Yellowstone fish deaths point to huge toll of human activity on rivers
A recent outbreak of a fish parasite on Yellowstone may have seemed unremarkable, but new research shows it could be linked to years of human activities that are slowly chocking river systems to death
The Yellowstone river has its headwaters in the mountain streams and snowy peaks of the famous US national park with the same name, and makes an unfettered downhill run all the way to the Missouri river, nearly 700 miles away. It is the longest undammed river in the Lower 48 states.
Last August, the Yellowstone made national headlines when a parasite killed thousands of fish, mostly whitefish. Fear of spreading the parasite to other waterways forced Montana officials to close the river to fishermen, rafters, and boaters. At the height of summer, the stunningly scenic, trout-rich river was eerily deserted. Fishing re-opened in the fall, but the parasite has been found in other Montana waterways.
That a non-native parasite somehow got into a river may seem like an unremarkable occurrence. But a new, expansive model of gravel-bed river systems in mountainous areas, such as the Yellowstone, depicts a more complex scenario in which a host of human activities combine to degrade river systems and render them more vulnerable to destructive outside influences such as parasites.
This body of research – 40 years in the making, but much of it summed up in a recent paper – rewrites the understanding of the ecological dynamics of these rivers. And it casts a harsh light on human river valley activities such as homebuilding, dam construction, irrigation, and channelization that may be slowly choking highly dynamic river systems – and the biodiversity that depends on them – to death.
The waters of the Yellowstone, for example, have been diverted for irrigation, and the course of the river has been altered by channelization for flood control and the placement of boulder breakwaters, or riprap, which landowners install to stem erosion. Although the Yellowstone is undammed, these other human activities can slow and change the river’s flow and, most significantly, alter the complex interaction between the above-ground course of the river and the unseen currents that stream beneath the Yellowstone Valley’s broad gravel and cobble bottom.Such human alterations to a river can impair its dynamism and resilience, especially in combination with rising temperatures from climate change and reduced water flows because of increased evaporation and irrigation.
In effect, these myriad human activities contribute to the weakening of the “immune systems” of rivers like the Yellowstone, making aquatic organisms more vulnerable to stresses like fish-killing parasites. The paper said these pernicious changes are being experienced in waterways across western North America and in other mountain river systems, including some found in Europe, the Andes, the Himalayas, and the high country of New Zealand.
Written by Jim Robbins / Environment 360
Photo by Jim Urquhart / Reuters
