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Home arrow Environment arrow Marine Anthropogenic Litter

Distribution

Beaches

Marine debris is commonly found at the sea surface or washed up on shorelines, and much of the work on marine litter has focussed on coastal areas because of the presence of sources, ease of access/assessment and for aesthetic reasons (McGranahan et al. 2007). Marine litter stranded on beaches is found along all coasts and has become a permanent reason for concern. Beach-litter data are derived from various approaches based on measurements of quantities or fluxes, considering various litter categories, and sampling on transects of variable width and length parallel or perpendicular to the shore. This makes it difficult to draw a quantitative global picture of beach litter distribution. In general, methods that are used for estimating amounts of marine debris on beaches are considered cheap and fairly reliable, but it is not clear how it relates to litter at sea, floating or not. Moreover, in some coastal habitats, litter may be of terrestrial origin and may never actually enter the sea. Most surveys are done with a focus on cleaning, thereby missing proper classification of litter items. When studies are not dedicated to specific items, litter is categorized by the type of material, function or both. Studies record the numbers, some the mass of litter and some do both (Galgani et al. 2013). Evaluations of beach litter reflect the long-term balance between inputs, land-based sources or stranding, and outputs from export, burial, degradation and cleanups. Then, measures of stocks may reflect the presence and amounts of debris. Factors influencing densities such as cleanups, storm events, rain fall, tides, hydrological changes may alter counts, evaluations of fluxes and, even if surveys can track changes in the composition of beach litter, they may not be sensitive enough to monitor changes in the abundance (Ryan et al. 2009). This problem can be circumvented by recording the rate, at which litter accumulates on beaches through regular surveys that are performed weekly, monthly or annually after an initial cleanup (Ryan et al. 2009). This is actually the most common approach, revealing long-term patterns and cycles in accumulation, requiring nonetheless much effort to do surveys. However, past studies may have vastly underestimated the quantity of available debris because sampling was too infrequent (Smith and Markic 2013).

It is unfeasible to review the hundreds of papers on beach macro-debris, which often apply different approaches and lack sufficient detail (see also Hidalgo-Ruz and Thiel 2015). Most studies range from a local (Lee et al. 2013) to a regional scale (Bravo et al. 2009) and cover a broad temporal range. Information on sources, composition, amounts, usages, baseline data and environmental significance are often also gathered (Cordeiro and Costa 2010; Debrot et al. 2013; Rosevelt et al. 2013) as such data are easier collected. Most studies record all litter items encountered between the sea and the highest strandline on the upper shore. Sites are often chosen because of their ecological relevance, accessibility and particular anthropogenic activities and sources. Factors influencing the accumulation of debris in coastal areas include the shape of the beach, location and the nature of debris (Turra et al. 2014). In addition, most sediment-surface counts do not take buried litter into account and clearly underestimate abundance, which biases composition studies. However, raking of beach sediments for litter may disturb the resident fauna. Apparently, a good correlation exists between accumulated litter and the amount arriving, indicating regular inputs and processes. Recent experiments with drift models in Japan indicate good correlation of flux with litter abundances on beaches (Yoon et al. 2010; Kataoka et al. 2013).

It appears that glass and hard plastics are accumulating more easily on rocky shores (Moore et al. 2001a). Litter often strands on beaches that lack strong prevalent winds, which may blow them offshore (Galgani et al. 2000; Costa et al. 2011). Abundance or composition of litter often varies even among different parts of an individual beach (Claereboudt 2004) with higher amounts found frequently at high-tide or storm-level lines (Oigman-Pszczol and Creed 2007). Because of this and beach topography, patchiness is a common distribution pattern on beaches, especially for smaller and lighter items that are more easily dispersed or buried (Debrot et al. 1999).

It is very diffi to compare litter concentrations of various coastal areas (with different population densities, hydrographic and geological conditions) obtained from various studies with different methodologies, especially when the sizes of debris items that are taken into account are also different. Nevertheless, common patterns indicate the prevalence of plastics, greater loads close to urban areas and touristic regions (Barnes et al. 2009). Data expressed as items m−2 or larger areas are more convenient for comparisons. Most studies have reported densities in the m−2 range (Table 2.1). High concentrations of up to 37,000 items per 50-m beach line (78.3 items m−2) were recorded in Bootless Bay, Papua New Guinea (Smith 2012) because of specifi local conditions, following typhoons (3,227 items m−2; Liu et al. 2013) or fl events (5,058 items m−2; Topçu et al. 2013). Data expressed as quantities per linear distance are more diffi to compare because the results depend on beach size/width. Plastic accounts for a large part of litter on beaches from many areas with up to 68 % in California (Rosevelt et al. 2013), 77 % in the south east of Taiwan (Liu et al. 2013),

Table 2.1 Comparison of mean litter densities from recent data worldwide (non-exhaustive list)

Region

Density (m−2)

Density (linear m−1)

Plastic (%)

References

SW Black Sea

0.88

(0.008–5.06)

24 (1.7–197)

91

Topçu et al. (2013)

Costa do Dende, Brazil

n.d.

