Seven meters of visibility straight into the water is a record in the Stockholm archipelago. Of course, it was last summer in a few quarters northeast of Stockholm. But in the outer archipelago, the water was worse than before, according to an annual environmental monitoring. Clear water shows that the amount of fertilizing substances has decreased in bays and bays. In the annual report from Svealand’s coastal water conservancy association, it appears that bays around Vaxholm and Värmdö have had records in visibility depth, the water is clearer than in many decades. After the treatment plants started introducing phosphorus purification in the 70s and nitrogen purification in the 90s, the water has improved, but the improvement can also be explained by the fact that there have been dry summers in recent years. This has meant that the waste water from the treatment plants has remained at great depths in the vicinity of the plants, and due to drier conditions has not been carried further out into the archipelago. Worse view for the outer archipelago So the question is whether the clear water will remain or become cloudier again. – We don’t really know. But in a number of years, the treatment plants will have improved their emissions even more, and this may lead to us continuing to see clearer water in the area in the future, says Jakob Walve, marine ecologist at Stockholm University. But the water samples that are taken regularly show that the trend is also going in the other direction. Last summer, the water in the outer archipelago was worse than before, and it seems to be a trend that is difficult to reverse, Jakob Walve thinks. – This is a boring trend in the outer archipelago. We can see that it drives algal blooms in the summer. They form in the open sea and the toxic algal blooms drift in and affect the outer coast.
t4-general