Macroinvertebrate ecosystem engineering affects streambed retention of microplastics
Data files
Oct 09, 2023 version files 29 KB
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Final_Microplastic_analysis.Rmd
24.20 KB
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flumestats_R.csv
1.47 KB
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README.md
3.34 KB
Abstract
Microplastic pollution of aquatic environments threatens human health, ecosystem processes, and biodiversity. Many existing models of microplastic movement in streams do not account for biotic effects on microplastic fate. Ecosystem engineering by net-spinning caddisflies (Hydropsychidae) has been shown to substantially affect sediment and organic matter transport as well as streambed hydrology. Caddisfly engineering may likewise affect the movement of microplastic pollution in streams. We used a controlled 11-d flume experiment to investigate the potential for caddisflies to serve as a biotic control on microplastic transport. Flumes containing a single gravel dune were randomly assigned to density treatments: control (0 caddisflies/m2) or stocked with 500, 800, or 2500 caddisflies/m2, incubated (d 1–10) to allow for caddisfly silk structure construction, inoculated (d 11) with PVC microplastics (333 µm–1 mm), and sampled (d 12). Microplastic was quantified as caught in a drift net (downstream transport), eaten by caddisflies (ingestion), or captured in caddisfly silk structures or settled into the gravel dune (i.e., total streambed retention). Mean downstream plastic transport was 9% lower than the control in the 800 caddisflies/m2 treatment and 10% lower in the 2500 caddisflies/m2 treatment (p < 0.001 and p = 0.003, respectively). Mean total streambed retention was 9% higher than control in the 800 caddisflies/m2 treatment (p < 0.001) and 910% higher in the 2500 caddisflies/m2 treatment (p = 0.004). Ingestion of plastic by caddisflies was rare and highly variable (0–0.55% of plastic particles) but did increase with caddisfly density (p = 0.002). This work represents one of the first investigations of animal ecosystem engineering as a control on the movement and fate of microplastic particles in fresh waters and establishes a foundation for future research on biotic control of microplastic transport. Our results suggest that ecosystem engineering by net-spinning caddisflies may serve as a biotic control of microplastic transport in freshwater streams.
The dataset contains counts of microplastic particles recovered from different locations within experimental flumes which were set up to test the effect of caddisfly population density on microplastic transport and fate. The used GLMMs to show that downstream transport of microplastics was reduced at the two highest stocked densities of caddisflies, which corresponded to an increase in microplastic stored in the streambed. Caddisflies also consumed a minimal amount of microplastic.
Description of the Data and file structure
The raw data is stored in the file “flumestats_R.csv”. Each row in the data represents measurements from a single trial in the experiment. The raw data includes the following variables:
Flume_Number : A numerical identifier for the experimental flume used for a given trial.
Trial_Number: A numerical identifier for the time block of a given trial.
Stock_Dense: The number of caddisflies per square meter stocked in the flume.
Stock_Number: The raw number of caddisflies stocked in the flume.
Final_Number: The number of live caddisflies recovered from the flume at the end of the experiment.
Per_Mort: The proportion of caddisflies which died before the conclusion of the trial.
Caddis_Biomass: The biomass of the dried bodies of caddisflies which were living at the end of the experiment, reported in grams.
Silk_Num: The number of microplastic particles recovered from caddisfly silk in the trial.
Silk_Per: The proportion of all recovered microplastic particles from the trial which were recovered from silk.
Net_Num: The number of microplastic particles recovered from the drift net in the trial.
Net_Per. The proportion of all recovered microplastic particles from the trial which were recovered from the drift net.
Caddis_Num: The number of microplastic particles recovered from caddisfly bodies in the trial.
Caddis_Per: The proportion of all recovered microplastic particles from the trial which were recovered from caddisfly bodies.
Dune_Num: The number of microplastic particles recovered from the gravel dune in the trial.
Dune_Per: The proportion of all recovered microplastic particles from the trial which were recovered from caddisfly bodies.
Total_Num: The total number of microplastic particles recovered from each trial.
MP_mg_caddis: The number of microplastic particles recovered in caddisfly bodies per milligram of dry caddisfly tissue.
The file named “Final Microplastic analysis.Rmd” contains the R code necessary to reproduce the analysis reported in the manuscript, as well as some code used for exploratory analysis and generation of figures for conference presentations. The analysis can be repeated by knitting the .Rmd file provided that the .csv file is stored in the same location. Running the code contained in the .Rmd will write additional .csv files used for making tables and several .tiff images containing figures to the working directory.
Sharing/access Information
The data can also be requested by contacting the lead author at samuel.fritz2@student.montana.edu
Raw counts of microplastic particles were derived from images taken under a Leica D60 dissecting microscope. The original images may be obtained upon request.