Re: Re: Why do lakes dry up?

Good question.  Below I offer some reasons that may provide your class 
with possibilities to investigate.

Erosion can cause lakes to fill up with soils and other solids.  The 
effect of this can be devestating to lakes.  In extreme cases a small 
lake could fill up with this solid material and displace water out but 
more likely the solids place a huge biological burden on the lake's 
"ability" to process waste.  This type of pollution is often caused 
by the removal of plants and trees whose roots hold the soil in place.  I 
found a good site for you and your class to do some work on this 
including some activities at  
http://www.deq.state.la.us/assistance/educate/liquid5.htm

A contributing cause in the demise of lakes is simply high levels of 
evaporation and low levels of rainfall, for example during a drought.  In 
the same way that water in a bowl will evaporate if placed outside on a 
hot day, a lake can slowly dry up.  Four years of crippling drought 
helped cause the drying up of Lake Hamoun in Afghanistan.

However there are usually other circumstances, as lakes generally hold 
vast quantities of water that is not easily evaporated.  According to The 
Toronto Star (22 June as reported in the journal Environment Oct 2002), 
the other contributing factor in this case was the Taliban 
Administration's decision to dam the Hirmand River.

Starving rivers of their much needed water is not unique to Afghanistan.  
The Walker Lake in Nevada is also going through tough times due to a dam 
up stream.  While the result is devastating to the lake ecosystem, the 
result is diverted water for thousands of acres of farmland (Dry Times at 
Walker Lake - A vital wildlife oasis in the sagebrush desert of western 
Nevada is fast disappearing - water being diverted for agriculture,
National Wildlife, Oct-Nov, 2002, by Mark Cheater).

In California, Owen's Lake has been dry for some time and is reported to 
be the USA's largest source of dust.  There is now a $250 US million 
project to reclaim the lake by piping water into it.  Why did it become 
dry in the first place?  California pipes mountain-stream water 250 miles 
south of the lake in the Sierra Nevada, water that would have flowed to 
feed the lake (Dried-up California lake gets muddy facial, efforts to 
saturate Owens Lake to reduce dust levels- Science News, Dec 1, 2001, by J. Raloff).

There are typically several reasons behind any environmental disaster,  
although you can usually bank on atleast 1 of them being a man-made or 
based on some financial decision.  But what is the cost of fixing it and 
even if you are prepared to spend the money, can it ever be the same 
again?

Good luck with your research.  I find www.askjeeves.com helpful as well 
as www.findarticles.com