Anthropogenic marine debris found in peri-urban and urban mangroves on Penang Island, Malaysia

The abundance diversity parameters and intertidal sorting of accumulated anthropogenic marine debris (AMD) were evaluated in the urban and peri-urban mangroves along the coast of Penang Island, Malaysia. Debris items were counted and classified along 80 m transects in progressively higher water marks from as close to the seaward side as practical, within a 100 m2 quadrat sampling frame. Abundance, diversity, evenness, and patterns of accumulation in relation to tidal levels were compared between four sites which were sampled at different periods over 2 months and constrained by possible changes in their previous individual wind fields, and neap-spring tidal development. Plastics made up most of the AMD with plastic bags, sheets, and fragments being the most common items found at all sites. More AMD was retained in the urban sites compared to peri-urban sites, consistent with their larger resident population density. Diverse debris forms were consistent with the type of land use and population livelihood in each area, with a clear separation between the most urbanised and peri-urban sites on the NE and NW coasts and the urban and peri-urban sites on the SE and SW coastlines on the island. At the low tidal levels close to the edge in the urban sites, we observed the largest differences in abundance, diversity, and evenness over a similar parameter compared to the transects away from the edge, owing to sorting and edge effect. These patterns of change and differences across transects and sites, suggested: 1) an independence of accumulated material with neap-spring phases, for a constant wind field; 2) a mangrove canopy and root structure away from the edge that efficiently retains deposited materials with little sorting through the main body of the canopy; and 3) materials deposited closer to the edge are increasingly lost to the water body due to the edge effect.本研究针对马来西亚槟岛沿岸城区及城郊红树林，评估了累积人为源海洋垃圾（anthropogenic marine debris, AMD）的丰度、多样性参数与潮间带分选特征。以100平方米样方为采样框架，沿尽可能贴近海侧的位置起始，按照水位线逐步升高的方向布设80米样带，对垃圾样本进行计数与分类。在为期2个月的采样周期内，4个采样点分别于不同时段完成采样，且采样过程受各站点既往风场变化及小潮-大潮周期演变的约束；研究对比了各采样点的垃圾丰度、多样性、均匀度及与潮位相关的累积模式。塑料类垃圾占AMD的绝大多数，其中塑料袋、塑料膜及塑料碎片为所有采样点均检出的最常见垃圾类型。城区采样点滞留的AMD量显著高于城郊采样点，这与城区更高的常住人口密度相一致。不同区域的垃圾形态多样性与当地土地利用类型及居民生计模式高度契合；槟岛东北、西北沿岸的高度城区化站点与城郊站点，同东南、西南沿岸的城区及城郊站点之间呈现出清晰的分布分异。在城区采样点靠近潮间带边缘的低水位区域，相较于远离边缘的样带，其丰度、多样性及均匀度在同类参数下的差异最为显著，该现象源于分选作用与边缘效应。上述样带与站点间的变化模式及差异表明：1）在风场稳定的前提下，累积垃圾的分布与小潮-大潮周期无关；2）远离边缘的红树林冠层与根系结构可有效滞留沉降的垃圾，且冠层主体内部几乎无分选作用；3）越靠近潮间带边缘沉积的垃圾，越容易因边缘效应流失至水体中。