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Mucking About in Boats

The Double Life of Salt Marshes

By Tamia Nelson
tamia@paddling.net

February 13, 2007

August on western James Bay. The resonant honk of a solitary snow goose breaks the chill silence enveloping the sodden landscape. Other wavies join in, and a discordant chorus heralds the flock's thunderous return to the air. The stillness that follows is broken only by the muted rattle of pellets of wet snow on the mud of the foreshore and the distant drumming of a low surf. A freshening breeze tosses the heads of alkali grass and bulrush.

September, further east and south. A wall of fog rolls landward from the Bay of Fundy, bringing with it the salt tang of the sea. Great blue herons stalk the weedy shallows of Dipper Harbour, New Brunswick, unmoved by the urban hustle of nearby Saint John. As the first tendrils of mist approach, an expectant hush falls over the marsh, a hush akin to the quiet busyness of city libraries or the fervid reverence of worshippers mouthing prayers in great cathedrals. Soon all is gray and muted. The herons continue their hunt.

November. Southern California. The tide is on the turn, and the traffic on the freeway is little more than a barely discernible rumble. A snowy egret drops gracefully out of a pale blue sky over Gunpowder Point, then rattles his pinions with a fluid shake of the shoulders before taking up his station at the bend of a nameless tidal creek. He is not alone. Other egrets have already settled themselves further upstream, and hundreds of sandpipers probe the mud of the foreshore. Out over San Diego Bay, an osprey checks his soaring flight for an instant before diving down to the water. A wriggling silver fish is his reward.

Back East. Florida Bay. February. Five bald eagles survey their world from vantage points on a long-dead cyprus. Each one claims a limb to himself. A brilliant cerulean sea dances before them, its surface flecked with patches of white. Massing thunderheads loom dark on the southern horizon, while three pelicans fly formation just above the waves, oblivious to the threat of stormy weather. Along the shore, a little blue heron picks his way deliberately through the sea grass.

 

Separated in time and space as these disparate scenes are, what can they possibly have in common? That's easy. They all take place in or near…

Salt Marshes

Land–water. Sea–air. Forest–field. Edges, those places where different elements or environments make contact, are found everywhere in nature. They're dynamic, diverse, lively. In other words, edges are where the action is. And seacoasts are edges writ large. Of course, not all coastal edges are equal. Some are "high energy" environments. On ironbound coasts, waves smash against towering cliffs, occasionally sending slabs of rock tumbling into the spume. Immovable object meets irresistible force, and the outcome is easy to guess. Over many centuries, force prevails. The sea advances. The land retreats. In the meantime, though, many sea birds cling precariously to the rugged, crumbling crags, raising their young in nooks and crannies only feet from the spray and tumult. But they're the exception. High-energy means high danger for any creature lacking mastery of the air. Canoeists and kayakers are no exception.

That's one extreme. At the other, the coast slopes gently into the sea, like a timid swimmer dipping her toes tentatively into the ocean before wading out to meet the breakers. The forces of wave and tide are blunted, and the quiet sea surrenders her burden of sediment to the ocean floor. The land grows outward — fitfully, to be sure, but over time the sea (literally) gives ground. Such places — "low-energy depositional environments" in the coldly precise jargon of science — are home to salt marshes. They're also the favorite haunts of many paddlers.

OK. Salt marshes are good. But where can you find them? Well, you might start by looking in the lagoons behind barrier islands and sandy spits.

Spitting Image

Of course, lagoons aren't the only places to look for salt marshes. You'll also find them in protected bays and along the lower reaches of estuaries, not to mention sloping foreshores sheltered from prevailing winds. Location matters, too. Though both the Atlantic and Gulf Coasts of North America are generally hospitable, less than 20 percent of the Pacific Coast is capable of supporting salt marsh.

