Alpine temporary ponds as overlooked sinks of anthropogenic macrolitter

Temporary ponds represent fragile habitats that host species of high ecological and conservation interest. High-altitude ponds, although often considered pristine environments, may instead act as important sinks for anthropogenic macrolitter. This study, conducted in eight temporary ponds at Nufenen Pass (Switzerland, 2478 m a.s.l.), aimed to assess the abundance and characteristics of anthropogenic macrolitter in these habitats, focusing on key aspects such as polymer type, origin, shape, size, and color. A total of 56 macrolitter items were recorded, with an average of 7.0 ± 14.8 items per pond, corresponding to 0.002 ± 0.004 items/m2. Among macrolitter items, most plastics (82%) consisted of food-related packaging (50%), artificial plants (15%), bottle labels (11%), and shotgun cartridges (4%), with smaller numbers of twist ties, clothing labels, cables, fruit boxes, and plastic rings. Non-plastic litter (18%) included bolts, cans, can tabs, aluminum packaging, and paper food packaging. The size of macrolitter was highly variable, with a total length of 695.5 cm and an average of 12.4 ± 15.4 cm per item. The most common polymers for plastics were PO hard (n = 26) and PO soft (n = 16). Macrolitter density increased significantly with pond area (R2 = 0.73, p = 0.006), while a negative effect of distance from the restaurant present in situ was observed, with density decreasing as distance increased (R2 = 0.58, p = 0.03). We reported for the first time the presence of macrolitter accumulated in alpine temporary ponds, showing alarming density of items and calling for immediate management actions.