RIVERS

Standing in the river, I peer into the pale green water. Needlefish, sting rays and snappers swim along the bottom, some in the sunlit areas, others along the sandy banks, or in the shadow of a great hardwood that has fallen into the river. The current piles up organic debris and sand against the log, now stripped of its bark by death and river erosion. On the down-river side there is a deep trench dug by the water pouring and bubbling over its slick surface. I follow the terra cotta trail the tree tore in the brush where it fell and slid into the river. Soon shrubs and young trees will fill this scar and stabilize the bank as this giant once did. The birdsÌ nests and orchids that this tree once sheltered are gone, so are the fruit and shade it provided, but now it has new purpose. Its slow disintegration releases a trail of nutrients to the animals and plants of the river and nearby shore, first from the disintegrating leaves, bark and epiphytes that lived on it, then from the softer tissues of the wood itself.

Its branches above water provide rest and safety for rust colored dragonflies and a pair of Brown-winged Kingfishers hunting small fish that like to lie along the sheltering edge of the log. Under water the branches comb the river, collect debris swept from banks or released upriver. Algae, a green fur on one end, have begun to root into the log, where waterbugs can hide and on which young fish can feed. Slowly, over decades, this tree will disappear, most of it into the river itself, some of it, the harder wood, buried, stabilizing the sandy bottom.

Rivers erode the rocks and soil through which they run and carrying sediments to the ocean shore. Gradually, as the soil moves down river, it is stripped of its organic content, and the small stones are rolled and eroded until they become gravel and sand. The current slows as it approaches the shore. The sand and rocky debris have gradually rasped away the rocks, widening the river mouth, depositing most of the heavier gravel, keeping the lightest sands for last. Along the last stretch there are sandy banks, on which Cassarinas, pine like, and Morning Glory vines with purple flowers grow. Shore birds strut along these banks, poking for crabs and other small crustaceans. A drongo wheels above the trees plucking insects out of the air, its black raquet-shaped tail swooping.

A long, sandy beach tells us that the river is large, and carries considerable sediment. I can see the river bar. It forms a protective barrier and a lagoon, keeping larger predators at sea. It is almost entirely closed during the dry season, with only a shallow opening. Fresh water seeps out through the sandbar into the sea at low tides and salt water flows into the river during high tides. The water is brackish for several kilometers up river. During the rainy season great gaps appear in the bar and it may disappear altogether. From the sea, you can judge the size of any fresh water source by the length and breadth of the sandy beach it produces.

Where sandy banks end up-river, mangroves on spidery legs obscure the river edges. Black crabs on the root shoulders, clicking, drop into the black water as I approach. A small crocodile sitting stealthily on a root, too visible, leaves with a splash. A civet watches from the canopy. Prawns have built tall mud towers on the shore. The mangroves, protected from the winds and salt of the sea, sport orchids and other epiphytes on their trunks. Their roots also comb the river for debris and provide a rich array of protective niches for young fish and invertebrates.

Rivers are the arteries of Mother Earth, central to life on land and in the sea. We should be wary of damming them, uncomfortable putting them in concrete channels, concerned about polluting them, and loathe to cut away trees that serve themÛjust as we would with our own circulatory system.