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How Warm Weather Affects Oxygen Levels in Your Pond

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How Warm Weather Affects Oxygen Levels in Your Pond

During summer, rising water temperatures can have a detrimental effect on oxygen levels in your pond. Find out why this occurs and what to do about it!

Don’t be caught out by the warmer weather and leave your fish gasping for air this summer. With rising water temperatures on their way, it is important to consider the effect this has on oxygen levels within your pond, especially on mature and established ponds.

Five key things to know about oxygen and your pond

1. As water warms it holds less oxygen. For instance, at 10oc the level of oxygen saturation in fresh water is 11.3mg/l; at 25oc this falls by 27% to 8.2mg/l.

2. With increasing water temperature, a fish’s metabolic rate also increases. This leads to a corresponding increase in the amount of oxygen it requires.

3. As fish grow, so does their oxygen requirement. So if your fish have grown in the past year they now need more than before!

4. Plants will affect oxygen levels differently during the day and night. Although established plants add to the oxygen concentration during daylight hours through photosynthesis, at night this can be negated through the process of respiration.

5. High silt levels will cause oxygen levels to be reduced. Established ponds that contain a silt layer will also harbour an extensive number of aerobic bacteria involved in the break down and recycling of this material.

Understanding the Diurnal Cycle

Within a pond, oxygen levels fluctuate on a 24 hour cycle, known as a diurnal cycle. This means levels increase steadily during the day through the process of photosynthesis, peaking at around 6.00pm. After this time, oxygen levels start to decrease until they reach a normal low at around 6.00am. Due to this diurnal cycle, most fish deaths resulting from low oxygen levels are discovered first thing in the morning.

It is also worth noting that a drop in atmospheric pressure, such as that which occurs during a thunderstorm, will also cause a drop in dissolved oxygen levels. This is because a reduction in the weight of the column of air pressing down on the pond’s surface will lead to less diffusion. As storms often occur at night, this can exasperate an already poor situation.

When oxygen levels do drop, it is always the largest inhabitant of the pond that will suffer first – your fish, whose oxygen requirement is greatest!

How to ensure your fish have enough oxygen

Here are four important actions you should take, especially during the warmer months of the year:

1. Proper maintenance of pond equipment. It’s important to ensure pumps and filters are maintained correctly and run 24hrs a day.

2. Install an air pump. Pond air pumps blow air into the bottom of your pond via an airline tube. This creates bubbles that agitate the surface of the water, which allows more essential oxygen to enter your pond.

3. Trim back excessive growth of submersed plants. As mentioned, plants respire at night which can further reduce oxygen levels during the most critical point in the diurnal cycle.

4. Remove and prevent the build up of silt layers. This is most easily done with a pond vac or a sludge treating chemical.

overgrown pond

Avoid letting submersed pond plants overgrow! Image credit: Rick Drew

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