Land use is the major control on macroplastic debris deposition at twenty-eight urban stormwater ponds

Dinithi Sandunika De SilvaPatricia Lynn Corcoran^*Douglas G Woolford

• Western University, London, Canada

Urban stormwater ponds play a crucial role in trapping pollutants carried in storm water runoff prior to their entry into natural waterways. Designed to be at lower elevations than the surrounding landscape, these pond areas also accumulate low density, wind-blown debris. A total of 138 quadrats, each measuring 20 m2 and surrounding twenty-eight stormwater ponds, were surveyed for macroplastic pollution (MaP; plastic waste items ≥ 5 mm long) in London, Canada, to determine key factors influencing their abundance, types, and distribution. Average item concentrations varied between ponds (1.7 ±1.2 to 40.0 ±16.3 per 20m2) as well as within individual ponds (0 to 87 per 20m2). Food & beverage packaging, household & garden, and leisure & sports were the most common applications represented by the MaP items. Influential factors were investigated using Poisson regression and hurdle models. Some concentration variations can be attributed to statistically significant relationships between MaP abundances and (i) source-specific inputs and (ii) pond-level factors. Land use is considered to have the greatest control on the types and average abundances of MaP items found at each pond. For example, smoking-related items were most concentrated in construction-and industrial/commercial-proximal ponds. For pond-level factors, the majority of MaP items were located near the pond inlets and outlets rather than in open pond areas. The results of this study are critical for municipal pollution mitigation efforts, and particularly for public education, as much of the debris consists of littered, single-use and multilayered plastic products.