The Roman Empire
The first conquests of the Roman Empire were in the East and immensely profitable. These old Mediterranean civilizations were rich and could afford much tribute. The profits funded new conquests.
Most of Italy was forested in BC 300. The newly cleared lands yielded large crops. The richness of the Italian soil was another basis of the Empire.
The western lands (Gaul, Spain, England, the Rhineland), which were conquered last, did not pay the costs of conquest. These lands were lightly settled and poor. While their soils were good, the cost of transporting crops like wheat overland was too great.
The Roman economy was overwhelmingly agricultural. Trade and industry were perhaps 10% of the economy. Once the conquests were over (about AD 1) agriculture had to pay the costs of administration.
A smallholder of the early Republic cultivated a hectare by hand with a hoe, growing olives, vines, fruit trees, grains, vegetables, forage crops and animals. The multistory canopy saved labor, reduced erosion, and was twice as productive in foodstuffs as plowing with an ox to grow grain. Some farmers applied manure, human manure, crushed limestone and ashes to their fields and grew cover crops on the grain fields left fallow every other year.
For large landowners plowing with oxen to grow grain was more profitable than hoe agriculture. While good farming practices were known, most large farmers didn’t follow them. In the two field system of the Greeks that was taken over by the Romans, land was plowed three times a year, whether cultivated or fallow, to control weeds. Erosion from plowland near Rome has been estimated at three quarters to four inches per century.
Iron had come into common use in Italy by BC 500 (for shovels, plow points and other tools) and forests were cut to smelt it, to fire pottery and burn brick. Trees were also cut for building material. Eroded soils from forests slid down the hillsides to the valley bottoms. Forests were often grazed after being cut.
As the more wealthy began to dominate Roman society after BC 200, large estates began to replace smallholdings, especially in the countryside around Rome. This landscape, the Campagna, fed the city until about BC 200.
Wheat, oil and wine could be profitably shipped by sea. The conquest of Egypt, with its soils renewed by the Nile, and the new lands of North Africa, let Rome feed itself after AD 1. The Imperial Middle East was completely deforested by AD 100 however and most of its upland soils were degraded by AD 200. Grazing replaced the cultivated grainland, which had replaced the forests. By the end of the Empire the silt carried by the Nile fed Rome. (The same African silt and the new lands of Sicily had also fed the declining Greek states 1000 years before.)
Land itself was taxed. No provision was made for varying yields. The government financed itself on a cash basis. Its single tax was inelastic and made it difficult to raise additional funds in time of need (as in war). Emperors in need of money debased the currency, an indirect tax.
Tenant farmers were taxed too highly to accumulate capital. When crops failed they abandoned their lands and left for Rome, where Egyptian wheat was distributed free to the citizens (the dole).
As more land fell into the hands of the large landowners, erosion increased. As yields fell, taxes became more difficult to pay and more and more land was abandoned. Abandoned land reached a third to a half of some provinces. Tax receipts collapsed. In AD 300 abandoned lands in the Campagna were estimated at 75,000 smallholdings. Taxes were doubled AD 324-364.
Eroded soil turned river valleys into marshlands. Malaria became a problem after AD 200. Malaria increases child mortality and reduces people’s capacity to work. In time, both slopes and valley bottoms were used for pasture rather than cultivated.
With the end of the conquests and the money they brought in, and the declining agricultural yields, and thus declining tax revenues, Rome no longer worked. The population of the Empire never recovered from the plague of the AD 160s. With the barbarian invasions of the AD 200s (crops destroyed, people killed and enslaved, animals killed or stolen), Rome began to go bankrupt. The literacy rate fell, but the size of the army and bureaucracy increased. The army was more and more staffed by barbarians.
