Lake water visability prediction

[NicInKorea]

South Korea has literally thousands of lakes. This is due to the coutry being 70% mountainous.

Korea has a monsoon season that causes soil erosion to muddy up it's lakes. Paddy fields also empty out silty water at harvest time.

No one that I'm aware of is diving these lakes. I would love to but can't get any info on annual changes in conditions. Also the lakes I'm interested in are spread far and wide so regular visits would be difficult (I seem to work 20 hours a day).

The only real probem is visiblity. Water samples I've taken show about 1 1/2 feet of visiblity.

My samples contain silt, algae and tiny (just visible to the eye) organisms.

My samples show at ambient temperature the silt drops out in a couple of days. Algae clears in less than a week. Yet when I return to the lake the viz in my new sample seems the same even though there has been no rain for some weeks.

The samples on my desk are 2 weeks old and look like faintly tinged drinking water.

So, does anyone know a scientific method I could use to make visiblitly predictions using water samples?

Thanks in advance,

Nic

 

[riguerin]

The scientific method is based on making an observation, formulating a hypothesis, then collecting empirical data to confirm or refute the hypothesis. Is there any previous history of empirical data for the aforementioned lake visibility ... (i.e. have you or anyone ever dove any of these lakes) ? Is there any previous evidence that would suggest that 1 1/2 feet of vis is reasonable ?

 

[NicInKorea]

Sorry, I guess I wasn't clear. You can proably tell I'm not a scientist

Specifically...

I am curious if there are any useful tests that can be applied to a sample of water (measuring O2 levels, analysis of marine flora/fauna etc.) that might yeild useful data as to possible changes in the viz of that water and a time frame for the change.

Does anyone know why my samples are clearing rapidly when the actual lakes are not even though silty water entering them is nearly at zero.

I realise this is a comlex area involving biology, chemisty, geography and more. But I am also willing to believe there is something (available to someone willing to learn) that can help me plan rec dives in these lakes.

Scuba is a small, minority sport in Korea, conducted exclusively in pools and the sea. Because of this I have not been able to get any data re: lakes at all.

That said, I am also willing to believe there is no alternative to regular on-site observation. I'm just keeping my fingers crossed!

 

[archman]

It sound like the problem is entrained sediment, which is the "usual" turbidity problem for divers. You have fine particulates stuck in your water column, and water mixing is keeping them from sinking down.

If your lakes are typically turbid to the extent you are describing, it is highly unlikely that forecasting clearer conditions will be of much value.

There are a few tricks that may help.
1. Avoid rainfall and irrigation periods (all forms of runoff)
2. Avoid seasons of high to moderate wind activity
3. Avoid ice melt periods

There is an easy way to verify that fine sediments are the culprit. Go down to the bottom and kick up some of the sediment. If the suspended sediments form a persistent, cloud-shape resembling smoke, you have fine sediments. Unless you have a strong current to sweep it away, those silts and clays will take bloody forever to sink back down... hours to weeks.

Typically one does not scuba dive freshwater areas with fine sediment bottoms. The preference is for rock or course sand bottom. Such lakes tend to be far clearer. I would specifically seek out this type for your diving.

 

[NicInKorea]

I think you are right... It is taking 48+ hours for the particulates to drop 18 inches under perfect conditions.

That said, these lakes freeze over for several months and so I guess, under the ice, the conditions may become good so long as the bottom isn't disturbed. Perhaps teaching Ice Diving Speciality is the only use to be squeezed from the silty ones...

Thanks for your advice