How a dam changes a river. These drawings show all kind of effects, but mostly how dams affect us directly:
Because of the rapidly changing water levels both below and above the dam, rivers become unsafe for recreation: it is a myth that dams can be good for tourism: in fact, dams exclude people!
Dams “catch” sediments which normally move downstream with the flow of the water. Below the dam, sediments still flow downstream, but no new ones are added from above. As a consequence, the river becomes ever deeper below the dam, which in turn lowers the groundwater in a wider region. This affects agriculture, drinking water availability and nature.
Because of the stagnant water in the artificial lake, water quality deteriorates, both in the lake and downstream. I showed this as a different water colour (green algae bloom) and toxic bubbles in the lake. In the long term, this will affect drinking water quality as well.
Because of the lowered groundwater level, the last old river meanders disappear (many are in fact already destroyed long ago, for other reasons). This greatly affects wildlife.
How European food production alters the world more than we want to know …
A considerable part of animal food for the European bioindustry comes from South America. In South America, soy and grains are grown on huge fields, in places where there used to be forest and small-scale agriculture.
European animal products, especially dairy, is exported all over the world, where it floods the market and outcompetes local small farmers, who cannot produce for a similarly low price.
The animal faeces containing “South American nutrients” stays in Europe, where it causes significant environmental damage (acid rain, nitrogen pollution, overfertilization).
At the same time, European small scale farmers have a problem to compete with this industry as well.
Much of European farming is no longer about feeding the people of Europe. It is about economics and making sure people from the rest of the world start to buy as many European products as possible.
It is about time to re-think European agricultural policy …
Many fish migrate downstream and upstream in rivers throughout their lives. They spawn in shallow, oxygen-rich headwaters and grow to a large size in the deep parts of the river, or even in the sea.
Dams interrupt these movements. This is only partly compensated by the construction of fish passages for several reasons:
Some fish, like trout, can survive in above-dam parts of a river, even when their overall populations are much reduced.
Other fish species, like sturgeons, need to be able to migrate through the entire river in order to survive. Even a single dam can mean that these fish go extinct in the entire river.
Carp are among the most popular fish for sports fishing, consumption fish and ornamental fish worldwide. However, they have a pronounced impact on their surroundings, especially when they are stocked at high densities. Carp change the ecology of ponds by:
Combined, this means that carp change the habitat in a pond from clear water with underwater plants, to murky green water (“algae bloom”) without underwater plants. Many fish and invertebrates depend on clear water and underwater plants: these species disappear from a pond with carp. Without them, also their predators cannot survive. This way, carp change a pond from species-rich to species-poor.
The left picture shows a traditional meadow, which is mown once a year. There are many different plants, which obtain the scarcely present nutrients (the red circles) in different ways underground: grass has dense roots near the surface, parsnip has a long, deep-reaching taproot, an orchid grows in symbiosis with a fungus and rattle draws nutrients from the grassroots. The multitude of plants combined with the sunlit, open ground between the plants provides a habitat for many animal species, of which I have depicted a small copper butterfly, a field cricket and a quail.
The picture on the right shows the situation that arises after intensive fertilization. There are many nutrients (the red circles), not only in the surface layer but also deeper in the soil, out of reach of the plant roots. Eventually, some of these nutrients wash out to the groundwater and end up in our drinking water (where some are carcinogenic …).
The excess of nutrients means that only the fastest-growing plants survive = grass. This grass grows so fast that it can be mowed five or more times a year. The dense grass is moist and cooler (hence the blue water droplets in the grass), combined with the low diversity of plants and the intensive use, means that virtually no animals in this meadow can survive. The grass itself becomes susceptible to diseases: this is the orange colour caused by traces of a rust fungus.