As large estates further consolidated (city magistrates, whose position had become hereditary, had to pay the cost of city services), and plowed lands increased, yields fell further, and the countryside grew emptier. It now took ten times the land to feed a Roman than in the days of the early Republic. (Five hundred years of erosion would have reduced topsoil in the Campagna by 4 to 20 inches, and more on sloping lands.) Laws tied tenants to the land to prevent them from abandoning it. What the land needed to become productive was known; perhaps the larger structural problems of the Empire were also known. The western provinces were let go AD 260-274. By the late 300s, the Romans waited—as the poet Cavafy said—for the barbarians to deliver them from the Empire.
(In this essay I am indebted to The Collapse of Complex Societies by Joseph Tainter and Dirt by David Montgomery.)
Saturday, February 19, 2011
Thursday, February 10, 2011
Biology Comics
Barges
Recent figures indicate one gallon of diesel will move a ton of cargo 59 miles by truck, 202 miles by train, 514 miles by canal barge (a single barge can carry 3000 tons or 100 truck loads).
Barges use rivers as highways. They motor through the still waters behind the dams, passing each dam in locks. On the Rhine, narrow canal boats carrying bulk cargoes push their way upstream through the currents.
By converting rivers into highways dams interrupt the flow of water, sediment and detritus along the stream. Flooding riverside wetlands eliminates their capacity to remove nutrients from water flowing into the river. Dams prevent fish migrations (and thus migrations of mussels, their glochidia transported by swimming fish). The water above dams is warmer, that below dams (released from the bottom of the reservoir) colder, thus changing the temperature cues the eggs and larvae of riverine invertebrates and fish use for hatching and development. (So they grow too early or too late—both want to develop when abundant food of the right size is available). The levees with which dams are associated prevent floods and limit the spawning of fish, many species of which prefer to spawn on flooded habitats. Dams alter the timing and abundance of flows to ocean estuaries, upon which marine fish (many of which spawn in nearshore waters) depend. Silt and silicon stored behind dams change the relative abundance of algal species in estuaries; less sand downstream causes erosion of beaches.
Dams also let people harvest river water to drink, bathe, fill swimming pools; to use in industry; to cool power plants; to irrigate crops. Together with levees, dams let people farm riverside land (much of which was farmable before dams, with free fertility provided by the river); build houses and cities near the river; and use the river to move freight.
The Romans thought the air, the waters, the ocean, the shores of the sea could not be owned. Under the Public Trust Doctrine (which the United States received through English common law from Roman Law), public assets, such as shore and river banks, are held by government for the common good. Similarly, the authority of the state to regulate wildlife derives from its authority to protect common resources. It would be much simpler to see where these matters lead us if we depended more directly on an abundance of wildlife and fish. But we have extinguished both for the ‘common good’ of economic development.
While fossil fuels let us lead lives separate from nature, our dependence on nature is clear, if poorly understood. For instance, trees and photosynthetic bacteria maintain the oxygen levels in the atmosphere, microbes, fungi, and invertebrates recycle the carbon (the lignins and carbohydrates) the plants produce annually, and many interconnected systems maintain the climate. Our dependence on nature is a dependence on ecological process.
The ‘common welfare’ includes the taking of water from rivers for human use, the right of fish to water (so they remain a resource for fishers), the right of beaches to sand (so beach goers, and the owners of houses that back the beach, may enjoy them). In an ideal world, the beach deserves sand and the fish water (and water a place in rivers; and even oil a place in its underground reservoirs), whether or not any human advantage flows from them. (But the advantage is that a given system works in a more or less predictable way—which is not to say it cannot be disturbed—by volcanic eruptions cooling or warming the earth; by landslides damming rivers.)
Some rivers no longer reach the sea (the Colorado, the Yangtze). All their water is used by people. So marine fish are deprived of deltas and estuaries to spawn and mature in, offshore waters of nutrients. Many rivers no longer flood so native fish have trouble surviving (the Mississippi-Misssouri, the Colorado, the Rhine). Or are so polluted with silt and nutrients their fish (mussel, invertebrate, waterbird, turtle) populations crash and other organisms take over. The Illinois, a booming native fishery a century ago is now dominated by two filter feeding Chinese carp, escapees from fish farms, that thrive in the turbid water, and terrify boaters and water skiers by leaping up as they pass—part of the fishes’ strategy for escaping predators.
