Water browning causes food shortage for fish, fauna in boreal lakes
Published : 19 May 2020, 01:06
Updated : 19 May 2020, 10:19
Water browning is feared to have major consequences on Finnish lake ecosystems. Invertebrate numbers diminish when surface water gets browner, and invertebrates are the main food source for many fish and duck species, according to the findings of a study conducted by the University of Helsinki.
During the last decades, surface waters have become browner throughout the northern Hemisphere. Acid recovery from past acid rain and increased precipitation owing to climate change are now contributing to this effect, said the university in a press release.
Over the past 30 years, the Lammi Biological Station at the university of has carried out water quality surveys in 20 lakes of the Evo Natura 2000 area in southern Finland. Over that time period, water browning has increased in each of the lakes studied.
Water colour is not just a visual effect; it is an important factor determining the structure and function of aquatic food webs.
By combining the water colour data with aquatic invertebrate data that had been collected in in 1989 to 2008 in five of the Evo area lakes, researchers found that when the water gets browner, the abundance of aquatic invertebrates declines.
“Aquatic invertebrates are the main food source for many secondary predators such as fish and waterbirds. Diminishing invertebrate populations may have major consequences for boreal ecosystem functioning. We also have a study showing a decline in the number of breeding pairs of waterbird that feed on invertebrates in boreal lakes in the same period,” said Dr. Céline Arzel from the Department of Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki.
Both results call for further investigations into loss of biodiversity and its drivers in boreal lakes to understand how and how much the whole ecosystem, its functions and services are impacted by water browning.