---
type: Concept
title: Microplastic Accumulation in Alpine Tarns
description: A preprint's survey finding that microplastic particle counts rose over
  a single melt season across three high-altitude tarns, highest in Black Tarn.
aliases:
- tarn microplastics
tags:
- microplastics
- alpine-lakes
- water-pollution
- hydrology
- environmental-science
resource: raw/preprint.pdf
timestamp: '2026-07-16T15:14:33Z'
citadel_version: 0.3.0
---

A preprint titled "Microplastic accumulation in three alpine tarns", by R. Halvorsen, M. Okonkwo, and L. Feretti of the Institute for Mountain Hydrology, surveyed microplastic concentrations in three high-altitude tarns over a single melt season; it is explicitly marked as not yet peer reviewed.[^s1][^s2]

## Methods

Triplicate 5-litre water samples were drawn from each tarn at two-week intervals, vacuum-filtered onto 0.45-micrometre membranes, and the retained particles counted by fluorescence microscopy after Nile Red staining.[^s3] The preprint cites this Nile Red staining approach to an existing protocol paper, Okafor (2018).[^s4]

## Results

Particle counts rose through the melt season at all three tarns and peaked in late summer.[^s5] Black Tarn was the most affected of the three, reaching up to 1,180 microplastic particles per litre — the season maximum, and, per the abstract, roughly six times the concentration recorded at the least affected site.[^s6][^s7] Glass Tarn recorded the lowest particle counts of the three tarns surveyed.[^s7] The name of the third, unnamed tarn is not given in the preprint.

## Discussion

The preprint discusses atmospheric deposition as a *likely* pathway for the microplastics reaching the tarns, without asserting it as an established mechanism.[^s8] For this it cites two other papers: Reyes and Duman (2020) on the atmospheric transport of fibres to remote lakes, and Vance et al. (2021) on deposition gradients above the treeline.[^s9][^s10] It also cites Nowak et al. (2019) as a general review of freshwater microplastics.[^s11]

The reference list additionally includes an earlier work by two of the same authors, Feretti and Halvorsen (2022), on tarn sampling design, published as an Institute for Mountain Hydrology technical note.[^s12]

## Sources
[^s1]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 1 — title, authors (R. Halvorsen, M. Okonkwo, L. Feretti), and Institute for Mountain Hydrology affiliation (ingested 2026-07-16)
[^s2]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 1 — labeled "preprint, not peer reviewed" (ingested 2026-07-16)
[^s3]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 1 — Methods: triplicate 5-litre samples at two-week intervals, vacuum-filtered onto 0.45-micrometre membranes, counted by fluorescence microscopy after Nile Red staining (ingested 2026-07-16)
[^s4]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 2 — References [3]: S. Okafor (2018), "Nile Red staining protocols for microplastic counts", Methods in Limnology 7, 88-97 (ingested 2026-07-16)
[^s5]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 2 — Results: particle counts rose through the season at all sites and peaked in late summer (ingested 2026-07-16)
[^s6]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 1 — Abstract: Black Tarn held up to 1,180 microplastic particles per litre, roughly six times the concentration at the least affected site (ingested 2026-07-16)
[^s7]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 2 — Results: Black Tarn's 1,180 particles per litre was the season maximum; Glass Tarn recorded the lowest counts (ingested 2026-07-16)
[^s8]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 1 — Abstract: "We discuss likely atmospheric-deposition pathways" (ingested 2026-07-16)
[^s9]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 2 — References [2]: P. Reyes and K. Duman (2020), "Atmospheric transport of fibres to remote lakes", Mountain Hydrology Letters 4, 55-61 (ingested 2026-07-16)
[^s10]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 2 — References [4]: J. Vance et al. (2021), "Deposition gradients above the treeline", Alpine Environments 33, 1201-1215 (ingested 2026-07-16)
[^s11]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 2 — References [1]: A. Nowak et al. (2019), "Freshwater microplastics: a review", Journal of Alpine Science 12(3), 210-229 (ingested 2026-07-16)
[^s12]: [raw/preprint.pdf](../../raw/preprint.pdf), p. 2 — References [5]: L. Feretti and R. Halvorsen (2022), "Tarn sampling design", Institute for Mountain Hydrology Technical Note 9 (ingested 2026-07-16)