A rule of thumb for functioning rivers is that no more than 20-25% of longterm average flow should be withdrawn; and less during droughts.
Such numbers cannot be applied to rivers like the Colorado, all of whose water is subscribed to human use. (In fact, more Colorado water is allocated than exists, since the early 20th century years used as a benchmark to determine its flow were unusually wet ones).
Like the Mississippi-Missouri, the Columbia, or the Rhine (each remade in its own way), the Colorado is a totally remade river. Once silty and unpredictable, it now has long reaches of clear cold water and a more even flow. It is twice as salty as before. (The yearly flow of the river before dams varied from 4 million acre-feet to 24 million acre-feet, an enormous range; an acre-foot is the water necessary to cover an acre a foot deep.)
Large dams transformed the Colorado. Irrigation of rancher’s hayfields along its upstream tributaries began to change it. The concrete plug of Hoover Dam stopped any movement of fish upstream from the lower river. That part of the river, below the canyons, where the Yuma once planted their corn in the wet mud left by the receding floods (the corn matured in 60 days) flowed through an wide riparian valley of marshes and backwaters, fed on silt, rearranged by floods. The backwaters were places young pike-minnow and other native fish (razorback sucker, humpbacked sucker, bonytailed chub) matured. Pike-minnow were the top predatory fish in the Colorado, reaching 6 feet in length and 80 pounds. Pike-minnow spawned in the clean gravel and cobble left by the spring floods, matured in backwaters, migrated 300 miles up and down the river to seek optimal places for spawning and survival. Like the other fish of the Colorado and its tributaries they were adapted to the warm low silty flows of summer and the turbulent spring floods, when water volumes might increase by 100 times.
The marshes and backwaters along the lower river have been consolidated into a 150 yard wide stream held back by Parker dam at the Mexican border. The water irrigates fields on either side. Protected by dam operations and levees, houses have crept up to the edge of the river, which is no longer allowed to flood.
The Delta of the Colorado in the Gulf of California once consisted of 2 million acres of fresh and tidal wetlands. (Aldo Leopold wrote a memoir of a bow hunting trip there with his brother.) A desert delta, it was an important habitat for west coast waterbirds. Shrimp and other invertebrates of the delta supported the marine fish and birds of the Gulf of California. Now starved of silt and water (wet years in the 1980s restored about 150,0000 acres of the marshes), its place in the avian world has been taken over by the Salton Sea, a desert sink that was filled by the Colorado early in the 20th century when the river abandoned its normal course to take over an irrigation canal into California’s Imperial Valley. The water filled the sea during the several years it took to return the river to its bed. (That this had happened before is the subject of Native American tales.) The Salton Sea is now maintained by runoff from irrigated farms in the Imperial Valley (irrigated with Colorado water). Its increasing content of salts, fertilizers, metals and pesticides make it something of a disaster as a sanctuary for birds, which suffer (like the fish introduced from the gulf) from periodic epidemic diseases and dieoffs.
Allotting 5% of the Colorado water to the delta would restore a third of it (about 750,000 acres). Then plans to desalinate the Salton Sea (to maintain it as a bird habitat) could be abandoned and the money put into buying out water rights from farmers. Irrigation runoff would matter less, and farmers could shift to less water using, more valuable crops (say, to winter greens from alfalfa and cotton). All this would leave more water in the river, some of which would reach the delta.
