Abstract: Aggregation is used to represent the real world in a model at an appropriate level of abstraction. We used the convection-diffusion equation to examine the implications of aggregation progressing from a three-dimensional (3D) spatial description to a model representing a system as a single box that exchanges sediment with the adjacent environment. We highlight how all models depend on some forms of parametric closure, which need to be chosen to suit the scale of aggregation adopted in the model. All such models are therefore aggregated and make use of some empirical relationships to deal with sub-scale processes. One such appropriately aggregated model, the model for the aggregated scale morphological interaction between tidal basin and adjacent coast (ASMITA), is examined in more detail and used to illustrate the insight that this level of aggregation can bring to a problem by considering how tidal inlets and estuaries are impacted by sea level rise.
Abstract: Growth in urban population, urbanisation, and economic development has increased the demand for water, especially in water-scarce regions. Therefore, sustainable approaches to water management are needed to cope with the effects of the urbanisation on the water environment. This study aimed to design novel configurations of tidal-flow vertical subsurface flow constructed wetlands (VFCWs) for treating urban stormwater. A series of laboratory experiments were conducted with semi-synthetic influent stormwater to examine the effects of the design and operation variables on the performance of the VFCWs and to identify optimal design and operational strategies, as well as maintenance requirements. The results show that the VFCWs can significantly reduce pollutants in urban stormwater, and that pollutant removal was related to specific VFCW designs. Models based on the artificial neural network (ANN) method were built using inputs derived from data exploratory techniques, such as analysis of variance (ANOVA) and principal component analysis (PCA). It was found that PCA reduced the dimensionality of input variables obtained from different experimental design conditions. The results show a satisfactory generalisation for predicting nitrogen and phosphorus removal with fewer variable inputs, indicating that monitoring costs and time can be reduced.
Abstract: The exotic species Spartina alterniflora (S. alterniflora) seriously threatens the stability and functioning of saltmarsh ecosystems in the Yangtze Estuary. Ambitious efforts have been undertaken to control this species, but subsequent re-invasion is frequent, presenting a significant barrier to restoration. The complexity and high cost of integrated physical control programs has necessitated a shift in focus, leading to considerable attention being paid to the potential of herbicides to control S. alterniflora. To find a strategy for emergency control of small and scattered patches of re-invading S. alterniflora, an in situ field experiment using Gallant (Haloxyfop-R-methyl) herbicide was conducted. The growth parameters of plant density and height were used to evaluate the control efficiency of different treatment dosages and times and sediment samples were taken for environmental toxicity analysis. The results show the following: (1) the control efficacy of the maximum proposed application dose (2.70 g/m2) was 92% for continuous swards and 100% for small patches, while those of other dosages (0.45 g/m2, 0.90 g/m2, and 1.35 g/m2) were lower than 40%; (2) the appropriate implementation time was July to August with 100% mortality resulting from a single application, while S. alterniflora was shown to be capable of recovering rapidly after treatment in May; and (3) there were no significant differences in the community structure of meiofauna among the herbicide treatments and the control, and no herbicide residues were detected in sediment samples collected from treatment areas. This chemical control method was implemented in the Shanghai Chongming Dongtan National Bird Nature Reserve (CDNR). The results of this study indicate that Gallant is an environmentally friendly herbicide with high efficiency, which can be adopted for emergency control of re-invading S. alterniflora.
Abstract: A saltmarsh has developed rapidly on the mudflat of Andong Shoal, in southern Hangzhou Bay, over the last decade since embankment. The saltmarsh vegetation changes are driven by both sediment dynamic conditions and the competition between the exotic species Spartina alterniflora (S. alterniflora) and the native species Scirpus mariqueter (S. mariqueter). This study attempted to investigate large-scale spatial variations in the exotic and native species, by analyzing and interpreting a time series (2016 to 2018) of high-resolution (less than 1 m) remote sensing images. The total area of the saltmarsh increased at a rate of 1.07 km2/year, due to the accretion of the whole tidal flat. The spatial patterns revealed a new bimodal pattern for S. alterniflora invasion. S. alterniflora expanded over the upper to middle saltmarsh at a rate of 1.68 km2/year. However, the S. alterniflora patches at the seaward edge expanded at a negative rate of -0.005 km2/year, indicating a different pattern in competition: S. alterniflora had more advantages in the upper saltmarsh, while S. mariqueter had more advantages in the pioneer zone with low elevation. Consequently, S. alterniflora mainly established new habitats by invading S. mariqueter in the middle saltmarsh, but S. mariqueter occupied the bare mudflat for tradeoff. Our results also indicated that the interspecific competition result between S. alterniflora and S. mariqueter depended on elevation, and low elevation might create a favorable environment for S. mariqueter to win the competition with exotic species. This finding could be applied to future invasive species control and saltmarsh management.
