Figure 5
A negative power-law relationship between microplastic concentration (particles kg−1 dry sediment) in subaqueous sediment and the distance from Providence, RI (km) exists (R2 = 0.85; a). Error bars represent one standard deviation from the mean. Some error bars are sufficiently small to be contained within the circle symbol. Using this relationship, the depth of the sediment sampled (top 5 cm), the average density of the sediment (1.7 g cm−3) and the average mass per plastic particle (5.86 × 10−5 g particle−1), the predicted amount of plastic contained in any given area of the Bay is calculated. This is mapped onto a grid of Narragansett Bay (b). When the total area of the bay is summed, the mass of microplastics contained in the top 5 cm of subaqueous sediment totals 9.76 × 105 kg, or 976 tonnes. Over 50% of microplastics are estimated to be stored in the upper Bay proximal to the city (c). Satellite image derived from Google Earth v7.3.6.9345 (December 14, 2015; https://earth.google.com/) and edited using a grid from Global Multi-Resolution Topography Synthesis (GMRT)70.