Irrigation lets you ignore climate. Colorado water supports the alfalfa, cotton and lettuce fields of the Imperial Valley; the citrus plantations and spinach and cotton fields of Arizona. Many commodity crops (cotton, corn) grown under irrigation could be grown in sufficient quantity further east, with irrigation (if necessary) from streamside reservoirs dug beside the rivers. Small farmsize irrigation ponds store irrigation water, recharge underground aquifers, provide spawning places for fish and habitat for waterbirds and amphibians, especially if the water is pumped from shallow wells and not from the reservoirs themselves, with all their plant and animal life. Such reservoirs, storing no more than say 10% of the spring runoff, might improve the habitat of degraded eastern rivers. (Somewhat similarly, floodwaters from the Colorado could be stored in underground aquifers rather then in reservoirs behind dams, from which the water, exposed to the desert sun, evaporates.)
Drylands are often rich in nutrients which have been banked by plants and soil cyanobacteria, but not much used or leached by rain (nitrogen in dryland subsoils can reach toxic levels). Some dryland soils take to irrigation well. Many drylands however were once ocean bottom and are underlain by salts, which irrigation tends to draw upwards, and which must be constantly drained and flushed away. In the Wellton-Mohawk Irrigation District of Arizona, the Bureau of Reclamation sunk wells into the briny groundwater and piped it to the Colorado. Not allowed to raise the salt content of the river, they reduced its salt input in other ways—by lining canals, using more efficient irrigation systems, taking some lands with very salty subsoils out of production. I suppose if agriculture wouldn’t pay to desalinate the briny drainage water, marketing the salts and metals, and reusing the water for irrigation or returning it to the river, the agriculture wasn’t economic. But agriculture never pays the cost of large scale irrigation systems, which enrich private landowners with public monies, and degrade rivers.
Suppose for rivers like the Colorado we reverse the usual figure and say 25% of its water should be kept in the river to support its normal flood cycle and its wildlife. It is estimated that pressurized irrigation systems (drip tubing, sprinklers) that use less water (and more power but once you install the equipment solar power is free in the desert), shifting to crops of higher value that use less water (such as winter greens) and urban water conservation could save a third to a half of the water taken from the river. (The potential for household savings is huge but irrigation uses most of the water.) Then even more water could be left in the river and through a new treaty with Mexico, to whom the U.S. is currently obligated to release 1.5 million acre feet of Colorado water a year of a certain salinity (the last standard usually not met), the delta could be partially restored.
Rivers like the Colorado need to flood. Floods distribute sediment and nutrients to the floodplain, dig new channels and backwaters, renew the vegetation of cottonwood and willow. Floods maintain habitat for fish. The vegetation that sprouts on the newly bare ground feeds small mammals and water and game birds. While levels of heavy metals, pesticides and herbicides in the lower Colorado are high enough to cause reproductive problems in fish, the lack of floods and the changes in patterns of seasonal flow may be greater problems for the fish.
Glen Canyon Dam, the last major dam on the Colorado, was constructed to provide additional water storage for Lake Mead (the reservoir behind Hoover Dam). Evaporation from Lake Powell (the reservoir behind Glen Canyon Dam) is about a million acre-feet a year. Because of this, removing it would not cause much change in Lake Mead’s capacity to provide water. It’s removal would restore a more natural flow to a long reach of the river and let more water reach the delta. It would end the dam’s power generation (Glen Canyon Dam provides 3-4% of the electricity used in the four corners states); the power is useful because it can be switched on immediately when needed. It would also end the cold water fishery for rainbow trout below the dam (the trout feed on diatoms that thrive in the clear water) and the growing population of bald eagles that eat them. The silt behind Glen Canyon Dam is contaminated with mercury and selenium (as is the silt in Lake Mead), much of it leached from the basin’s sedimentary rocks. The dam also captures phosphorus (bound to the silt). The building of Glen Canyon Dam dramatically reduced the abundant artificial fishery in Lake Mead, which is based on phosphorus eating algae, algae eating gizzard shad and striped bass.
