zondag 3 februari 2013

2013-02-03 09:54 hbos Viz test big Secchi


Weather : Clouded / SW wind 5 bft / Rain 0 mm / 1014.7 hpa
Divers : John, Patrick, Koos, Kacper, Axel,
Goal : Visibility test Secchi 20 cm horizontal and vertical verus 10 Secchi and Dutchi /  SETL check
Max depth : 16.1 mtr
Duration : 41 minutes
Air temp : 5.0 celsius
Water temp : 4,6 celsius minimum
Fish: > 2 Perch
Dutchi visibility: 3 mtr depth -> 8 meters.
Secchi visibility:  3 meter depth -> 11,5 mtr
Plants: Elodea only found in scattered small bushes at 10 mtr and deeper.
Comment: Mussels at 3 meters and 6 meter now dislodged from measurement pile.
A lot of copepods are swimming in the watercolumn from surface to 16 mtr depth.
Visibility is amazing you can see the slopes at the bottom. 

SETL H136 Start 27-09-12 (grows very small mussels on it which are now bigger than the ones I had found on H135.
SETL H106 Start 15-12-12 has some brown patches (diatoms) on it.
AT both plates many shrimp use it as a savehaven.

Secchi disk 20 cm  
Vertical from surface using divemask. = 11,5 mtr
Horizontal at 3 mtr depth                   = 11,5 mtr
Horizontal at 6 mtr depth                   = 11,5 mtr
Secchi plate test 10 cm
Vertical from surface not possible       = n/a
Horizontal at 3 mtr depth                   = 11,5 mtr
Horizontal at 6 mtr depth                   = 11,5 mtr

Dutchi plate test
Vertical from surface not possible
Horizontal at 3 mtr depth                   = 8 mtr
Horizontal at 6 mtr depth                   = 8 mtr

Conclusion  from this one-off test is that regardless the size both Secchi disk and plate give the same readings.
There is no difference between horizontal and vertical reading when using divemask at surface. There will be a significant difference when you do not have a waterscope or divemask. Reflections / glare and waves at the watersurface have a negative affect on the reading.

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