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is due to air pollution caused by the burning of fossil fuels by factories, power-stations and vehicles. Sulphuric acid and nitric oxides in rainfall cause the acidification of lakes, pools and wetlands (below PH 7). Metals such as aluminium and mercury are released into the water, poisoning the inhabitants. We feed Stockholm’s rainwater directly into our acid pool, with a PH value of 5,5. Some examples of acidification: – The water is bluish in colour, sterile and clear. – Fallen leaves do not decompose, but remain lying intact on the bottom. Peat moss grows on the lake bottom, and water-lilies bloom underwater. – Fish species die out. First to disapperar are whitefish, bream and roach. Hardier species such as perch may survive, but risk becoming sterile, thus unable to reproduce. Soon the acid lake can sustain no fish life whatsoever. – The numbers of water-lice increase at the expense of gammarids, which completely disappear. To raise the PH of an acidified lake, lime is poured directly into its waters. This may result in a temporary improvement, but only a decrease in air pollution can fully heal our lakes. |
The discharge of large amounts of chemical fertilizers and biological waste into our lakes leads to nutrient overload. High levels of nutrients cause a rapid increase in the growth of planktonic algae and aquatic plants. The fish population also increases, especially whitefish, bream and roach, which thrive in the nutrient-rich water. Oxygen is necessary for the decomposition of vegetable and animal matter. Since waters rich in nutrients contain large amounts of biological material, they easily become oxygen-deficient. In extreme cases, such as algae explosions in summer, or surface freezing in winter, the lack of oxygen can be so great as to suffocate all fish and insect life. The lake turns into a foul-smelling algae soup, and is eventually choked by weeds and plants. Last modified 980423 Webmaster |