Letting the river flood below Hoover Dam would restore the lower river. Thanks to dam operations, levees and dredging, people now build up to the edge of the dredged river. About 123,000 acres of riparian vegetation remain along the lower Colorado (one fourth of the original), 23,000 of them in a natural state (5% of the original vegetation, then, the rest in introduced salt cedar which outcompetes cottonwoods and willows on salty, dry soils). Removing levees along contiguous parts of this (connecting the floodplain to the river) and letting the land flood would restore parts of the floodplain (then salt cedar is likely to become a part of the ecosystem, not a dominant). Some people would have to be bought out, which puts the government in the position of paying people to surrender what it paid to provide them.
A river disconnected from its flood plain no longer works. Without a floodplain, a river cannot store floodwaters, provide spawning habitat for fish, turn silt and nutrients into herbs and trees, adjust its bed to its flow and silt load, shelter abundant amphibians, song and water birds, and game animals, and provide water of an amount, timing, and with the nutrients, the fish and invertebrates in its delta expect.
By damming rivers and turning them into highways, we interfere with fundamental ecological process. Rivers can handle some interference but control beyond a point turns them into drains, barge highways, water delivery canals. Ecological process is what provides the fish and mussels in the river, the fish of the estuaries and the sea. Do people own the ecological processes that maintain our green world; or have a right to extinguish them?
We live more and more in a world separate from the rest of creation. The separate world always existed—all plants and animals create their own worlds, some more than others. The separate world became more so with cities and writing. It got a push forward with the printing press, the secularization of thought, the use of fossil fuels. Now most of us live in one separate world (that supported by fossil fuels), while scanning (through the internet) another. In these worlds what does nature matter? Who knows about it?
Moving freight by river barge takes less fuel but is biologically very expensive. If all the costs of maintaining the river as a highway were charged to the barges, it would be economically expansive too.
Human use and ownership of the landscape move along a continuum. One way to approach biological economics is to assign values to things (fish, forests, underground waters) that are extremely hard to value; and which receive very low values under modern economic theory (once used up, a resource will be replaced by something else); but whose loss is likely to have far-reaching effects (what will we drink?). I think an enlightened state should set biological limits through its interest in the common good; and let the cornucopian human economic society deal (as it will) with a much more limited landscape and resources.
(In this essay I am indebted to Restoring Colorado River Ecosystems by Robert Adler.)
Recent figures indicate one gallon of diesel will move a ton of cargo 59 miles by truck, 202 miles by train, 514 miles by canal barge (a single barge can carry 3000 tons or 100 truck loads).
Barges use rivers as highways. They motor through the still waters behind the dams, passing each dam in locks. On the Rhine, narrow canal boats carrying bulk cargoes push their way upstream through the currents.
By converting rivers into highways dams interrupt the flow of water, sediment and detritus along the stream. Flooding riverside wetlands eliminates their capacity to remove nutrients from water flowing into the river. Dams prevent fish migrations (and thus migrations of mussels, their glochidia transported by swimming fish). The water above dams is warmer, that below dams (released from the bottom of the reservoir) colder, thus changing the temperature cues the eggs and larvae of riverine invertebrates and fish use for hatching and development. (So they grow too early or too late—both want to develop when abundant food of the right size is available). The levees with which dams are associated prevent floods and limit the spawning of fish, many species of which prefer to spawn on flooded habitats. Dams alter the timing and abundance of flows to ocean estuaries, upon which marine fish (many of which spawn in nearshore waters) depend. Silt and silicon stored behind dams change the relative abundance of algal species in estuaries; less sand downstream causes erosion of beaches.
Dams also let people harvest river water to drink, bathe, fill swimming pools; to use in industry; to cool power plants; to irrigate crops. Together with levees, dams let people farm riverside land (much of which was farmable before dams, with free fertility provided by the river); build houses and cities near the river; and use the river to move freight.
