Webinar of Dr Lisa WEISS
June 2nd 2022
How to strengthen the links between field observation and physical modeling for a better understanding of the plastic cycle in the marine environment?
Synopsis
Although the impact of plastic pollution on marine ecosystems is alarming, we still have little hindsight on its cycle in the oceans. The modeling community has therefore quickly mobilized on this societal issue to better understand the oceanic transport of plastic debris and identify the most vulnerable areas. However, so far, the modeled scenarios are mainly based on the impact of the physical ocean hydrodynamics and the characteristics and processes inherent to plastics are poorly taken into account. Simulations are currently very difficult to validate due to a lack of in situ observations, related to a quantification and characterization of plastic debris still too laborious and expensive. The research community working on plastic pollution is very multidisciplinary, growing and better identified, however the bridges between the various disciplines from social sciences to natural sciences and particularly between the communities of environmental observers and physical modelers are still rare and little used.We propose in this first Webinar of the IRN PASSPORT-2C to address the issue of the link between field observations and modeling to improve the study of the plastic cycle from the continental to the marine environment. How to better adapt plastic sampling methods to meet the needs of modeling? And conversely, how could models become decision aids for measurement campaigns, for impact understanding and for durable solutions?
Back home message
1. How to improve river fluxes in models? What river input models need from observations ?
• Working with homogeneous unitsFor example item.m-3 for microplastics
• When possible providing the corresponding mass data (to calculate conversion factors)
By weighing a few items in the sample or a sub-sample
• Providing the instantaneous water flow at the sampling location
To link plastic flux with water flow seasonality
• When possible categorizing the sampled items according to their properties
Size class, shape, polymer type?
• Need to characterize the sampling locations
• Need to use homogeneous sampling protocols
To be able to compare the measures in models
2. How to improve plastic dispersion? What dispersion models need from observations?
• Accurate size distribution of plastic debris sampled in rivers but also in other sourcesTo calculate specific sinking and rising velocities
• Accurate chemical composition of plastic debris
To characterize the dynamic behavior (rising or sinking ?)
• Shape characteristic of plastic debris
To characterize the effect of wind or turbulence on the plastic waste
• Empirical formulas for the calculation of specific vertical velocities according to the shape
Different shapes could have different dynamic behaviors
Experimental experiments
3. How to improve the simulation of Sinks? What perspectives to improve models based on the observations of sinks ?
• Need high-frequency time monitoring of the plastic quantities at seaTo be able to validate the simulations with the observations
• Need to estimate the stranding rates to improve stranding modeling assumptions
Annual monitoring on beaches
• Need to define hypotheses about sedimentation
Remobilization rate to the water column? Coupling with sediment transport?
• Need to define hypothesis about degradation and fragmentation
Multiplication of the number of particles over time with size reduction?
• Need to characterize bio-accumulation and biofouling
Ingestion rate or aggregation rate over time?
Coupling with bio-geochemical model?
• Models & Observations could work together at the local scale to define and test hypotheses that can be transposed to a larger scale in the models