9.1

75

Santos et al. (2009)

Cassina, Brazil

n.d.

5.3–10.7

48

Tourinho and Fillmann (2011)

Gulf of Aqaba

2 (1–6)

n.d.

n.d.

Al-Najjar and

Al-Shiyabet (2011)

Monterey, USA

1 ± 2.1

n.d.

68

Rosevelt et al. (2013)

North Atlantic, USA

n.d.

0.10 (0.2)

n.d.

Ribic et al. (2010)

North Atlantic, USA

n.d.

0.42 (0.1)

n.d.

Ribic et al. (2010)

North Atlantic, USA

n.d.

0.08 (0.2)

n.d.

Ribic et al. (2010)

South Caribbean, Bonaire

1.4 (max. 115)

n.d.

n.d.

Debrot et al. (2013)

Bootless Bay, Papua New Guinea

15.3 (1.2–78.3)

n.d.

89

Smith (2012)

Nakdong, South Korea

0.97–1.03

n.d.

n.d.

Lee et al. (2013)

Kaosiung, Taiwan

0.9 (max. 3,227)

n.d.

77

Liu et al. (2013)

Tasmania

0.016–2.03

n.d.

n.d.

Slavin et al. (2012)

Midway, North Pacific

n.d.

0.60–3.52

91

Ribic et al. (2012a)

Chile

n.d.

0.01–0.25

n.d.

Thiel et al. (2013)

Heard Island, Antarctica

n.d.

0–0.132

n.d.

Eriksson et al. (2013)

Ranges of values are given in parentheses

86 % in Chile (Thiel et al. 2013), and 91 % in the southern Black Sea (Topçu et al. 2013). However, other types of litter or specifi types of plastic may also be important in some areas, in terms of type (Styrofoam, crafted wood) or use (fi gear).

For trends in the amount of litter washed ashore and/or deposited on coastlines, beach litter monitoring schemes provide the most comprehensive data on individual litter items. Large data sets have already been held by institutions (Ribic et al. 2010) or NGO's such as the Ocean Conservancy through their International Coastal Cleanup scheme for 25 years, or the EU OSPAR marine litter monitoring program, which started over 10 years ago and covers 78 beaches (Schultz et al. 2013). The lack of large-scale trends in the OSPAR-regions is probably due to small-scale heterogeneity of near-shore currents, which evoke small-scale heterogeneity in deposition patterns on beaches (Schulz et al. 2013).

Ribic et al. (2010, 2012b) derived several nonlinear models to describe the development of pollution of coastal areas with marine litter. There were long-term changes in indicator debris on the Pacifi Coast of the U.S. and Hawaii over the nine-year period of the study. Ocean-based indicator debris loads declined substantially while at the same time land-based indicator items had also declined, except for the North Pacifi coast region where no change was observed. Variation in debris loads was associated with landand ocean-based processes with higher land-based debris loads being related to larger local populations. Overall and at the local scale, drivers included fi activities and oceanic current systems for ocean-based debris and human population density and land use status for land-based debris.

At local scales, concentrations of specifi items may be largely driven by specifi activities or new sources. For example, 41 % of the total debris from beaches in California was of Styrofoam origin, with no other explanation than an increased use of packaging, which degrades very easily (Ribic et al. 2012b). Small-sized items may form an important fraction of debris on beaches. For example, up to 75 % of total debris from the southern Black Sea was smaller than 10 cm (Topçu et al. 2013). Small-sized particles include fragments smaller than 2.5 cm (Galgani et al. 2011b), the so-called meso-particles or mesodebris, which is, unlike macrodebris, often buried and not always targeted by cleanups. Stranding fl es are then diffi to evaluate and a decrease in the amount of litter at sea will only slow the rate of stranding. Little attention has been paid to sampling design and statistical power even though optimal sampling strategies have been proposed (Ryan et al. 2009). Densities of small-sized debris were found to be very high in some areas where, in addition to fl debris, hey can pose a direct threat to wildlife, especially to birds that are known to ingest plastic (Kühn et al. 2015; Lusher 2015).

 
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