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Sample size requirements for riverbank macrolitter characterization
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  • Sjoukje Irene de Lange,
  • Yvette Mellink,
  • Paul Vriend,
  • Paolo Tasseron,
  • Finn Begemann,
  • Rahel Hauk,
  • Heleen Aalderink,
  • Eric Hamers,
  • Peter Jansson,
  • Nonna Joosse,
  • Ansje Löhr,
  • Romi Lotcheris,
  • Louise Schreyers,
  • Vivien Vos,
  • Tim Van Emmerik
Sjoukje Irene de Lange
Wageningen University, Wageningen University

Corresponding Author:[email protected]

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Yvette Mellink
Wageningen University, Wageningen University
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Paul Vriend
Dutch Ministry of Infrastructure and Water Management, Directorate-General for Public Works and Water Management, Utrecht, the Netherlands, Dutch Ministry of Infrastructure and Water Management, Directorate-General for Public Works and Water Management, Utrecht, the Netherlands
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Paolo Tasseron
Wageningen University, Wageningen University
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Finn Begemann
Wageningen University, Wageningen University
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Rahel Hauk
Wageningen University, Wageningen University
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Heleen Aalderink
Wageningen University, Wageningen University
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Eric Hamers
University of Applied Science Zuyd, University of Applied Science Zuyd
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Peter Jansson
Wageningen University, Wageningen University
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Nonna Joosse
Wageningen University, Wageningen University
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Ansje Löhr
Open University, Open University
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Romi Lotcheris
Wageningen University, Wageningen University
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Louise Schreyers
Wageningen University, Wageningen University
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Vivien Vos
Wageningen University, Wageningen University
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Tim Van Emmerik
Wageningen University, Wageningen University
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Abstract

Anthropogenic litter is omnipresent in terrestrial and freshwater systems, and can have major economic and ecological impacts. Monitoring and modelling of anthropogenic litter comes with large uncertainties due to the wide variety of litter characteristics, including size, mass, and item type. It is unclear as to what the effect of sample set size is on the reliability and representativeness of litter item statistics. Reliable item statistics are needed to (1) improve monitoring strategies, (2) parameterize litter in transport models, and (3) convert litter counts to mass for stock and flux calculations. In this paper we quantify sample set size requirement for riverbank litter characterization, using a database of more than 14,000 macrolitter items (>0.5 cm), sampled for one year at eight riverbank locations along the Dutch Rhine, IJssel and Meuse rivers. We use this database to perform a Monte Carlo based bootstrap analysis on the item statistics, to determine the relation between sample size and variability in the mean and median values. Based on this, we present sample set size requirements, corresponding to selected uncertainty and confidence levels. Optima between sampling effort and information gain is suggested (depending on the acceptable uncertainty level), which is a function of litter type heterogeneity. We found that the heterogeneity of the characteristics of litter items varies between different litter categories, and demonstrate that the minimum required sample set size depends on the heterogeneity of the litter category. More items of heterogeneous litter categories need to be sampled than of heterogeneous item categories to reach the same uncertainty level in item statistics. For example, to describe the mean mass the heterogeneous category soft fragments (>2.5cm) with 90% confidence, 990 items were needed, while only 39 items were needed for the uniform category metal bottle caps. Finally, we use the heterogeneity within litter categories to assess the sample size requirements for each river system. All data collected for this study are freely available, and may form the basis of an open access global database which can be used by scientists, practitioners, and policymakers to improve future monitoring strategies and modelling efforts.