Microplastics and leaf litter decomposition dynamics: New insights from a lotic ecosystem (Northeastern Italy)

Microplastics represent one of the main environmental concerns of our time and their presence is well known in all freshwater ecosystems. However, there is still a lack of knowledge about the interference with some environmental dynamics, such as the leaf litter decomposition, which represents a key process in freshwater ecosystems. The work presented herein analyzed the leaf litter decomposition in a lotic ecosystem, in relation to water physicochemical parameters, macrobenthic invertebrate functional feeding guilds (FFG) and, as a novelty, the microplastics as additional factor. Physicochemical features were monitored every 15 days for one year. Phragmites australis decomposition rates were investigated during four seasons (summer, autumn, winter, and spring) using the leaf bag technique. Microplastic items were also collected within the leaf bags (used as retaining tool) and within macrobenthic invertebrate colonizers. Shredders were the most contaminated FFG in summer and autumn, while scrapers showed high microplastics levels in autumn and winter. Decomposition rates significantly differed among seasons (0.007 < k < 0.022) and water temperature was the main driver of the decomposition dynamics (relative importance = 70.3 %), positively affecting the decay rates, followed by pH (9.7 %), which showed a negative contribution. Microplastics showed a negative effect (3.1 %), with a relative importance similar and opposite to that observed for the shredders (3.9 %), which value was similar to those recorded for scarpers (2.7 %). This study represents a field investigation regarding the microplastic effects on the organic matter decomposition rates in freshwater environments carried out directly on field. Our results provide new insights about the microplastic interference on environmental dynamics and could represent a starting point for further studies.