The Changing Face of Our Oceans Part 4: Dammed? More Like Damned.

Part 1, Part 2, Part 3

Last time we talked about how too many nutrients being pumped into the ocean can lead to dead zones forming in it. This time we're going to talk about how too few nutrients pumping into the ocean can hurt it. In order to do that, we're going to travel to the oldest continuous civilization on the planet- Egypt.

The Nile River. [Image source]

The Nile brings life. It always has. The yearly floods washed over the fields of Egyptian farmers, watering the fields and depositing nourishing silt atop their fields. Egypt is the only of the great civilizations of antiquity to have endured as intact as it has, despite being conquered countless times, and it's entirely thanks to the Nile. And now, in the name of progress, we've likely doomed Egypt.

In the 1970s, construction on the Aswan High Dam was completed. This massive structure gave the Egyptian government the ability to control the floods, provide irrigation, and generate hydroelectricity. This sounded like a good idea on paper- it would prevent the intermittent powerful floods that would ravage riverside communities and it would store water for drought years. The other thing it did, though? It stopped the silt.

I could go on about the environmentally devastating side effects of the dam for a long, long time. It resulted in a massive epidemic of the horrific snail borne disease schistosomiasmis. Over 100,000 Egyptians were displaced by the Nasser reservoir. The now silt free river is rapidly eroding irrigation channels. The immense fertility of the Nile river soil has begun to plummet. For the first time in 7,000 years, Egypt has to import food. Now that the farmers can irrigate year round and the floods are no longer there to wash away salt, salt is rapidly building up in the soil and water table, rapidly poisoning both. (Salt poisoning due to irrigation is what brought low the ancient Mesopotamian civilization of Sumeria.) We're talking about the oceans right now, though- and wow has the Aswan Dam done a number on the Mediterranean.

The Aswan High Dam as seen from space. [Image source]

The huge size of the Nasser Reservoir behind the dam exposes significantly more water surface area to the air. This has the result of greatly increased evaporation of water. The Nile is actually delivering less water to the Mediterranean than ever, which definitely isn't good. It also bears very little silt, however. For the first time since the seas stabilized at the end of the last Ice Age, the Nile River Delta is actually retreating. To start with this threatens the human, plant, and animal inhabitants of the delta. River deltas are some of the most fertile environments on the planet, and are key centers of biodiversity.

The sealife of the Mediterranean had evolved to feast of the yearly silt deposits. Huge natural algae blooms resulted every year, but the fish and zooplankton present had evolved to manage it. When the dam was built, the populations of anchovies and other algae eaters collapsed. The anchovy fishery has since recovered- but now it's the result of man made additions to the Nile. Egyptian waste treatment facilities are... of mixed quality, to say the least, so huge amounts of raw human sewage are entering the river. On top of that, due to plummeting soil quality, Egyptian farmers now use more fertilizers than nearly anyone else on the planet. While the Mediterranean ecosystem is coping for now, the balance isn't nearly as healthy as it had been before. (And, one would hope that many people would lack interest in shit and fertilizer fed anchovies.)

The European Anchovy, Engraulis encrasicolus. [Image source]

The Nile isn't unique, though. Dam building across the world has resulted in ecosystem imbalances. China's Three Gorges Dam cut off silt from the Yangtze River, just like the Aswan Dam did to the Nile. The resulting nutrient loss has caused an 86 percent drop in phytoplankton production in the East China Sea. The extreme amounts of fertilizer being used on many regions downhill of dams has also caused algal blooms in the rivers, leading to dead zones in the oceans. It's a depressing irony that dam building can harm the ocean both by starving and overfeeding algae.

Fish migrations are also another victim of dams. Many species, like salmon, live in the ocean but reproduce in rivers. Damming rivers prevents the salmon from reaching their spawning grounds, which not only collapses their populations but badly harms the oceanic ecosystems that they're a part of. Efforts like building salmon ladders mitigates this to an extent, but not enough. The dams also make it difficult for fish to access floodplain habitats that they tend to breed in, and also heavily damage estuaries, essential breeding grounds and heavily diverse habitats.

The Three Gorges Dam. [Image source]

Many dams actually divert so much water to irrigation, industrial, and municipal use that the river no longer reaches the ocean at all. The Colorado River ranks among the most heavily dammed and diverted rivers on the planet. It's so bad that many years, absolutely no water reaches the Sea of Cortez (also known as the Gulf of California). Less than 5% of the original delta wetlands environment remains. This has endangered countless species and threatened the travel routes of migratory birds that depended on the delta, leaving many of them endangered as well. The lack of fresh water entering the Sea of Cortez has resulted in a steadily growing salinity level as well, threatening some of its more salt sensitive inhabitants. (In general, the Sea of Cortez is one of the most endangered and environmentally damaged bodies of water on the planet.)

On top of all that, despite being frequently labeled as green energy, dams actually contribute to climate change! Their construction results in huge amount of C02 emissions. The ecosystems that form in reservoirs often produce large amounts of methane, a major greenhouse gas. The silt that undammed rivers often carry is often highly carbon rich, and when deposited acts as a carbon sink, which we've removed.

The dried up Colorado River Delta. Visible north of it is the Salton Sea, an artifical inland sea that was created by a rupture in a major irrigation channel in 1905. [Image source]

I haven't even come close to enumerating all of the harmful effects of dams. They're among the greatest environmental catastrophes on the planet- the Aswan High Dam is often called the single worst environmental catastrophe, period. (Though it has some steep competition.) I've barely talked about their harmful effects on land, or their detrimental social effects.

There is, thankfully, a solution: Stop building dams. Start decommissioning old ones. Politicians wanting to build a dam in your area? Fight it. Sign petitions, or start them if there aren't any. Protest. Contact your politicians. Worst comes to worse, engage in some civil disobedience and stand in front of some construction equipment. There are much, much better forms of green energy out there- hell, take a nuclear power plant any day over a dam. Need the water for agriculture? Use low water crops and non-water intensive irrigation methods, like drip irrigation. Or just farm somewhere else that has plenty of water. No more dams already.

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Bibiliography:

Dirt: The Erosion of Civilization, by David R. Montgomery
The Ocean of Life: The Fate of Man and the Sea, by Callum Roberts
Cadillac Desert, by Marc Reisner
https://www.internationalrivers.org/blogs/227/scientists-question-dam-building-in-the-amazon-congo-and-mekong
https://www.internationalrivers.org/environmental-impacts-of-dams
https://www.scientificamerican.com/article/how-do-dams-hurt-rivers/
https://en.wikipedia.org/wiki/Aswan_Dam
https://en.wikipedia.org/wiki/Nile
https://en.wikipedia.org/wiki/Environmental_impact_of_reservoirs
https://en.wikipedia.org/wiki/Gulf_of_California
https://en.wikipedia.org/wiki/Colorado_River_Delta