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On the Trails: Learned in Alaska

Posted: July 26, 2013 - 12:03am
In this photo, I am learning that estuaries are important winter habitat for American Dippers, a songbird that nests along the freshwater streams.  Photo by Kathy Hocker
Photo by Kathy Hocker
In this photo, I am learning that estuaries are important winter habitat for American Dippers, a songbird that nests along the freshwater streams.

When I moved to Juneau, almost 25 years ago, I knew no people, almost no plants and about five birds in this area. So I had a lot of learning to do! I’ve been working on that. Of all the things I’ve been learning, two big patterns stand out.

First: I grew up in the Midwest and spent most of my professional career there. So I was accustomed to seeing much the same landscape from year to year. Yes, the Pleistocene glaciers had come and gone, more than 10,000 or 12,000 years ago, the Mississippi occasionally shifted its channel and there was a massive earthquake back in the 1800s. But day to day, week to week, month to month, the look of the land was pretty similar. So it was easy to think of the ecological landscape as being quite stable.

Not so in Juneau! We have earthquakes, sometimes with many aftershocks. There are landslides and avalanches, jökulhlaups and tsunamis (small ones…). The most recent glaciation was only 200 or 300 years ago (my house would have been under the ice), and glaciers continue to recede (and occasionally advance). There is the continual rise of land that follows disappearance of the glaciers; this isostatic rebound amounts to almost an inch a year in some places, bringing meadows up out of the sea. This is a very dynamic landscape, and any sense of landscape stability gets blown right out the window!

Second: As an ecologist, I am accustomed to thinking about interactions among organisms: predator and prey, pollinator and flower, succulent fruits and seed dispersal by fruit-eaters, and so on. I can do that here too. But the striking thing is that here the scale of interactions is huge, occurring over many miles.

This initially came home to me when (24 years ago) I first watched salmon making their way upstream to spawn, after spending a year or more in the ocean, growing to adult size by eating oceanic foods. Then I began to appreciate the many connections to this influx from the ocean: We studied the predators on the incoming salmon, and these consumers spread marine-derived nutrients over the landscape, by hauling fish carcasses into the forest and by voiding waste products, sometimes miles away from the stream. These nutrients get into the vegetation, both in the water and on land, and help feed the many creatures that eat vegetation. Fish carcasses are a bonanza for many insects and other scavengers. A further spin-off is that more birds nest near salmon-spawning streams than along streams that don’t host spawners, perhaps because the vegetation is denser or because there is more insect prey. Most of our coastal streams are relatively small, but on bigger systems, such as the Taku River, many of the tributaries support salmon runs, spreading the inflow of nutrients over a wide watershed. The basic story of the “salmon forest” is well-known to most of us here.

Less well known is the story about what goes downstream. Of course we all know that fresh water flows downhill and much of it eventually reaches salt water. However, we often do not think about what that water carries to the sea. It bears a load of sediment that gets deposited in estuaries, often changing their configuration, and providing fine habitat for migrating shorebirds. It also carries lots of nutrients, from many different sources: nitrogen and carbon from forests and muskegs, iron and phosphorus from weathered rocks, a diversity of materials from the decomposition of salmon and from the rich bacterial community that inhabits glaciers. All these nutrients enter the nearshore zone, where they nourish algae and eelgrass and even the sedges and other plants that grow in the upper intertidal zone. Some of that rich input is eventually entrained by the coastal currents that sweep north and west in the Gulf of Alaska and carried along for great distances.

In addition, at the mouths of large rivers (such as the Copper River), broad deltas often form. At seasons of low water flow, huge dust storms sometimes develop over the dry deltas; these storms blow sediment and lots of nutrients far out to sea, providing iron and other necessary nutrients for marine organisms.

All the organisms that benefit directly from the influx of nutrients from land and fresh water to the sea have a multitude of effects on still more organisms. The eelgrass makes great habitat for lots of little fishes, the sedges and grasses feed geese and finches. Some algae, attached to rocks and shells, make habitat and food for many invertebrates. Other algae, particularly the tiny phytoplankton floating in the open water, feed small crustaceans (such as krill) that feed herring and other forage fishes; both krill and the forage fishes feed our locally famous humpback whales. So you could say that the glaciers, forests and muskegs and streams feed the whales.

Here in Southeast, there are hundreds of small, coastal streams, along with a few large, transmontane rivers. These dump huge amounts of fresh water into the sea every year. Coastal Alaska streams have been estimated to be equivalent to one or two Mississippi rivers or perhaps four Yukon rivers, in terms of their output. A big difference is that the coastal streams enter the sea all along the coast, so the input is more spread out along the coast. Because most of these streams are short, much of the material goes directly into the sea, with less in-stream processing of material on the way than is the case for longer, bigger rivers. Another big difference is that a number of coastal streams have glaciers at their headwaters, and these provide unique combinations of nutrients to the coast, different from streams originating in muskegs or forest.

Many aspects of these far-reaching connections are still subjects of active research. A nice, and very productive, feature of this research is that, at last, biologists and geologists and hydrologists and biogeochemists and oceanographers are talking more to each other, and the land and sea, once treated as totally separate entities, are no longer viewed that way, but rather as parts of a connected whole.

The bottom line, in personal terms, is that this old Midwesterner had her eyes opened when she came to Juneau. New thoughts barged in, forever changing her perspectives. That has been great fun.

• Mary F. Willson is a retired professor of ecology.

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