Wednesday, October 21, 2015

Nakano’s Legacy

Twenty years ago now, in 1995, Shigeru Nakano embarked on research that would change the way scientists who study streams and rivers think about these ecosystems. Nakano used the bold approach of covering a small stream in Hokkaido, northern Japan, with mosquito netting stretched over a greenhouse frame to cut off the insects falling into the stream from the streamside (riparian) forest. It also stopped the flow of adult aquatic insects that were emerging from the stream from entering the forest. As I describe in For the Love of Rivers, the results were astounding. Nakano and his colleagues, and later other scientists in other regions, found that about half or more of the animals in the forest that depend on insects emerging from streams, like bats, birds, lizards, and spiders, disappeared when a critical part of their food supply was cut off. Likewise, when forest insects no longer fell into the stream, half the fish left.

Shigeru Nakano drowned in a tragic boat accident in Baja California in March 2000, while visiting field sites of another ecologist who was studying flows of insects to desert islands created by the rich sea wrack that washes up on beaches from the Sea of Cortez. I will never forget when I heard the news, and the trying weeks afterwards as the US Coast Guard and Mexican Navy searched for him without success. Many of our lives were forever changed by his loss, but our understanding of streams and their importance to landscapes and humans was also forever changed, and this brings me joy despite the loss.

Nakano’s work inspired many other river and stream ecologists to look more closely and delve more deeply into the unintended consequences of our human activities on streams and their riparian forests. Nearly every action we take in forests and grasslands, such as grazing cattle, cutting trees, mining metals, and spraying chemicals to kill insects or weeds can affect the flow of terrestrial insects that fall into streams and feed the fish. At the same time, nearly every action we take in streams, such as diverting water or straightening streams into ditches to speed flood waters away, can harm the immature invertebrates living on the stream bed and ultimately reduce the total amount of adult insects that emerge from the water surface and feed the animals that live along streams.

Every year the scientists who study streams gather at professional meetings to present their work to each other, meetings held by societies like the Society for Freshwater Science and the American Fisheries Society. This year, each of these meetings had whole sessions with titles like “Land-Water Interfaces” and “Cross-Ecosystem Resource Subsidies: From Land to Water and Back Again”. Scientists are working actively to understand, for example, how pollution and channelization of streams in urban areas affects these “subsidies” of insects that emerge from streams to riparian forests. Others want to know how wildfire in natural watersheds affects the flux of insects in both directions. It is clear that Nakano’s ideas, along with those of other scientists like Dr. Mary Power and her colleagues at UC Berkeley who came up with very similar conclusions at the same time, have continued to inspire a new generation of scientists to study the real importance of these stream-forest connections.

In the past few weeks, I have been corresponding with Dr. Yoshi Taniguchi, one of Nakano’s former students, about translating the title of For the Love of Rivers into Japanese. This is not easy, given the multiple meanings of this phrase in English. I also wrote him about how proud Shigeru Nakano would have been to see so many of his former students become accomplished scientists and continue to study how connected streams are to their surrounding landscapes. In return, I know that many of them still think and dream about Nakano, and gather strength and inspiration for continuing their work.

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