Abstract: Salt marshes are among the most common morphological features found in tidal landscapes and provide ecosystem services of primary ecological and economic importance. However, the continued rise in relative sea level and increasing anthropogenic pressures threaten the sustainability of these environments. The alarmingly high rates of salt marsh loss observed worldwide, mainly dictated by the lateral erosion of their margins, call for new insights into the mutual feedbacks among physical, biological, and morphological processes that take place at the critical interface between salt marshes and the adjoining tidal flats. We combined field measurements, remote sensing data, and numerical modeling to investigate the interplays between wind waves and the morphology, ecology, and planform evolution of salt marsh margins in the Venice Lagoon of Italy. Our results confirm the existence of a positive linear relationship between incoming wave power density and rates of salt marsh lateral retreat. In addition, we show that lateral erosion significantly decreases when halophytic vegetation colonizes the marsh margins, and that different erosion rates in vegetated margins are associated with different halophytes. High marsh cliffs and smooth shorelines are expected along rapidly eroding margins, whereas erosion rates are reduced in gently sloped, irregular edges facing shallow tidal flats that are typically exposed to low wind-energy conditions. By highlighting the relationships between the dynamics and functional forms of salt marsh margins, our results represent a critical step to address issues related to conservation and restoration of salt marsh ecosystems, especially in the face of changing environmental forcings.
Abstract: China’s continuous and rapid economic growth has led to the reclamation of large sections of the intertidal mud coast in combination with port construction, such as that of the proposed Tongzhou Bay port on the Jiangsu coast. These reclamations threaten the local ecosystem services. An ecotope distribution map was created and a hydrodynamic numerical model of Tongzhou Bay was set up to quantify the impacts of reclamation on the ecosystem. Based on the field data and model results, several abiotic features were classified into 11 ecotopes and visualized in an ecotope map of the Tongzhou Bay ecosystem. Validation with spatial distributions of two threatened shorebird species (bar-tailed godwit and great knot) showed confirmation with the mid-range and low-range littoral zones (inundated from 40% to 100% of a tidal cycle), indicating the importance of the areas with these conditions to these populations. Overlaying the ecotope map with recent and proposed land reclamation schemes revealed a loss of ecotopes, composed of the high-range (42%), mid-range (48%), and low-range (38%) littoral habitats, corresponding to a 44%–45% loss of the most important ecotopes for bar-tailed godwit and great knot (mid-range and low-range littoral zones). These results confirm the applicability of the novel ecotope assessment approach in practice.
Abstract: This study investigated the removal of hexavalent chromium (Cr(VI)) in aqueous solutions using pomelo peel (PP) and FeCl3-modified pomelo peel (FPP) as novel biomass adsorbents. Batch adsorption experiments were performed to evaluate the effects of pH, time, temperature, initial concentration, and adsorbent dose on Cr(VI) removal by PP and FPP. The results show that the maximum adsorption capacity of Cr(VI) was 21.55 mg/g for FPP and 0.57 mg/g for PP at a pH of 2.0 and a temperature of 40 ℃. The surface shape, microstructure, and chemical composition of FPP were analyzed with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and energy dispersive spectroscopy (EDS), and compared with those of PP. The results show that the adsorption performance of FPP was much better than that of PP, indicating that FPP can be an alternative high-efficiency adsorbent for Cr(VI) removal.
Abstract: Pile foundations have been widely used in offshore engineering. In this study, a three-dimensional numerical model was used to investigate the seabed response around a mono-pile under wave-current loading. Reynolds-averaged Navier-Stokes equations were used to simulate the flow field, and Biot’s consolidation equations were used for simulating the response of a porous seabed. The pore water pressure within soil and the effective stress along the depth of the seabed were simulated for various current velocities, with currents traveling either along or against the wave. Results indicate that the current has a significant effect on the effective stress and the pore water pressure distributions, which increases with the current velocity, and that the current traveling against the wave increases the liquefaction depth of the porous seabed.
