[Tagging] wetland=bog, why only "receive their water and nutrients from rainfall"?

Christoph Hormann chris_hormann at gmx.de
Sat Jan 23 21:37:07 UTC 2016


On Saturday 23 January 2016, David Marchal wrote:
>
> I tagged some bogs today, and I wondered: why does the wiki restricts
> bogs to "depressions that receive their water and nutrients from
> rainfall"? AFAIK, bogs are not necessarily isolated from water
> streams or bodies. Wikipedia talls about sloping bogs where running
> water is intercepted in the soil by plants; 

There are of course all kind of boundary cases but the typical bog as 
common in many parts of northern Europe is rain fed.  In German we have 
the more specific term 'Regenmoor' which indicates this.  Mires fed by 
groundwater or water inflow from the outside are usually not bogs.  
See:

https://en.wikipedia.org/wiki/Mire

Of course wetland=bog is currently widely used incorrectly in OSM in 
that regard.  But assessing the specifics of water chemistry and plant 
communities is not easy so this is somewhat understandable.

> at least one well-known 
> example comes to my mind, the lac de Lispach, in France, which is
> crossed by a river and still hosts a bog, and I saw 2 more exeamples
> today on a hike in the French mountains Vosges. Shouldn't this
> restriction be lifted, as it does not seem to be justified?

Note this is not a restriction of OSM, it is simply what bogs are.  If 
you'd lift it you could simply drop most of the wetland=* distinction 
alltogether.

There are true bogs in the Vosges - like around Le Tanet and Gazon du 
Faing but it seems unlikely that what you observe at the Lac de Lispach 
is a bog.

> Furthermore, how could rain bring nutrients? It only brings, at least
> directly, water, and can only bring nutrients indirectly, like with
> erosion or bringing leaves.

Nutrients can arrive via air and through rainfall.  Dust from the Sahara 
has been found to be an important source of nutrients for the Amazon 
rain forest for example.

-- 
Christoph Hormann
http://www.imagico.de/



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