The Romans thought the air, the waters, the ocean, the shores of the sea could not be owned. Under the Public Trust Doctrine (which the United States received through English common law from Roman Law), public assets, such as shore and river banks, are held by government for the common good. Similarly, the authority of the state to regulate wildlife derives from its authority to protect common resources. It would be much simpler to see where these matters lead us if we depended more directly on an abundance of wildlife and fish. But we have extinguished both for the ‘common good’ of economic development.
While fossil fuels let us lead lives separate from nature, our dependence on nature is clear, if poorly understood. For instance, trees and photosynthetic bacteria maintain the oxygen levels in the atmosphere, microbes, fungi, and invertebrates recycle the carbon (the lignins and carbohydrates) the plants produce annually, and many interconnected systems maintain the climate. Our dependence on nature is a dependence on ecological process.
The ‘common welfare’ includes the taking of water from rivers for human use, the right of fish to water (so they remain a resource for fishers), the right of beaches to sand (so beach goers, and the owners of houses that back the beach, may enjoy them). In an ideal world, the beach deserves sand and the fish water (and water a place in rivers; and even oil a place in its underground reservoirs), whether or not any human advantage flows from them. (But the advantage is that a given system works in a more or less predictable way—which is not to say it cannot be disturbed—by volcanic eruptions cooling or warming the earth; by landslides damming rivers.)
Some rivers no longer reach the sea (the Colorado, the Yangtze). All their water is used by people. So marine fish are deprived of deltas and estuaries to spawn and mature in, offshore waters of nutrients. Many rivers no longer flood so native fish have trouble surviving (the Mississippi-Misssouri, the Colorado, the Rhine). Or are so polluted with silt and nutrients their fish (mussel, invertebrate, waterbird, turtle) populations crash and other organisms take over. The Illinois, a booming native fishery a century ago is now dominated by two filter feeding Chinese carp, escapees from fish farms, that thrive in the turbid water, and terrify boaters and water skiers by leaping up as they pass—part of the fishes’ strategy for escaping predators.
A rule of thumb for functioning rivers is that no more than 20-25% of longterm average flow should be withdrawn; and less during droughts.
Such numbers cannot be applied to rivers like the Colorado, all of whose water is subscribed to human use. (In fact, more Colorado water is allocated than exists, since the early 20th century years used as a benchmark to determine its flow were unusually wet ones).
Like the Mississippi-Missouri, the Columbia, or the Rhine (each remade in its own way), the Colorado is a totally remade river. Once silty and unpredictable, it now has long reaches of clear cold water and a more even flow. It is twice as salty as before. (The yearly flow of the river before dams varied from 4 million acre-feet to 24 million acre-feet, an enormous range; an acre-foot is the water necessary to cover an acre a foot deep.)
Large dams transformed the Colorado. Irrigation of rancher’s hayfields along its upstream tributaries began to change it. The concrete plug of Hoover Dam stopped any movement of fish upstream from the lower river. That part of the river, below the canyons, where the Yuma once planted their corn in the wet mud left by the receding floods (the corn matured in 60 days) flowed through an wide riparian valley of marshes and backwaters, fed on silt, rearranged by floods. The backwaters were places young pike-minnow and other native fish (razorback sucker, humpbacked sucker, bonytailed chub) matured. Pike-minnow were the top predatory fish in the Colorado, reaching 6 feet in length and 80 pounds. Pike-minnow spawned in the clean gravel and cobble left by the spring floods, matured in backwaters, migrated 300 miles up and down the river to seek optimal places for spawning and survival. Like the other fish of the Colorado and its tributaries they were adapted to the warm low silty flows of summer and the turbulent spring floods, when water volumes might increase by 100 times.
The marshes and backwaters along the lower river have been consolidated into a 150 yard wide stream held back by Parker dam at the Mexican border. The water irrigates fields on either side. Protected by dam operations and levees, houses have crept up to the edge of the river, which is no longer allowed to flood.
