Temporal Variability of Microplastic Concentrations in Inland Waters: An Automated, Semicontinuous Sampling of Microplastics ≥11 μm in a Stream in Southern Germany

To advance understanding about the temporal variability of microplastic concentrations in inland waters, this study presents a fully automatic sampling unit for microplastics (SAM), which collects daily mixed samples using fractionated filtration. Method validation with five different polymer types revealed an overall recovery of 77 ± 29% for sampling, sample preparation, and analysis of particles ≥11 μm using Fourier transform infrared micro spectroscopy. During an 8 day field test, SAM was applied in a stream in Southern Germany. Microplastic concentrations in the daily mixed samples differed by a factor of 10.8 within the study period, ranging from 1210 to 13 052 particles and fibers per m3. Polypropylene and polymer cluster acrylates/polyurethanes/varnish were the most abundant polymer types observed. The comparison of day-to-day variability of microplastic concentrations with the total particle count, turbidity, precipitation, as well as discharge in the stream did not reveal distinct interrelations. The field application, as well as the good 20 recovery rates of SAM, demonstrates its suitability for future long-term studies focusing on the temporal variability of microplastic concentrations

Spatial structure: semivariograms for selected dates.

<p>Spatial structure of green LAI expressed as semivariograms from simulation (<i>sim</i>), 5 m resolution spaceborne remote sensing (<i>rs5m</i>), and from LAI field means (<i>rsfm</i>) derived from <i>rs5m</i>. Each for three separate crops and for the overall arable area of the test region for four selected dates of remote sensing scenes (overpass dates of RapidEye). Experimental semivariograms are shown as dots and theoretical semivariograms as lines. There is no data for dates outside the growing season of the respective crop. Y-axes have the same scale and are clipped to save space.</p

Map of the test area.

<p>Land use map (2011) and location of field measurement sites for the fertile loess plain in the northern part of the Rur catchment. White areas are non-vegetated.</p

Mean LAI temporal course.

<p>Temporal course of the mean LAI of single agricultural fields (<i>field</i>, gray symbols) and of the test area from <i>sim</i>ulation and remote sensing (<i>rs5m</i>: 5 m resolution, <i>rsfm</i>: mean LAI of agricultural fields) for three separate crops and for the overall arable area. There is no <i>field</i> data for the arable area since the measured fields were too few and thus not representative for the test area.</p

Dates, sites and methods for the destructive field measurements of LAI.

<p>Descriptions of the methods 1 and 2 are given in the text.</p

Maximum LAI of the three main crops from field measurements (<i>field</i>), simulation (<i>sim</i>) and remote sensing (<i>rs5m</i> 5 m resolution, <i>rsfm</i> means for agricultural fields).

<p>Maximum LAI of the three main crops from field measurements (<i>field</i>), simulation (<i>sim</i>) and remote sensing (<i>rs5m</i> 5 m resolution, <i>rsfm</i> means for agricultural fields).</p

Spatial variability: relative frequency distributions temporal course.

<p>Temporal development of LAI spatial variability expressed as (vertical) color-coded relative frequency distributions (RFD). (a) RFD of simulated LAI (<i>sim</i>), (b) RFD of LAI derived from 5 m resolution spaceborne remote sensing (<i>rs5m</i>), (c) RFD of LAI field means (<i>rsfm</i>) derived from <i>rs5m</i>. Each for three separate crops and for the overall arable area of the test region. Width of LAI classes in the RFDs is 0.1.</p

Spatial structure: temporal course of semivariogram ranges.

<p>Ranges of fitted exponential semivariogram models from simulation (<i>sim</i>), 5 m resolution remote sensing (<i>rs5m</i>), and from LAI field means (<i>rsfm</i>) derived from <i>rs5m</i>. Each for three separate crops and for the overall arable area of the test region for four selected dates of remote sensing scenes (overpass dates of RapidEye). Symbols denote whether fit was accomplished using a simple model, a nested model, or a simple model cut off at lags of 6000 m.</p