Occurrence of microplastics in a pond-river-lake connection water system: How does the aquaculture process affect microplastics in natural water bodies

Aquaculture activities have been considered to be important sources of microplastics to the water. Microplastic contamination closely related to aquaculture activities has been found in mariculture areas as well as in there nearby natural water bodies. However, for freshwater bodies with complex connectivity, it remains to be revealed how aquaculture activities affect microplastics in neighboring natural water bodies. In this study, we investigated the occurrence of microplastics of a water system consisting of aquaculture ponds, rivers, and lakes in June and December, which represented different aquaculture stages. The average microplastic abundances in June were 167 (67-367) items/m(3), 129 (67-233) items/m(3), and 372 (100-1167) items/m(3), respectively in the lake, river, and aquaculture ponds, while in December, those were 533 (200-933) items/m(3), 311 (200-600) items/m(3), and 429 (200-600) items/m(3), respectively. Microplastic abundance in ponds was significantly higher than in the river in June, while there was no significant spatial difference of microplastic abundance in December. Microplastics abundances in both river and lake were significantly higher in December than in June. The characteristics of morphology, size, color, and polymer type of microplastics were also different among different water bodies in June. However, the differences became smaller in December. The results of this study implied that the drainage of aquaculture ponds might increase the microplastics abundances of natural water in the water system predominated by aquaculture ponds. Further studies of the environmental fate of microplastics in ponds would be beneficial for understanding and controlling microplastics in the whole water system.

Automated summary

Aquaculture activities contribute significantly to the microplastic contamination in water bodies, particularly in mariculture areas and nearby natural water bodies. The study found that aquaculture ponds could increase the microplastic abundances in neighboring natural water bodies. The abundance and characteristics of microplastics varied with seasons and different water bodies.