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Prolonged heat

Barbel Fishing World has a well earned, well respected tradition for reasoned discussions, and members' respectful acceptance of the view of others. But this thread has descended into a slanging match of nastiness, unworthy of BFW. Every member should be entitled to have and express their personal opinion, but some sniping posts on this thread have left me feeling somewhat embarrassed for the 'contributors'.
 
Dont feel embaeassed for me Terry, i'll argue it all day long , not asking to stop fishing this year ffs , just until it cools a bit , you'd think i was asking for their pin numbers !!
 
IMHO do we really need science to determine that it is too hot to fish? I don't think so, with that in mind;

100% air saturation is the equilibrium point for gases in water. This is because gas molecules diffuse between the atmosphere and the water’s surface. According to Henry’s Law, the dissolved oxygen content of water is proportional to the percent of oxygen (partial pressure) in the air above it 13. As oxygen in the atmosphere is about 20.3%, the partial pressure of oxygen at sea level (1 atm) is 0.203 atm. Thus the amount of dissolved oxygen at 100% saturation at sea level at 20° C is 9.03 mg/L ¹⁰.

What Affects Oxygen Solubility?
Dissolved oxygen concentrations decrease as temperature increases

Two bodies of water that are both 100% air-saturated do not necessarily have the same concentration of dissolved oxygen. The actual amount of dissolved oxygen (in mg/L) will vary depending on temperature, pressure and salinity ¹.

First, the solubility of oxygen decreases as temperature increases ¹. This means that warmer surface water requires less dissolved oxygen to reach 100% air saturation than does deeper, cooler water. For example, at sea level (1 atm or 760 mmHg) and 4°C (39°F), 100% air-saturated water would hold 10.92 mg/L of dissolved oxygen. ³ But if the temperature were raised to room temperature, 21°C (70°F), there would only be 8.68 mg/L DO at 100% air saturation ³.

Second dissolved oxygen decreases exponentially as salt levels increase ¹. That is why, at the same pressure and temperature, saltwater holds about 20% less dissolved oxygen than freshwater ³.

Dissolved oxygen concentrations decrease as altitude increases (pressure decreases)

Third, dissolved oxygen will increase as pressure increases ¹. This is true of both atmospheric and hydrostatic pressures. Water at lower altitudes can hold more dissolved oxygen than water at higher altitudes. This relationship also explains the potential for “supersaturation” of waters below the thermocline – at greater hydrostatic pressures, water can hold more dissolved oxygen without it escaping ¹. Gas saturation decreases by 10% per meter increase in depth due to hydrostatic pressure ¹². This means that if the concentration of dissolved oxygen is at 100% air saturation at the surface, it would only be at 70% air saturation three meters below the surface.

In summary, colder, deeper fresh waters have the capability to hold higher concentrations of dissolved oxygen, but due to microbial decomposition, lack of atmospheric contact for diffusion and the absence of photosynthesis, actual DO levels are often far below 100% saturation ¹⁰. Warm, shallow saltwater reaches 100% air saturation at a lower concentration, but can often achieve levels over 100% due to photosynthesis and aeration. Shallow waters also remain closer to 100% saturation due to atmospheric contact and constant diffusion ¹⁰.

If there is a significant occurrence of photosynthesis or a rapid temperature change, the water can achieve DO levels over 100% air saturation. At these levels, the dissolved oxygen will dissipate into the surrounding water and air until it levels out at 100% ³.
 
Anthony James said:
IMHO do we really need science to determine that it is too hot to fish? I don't think so, with that in mind;

100% air saturation is the equilibrium point for gases in water. This is because gas molecules diffuse between the atmosphere and the water’s surface. According to Henry’s Law, the dissolved oxygen content of water is proportional to the percent of oxygen (partial pressure) in the air above it 13. As oxygen in the atmosphere is about 20.3%, the partial pressure of oxygen at sea level (1 atm) is 0.203 atm. Thus the amount of dissolved oxygen at 100% saturation at sea level at 20° C is 9.03 mg/L ¹⁰.

What Affects Oxygen Solubility?
Dissolved oxygen concentrations decrease as temperature increases

Two bodies of water that are both 100% air-saturated do not necessarily have the same concentration of dissolved oxygen. The actual amount of dissolved oxygen (in mg/L) will vary depending on temperature, pressure and salinity ¹.

First, the solubility of oxygen decreases as temperature increases ¹. This means that warmer surface water requires less dissolved oxygen to reach 100% air saturation than does deeper, cooler water. For example, at sea level (1 atm or 760 mmHg) and 4°C (39°F), 100% air-saturated water would hold 10.92 mg/L of dissolved oxygen. ³ But if the temperature were raised to room temperature, 21°C (70°F), there would only be 8.68 mg/L DO at 100% air saturation ³.

Second dissolved oxygen decreases exponentially as salt levels increase ¹. That is why, at the same pressure and temperature, saltwater holds about 20% less dissolved oxygen than freshwater ³.

Dissolved oxygen concentrations decrease as altitude increases (pressure decreases)

Third, dissolved oxygen will increase as pressure increases ¹. This is true of both atmospheric and hydrostatic pressures. Water at lower altitudes can hold more dissolved oxygen than water at higher altitudes. This relationship also explains the potential for “supersaturation” of waters below the thermocline – at greater hydrostatic pressures, water can hold more dissolved oxygen without it escaping ¹. Gas saturation decreases by 10% per meter increase in depth due to hydrostatic pressure ¹². This means that if the concentration of dissolved oxygen is at 100% air saturation at the surface, it would only be at 70% air saturation three meters below the surface.

