Seasonal samples of water, sediments, and two submerged plants, Ceratophyllum demersum and Potamogeton pectinatus, were collected from four sites within Al-Hawizeh marsh between December 2017 and November 2018 to assess several heavy metal concentrations (Fe, Cu, Ni, Cd, Pb, Cr, and Zn) and analyzed by using Flame Atomic Absorption Spectrophotometer. All concentrations were compared to permissible limits for aquatic life. The findings have clarified levels of metals so as the following: Sediments > plants > water. Concentrations of heavy metals in sediment decreased within the sequence Fe > Ni > Cd > Cu > Cr > Zn > Pb (mg/kg), plants as Fe > Zn > Cd > Cr > Ni > Pb > Cu (mg/kg dry weight), in water as Fe > Ni > Zn > Pb > Cr > Cd (mg/L). The concentrations of all metals in water didn’t exceed the permissible limit, thus Fe, Ni, and Pb showed a greater concentration in water samples than other metals. In sediments Fe, Ni, and Cd have exceeded the permissible limits except Cd wasn’t detected (ND) during the winter, whereas, Zn and Pb didn’t exceed the recommended limits. In-plant samples as C. demersum Fe, Cd, Zn, and Cr have exceeded the allowable limits, while Cu and Pb didn’t exceed the permissible limits, also in P. pectinatus Fe, Cd, and Zn have exceeded the permissible limits, whereas, Ni, Cu, Cr, and Pb didn’t exceed the permissible limits altogether seasons during this study. The correlation of Pearson was administered to detect the interrelationship between metal concentrations. A significant positive correlation (p ≤ 0.05) was found in sediment rather than plants and water samples.

The construction of dams across rivers controls the magnitude of downstream floods and limits the suspended sediment transport into the downstream areas. We elucidated the downstream hydrological alterations compared to upstream after the construction of Kali Gandaki ‘A’ hydropower dam, Syangja, Nepal using continuous wavelet analysis, cross wavelet analysis and wavelet coherence. The downstream fluvial flow in winter and pre-monsoon seasons showed highest water deficit condition compared to monsoon and post-monsoon seasons. The dam-induced changes in fluvial flow with decreasing amount of sediment alter the downstream flood morphological characteristics of river reach such as flood depth, wetted perimeter of river section, flow velocity, and maximum and minimum floods together with the decrease in amount of suspended sediment. The dam-induced downstream alterations directly or indirectly create stress on the aquatic as well as terrestrial ecosystems. The findings of this study will be useful for hydropower dam gates operation that fulfils the minimum ecological threshold.

Ascertaining peak oxygen demand is crucial for plant designers to determine blower capacities of wastewater treatment plants in planning phase. To obtain this technical information without cumbersome influent sampling and analysis, a set of field-test activated sludge reactors equipped with DO and nitrate-N sensors was installed at 3 sites and continuously operated for a couple of months in each field. Under the controlled aeration and hydraulics of the reactors, the hourly influent oxygen demands were back-calculated as biodegradable constituents using the IWA-Activated Sludge Model #1. The daily maximum concentrations (rounded to last for 1-hour) of biodegradable organics and nitrogen were ranged between 45~258 mg-COD/L and 10.4~32.3 mg-N/L in Site #1; 119~244 mg-COD/L and 28.3~38.7 mg-N/L in Site #2; 194~552 mg-COD/L and 30.2~51.7 mg-N/L in Site #3 respectively. The marginal blower capacities to maintain at least 1.0 mg-O₂/L of DO in the daily maximum oxygen demand were estimated based on the datasets using the statistical method, Extreme Value Distribution analysis. To maintain the DO concentration for 99 days out of 100 days of the plant operations, the blower capacity was supposed to be designed as high as 1.4~2.2 times than those of the blower calculated from the daily average concentration.

The results of acute test on suppression of Daphnia magna filtration activity for one toxicant (K₂Cr₂O₇, ZnSO₄ and MnSO₄) were applied to carry out acute binary tests for 3 binary solutions: “Cr-Mn”, “Cr-Zn” and “Cr-Zn”, where the daphnids were exposed for 1, 2, 3, 4 and 5 hs. While the level of toxicity manifested by the “Cr-Mn” binary systems was lower than “additive”, the results that were observed in the binary solution of “Cr-Zn”, especially for the shorter exposure time of 1–3 hours, showed toxicity above “additive”. A nearly “additive effect” was observed in the binary solution of “Zn- Mn”. We supposed that the theory of metals competing for binding to biotic ligands or any yet unidentified physiological interactions of the metals could explain the toxicity effect on filtration activity of D. magna exposed in three binary solutions. So, the more-than-additive effect for the “Cr-Zn” binary system may indicate that Zn (II) demonstrated its high ability building up protein complexes due to competition with Cr (VI). The less-than-additive toxicity for the “Cr-Mn” solution likely revealed the fact that bioavailability of Cr (VI) to D. magna was reduced in the presence of Mn (II).

Field experiments were conducted at brackish-water sites (Lake Hinuma, Hinuma River, and Naka River) to investigate oxidative stress responses of a brackish-water clam, Corbicula japonica, to sediment composition and water quality. To ascertain the influence of the sediment composition, clams were subjected to three test sediments with different contents of clay/silt and organic matter from the same site. Sediment with ~33% of clay/silt content and ~10% of ignition loss exhibited decreased oxygen radical absorbance capacity (ORAC) within two weeks (p < 0.05). However, sediment with less than ~20% of clay/silt content and/or ~7% of ignition loss had no influence on ORAC (p > 0.05). To ascertain the influence of the water quality, clams were placed in baskets without sediment at four brackish-water sites. Significant differences in ORAC were observed in response to salinity and chlorophyll a (Chl a) (p < 0.05). Multiple regression analysis indicated that the levels of salinity and water temperature as well as variations in Chl a, dissolved oxygen, and turbidity for 1 d prior to the sampling date affected ORAC. We concluded that natural influencing factors need to be considered in ORAC assays for C. japonica, when anthropogenic impacts are assessed.

This study developed a fate model of pharmaceuticals and personal care products (PPCPs), including acetaminophen, caffeine, and crotamiton, derived from combined sewer overflow (CSO) in the Tokyo coastal area. The target PPCPs were proposed as promising sewage markers having different persistency during treatment processes and in the environmental water. The PPCP model consists of hydrodynamic calculations and environmental kinetics by biodegradation and photodegradation. We considered inputs from pumping stations, sewage treatment plants, and urban rivers as CSO sources. We measured the PPCPs concentrations, Escherichia coli, and salinity in the collected surface water samples from several locations around Tokyo coastal area for consecutive days after rainfall events in October 2017 (113 mm), June 2018 (81 mm), and July 2018 (67 mm). We found high correspondence between simulation and monitoring results on E. coli and three PPCPs in the coastal locations for all events, suggesting that the model has the potential to quantitatively evaluate CSO-derived contaminants in the Odaiba Seaside Park and nearby locations. Simulation showed that acetaminophen concentration rapidly declined due to its susceptibility to sunlight and biodegradation. Caffeine and E. coli showed different attenuation rates, whereas crotamiton concentration did not change because of its comparable concentration level in CSO.