Mountain streams flushing litter to the sea - Andean rivers as conduits for plastic pollution.

Rivers polluted by anthropogenic litter are major transport routes of litter from inland to the coastal zone and the ocean. However, litter studies have primarily focused on marine environments, and the litter dynamics in rivers are still poorly understood. Herein, we explored the abundances, composition and sources of litter at the riversides and in surface waters of mountain rivers from continental Chile in two different years. Additionally, we evaluated whether different temporal, geographic, topographic, hydrologic or anthropogenic factors influence the abundances of litter. Anthropogenic litter was prevalent in Chilean rivers, both at the riversides and in surface waters. Average abundances of riverside litter, floating macrolitter, and small floating plastics were 1.8 items m-2, 10.1 items h-1 and 5.8 items h-1, respectively, and abundances were generally higher in northern Chile. Plastics dominated in all compartments, comprising 29% of riverside litter and more than 70% of small floating litter, but other litter categories were also present at riversides. Sources of litter in Chilean rivers were mostly local, such as recreational visitors, residents, and illegal dumping, and there were no clear effects of the different tested factors on the abundances of litter. Litter densities in surface waters were low compared to those in lowland slow-flowing rivers in other countries, suggesting that retention of litter is limited in the highly dynamic and rapidly flushing mountain rivers, and thus most litter (primarily plastics) is transported directly to the sea. The results suggest that to adequately address this problem in Chile, prevention measures should be aimed at the identified local sources, by means of education, public policies, legislation, and enforcement.

Schoolchildren discover hotspots of floating plastic litter in rivers using a large-scale collaborative approach.

Rivers are an important transport route of anthropogenic litter from inland sources toward the sea. A collaborative (i.e. citizen science) approach was used to evaluate the litter pollution of rivers in Germany: schoolchildren within the project "Plastic Pirates" investigated rivers across the entire country during the years 2016 and 2017 by surveying floating macrolitter at 282 sites and taking 164 meso-/microplastic samples (i.e. particles 24.99-5 mm, and 4.99-1 mm, respectively). Floating macrolitter was sighted at 54% of sampling sites and floating macrolitter quantities ranged from 0 to 8.25 items m-1 h-1 (average of 0.34 ± 0.89 litter items m-1 h-1). Floating meso-/microplastics were present at 57% of the sampling sites, and floating meso-/microplastic quantities ranged from 0 to 220 particles h-1 (average of 6.86 ± 24.11 items h-1). As only particles >1 mm were sampled and analyzed, the pollution of rivers in Germany by microplastics could be a much more prevalent problem, regardless of the size of the river. We identified six plastic pollution hotspots where 60% of all meso-/microplastics collected in the present study were found. These hotspots were located close to a plastic-producing industry site, a wastewater treatment plant, at and below weirs, or in residential areas. The composition of the particles at these hotspots indicates plastic producers and possibly the construction industry and wastewater treatment plants as point sources. An identification of litter hotspots would enable specific mitigation measures, adjusted to the respective source, and thereby could prevent the release of large quantities of small plastic particles in rivers. The adopted large-scale citizen science approach was especially suitable to detect pollution hotspots by sampling a variety of rivers, large and small, and enabled a national overview of litter pollution in German rivers.

A desert in the ocean - Depauperate fouling communities on marine litter in the hyper-oligotrophic South Pacific Subtropical Gyre.

The hyper-oligotrophic waters of the South Pacific Subtropical Gyre (SPSG) and the productive coastal Humboldt Current System (HCS) constitute an extreme nutrient gradient in the eastern South Pacific Ocean. Rich and dense fouling communities are known from floating objects in the HCS, but they have not been studied in the SPSG and it is not known which factors are influencing their richness and abundance. Here we present the first extensive study of rafting by marine invertebrates on floating anthropogenic debris in the eastern SPSG. We compared the effect of 9 raft-related categorical predictors on epibiont richness and fouling cover. Raft complexity was the most important predictor of richness. Fouling was dominated by thin crusts and biofilms, with more advanced communities only observed on few items. Fouling cover could not be predicted by any of the categorical factors tested. However, when tested as continuous predictors, raft volume and surface area were significantly correlated with both cover and richness. The most frequently encountered epibionts were common pelagic rafters, particularly Lepas spp., Planes spp., and Jellyella spp. Low fouling cover suggests that the SPSG's hyper-oligotrophic conditions strongly limit fouling growth, while the low frequency of coastal taxa points to the HCS/SPSG nutrient gradient acting as a filter for such organisms.

Spatio-temporal variation of anthropogenic marine debris on Chilean beaches.

We examined the hypothesis that in an emerging economy such as Chile the abundances of Anthropogenic Marine Debris (AMD) on beaches are increasing over time. The citizen science program Científicos de la Basura ("Litter Scientists") conducted three national surveys (2008, 2012 and 2016) to determine AMD composition, abundance, spatial patterns and temporal trends. AMD was found on all beaches along the entire Chilean coast. Highest percentages of AMD in all surveys were plastics and cigarette butts, which can be attributed to local sources (i.e. beach users). The Antofagasta region in northern Chile had the highest abundance of AMD compared with all other zones. Higher abundances of AMD were found at the upper stations from almost all zones. No significant tendency of increasing or decreasing AMD densities was observed during the 8years covered by our study, which suggests that economic development alone cannot explain temporal trends in AMD densities.