With the arrival of April we welcome Earth Day, a time to consider our obligation to the environment in light of the responsibilities assigned to humanity in biblical stories of creation.
In Genesis, humans receive dominion over the fish of the sea, and presumably the sea in which the fish live; over the fowl of the air and the atmosphere in which the fowl live, and over every living thing that moves upon the Earth that humans must replenish.
We have the means to carry out this obligation. Our bodies, while not the strongest of all nature's creatures, are by far the most flexible, and our brains are without peer.
Earth Day is an appropriate time for Americans to consider their record as keepers of our nation's lands and waters, a country blessed with bountiful natural resources.
But as we look east, we see Appalachian mountain forests, clear-cut so as to blast mountain tops off into the valleys, retrieving small seams of coal while blocking miles of streams in the ruined valleys below.
In the Midwest, we have plowed dry-area grasslands that once supported countless birds and buffalo.
Now we grow crops intended by nature for wetter regions. To accomplish this, we take up to 3 feet of irrigation water annually from underground aquifers, which are replenished by nature at the rate of one inch per year.
The fate of those aquifers is not difficult to forecast. In the arid west, we dam rivers so that people and crops can live in deserts. The land becomes more saline, and the rivers no longer reach the sea.
The Earth's lines of meridian run from pole to pole, and they mark westward progress in degrees of longitude from the prime meridian at Greenwich, England. The 100th meridian emerges from central Canada.
It bisects the Dakotas, Nebraska, Kansas, Oklahoma and Texas. To the east of the 100th is wet America, with its corn and soybeans. To the west, except for part of the Pacific Northwest, is dry America -- wheat, cattle ranches and irrigation.
The primary water sources for dry America are the snowpacks of its mountain ranges, which feed the rivers during dry seasons. The west's major river is the Colorado.
It brings life to hundreds of cities, an increasingly thirsty 21 million people, and more than 2 million acres of irrigated farmland in seven states and two countries. The Colorado's dams and diversions were planned and built at time when the river's annual flow ranged from 16 million acre-feet to more than 20 million.
In the drier 21st century, the flow is now averaging 14 million to 15 million acre-feet. The river's two major reservoirs are Lake Powell, behind Glen Canyon Dam, and Lake Mead, behind Hoover Dam. Those reservoirs are in slow decline, and they are currently averaging half-full.
Before the Europeans, Minnesota was a natural-resource treasure, with forests of virgin White Pine, and some of the world's largest deposits of rich iron ore. Deep layers of our glacially deposited soil were nourished by the ample waters of our lakes, streams and aquifers.
Now those forests are clear-cut, their lumber exported to the world. Most of the iron ore has also gone everywhere, leaving behind those empty pits. We need to protect our remaining soil and the waters that nourish it.
All over the Earth, this drawing-down of nature's resources continues. More than a billion people are hungry, while the rest of us make a place at the table for nearly a billion cars and trucks to consume their diet of food-based biofuels.
The vengeance for these acts of desecration will not be sudden, as in the great flood of biblical history. Instead, the rivers will gradually silt up the dams, overtop and remove them, and resume their destined routes to the sea.
Soils, impoverished and eroded from single-cropping and excessive fertilizers, will no longer nourish our billions. A warming atmosphere, polluted by overuse of carbon fuels, will wreak its own havoc.
There is still time, but not much time, to take seriously the responsibility for the Earth that dominion gives us.
Rolf Westgard, of St. Paul, is a professional member of the Geological Society of America.
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