The reasons for this variability are almost too numerous to catalog. If a coast is too steep, sediment can't settle, and emergent plants struggle to keep their heads above water. On the other hand, gently-sloping foreshores are often muddy, and mud is an ideal nursery for growing plants. What's mud's secret? It's all in the recipe: a surprisingly complex mixture of clays and silts, along with sand, fragments of marine shell, and dollops of organic detritus. Where does mud come from? Here's a hint: Another name for salt marsh is tidal marsh. This gives the game away. Unlike their freshwater cousins, salt marshes breath with the tides, flooding and drying as the water rises and falls. And with each cycle, the sea deposits a fresh mantle of sediment. Estuarine marshes enjoy a double bounty, receiving sediments from both sea and land, borne by tide and river. Salt-tolerant plants take root in the resulting mud, and their roots in turn trap still more sediment, holding it fast against the tug of the tide. As generation succeeds generation over many years, a rich organic mortar forms. The end product of this process is peat, and in the fullness of time shrubs and trees may colonize the peaty shallows, as meadowland grows outward toward the sea.

 

Here we see the secret behind the first of the salt marsh's two pivotal roles:

Bulwark of the Land

Salt marshes are natural sponges. When a high wind joins forces with a high tide to send a storm surge sweeping toward the coast, the resilient matrix of mud and interfingered roots absorbs the blow, sparing the land from the full might of the sea. Even when this defense fails to halt the onrush of water, the marsh endures. And when the storm waters finally recede, as recede they must, the marsh stands in their way, recapturing much of what the waves had claimed. The upshot? The marsh emerges from the battle even stronger than it was before the first wave fell. Now that's triumph in adversity!

Tough as they are when put to the test, however, salt marshes also have a tender side. In fact, they might well be called…

The Sea's Nursery

Like freshwater marshes, salt marshes support a rich diversity of plant and animal life, beginning with marine plankton and moving up the pyramid from there. Lugworms and other marine worms flourish in the mud of the intertidal zone, as do a bewildering variety of molluscs, crustaceans, and other invertebrate life-forms. Land animals, too, depend on salt marshes. Shore birds, squirrels, mice, raccoons, coyotes, deer, and muskrats come to the marsh to forage for their meals. Ospreys and gulls build nests on land, finding rich pickings just offshore in open water. Wading birds, ducks, and geese feed in the shallows and stalk the fish that sweep in with each tide.

Fish. Here we come near the heart of the matter — and the marsh. For many species of fish, including some commercially important species, and for the young of sea turtles as well, the salt marsh provides both shelter and nourishment. Some species move on into the open sea as adults, others (like the flounder) remain behind to get their living in the shallows. And speaking of moving on, salt marshes play host to countless species of migratory songbirds, waterfowl, and waders on their semiannual flights to and from their wintering grounds. Some stay only long enough to rest and refuel before taking to the air for the next leg of their journey. Others stop over for a season, or even longer.

Canoeists and kayakers, too, find welcome shelter from wind and wave in salt marshes. But — for birds and paddlers alike — these refuges are now becoming scarce. And their fate is our hands, because, like all vital things…

Salt Marshes Are Fragile

They're fascinating places to visit, but they're also easily damaged, and the cumulative impact of thousands of visitors, even thousands of well-meaning visitors, can wreak havoc: even a discarded plastic bag can kill, after all. Yet other threats are far graver. Waterfront development. Wetland "reclamation." Pollution from industrial effluent, agricultural runoff, sewage-treatment plant outflows, and storm drains. Erosion from wakes. Overfishing. The list is long and disheartening, and remedies are few and far between. But the damage must not continue. Much has already been lost. Less and less remains to save. And time is running out.

What can we paddlers do? Give wildlife and waterfowl plenty of space, especially during the breeding season and when they're raising their young. Pick up after ourselves (and others). Watch where we step, and even then tread lightly. Leave our pets at home. None of these things will address the big problems, of course, but at least we won't be making things worse. And that's something.

Salt marshes are dynamic, fluid and ever-changing. Sometimes dry and sometimes wet, they partake of both water and land. Yet theirs is a benign duplicity. After all, they protect the shore from the sea's assault at the same time that they nourish the hungry. And our species is no exception. Salt marshes protect and feed us, too. But for how long? That's the question, isn't it?

Copyright 2007 by Verloren Hoop Productions. All rights reserved.
















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