Riverine transport of floating macro litter to the Southeastern Black Sea

<p>Marine litter, especially plastic, is the fastest growing environmental problem in the Black Sea. Rivers are recognized as the major sources of litter in the basin, but information on the transport of litter by rivers is still limited. This study presents the first estimates of riverine floating macro-litter in the SE Black Sea (Turkey), based on monthly visual counting in three relatively small rivers between January and August of 2020. Plastic represented 99 % of the identified items with fragments (2.5–50 cm) (40.3 %) and shopping bags (26.2 %) being the most abundant items. Riverine litter fluxes median values varied between 35 and 96 items/hour in three rivers. Results show that small rivers can carry a considerable amount of plastic to the SE Black Sea. This calls for increased monitoring of riverine litter transport to develop effective prevention and removal strategies for tackling the problem of plastic pollution in the Black Sea.</p>

Endless journey of macroplastics in rivers: From hours to decades tracking in the Seine River

<p>Rivers are major pathways of plastics from lands into the Ocean. However, there is still a huge lack of knowledge on how riverine litter, including macroplastics, is transferred into the Ocean. Quantitative measurements of macroplastic emissions in rivers even suggest that a small fraction (0.001 to 3%) of the Mismanaged Plastic Waste (MPW) generated within a river basin finally reach the sea. Instead, macroplastics may remain within the catchment and on coastlines because of complex transport dynamics that delay the transfer of plastic debris. In order to better understand those dynamics, we performed tracking of riverine litter over time. First, hundreds of date-prints items were collected on riverbanks in the Seine estuary. The distribution of their Use-By-Dates suggest that riverine litter may remain stored on riverbanks for decades. Second, we performed real time tracking of floating and sub-floating bottles using GPS-trackers. Between March 2018 and April 2019, 39 trajectories were recorded in the estuary under tidal influence and 11 trajectories upriver, covering a wide range of hydrometeorological conditions. Results show a succession of stranding/remobilization episodes in combination with alternating upstream and downstream transport in the estuary related to tides. In the end, tracked bottles systematically stranded somewhere, for hours to weeks, from one to several times on different sites. The overall picture shows that different hydrometeorological phenomena interact with various time scales ranging from hours/days (high/low tides) to weeks/months (spring/neap tides and highest tides) and years (seasonal river flow, vegetation and geomorphological aspects). Thus, the fate of plastic debris is highly unpredictable with a chaotic-like transfer of plastic debris into the Ocean. The residence time of these debris is much longer than the transit time of water. This offers the opportunity to collect them before they get fragmented and/or reach the Sea.</p>

Monitoring submerged riverine macroplastics using echo sounding

<p>Riverine plastics cause severe global problems, regarding the risk for human health and environmental damage. The major part of the plastic waste that ends up in the oceans is transported via rivers. However, estimations of global quantities of plastics entering the oceans are associated with great uncertainties due to methodological difficulties to accurately quantify land-based plastic fluxes into the ocean. Yet, there are no standard methods to determine quantities of plastics in rivers. For the sake of reducing the amount of plastic waste in the natural environment, information on plastic fluxes from rivers to seas is needed. Focussing on monitoring of the plastic litter that is transported by rivers is useful because measures can easier be implemented in rivers than in seas. Moreover, consistent measuring techniques are crucial to optimise prevention-and mitigation strategies, especially in countries with high expected river plastic emissions.</p><p>Additionally, based on plastic characteristics and turbulent river flow conditions, a considerable portion of the riverine litter can also be transported underneath the surface in the water column. Current monitoring methods regarding macro plastics are labour intensive and do not provide continuous measurements for submerged riverine plastics. Besides, most research done focussed on floating macro litter, instead of submerged plastics. The aim of this research was to find a standard method, applicable in different river systems, for detecting submerged macro plastics.</p><p>With the use of the Deeper Chirp+ fishfinder, several tests were conducted both in the Guadalete river basin in southern Spain and in the lab at the TU Delft. Spanish, and in general European rivers are estimated to transport two to three orders of magnitude below rivers in Asia (Malesia and Vietnam), and should not be neglected. The Guadalete river basin formed a suitable location to test this new method. First, monitoring in the Guadalquivir river was executed, with the use of a net to validate the readings of the sonar. Furthermore, the detecting abilities of the echosounder, in the Guadalete river basin, were tested with the use of plastic targets. The targets were released in the river and passed the sensor at a certain time. Moreover, tests in the lab at the TU Delft were conducted to investigate relations between sonar signal and flow velocity, object depth, and object size.</p><p>The tests show that submerged macro plastics can be detected with the use of echo sounding. Moreover, a relation between the sonar signal and litter size is found. Finally, signal intensities can be related to object properties. In conclusion, the use of echo sounding has a high potential for obtaining more accurate plastic flux estimations.</p>