Monitoring macroplastics in aquatic and terrestrial ecosystems: Expert survey reveals visual and drone-based census as most effective techniques.

Anthropogenic litter, such as plastic, is investigated by the global scientific community from various fields employing diverse techniques. The goal is to assess and finally mitigate the pollutants' impacts on the natural environment. Plastic litter can accumulate in different matrices of aquatic and terrestrial ecosystems, impacting both biota and ecosystem functioning. Detection and quantification of macroplastics, and other litter, can be realized by jointly using visual census and remote sensing techniques. The primary objective of this research was to identify the most effective approach for monitoring macroplastic litter in riverine and marine environments through a comprehensive survey based on the experiences of the scientific community. Researchers involved in plastic pollution evaluated four litter occurrence and flux investigation methods (visual census, drone-based surveys, satellite imagery, and GPS/GNSS trackers) through a questionnaire. Traditional visual census and drone deployment were deemed as the most popular approaches among the 46 surveyed researchers, while satellite imagery and GPS/GNSS trackers received lower scores due to limited field validation and short performance ranges, respectively. On a scale from 0 to 5, visual census and drone-based surveys obtained 3.5 and 2.0, respectively, whereas satellite imagery and alternative solutions received scores lower than 1.2. Visual and drone censuses were used in high, medium and low-income countries, while satellite census and GPS/GNSS trackers were mostly used in high-income countries. This work provides an overview of the advantages and drawbacks of litter investigation techniques, contributing i) to the global harmonization of macroplastic litter monitoring and ii) providing a starting point for researchers and water managers approaching this topic. This work supports the selection and design of reliable and cost-effective monitoring approaches to mitigate the ambiguity in macroplastic data collection, contributing to the global harmonization of macroplastic litter monitoring protocols.

River functionality influences the distribution of the dipper Cinclus cinclus (Linnaeus, 1758).

The dipper (Cinclus cinclus) is a species strongly linked to the riparian ecosystem, known to feed on aquatic macroinvertebrates, which are sensitive to water pollution. For this, dippers have been proposed as useful bioindicators of water quality. While the distribution and ecology of the dipper are well known in Northern European rivers, few studies focus on this in Central Italy, lacking data for dipper conservation. Here, we aimed to (i) assess the dipper occurrence related to water quality using biotic indices based on diatom and macroinvertebrate communities, and (ii) evaluate the river ecosystem's overall state, through the River Functionality Index and land-use analysis in buffer areas. Overall, water quality alone does not explain the dipper occurrence, as the species was not found in many potentially suitable sites with good or high-water quality. Moreover, the diversity of the diatom and macroinvertebrate communities was not a sufficient constraint either. Conversely, the dipper occurrence significantly correlated with the River Functionality Index, which integrates several riparian ecosystem factors, indicating that well-preserved ecosystems with high functionality levels are important for dipper occurrence. Land use analyses in the areas surrounding the presence sites have shown, although not significantly, a fair level of naturalness, potentially favouring the riparian zone maintenance. As the dipper was considered in decline and threatened in Central Italy, further research on its auto-ecology and conservation threats is urgently needed. Finally, given the link between the species and the riparian ecosystem, a charismatic species such as the dipper could be used as an umbrella species in protection and conservation projects for the benefit of the entire riparian belt, which represents a buffer area of fundamental importance between terrestrial and aquatic ecosystems, although often resulted severely reduced and fragmented.

Life on bottles: Colonisation of macroplastics by freshwater biota.

While rivers are known to be the main vectors of plastics to the sea, it seems surprising that studies on interactions (e.g. colonisation/entrapment and drift) between macroplastics and biota continue to remain largely neglected, notwithstanding they represent unexpected threats to freshwater biota and riverine habitats. To fill these gaps, here we focused on the colonisation of plastic bottles by freshwater biota. To do so, we collected 100 plastic bottles from the River Tiber in summer 2021. Overall, 95 bottles were colonised externally and 23 internally. Specifically, biota mainly occurred within and outside the bottles rather than plastic pieces and organic debris. Moreover, while bottles were externally covered mainly by vegetal organisms (i.e. macrophytes), they internally entrapped more animal organisms (i.e. invertebrates). The taxa most occurring within and outside the bottles belonged to pool and low water quality-associated taxa (e.g. Lemna sp., Gastropoda, and Diptera). In addition to biota and organic debris, plastic particles also occurred on bottles reporting the first observation of 'metaplastics' (i.e. plastics encrusted on bottles). Furthermore, we observed a significant positive correlation between the colonising taxa abundance and the bottle degree degradation. In this regard, we discussed how bottle buoyancy may change due to the organic matter on the bottle, affecting bottle sinking and transport along rivers. Our findings might be crucial for understanding the underrepresented topic of riverine plastics and their colonisation by biota, given that these plastics may act as vectors and cause biogeographical, environmental, and conservation issues to freshwater habitats.