The Delta of the Colorado in the Gulf of California once consisted of 2 million acres of fresh and tidal wetlands. (Aldo Leopold wrote a memoir of a bow hunting trip there with his brother.) A desert delta, it was an important habitat for west coast waterbirds. Shrimp and other invertebrates of the delta supported the marine fish and birds of the Gulf of California. Now starved of silt and water (wet years in the 1980s restored about 150,0000 acres of the marshes), its place in the avian world has been taken over by the Salton Sea, a desert sink that was filled by the Colorado early in the 20th century when the river abandoned its normal course to take over an irrigation canal into California’s Imperial Valley. The water filled the sea during the several years it took to return the river to its bed. (That this had happened before is the subject of Native American tales.) The Salton Sea is now maintained by runoff from irrigated farms in the Imperial Valley (irrigated with Colorado water). Its increasing content of salts, fertilizers, metals and pesticides make it something of a disaster as a sanctuary for birds, which suffer (like the fish introduced from the gulf) from periodic epidemic diseases and dieoffs.
Allotting 5% of the Colorado water to the delta would restore a third of it (about 750,000 acres). Then plans to desalinate the Salton Sea (to maintain it as a bird habitat) could be abandoned and the money put into buying out water rights from farmers. Irrigation runoff would matter less, and farmers could shift to less water using, more valuable crops (say, to winter greens from alfalfa and cotton). All this would leave more water in the river, some of which would reach the delta.
Irrigation lets you ignore climate. Colorado water supports the alfalfa, cotton and lettuce fields of the Imperial Valley; the citrus plantations and spinach and cotton fields of Arizona. Many commodity crops (cotton, corn) grown under irrigation could be grown in sufficient quantity further east, with irrigation (if necessary) from streamside reservoirs dug beside the rivers. Small farmsize irrigation ponds store irrigation water, recharge underground aquifers, provide spawning places for fish and habitat for waterbirds and amphibians, especially if the water is pumped from shallow wells and not from the reservoirs themselves, with all their plant and animal life. Such reservoirs, storing no more than say 10% of the spring runoff, might improve the habitat of degraded eastern rivers. (Somewhat similarly, floodwaters from the Colorado could be stored in underground aquifers rather then in reservoirs behind dams, from which the water, exposed to the desert sun, evaporates.)
Drylands are often rich in nutrients which have been banked by plants and soil cyanobacteria, but not much used or leached by rain (nitrogen in dryland subsoils can reach toxic levels). Some dryland soils take to irrigation well. Many drylands however were once ocean bottom and are underlain by salts, which irrigation tends to draw upwards, and which must be constantly drained and flushed away. In the Wellton-Mohawk Irrigation District of Arizona, the Bureau of Reclamation sunk wells into the briny groundwater and piped it to the Colorado. Not allowed to raise the salt content of the river, they reduced its salt input in other ways—by lining canals, using more efficient irrigation systems, taking some lands with very salty subsoils out of production. I suppose if agriculture wouldn’t pay to desalinate the briny drainage water, marketing the salts and metals, and reusing the water for irrigation or returning it to the river, the agriculture wasn’t economic. But agriculture never pays the cost of large scale irrigation systems, which enrich private landowners with public monies, and degrade rivers.
Suppose for rivers like the Colorado we reverse the usual figure and say 25% of its water should be kept in the river to support its normal flood cycle and its wildlife. It is estimated that pressurized irrigation systems (drip tubing, sprinklers) that use less water (and more power but once you install the equipment solar power is free in the desert), shifting to crops of higher value that use less water (such as winter greens) and urban water conservation could save a third to a half of the water taken from the river. (The potential for household savings is huge but irrigation uses most of the water.) Then even more water could be left in the river and through a new treaty with Mexico, to whom the U.S. is currently obligated to release 1.5 million acre feet of Colorado water a year of a certain salinity (the last standard usually not met), the delta could be partially restored.
