disolved oxygen in water

[John Weddup]

Has anyone studied the levels and affects of dissolved oxygen levels in ponds and stillwaters.

 

What measurements should be achieved in a healthy water.

 

I measured a Stillwater this afternoon at 5.5ppm and a river at 10.2. I realise that early morning as sunrises the level will be less.

 

Thanks

 

John

[Chris Plumb]

5.5 is a little on the low side - my club puts a lake 'on watch' if it goes below 6 (IIRC). They undertake regular monitoring which this summer have started to share with members.

 

http://www.newburyaa.org.uk/index.php/en/fisheries/water-quality-measurements

 

And not sure if you'll get access to the forum - here:

 

http://naamembers.proboards.com/index.cgi?board=general&action=display&thread=179

 

 

C.

Edited September 1, 2013 by Chris Plumb

[philocalist]

Just curiosity John /Chris, as this topic was (sort of) raised in a recent topic - how did you measure the dissolved oxygen levels / what did you use?

FWIW, your stillwater reading might be very misleading - when I had easy access to lab equipment the levels of DO could vary quite a lot, top-to-bottom, even within the confines of a large fish tank, let alone a much deeper stillwater.

[John Weddup]

Mines an oxygaurd handy alpha if that makes sense.

 

It is hardly used but the tip was corroded under cap. The kit came with new parts which I fitted and a bottle of electrolyte. It then calibrated easily.

 

I tried it in the Stillwater at a depth of 1ft and waved it around. I played with the calibration up and down to see if it was that critical but it didn't make too much difference.

 

I then did the same in the river incase my readings were not usefull but could act as a comparison. I did the same and hence the huge difference in readings.

 

The Stillwater is a problem one with loss of fish (although no bodies found) and no one now fishes it as nothing comes out. I am not sure if fish are dead or there and hard to get.

 

John

[Phone]

John,

 

Is there a particular species you're targeting?

 

Dissolved oxygen concentrations below 3.5 ppm stress most warmwater species of fish and concentrations below 3 ppm will kill some species. Often fish that have been stressed by dissolved oxygen concentrations in the range of 3 or 3.5 ppm will become susceptible to disease.

 

No such thing as "perfect" but 6.5 for carp seems ideal.

 

Here's a maximum table. Should your reading exceed this level you probably need a new disc.

 

Phone

 

Edit: Well, my table didn't work. I'll try to find something else.

Edited September 1, 2013 by Phone

[John Weddup]

Its in a SSSI so no carp thankfully.

 

Roach rudd bream and tench mainly with a few perch and pike. Very low stock density and natural.

 

stock levels are very low and have only been added to with roach skimmer bream and a few small tench. We wonder about predation but I am more thinking about poor water quality. It is surrounded by tree's and full of weed and algae. Also silty area's as its an old water and the river floods in regularly.

 

John

[MattyJD]

Normally rivers will give a much higher D/O (dissolved oxygen) reading than a stillwater - this does vary though. Rivers that are impounded (damned) by weirs and consequently are very slow moving (much like a stillwater) tend to give lower levels. This can be due to the presence of diatoms (algae), which generate oxygen by day but use it by night - hence why lowest D/O levels will be at sunrise. Temperature also plays a part - higher water temperatures result in less D/O and vice versa (low water temperature will allow higher D/O levels)

 

D/O levels of below 5mg/l MAY (and only may) result in some adverse effects, probably not on fish, but possibly on inverts and the like. D/O levels of below 2mg/l will have a very adverse effect on pretty much anything in there including fish. Anything above 7mg/l is pretty healthy I would say, unless you are trying to breed salmonids! Most fish will survive a short term drop in D/O levels, but nothing too long term. Salmonids tend to be the first to be affected, followed by pike, perch, roach, bream. Carp are pretty hardy and will survive very low levels most of the time.

 

Latter two points are from experience....but there are a few papers and thesis' on D/O levels kicking around on the web and other places for those interested.

[Phone]

John,

 

http://www.arlis.org/docs/vol2/hydropower/SUS281.pdf

 

Go to chapter 6. It's kinda old but good stuff from an FAO guy.

 

My (non-scientific) watercraft rule of thumb

1. If the water is green there are to many nutrients and alot of algae is present.

2. If the algae is dying, smothering the bottom the surface will be streaky.

3. If the pond is 8ft or deeper there is 100% chance of DO stratified or layered water. The bottom will be LOWER DO than the surface.

 

Phone

Any idea the cost of your meter? (looking for one for Philo) ha ha. I thought they were about 20 bucks NOT 200 bucks.

[philocalist]

John - if it helps? There is a commercial very close to me that was dug out about 7 - 8 years ago. Overall depth was initially a fairly standard 2 metres with no intentional deviation. In fairness to the owners, they spent a lot of money at that time planting all sorts of aquatic plants and sundry stuff around the margins (but no trees to speak of that might case a problem dropping leaves etc.

Two of the lakes are match-fished regulary; one of maybe 2.5 acres, the other one closer to 4 acres - both are very heavily stocked in a typical commercial fashion, and provide prolific, easy fishing to anyone who spends their money there. The fish-mix is typical commercial, being mixed coarse with a heavy bias towards carp.

She publishes match results a couple of times a week ... pretty much every week for the last 6 years or so, and also includes a lot of other data including water temperature, pH values, moon phase etc ... and dissolved oxygen levels.

Readings on the larger lake are currently running around ph 7.7, temp around 16 degrees and DO around 5.3 - and its giving up nets in excess of 150lbs in a 3 hour match! Smaller lake is running a bit warmer with similar pH values and DO fluctuating fro 4.8 through 5.4, with similar match results. It's notable that aerators are running on the akes 24/7

The fish seem to be thriving at those DO levels, so I'd hazard a guess that you problem, if one exists, is likely elsewhere ... though bear in mind that a smaller, shallow water can be virtually depleted of oxygen if bacteria or algae put in an unwanted appearance at the wrong time and temperature.

Edited September 2, 2013 by philocalist

[John Weddup]

Thanks very much for all the info very interesting.

 

Have arranged a meeting with Natural England to discuss the future of the pits and will endeavour to do the same with Local EA fisheries man whom I met there 9 years ago. The pits are going downhill both in fishing terms but more importantly in their ability to support the varied wildlife there. In particular they are a SSSI for dragonfly. I presume healthy clean water is important for them rather than stagnant silting up pools.

 

John