Current Issue

2022, Volume 15,  Issue 2

Water Resources
Abstract:
Tidal flats and saltmarshes have been a long-standing research focus because of their high socio-economic and ecological values. The evolution of tidal flatemarsh systems is highly complex due to the intertwined processes operating over a variety of spatial and temporal scales. As a traditional research highlight, the role of regular hydrodynamic processes such as tides, waves, and river flows have been explored comprehensively with fruitful outcomes. Over past decades, the changing environment (e.g., sea level rise, increasing anthropogenic activities, and extreme weather conditions) has attracted more attention with many reported insightful results. More recent advances indicate that biological activities play a critical role in tidal flatemarsh morphodynamics but are still poorly understood. The field of research that connects the biological and physical processes is commonly described as "biogeomorphology" and requires the joint efforts by scientists from multiple disciplines ranging from hydraulics, ecology, and geography to sociology. This review aims to provide a synthesis of the current research status of tidal flatemarsh morphodynamics, with a particular emphasis on the understanding of various processes and feedbacks underlying the development of morphodynamic models. Some future research needs and challenges are identified to facilitate a more sustainable management strategy for tidal flats and saltmarshes under climate change.
Abstract:
Anomalous characteristics of the atmospheric water cycle structure are highly significant to the mechanisms of seasonal-scale meteorological droughts. They also play an important role in the identification of indicative predictors of droughts. To better understand the causes of seasonal meteorological droughts in the middle and lower reaches of the Yangtze River (MLRYR), characteristics of the atmospheric water cycle structure at different drought stages were determined using standardized anomalies. The results showed that the total column water vapor (TCWV) was anomalously low during drought occurrence periods. In contrast, there were no anomalous signals at the drought persistence and recovery stages in the MLRYR. Moreover, there was no significant temporal correlation between the TCWV anomaly and seasonal-scale drought index (the 3-month standardized precipitation index (SPI3)). During drought events, water vapor that mainly originated from the Bay of Bengal was transported southwest of the MLRYR. Meanwhile, the anomalous signal of water vapor transport was negative at the drought appearance stage. At the drought persistence stage, the negative anomalous signal was the most significant. Water vapor flux divergence in the MLRYR showed significant positive anomalous signals during drought events, and the signal intensity shifted from an increasing to a decreasing trend at different drought stages. In addition, a significant positive correlation existed between the anomaly of water vapor flux divergence and regional SPI3. Overall, water vapor flux divergence is more predictive of droughts in the MLRYR.
Abstract:
Hydrological, sediment, and bathymetric data of the Shashi Reach in the middle Yangtze River for the period of 1975e2018 were collected, and the characteristics of low water level changes and their impacts on utilization of water depth for navigation were investigated. The results showed that, during the study period, the Shashi Reach riverbed was significantly scoured and incised, with cross-sectional profiles showing overall narrowing and deepening. This indicated a strong potential to improve the water depth of the channel. The analysis of the temporal variation of in-channel topographical features showed that the Taipingkou diara underwent siltation and erosion, with its head gradually scoured and relocated downstream after 2008, and the Sanbatan diara continued to shrink and migrate leftwards. Low water levels with the same flow rate over the study period decreased. For instance, from 2003 to 2020, the water level at the Shashi hydrological station decreased to 1.37 m with a flow rate of 6 000 m3/s. Furthermore, the designed minimum navigable water level of the Shashi Reach was approximately 2.11 m lower than the recommended level. In terms of utilization of the channel water depth, continuous scouring of the river channel is expected to result in a reduction in discharge at the Taipingkou mouth, which will improve the water depth conditions of the channel during the dry season in the Shashi Reach. With several channel regulation projects, the 3.5-m depth of the Shashi Reach would basically be unobstructed. This promotes utilization of the shipping route from the Taipingkou south branch to the Sanbatan north branch as the main navigation channel during the dry season. Considering the factors of current water depth and the clear width limitation of the navigation hole at the Jingzhou Yangtze River Bridge, this route can still be favored as the main navigation channel with a 4.5-m depth during the dry season.
Aquatic Environment
Abstract:
In this study, a microbial consortium isolated from an activated sludge tank of a conventional wastewater treatment plant was immobilized using sodium alginate (SA) as a support material for contaminant biodegradation in wastewater. A volume of 500 mL of activated sludge was immobilized in the SA beads (with a mass concentration of 25 g/L). The resulting SA beads were characterized, introduced into a fluidized bed reactor, fed with 1000 mL of the sample, and characterized again after the treatment process. The SA-immobilized microorganisms were tested first for degradation of organic matter (expressed as chemical oxygen demand) and total phosphorous in domestic wastewater, achieving removal efficiencies of 71% and 93%, respectively, after 12 h. Subsequently, the SA-immobilized microorganisms were tested for degradation of a basic blue 9 (BB9) textile dye in a condition that simulated textile wastewater. The efficiency of the BB9 degradation was found to be as high as 99.5% after 2 h. According to these results, SA-immobilized microorganisms were found to be an environmentally friendly and cost-effective alternative for treatment of municipal and industrial wastewater effluents.