In summary, colder, deeper fresh waters have the capability to hold higher concentrations of dissolved oxygen, but due to microbial decomposition, lack of atmospheric contact for diffusion and the absence of photosynthesis, actual DO levels are often far below 100% saturation ¹⁰. Warm, shallow saltwater reaches 100% air saturation at a lower concentration, but can often achieve levels over 100% due to photosynthesis and aeration. Shallow waters also remain closer to 100% saturation due to atmospheric contact and constant diffusion ¹⁰.

If there is a significant occurrence of photosynthesis or a rapid temperature change, the water can achieve DO levels over 100% air saturation. At these levels, the dissolved oxygen will dissipate into the surrounding water and air until it levels out at 100% ³.
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Thank you!
Only took 5 pages but finally something infromative.
 
Graham Elliott said:
yourherefordshire.co.uk

BREAKING | River Wye in Herefordshire placed on 'amber alert' by Environment Agency

The Environment Agency has issued an amber alert on the River Wye. The Environment Agency have currently evaluated the early warning system at ‘amber’ as the water temperature has exceeded 20ºC. Current status The Environment Agency have currently evaluated the early warning system at ‘amber’ as...
yourherefordshire.co.uk yourherefordshire.co.uk
Click to expand...
Has that happened before on the Wye? Or other rivers for that matter?
 
Biochemical oxygen demand (BOD) is the amount of dissolved oxygen (DO) needed (i.e. demanded) by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20 °C and is often used as a surrogate of the degree of organic pollution of water.[1]
 
In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution which in SI units is milligrams per litre (mg/L). A COD test can be used to easily quantify the amount of organics in water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g. lakes and rivers) or wastewater. COD is useful in terms of water quality by providing a metric to determine the effect an effluent will have on the receiving body, much like biochemical oxygen demand (BOD).
 
I will search for papers on heat stress deaths in fish. Well known for certain freshwater species of fish.
 
With regard to the conversation there was a request for science and my club has been looking at improving the oxygen level and small waterfalls were proposed for the stretch of river but these can cause pooling and the water can heat quick plus any rotting plants etc will give oxygen fluctuations in the pools due to slower flow.
The image is a recent test and the information confirms what most of us believed.

Image.png


From the update.
We have good oxygen levels at the moment especially in central flow channels. That reading above - taken this week at upper iron bridge, shows 90.9 saturation levels. EA would expect say 80 per cent currently. Better than perhaps could be expected. The one to watch is that 19.7 degrees c temperature. If it gets to 21 degrees then some larger, more sensitive, species ( let’s say a 4-5 lb female barbel post spawning ) could look as though it’s been recovered fully after being caught .. but is still very vulnerable to going belly up despite looking fit and well. One of the baby barbel I caught recently of around 9 inches took a full three minutes in net to recover sufficiently to swim off in an upright position.
 
Chris Thomson said:
I feel justified in "whinging " , go boil yer head clive , if i prick the concience of one angler who decides not to go out and it saves the life of one barbel then thats job done for me , you carry on
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Why not whinge on the social media site that so offends you instead of on here? The 'if I can save one life' argument is soooh tired. Climb down off your soap box and take the debate to where it started. That is my advice.
 
Gerry Giles said:
stop being so pathetic ?
we have all seen Fish go belly up in extreme temps in lakes and rivers its not rocket science no bodys telling anyone what too do but we all have opinions just like we all have a bum hole
luckily some clubs have a decent commity that make the call to protect the fish
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So, you can't demonstrate any reasoning for the therrmal shock and dissolved oxygen arguments then? Thought not.

Yes, we might have seen fish go belly up. But that does not mean that there aren't places where fish are going about their business as if nothing has happened. That is why I choose the fishing spots as I do.

Question for you, Terry Two-Swivels and Chris Thomson; if you have come to the conclusion that it is not suitable to fish because of the conditions, how do you know when it is suitable? You are not basing your decisions on anything other than the air temperature. So what criteria are you using?
 
Garry Hall said:
With regard to the conversation there was a request for science and my club has been looking at improving the oxygen level and small waterfalls were proposed for the stretch of river but these can cause pooling and the water can heat quick plus any rotting plants etc will give oxygen fluctuations in the pools due to slower flow.
The image is a recent test and the information confirms what most of us believed.

View attachment 20020

From the update.
We have good oxygen levels at the moment especially in central flow channels. That reading above - taken this week at upper iron bridge, shows 90.9 saturation levels. EA would expect say 80 per cent currently. Better than perhaps could be expected. The one to watch is that 19.7 degrees c temperature. If it gets to 21 degrees then some larger, more sensitive, species ( let’s say a 4-5 lb female barbel post spawning ) could look as though it’s been recovered fully after being caught .. but is still very vulnerable to going belly up despite looking fit and well. One of the baby barbel I caught recently of around 9 inches took a full three minutes in net to recover sufficiently to swim off in an upright position.
Click to expand...
The trouble with waterfalls Garry is that in many cases they just skim of the surface layer which in summer is the warmest. The run off can be good areas to fish in winter if there has been some sun, but not in summer. Mill pools that still have the sluice lower down are a better idea.
 
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