Abstract
Eighty surveys of ten Scottish beaches recorded litter sizes and weights. A simple model of fragmentation explains the distribution of plastic beach litter weights, producing a logarithmic cascade in weight-frequencies having a power law exponent of 1.6. Implications of fragmentation are numerous. Heavy litter is rare, light fragments are common. Monitoring by number is sensitive to minimum observable fragment size, age of the litter, and energy of the foreshore. Mean litter item weights should be used to calculate beach plastic loadings. Presence/absence of mega litter can distort monitoring by weight. Multiple surveys are needed to estimate mega litter statistics. Monitoring by weight can change the perception of the importance of litter sources (e.g., in our surveys, contribution from fishing was 6% by number, 41% by weight). In order to introduce consistency between beach surveys using visual methods by number, a standard minimum plastic fragment size should be introduced.
Highlights
Marine litter poses environmental and ecological hazards worldwide (Galgani et al, 2015; Beaumont et al, 2019)
By numbers, 88.3% of northeast Scotland beach litter consisted of plastic litter items, while by weight 86.6% was plastic
By number, rubber, paper, metal, and sanitary items each represented about 2–3% of the total load, but by weight rubber and metal dominated, with 7.1 and 3.5%, respectively. These results show that different compositions are inferred from beach litter monitoring data depending on whether number or weight is used as the measure, owing to the difference in weight of individual litter items in each of the litter types
Summary
Marine litter poses environmental and ecological hazards worldwide (Galgani et al, 2015; Beaumont et al, 2019). Data from monitoring programs globally are being used to try to quantify budgets of marine plastics, and to match the predicted inputs of plastic into the sea since the 1950s (e.g., Jambeck et al, 2015; Mai et al, 2020) with the total amounts of plastic that monitoring suggests exists in our oceans today (e.g., Cózar et al, 2014; Koelmans et al, 2017; Lebreton et al, 2019). Galgani et al (2021) have pointed out that despite the growing number of global time series from beach, floating and seabed plastic litter monitoring, there are currently few discernible trends in the plastic content of the sea, possibly suggesting a steady state between inputs and removals. This paper addresses three aspects requiring improvement; an understanding of how large plastic breaks down into small plastic items (i.e., fragmentation), knowledge of the weights of plastic litter items in the sea, and the standardization of monitoring programs so that data around the world can be compared and merged (e.g., Carvalho et al, 2021)
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