Soil subsides under cities, but every cloud has a silver lining

In a recent scientific publication it was noticed that in most of the coastal cities around the world part of the land is subsiding even more quickly than a sea level is rising. Therefore it can be expected that these cities will be challenged by flooding much sooner than the current sea level rise models predict. 

The problem is most serious in South, Southeast, and East Asia, but the phenomenon is also observed in North America, Europe, Africa, and Australia. The main driving force for this subsidence is groundwater extraction.

I live in Finland, and here the soil - including that under the coastal towns - is rising due to a return from a subsidence that occurred during the last ice age. The problem, however, will also affect our life, as the Baltic sea is connected to other seas via Danish straits, and the land there is subsidizing even without human contribution. 

The outcome of this development will be higher rate of water change between the Baltic sea and Oceans. It will have the following two consequences. 

First. The sea water will become more salty than today, which probably affects also the fauna and flora of the unique brackish water ecosystem along our coasts. And as the level of the Baltic sea uniqueness - i.e. exceptional salinity - will be reduced, it will become even more receiving for all kinds of alien species dispersed by human actions, especially via ballast waters from ships sailing between different geographical areas.

This will worsen the biodiversity problem, which already now is considerable. According to this report, around 140 non-indigenous species or new species with unknown origin have been recorded in the Baltic Sea. And as easily understood, the situation cannot be fixed as eradication of non-indigenous species is not a viable management option for a whole sea.  

Second. The deep waters of Baltic sea are largely suffering of hypoxia, i.e. lack of oxygen. Its ultimate cause is an excess nutrient loading from human activities and in summertime its effects are visible as algal blooms. These blooms sink to the bottom and overuse the available oxygen, which leads to mortality of bottom-living organisms, and ultimately creates dead zones.

The situation is partially regenerative, as in some years more salty water from Oceans enter to the Baltic sea, and due to its heaviness compared to the brackish water, sink down to the bottoms. There it pushes the oxygen-free bottom water upwards and reoxidizes the deep sea basins. 

Now, if water change via the Danish straits increases due to the climatic change and land subsidence, also the area of deep basins suffering from hypoxia will reduce. That will ultimately lead to decrease in algal blooms, which currently considerably reduce the recreational value of the marine nature along the coasts of Finland and other Baltic sea countries. 

Taken together, the sea level rise expected due to the predicted climate change and land subsidence, as well as other human actions, can be expected to have negative effects to the nature of the Baltic sea, but  probably increase the recreational value of the sea to humans. 

For such a situation, we have a proverb in Finnish: "ei niin pahaa, ettei jotain hyvääkin". That means "not so bad, that there would not be something good", or to express that with an English proverb: "every cloud has a silver lining".

Previous thoughts on the same topic:
Measurements of arctic temperatures and sea ice area agree with each other
World Resources Institute had an arrogant demand