Sensitivity Analysis of a Riparian Vegetation Growth Model

The paper presents a sensitivity analysis of two main parameters used in a mathematic model able to evaluate the effects of changing hydrology on the growth of riparian vegetation along rivers and its effects on the cross-section width. Due to a lack of data in existing literature, in a past study the schematization proposed here was applied only to two large rivers, assuming steady conditions for the vegetational carrying capacity and coupling the vegetal model with a 1D description of the river morphology. In this paper, the limitation set by steady conditions is overcome, imposing the vegetational evolution dependent upon the initial plant population and the growth rate, which represents the potential growth of the overall vegetation along the watercourse. The sensitivity analysis shows that, regardless of the initial population density, the growth rate can be considered the main parameter defining the development of riparian vegetation, but it results site-specific effects, with significant differences for large and small rivers. Despite the numerous simplifications adopted and the small database analyzed, the comparison between measured and computed river widths shows a quite good capability of the model in representing the typical interactions between riparian vegetation and water flow occurring along watercourses. After a thorough calibration, the relatively simple structure of the code permits further developments and applications to a wide range of alluvial rivers

Vulnerability, impacts and assessment of climate change on Jakarta and Venice

In the next future, cities located in coastal areas are likely to suffer for climatic changes more than all other human systems. The demographic growth, combined with sea-level rise and global warming related to natural causes and anthropogenic activities, endanger those systems. Thence, to effectually cope with new climate forcing, coastal cities need improvements to be sustainable, resilient and liveable, applying flexible design approaches rather than a traditional one. The paper highlights such concepts presenting two case studies of important coastal cities: Venice, in Northern Italy, and Jakarta, the capital city of Indonesia. Although characterized by completely different climatic conditions and living habits, these two metropolises are highly impacted by humans and threatened by similar factors like subsidence and sea-level rise, which increase their exposure to future calamities principally driven by climate change but strictly related to anthropic pressures. The present situation shows that, for the future, the resilience of coastal megalopolis can be increased only using a mix of approaches at various levels, spanning from technical measures to adaptable planning instruments that consider future uncertainties

Threshold surface concentration of microplastics triggering higher mobility on gravel bed

To study the effects of different surface concentrations of microplastics (MPs) on their mobility, a series of experiments was run in a flume with gravel bed. Different amounts of two types of compact MPs (with densities of 1.1 and 1.4 g/cm3) were released. The surface concentration of MPs spanned between 0.3 and 30 g/kg of surface clasts (corresponding to a surface cover ranging from 0.04% to 4%) and the MPs were allowed to deposit under low flow velocity conditions. As the flow rate was increased, stepwise, exceeding the MPs-specific reference threshold conditions (observed in previous studies of MPs moving on a microplastic bed) two different behaviours were observed: i) low-density MPs mobilised at conditions similar to the reference ones up to approximately a concentration of 3g/kg surface clasts (0.04% surface cover) while, ii) high-density MPs were not mobilised at their reference threshold conditions up to a concentration of 15g/kg surface clasts, corresponding to 2% surface concentration. As the mentioned values were surpassed, both MPs types showed a higher mobility (compared to the reference), meaning lower mean flow velocities triggered motion of a larger number of particles. Preliminary analysis of mean flow conditions and videos of moving particles suggest that a "critical concentration" exists, above which the chosen microplastic particles assume higher mobility, requiring lower flow velocities to get into motion. This higher mobility may be ascribed to the changed morphology of the bed which corresponds to critical concentrations of added plastic particles over the gravel bed. This n̈ew morphologym̈odifies the near-bed flow characteristics, thus imposing new conditions to the MPs' mobility. Further investigations are needed to confirm such hypothesis, with specific focus on the near-bed flow field. Also see: https://micro2022.sciencesconf.org/426572/documentIn MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nan

Microplastics:What Can We Learn from Clastic Sediments?

Microplastics research has gained momentum in the 21st century but lags behind the long-standing research on clastic sediment. An interdisciplinary review paper was conducted, comparing microplastics with natural sediments in terms of particle properties, transport processes, sampling techniques, and ecotoxicology. The paper identifies seven research goals to enhance our understanding of microplastics in freshwater environments while learning from sediment research. This extended abstract presents the core message of the review paper, emphasizing the need to improve descriptions of microplastic particles, understand their transport processes, develop standardized sampling methods, and study their ecotoxicological effects. The research goals outline specific tasks to achieve these objectives and emphasize the importance of comparing microplastics to sediments to gain insights into their toxicity. Addressing these research goals will contribute to a comprehensive understanding of microplastics and their impact on freshwater ecosystems. For detailed insights, the original paper should be consulted.</p