Replicate surveys of beach litter have seldom been performed in the past. In this study, replicate surveys of beach litter were conducted on the beach north of Hörnum (Sylt, Germany), from 2015 to 2019, applying a slightly modified OSPAR protocol of beach litter monitoring. Descriptive statistics and power analyses were calculated on data resulting from these replicate surveys, to find out whether the scatter of replicate beach litter data decreases and the statistical power increases with increasing numbers of replicate surveys. From 2015 to 2019, mean total abundances, given as numbers of litter items, ranged from 19 to 185 litter items on a 50 m section of beach. With increasing numbers of replicate surveys, the scatter given by the coefficient of variation (CV) significantly increased up to 113%. Statistical power considerably increased with increasing numbers of replicate beach sections, e.g. from 82% (two beach sections) to nearly 100% (five beach sections) for a given reduction of beach litter of 50%. Based on these results from a morphologically straight coastline, the use of replicate surveys would be sensible for the future monitoring of beach litter. However, there is high need for studies, which consider coastlines with varying morphology.

过去很少对海滩垃圾进行重复调查。在这项研究中，从 2015 年到 2019 年，在 Hörnum（德国叙尔特岛）以北的海滩上进行了海滩垃圾的重复调查，应用了稍微修改的 OSPAR 海滩垃圾监测协议。对这些重复调查产生的数据进行描述性统计和功效分析，以了解重复调查海滩垃圾数据的分散性是否会随着重复调查数量的增加而减少和统计功效是否增加。从 2015 年到 2019 年，平均总丰度（以垃圾项目数量表示）范围为 50 m 海滩段上的 19 至 185 个垃圾项目。随着重复调查数量的增加，变异系数 (CV) 给出的分散度显着增加至 113%。随着重复海滩部分数量的增加，统计能力显着增加，例如，对于给定的海滩垃圾减少 50%，从 82%（两个海滩部分）到接近 100%（五个海滩部分）。根据形态上笔直的海岸线的这些结果，重复调查的使用对于未来的海滩垃圾监测是明智的。然而，非常需要研究，考虑具有不同形态的海岸线。