Anthropocene Coasts最新文献

Two field campaigns in Dafeng and Jianggang were organized to compare spatial variations of hydrodynamic characteristics and sediment transport patterns on intertidal flats of different types with distinct human interferences along middle Jiangsu coast, China. The major contributors to the different patterns of sediment dynamics between the two tidal flats were offshore tidal current field and human interference. Offshore tidal force provide the basic setup of tidal current patterns on tidal flats, which is then modified by local morphology. Seawalls parallel to coast reduce tidal flat width, forcing tidal energy to dissipate within a shorter distance and thus influencing tidal flat morphology. Seawalls vertical to coast and major tidal current significantly reduce tidal current speed, which favors sediment deposition on tidal flats. Two seawalls built on both sides of the observational tidal flat profile caused much reduced current speed at Dafeng tidal flat, comparing to the offshore station. Being exposed to offshore radial tidal currents, hydrodynamics at Jianggang was much stronger than that at Dafeng. Residual currents at both areas showed net landward transport at the lower flat and net seaward transport at the upper flat, in favor to sediment accumulation at the middle flat. Sediment flux over tidal cycles showed net landward sediment transport at Dafeng, and net seaward transport at Jianggang, consistent with the convex-up accretion-dominated profile observed at Dafenge, and concave-up erosion-dominated profile observed at Jianggang. The instantaneons sediment flux changed significantly due to variations in velocity and sediment concentrations, but these terms counteracted with each other within tidal cycles, leading to the dominant role of Eulerian flux in determining net sediment flux over tidal cycles.

Delta evolution in the context of no sediment discharge has become a global concern, and an accretion-to-erosion conversion is occurring in the Yangtze estuary. This conversion could threaten Changjiang subaqueous delta development. Sediment erodibility is an important indicator of subaqueous delta vulnerability. However, the present and future erodibility of the Changjiang subaqueous delta remains unclear. In this study, 37 short cores were collected from the Changjiang subaqueous delta, and the critical shear stress of the sediment was measured using a cohesive strength meter (CSM) and compared with estimates based on an empirical Shields diagram. The sediment erodibility was analyzed by comparing the sediment critical shear stress with the bed shear stress simulated using a numerical model (i.e., FVCOM), and sediment activity was introduced to discuss the geomorphological change in the subaqueous delta. The CSM-derived critical shear stress is significantly higher than that derived from the empirical Shields formula, but it better shows the erodibility of the sediment. The annual surface sediment activity ranges from 5% to 30% based on the CSM, indicating low surface erodibility. Moreover, the critical shear stress in this region increases as water depth increases, but the bed shear stress shows the opposite trend. Therefore, the erodibility of the Changjiang subaqueous delta is lower than that of the shallow area, indicating no accretion-erosion conversion or continued vertical erosion under sediment starvation in the coming decades. These findings can provide suggestions for erosion assessment and management in large river deltas under decreasing sediment discharge.

Urban coastal wetlands are fragile ecosystems that provide important ecosystemic services. However, these ecosystems are subject to considerable external pressures from urban development, which leads to serious disturbances in their structure, functioning, and diversity as a result of the advancement of urban, agricultural, foraging, and drainage activities, as well as displacement of endemic species by invasive ones. Within the biological communities of these ecosystems, arthropods play an important trophic and ecological role as food resource, pollinating agents, biological controllers, organic matter decomposers, and nutrient cyclers. In this paper we characterize the taxonomic richness and abundance of the terrestrial arthropod fauna of the Aguada de La Chimba urban coastal wetland (Antofagasta Region, Chile) using various methods. From a total of 1,874 specimens, we identified 109 terrestrial arthropod species, where Insecta was the most represented taxon, with 85 species, 47 families, and 15 orders. The estimated species richness values were higher than the observed values for the different groups under study, and insects showed the highest species values in all estimators. Based on their origin, the communities identified included native (24%), naturalized (22%), and to a lesser extent, endemic species. We also characterize the major threats to this urban wetland and discuss the importance of building public–private partnerships with the local community for the success of biodiversity conservation programs in coastal ecosystems.

Microplastics are ubiquitous in the environment, eventually becoming part of the geological record as ‘technofossils’. However, research on the chronological characteristics of microplastics remains limited. This study reviewed dating methods, microplastic abundance, and microplastic polymer type in sedimentary cores globally. Furthermore, the ‘evolution’ of plastic types was compiled in sequence, and a microplastic chronological sequence in the sedimentary record was established. This microplastics chronological sequence was applied to 39 published cores with microplastic polymer analysis. The sediment age ranges determined by microplastic type were found to correspond to the published ages, indicating that microplastics could be useful for dating sedimentary cores on a centennial scale. Furthermore, good preservation and limited mobility of microplastics in burial records make microplastic dating an effective supplementary dating method for determining ages of Anthropocene sediments.