Rivers like the Colorado need to flood. Floods distribute sediment and nutrients to the floodplain, dig new channels and backwaters, renew the vegetation of cottonwood and willow. Floods maintain habitat for fish. The vegetation that sprouts on the newly bare ground feeds small mammals and water and game birds. While levels of heavy metals, pesticides and herbicides in the lower Colorado are high enough to cause reproductive problems in fish, the lack of floods and the changes in patterns of seasonal flow may be greater problems for the fish.
Glen Canyon Dam, the last major dam on the Colorado, was constructed to provide additional water storage for Lake Mead (the reservoir behind Hoover Dam). Evaporation from Lake Powell (the reservoir behind Glen Canyon Dam) is about a million acre-feet a year. Because of this, removing it would not cause much change in Lake Mead’s capacity to provide water. It’s removal would restore a more natural flow to a long reach of the river and let more water reach the delta. It would end the dam’s power generation (Glen Canyon Dam provides 3-4% of the electricity used in the four corners states); the power is useful because it can be switched on immediately when needed. It would also end the cold water fishery for rainbow trout below the dam (the trout feed on diatoms that thrive in the clear water) and the growing population of bald eagles that eat them. The silt behind Glen Canyon Dam is contaminated with mercury and selenium (as is the silt in Lake Mead), much of it leached from the basin’s sedimentary rocks. The dam also captures phosphorus (bound to the silt). The building of Glen Canyon Dam dramatically reduced the abundant artificial fishery in Lake Mead, which is based on phosphorus eating algae, algae eating gizzard shad and striped bass.
Letting the river flood below Hoover Dam would restore the lower river. Thanks to dam operations, levees and dredging, people now build up to the edge of the dredged river. About 123,000 acres of riparian vegetation remain along the lower Colorado (one fourth of the original), 23,000 of them in a natural state (5% of the original vegetation, then, the rest in introduced salt cedar which outcompetes cottonwoods and willows on salty, dry soils). Removing levees along contiguous parts of this (connecting the floodplain to the river) and letting the land flood would restore parts of the floodplain (then salt cedar is likely to become a part of the ecosystem, not a dominant). Some people would have to be bought out, which puts the government in the position of paying people to surrender what it paid to provide them.
A river disconnected from its flood plain no longer works. Without a floodplain, a river cannot store floodwaters, provide spawning habitat for fish, turn silt and nutrients into herbs and trees, adjust its bed to its flow and silt load, shelter abundant amphibians, song and water birds, and game animals, and provide water of an amount, timing, and with the nutrients, the fish and invertebrates in its delta expect.
By damming rivers and turning them into highways, we interfere with fundamental ecological process. Rivers can handle some interference but control beyond a point turns them into drains, barge highways, water delivery canals. Ecological process is what provides the fish and mussels in the river, the fish of the estuaries and the sea. Do people own the ecological processes that maintain our green world; or have a right to extinguish them?
We live more and more in a world separate from the rest of creation. The separate world always existed—all plants and animals create their own worlds, some more than others. The separate world became more so with cities and writing. It got a push forward with the printing press, the secularization of thought, the use of fossil fuels. Now most of us live in one separate world (that supported by fossil fuels), while scanning (through the internet) another. In these worlds what does nature matter? Who knows about it?
Moving freight by river barge takes less fuel but is biologically very expensive. If all the costs of maintaining the river as a highway were charged to the barges, it would be economically expansive too.
Human use and ownership of the landscape move along a continuum. One way to approach biological economics is to assign values to things (fish, forests, underground waters) that are extremely hard to value; and which receive very low values under modern economic theory (once used up, a resource will be replaced by something else); but whose loss is likely to have far-reaching effects (what will we drink?). I think an enlightened state should set biological limits through its interest in the common good; and let the cornucopian human economic society deal (as it will) with a much more limited landscape and resources.
(In this essay I am indebted to Restoring Colorado River Ecosystems by Robert Adler.)
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