The critical role of headwaters in river biodiversity
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A recent study shows that microbial biodiversity is highest in the uppermost reaches of river networks. This runs counter to the dominant view that species diversity is richest in mid-sized streams.
Where along a river’s course would you expect to find the greatest biodiversity? A recent paper co-authored by EPFL researcher Enrico Bertuzzo from EFPL’s Laboratory of Ecohydrology highlights the primary importance of fluvial headwaters, the uppermost tips of river networks, in maintaining microbiological biodiversity in rivers. These finds are especially important today given that these very ecosystems are increasingly under threat due to human activities such as mountain-top mining and water-transfer between valleys for hydroelectric applications.
The study, led by researchers from the University of Vienna, defies the prevailing assumption that river biodiversity peaks in mid-sized streams, as is the case for fish and invertebrate species. Using genetic analysis of biofilms extracted through an alpine river network, the researchers revealed that, instead, biodiversity is greatest in the river upper reaches.
While until now, it has largely been assumed that species spread and mix, increasing biodiversity, when rivers carry them downstream, this view was not borne out by the data. To explain their findings, the scientists cite higher habitat variability near the source of rivers, due to their isolated location and the branched structure of the river network. As species disperse downstream and encounter rival species at river confluences, the authors suggest that particularly well-adapted species come to dominate, ultimately reducing biodiversity.
Reference:
Headwaters are critical reservoirs of microbial diversity for fluvial networks
Katharina Besemer, Gabriel Singer, Christopher Quince, Enrico Bertuzzo,William Sloan, and Tom J. Battin; Proc R Soc B 2013 280:20131760;