Abstract:
As major contributor to the blue carbon sink, intertidal zones play a crucial role in the global carbon cycle. In recent years, more attention has been given to the carbon cycle in intertidal wetlands. However, due to highly variable and uncertain environmental conditions, it is difficult to clarify the quantitative relationship between soil respiration and environmental factors through in-situ experiments. In this study, the response of soil respiration characteristics to variations in the temperature and water table was investigated using a monitoring apparatus of CO2 flux at the soileair interface in the intertidal zone. The results showed that soil respiration flux was significantly correlated with temperature, and the correlation best fitted the DoseResp function. Meanwhile, the respiration flux was enhanced with the descent of water table, a relationship could be described by a quadratic function. The effect of the water table on soil respiration became more pronounced with the rise of temperature. These results provide significant clarification of the impact of human activities on the carbon cycle in bare intertidal zones and as well as support for numerical simulations of the carbon cycle in bare intertidal zones.
Abstract:
Wetlands play an important role in the global carbon cycle as they can be sources or sinks for greenhouse gases. Groundwater discharge into wetlands can affect the water chemistry and act as a source of dissolved greenhouse gases, including CO2 and CH4. In this study, surface water quality parameters and CO2 and CH4 concentrations were evaluated in a tidal wetland (Hunter Wetlands National Park, Australia) using time series measurements. Radon (222Rn), a natural groundwater tracer, was used to investigate the role of groundwater as a pathway for transporting dissolved CO2 and CH4 into the wetland. In addition, water-to-air CO2 and CH4 fluxes from the wetland were also estimated. The results showed a high concentration of radon in wetland surface water, indicating the occurrence of groundwater discharge. Radon concentration had a strong negative relationship with water depth with a determination coefficient (R2) of 0.7, indicating that tidal pumping was the main driver of groundwater discharge to the wetland. Radon concentration also showed a positive relationship with CO2 and CH4 concentrations (R2=0.4 and 0.5, respectively), while the time series data revealed that radon, CO2, and CH4 concentrations peaked concurrently during low tides. This implied that groundwater discharge was a source of CO2 and CH4 to the wetland. The wetland had an average water-to-air CO2 flux of 99.1 mmol/(m2·d), twice higher than the global average CO2 flux from wetlands. The average CH4 flux from the wetland was estimated to be 0.3 mmol/(m2·d), which is at the higher end of the global CH4 flux range for wetlands. The results showed that groundwater discharge could be an important, yet unaccounted source of CO2 and CH4 to tidal wetlands. This work has implications for tidal wetland carbon budgets and emphasizes the role of groundwater as a subsurface pathway for carbon transport.
 Water Engineering
Abstract:
Given that the development of scour downstream of hydraulic structures increases the risk of structural damage, it is important to find costeffective and environmental approaches to reduce this risk. This study aimed to experimentally evaluate the effect of synthetic fibers on the scour profile downstream of a sluice gate with a rigid apron. Experiments were performed with the same Froude number and with different weight percentages of synthetic fibers on both non-cohesive and cohesive sediments. One uniform sand was used as the non-cohesive sediment, and three different cohesive sediments were prepared by mixing different percentages of kaolinite soil with the used sand. The scouring experiments showed that the presence of synthetic fibers did not considerably affect the scour hole dimension in non-cohesive sediments. Evaluation of the scour in the cohesive sediments in silty sand (SM) texture found that an increase in the percentage of silt reduced the scour hole dimensions. The effect of synthetic fibers on scour of SM-texture-based sediments was also investigated, and the results showed that increasing the percentage of synthetic fibers decreased the scour hole dimensions. In addition, the cohesive sediments in SM texture did not have a similar non-dimensional scour profile, and the presence of synthetic fibers did not significantly affect the scour hole.
Abstract:
In order to determine water losses in irrigation canals, a systematic approach was developed, consisting of two main components:a seepage simulation model and a hydraulic simulation model. The SEEP/W module of the Geo-Studio software was used to simulate the seepage rate, and the Hydrologic Engineering Center-River Analysis System (HEC-RAS) hydrodynamic model was used for hydraulic simulation. Different operation scenarios were designed to investigate all possible situations in daily operation of water distribution and delivery systems. The seepage simulation results show that the seepage losses were higher at the bottom and corners of the canal, because the hydraulic gradient was affected by the hydraulic load. The hydraulic simulation results show that due to physical and management infrastructure (using non-automated and operator-based regulation structures), operational losses accounted for a significant volume of losses compared to seepage losses. In most operation scenarios, the maximum seepage loss was 10%, and the remaining 90% was related to operational losses. It is concluded that any factor (decrease or increase of inflow to the canal) that causes an increase or decrease of operational losses is ultimately a determining factor in reducing or increasing total losses. Therefore, management approaches should be adopted to improve performance of the system and reduce losses, especially operational losses, by improving the operation methods of water level regulation and off-take structures.
Abstract:
Traditional methods for early warning of dam displacements usually assume that residual displacements follow a normal distribution. This assumption deviates from the reality, thereby affecting the reliability of early warning results and leading to misjudgments of dam displacement behavior. To solve this problem, this study proposed an early warning method using a non-normal distribution function. A new early warning index was developed using cumulative distribution function (CDF) values. The method of kernel density estimation was used to calculate the CDF values of residual displacements at a single point. The copula function was used to compute the CDF values of residual displacements at multiple points. Numerical results showed that, with residual displacements in a non-normal distribution, the early warning method proposed in this study accurately reflected the dam displacement behavior and effectively reduced the frequency of false alarms. This method is expected to aid in the safe operation of dams.