Skip to main content
Dryad logo

Benthic macroinvertebrates of 63 northern Finnish streams along a dissolved organic carbon gradient

Citation

Brüsecke, Joanna et al. (2022), Benthic macroinvertebrates of 63 northern Finnish streams along a dissolved organic carbon gradient, Dryad, Dataset, https://doi.org/10.5061/dryad.xksn02vk7

Abstract

Concentrations of dissolved organic carbon (DOC) have increased over the past few decades, causing freshwater browning. The impacts of browning on biodiversity have been little studied, despite many of the individual stressors associated with browning being known to control freshwater communities. We explored the responses of benthic invertebrates along a wide gradient of DOC concentrations (3.6 mg to 27 mg L-1) in 63 boreal streams variously impacted by peatland drainage or peat production. DOC was a prime determinant of macroinvertebrate diversity and abundance, with the strongest negative response in algal scrapers. Threshold indicator taxa analysis indicated a community change at 12-13 mg DOC L-1, with only four taxa increasing, while 13 taxa decreased along the DOC gradient. Our findings of both a gradual loss and an abrupt change of biodiversity along a browning gradient provide a benchmark against which changes to stream biodiversity relative to the predicted browning trend can be gauged.

Methods

Benthic macroinvertebrates were sampled in late September 2019 (50 sites) or 2020 (13 sites) with a 2-min kick-net (Ø 500-μm) sample at each site. A sample of this size covers about 1.3 m2 of the stream bed and is known to capture about 75% of all species present in a riffle (Mykrä et al. 2006). Samples were preserved in 70% ethanol in the field and later identified to species or genus level.

We collected water samples simultaneously with macroinvertebrate sampling and they were analysed for dissolved organic carbon (DOC, mg L-1), water colour (mg Pt L-1), total phosphorus (TP, µg L-1), nitrate-N (NO3, µg L-1), and pH following national standards (National Board of Waters 1981) (see Table S1). DOC concentration was measured from filtered (Ø 0.45 µm Whatman GF/F) water samples by infrared spectrometry with Shimadzu TOC-VCPH analyzer (Shimadzu Scientific Instruments, Kyoto, Japan). Absorbance spectra (190-800 nm; 1 nm intervals) were recorded for filtered water samples (Ø 0.2 µm PES membrane filter) using Lambda 650 (Perkin Elmer) spectrophotometer and 1-cm quartz cuvettes.

Water temperature (°C) was recorded at 1–h intervals by HOBO Pendant (Onset, Massachusetts) data loggers for five weeks prior to invertebrate sampling. Mean substratum size was determined as the weighted average of particle size classes in ten randomly distributed 0.25 m2 plots using a modified Wentworth scale from 1 (clay/silt 0.001–0.07 mm) to 10 (large boulder to bedrock >512 mm). Substrate diversity was quantified by calculating Simpson diversity index based on the relative cover of each Wentworth class in each quadrat. Moss cover (%) was estimated in 20 0.25 m2 plots distributed randomly across the study section. Current velocity (cm s−1; Schiltknecht® MiniAir20) and water depth (cm) were measured at three positions along each of five randomly placed transects perpendicular to the flow. Stream width (cm) was measured at the same transects.

Funding

Academy of Finland, Award: 318230