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

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.