Small plastic debris changes water movement and heat transfer through beach sediments
Henry S. Carsona b✉, Steven L. Colbertb, Matthew J. Kaylorb, Karla J. McDermidb
- aMarine Science Department, University of Hawai'i at Hilo, 200 W. Kawili St., Hilo, HI 96720, United States. hcarson@hawaii.edu
- bMarine Science Department, University of Hawai‘i at Hilo, 200 W. Kawili St., Hilo, HI 96720, United States
- ✉Corresponding author
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Abstract
We investigated the physical properties of beaches contaminated with plastic fragments. We compared sediment cores from Hawai'i Island's Kamilo Beach, notable for plastic accumulation, to cores from a nearby beach. Compared to the nearby beach, Kamilo sediments contained more plastics (up to 30.2% by weight), were coarser-grained, and were more permeable (t-test, p<0.0001). 85% of the fragments were polyethylene, and 95% were concentrated in the top 15 cm of the cores. We constructed artificial cores of standardized grain size and varying plastic-to-sediment ratios. Adding plastic significantly increased the permeability (ANOVA, p=0.002), which was partially attributed to the fragments increasing the mean grain size. Sediments with plastic warmed more slowly (16% maximum decrease in thermal diffusivity), and reached lower maximum temperatures (21% maximum increase in heat capacity). These changes have a variety of potential effects on beach organisms, including those with temperature-dependent sex-determination such as sea turtle eggs.