modeling (SEM) for the Kinki region (KIN) of Japan, which consists of seven prefectures and includes the Japan-sea side of KIN (JSK), with the objectives of identifying the specific mechanism of NO₃⁻ leaching for the JSK and comparing it with the one for the entire KIN. In the previous study, stream water was collected from 1,691 watersheds without human-created features in KIN (405 from JSK) between 1997 and 2012, and key factors regulating NO₃⁻ leaching were clarified using Random Forest regression. SEM mostly supported the previously suggested mechanisms. Deposited N was incorporated into the ecosystem, enhanced N mineralization and nitrification in the soil, and increased NO₃⁻ leaching. Heavy rain over the entire KIN and snow along JSK lowered NO₃⁻ concentration in soil water and NO₃⁻ leaching. Contrary to the expectation, precipitation during the growing season along JSK contributed to N input into the ecosystems. We provided the first statistical mechanism of NO₃⁻ leaching using SEM.

U Minh Thuong National Park is a key site for wetland biodiversity conservation in Vietnamese Mekong Delta. This paper outlines a field experiment carried out in U Minh Thuong National Park in the dry season 2019. The study aimed to compare methane emissions and related physicochemical soil and water parameters between the Peat swamp forest and Melaleuca forest. The results show that both water and soil parameters at 8 examined sites in Melaleuca forest and Peat swamp forest fluctuated highly over the sampling intervals. The average hourly C-CH₄ emission rates in Melaleuca forest (26.58 mg/m²/h) was higher than that in Peat swamp forest (21.18 mg/m²/h). Generally, water level and redox potential were important factors regulating emissions of methane gases. The Eh values were all negative values, ranged between −196.5 ± 22.75 mV and −27.75 ± 15.37 mV, indicative of high electron activity and intense anaerobic. Peat swamp forest’s soil had relatively higher organic matter, CEC, TN and TP values than Melaleuca forest’s soil. The COD values fluctuated between 197.3 ± 51.78 mg/L and 396.8 ± 25.77 mg/L, indicative of organic pollution of surface water. It is suggested shorter time measurement (at least twice a day) of methane emission for more accurate evaluation.

Tidal flow constructed wetlands (TFCWs) have been proposed as a new type of CW for enhanced wastewater treatment. However, the characterization of TFCWs in the removal of organic carbon and nitrogen remains unclear. This study investigated the efficiencies and characteristics of lab-scale TFCWs in removing organic carbon and nitrogen from sewage; in particular, the dynamics of dissolved total organic carbon (DOC), nitrogen, and dissolved oxygen (DO) were observed. Pumice- and zeolite-TFCWs were prepared, which treated sewage at 21 h fill and 3 h rest cycles. Sewage was rapidly oxidized in these TFCWs after inflow. The experimental results showed that DOC was efficiently decreased by aerobic biodegradation with DO consumption. Additionally, NH₄⁺-N was oxidized to NO₃⁻-N by nitrification, the DO content decreased, and NO₃⁻-N was removed by denitrification in the TFCWs. The processes of aerobic-anaerobic switching, organic carbon biodegradation, and nitrification-denitrification were observed in the TFCWs. During 128-days of operation, the pumice- and zeolite-TFCWs exhibited the DOC removal capacities of 4.2 and 4.3 g-DOC/m²/d, respectively, and total dissolved inorganic nitrogen removal capacities of 3.1 and 5.1 g-N/m²/d, respectively. These results revealed the higher organic carbon and nitrogen removal capacities and mechanisms of pumice- and zeolite-TFCWs treating sewage.