## 3 Results  
### Composition, Abundance, and Distribution of Microplastics in the Lake Sediment  
No plastic particles were found in procedure blanks, suggesting that the detected plastic debris were all from the sediment samples. Microplastics were found at all sites except at sites DSL-9, DSL-11, DSL-12, D-1, and D-3. The abundance and distribution of microplastics is shown in Figure 2. The sampling sites were grouped as around the lake sites (ALS, 11 sites) and the canal sites (TCS, 3 sites). Average microplastic concentration at the TCS sites (230 items kg\({}^{-1}\) d.w.s., dry weight sediment) was much higher than at the ALS sites (46 items kg\({}^{-1}\) d.w.s.). The three ALS sampling sites (DSL-1, DSL-3, DSL-5) close to the populated towns on the west of the lake had higher concentrations of microplastics than sites on the eastern and northern sides of the lake. Site D-2, located close to a power supply control center on the north side of the lake, had the highest level among all the ALS sites, 221 items kg\({}^{-1}\) d.w.s. At the TCS sites, the highest concentration was detected at site DSL-13 in the middle of the canal, 340 items kg\({}^{-1}\) d.w.s., followed by site NHZ at the junction point between the canal and ECS, 280 items kg\({}^{-1}\) d.w.s.  
The physical characteristics of the microplastics are shown in Figure 3. The color, shape, and its composition are important factors in pinpointing the source of the plastic. Among the detected microplastic debris, white microplastics accounted for the majority (54%), followed by blue (30%) and green pieces (13%). In addition, small amounts of yellow (2%) and orange (1%) pieces were also detected in the sediments. Line microplastics (22%) were most widely distributed, in all 10 sampling sites except site D-2. Some of the line microplastics can be identified as fishing line. However, the highest concentration was observed for sheet microplastics (53%), particularly DSL-13 and site D-2. The foam microplastics (12%) ranked third, and then pellet (8%) and film microplastics (5%). For size distribution, microplastics in the Dishui Lake were mostly in the range of 1-5 mm, 91%. Particles in sizes between 0.1-0.5 mm and 0.5-1 mm accounted for 3% and 6%, respectively.  
Figure 3: Color (**a**), shape (**b**), size (**c**), and polymer type (**d**) distribution of microplastics in sediment of the Dishui Lake.  
Figure 2: Abundance and distribution of microplastics (**a**), mesoplastic and macroplastic (**b**) in Dishui Lake sediment. ALS: Sampling sites around the Dishui Lake, including sites in the north (D1, D2, D3, DSL-11, and DSL-12), the east (DSL-9 and DSL-10), and the south (DSL-1, DSL-3, and DSL-5). TCS: Sampling sites int the canal connecting the lake to the East China Sea (DSL-6, DSL-13 and NHZ).  
The microplastic particles were further examined by FT-IR to determine their composition and polymer type. A total of seven polymer types were identified in the Dishui Lake sediment, including polypropylene (PP), polystyrene (PS), polyethylene (PE), acrylic, high density polyethylene (HDPE), low density polyethylene (LDPE), acrylonitrile, acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate (PET) (Figure 3d). PP was the most abundant polymer type (69%). PP microplastics in Dishui Lake sediment had various shapes, including sheets, pellets, and lines. The second most abundant polymer type was PS (12%), all of which were foam fragments. The PE microplastic account for 8% of the total, then LDPE and HDPE, which were 5% and 2%. PE microplastics were mainly films. HDPE and LDPE were mainly pellet shaped.