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There is compelling evidence that the rate of climate change is gathering pace. Scientists report that the Earth’s average temperature has risen by 1°C (2°F) since the late 19th century, with most of the change occurring within the last 40 years. This is leading to melting ice sheets, rising sea levels, and more frequent and intense heat waves.
Here in the UK, we have just had the warmest June on record, with temperatures achieving a monthly average of 15.8°C. This surpasses the previous joint record of 1940 and 1976 by 0.9°C. According to a report by the BBC, climate change played a significant role in the record-breaking temperatures.
Met Office’s Climate Science Manager Mark McCarthy said: “It’s officially the hottest June on record for the UK, for mean temperature as well as average maximum and minimum temperature.”
Meanwhile, Paul Davies, Met Office chief meteorologist and climate extremes principal fellow, told BBC News: “An increase of 0.9C may not seem a huge amount, but it’s really significant because it has taken the average daytime and the night time temperature for the whole of the UK.”
Last month was also particularly dry, with some areas experiencing just half of the average rainfall for June. This has consequences for wildlife, as plants wilt or die from lack of moisture and animals have fewer food sources available.
During these times ponds can be an especially valuable source of water for insects when all other sources have dried up. For ponds and waterways, the combination of high temperatures and low rainfall is especially bad news.
During hot weather, water evaporates at a faster rate than usual, lowering the overall water level. This means that there is less oxygen available for fish and amphibians, causing them to suffocate. The sudden rainstorms that often occur when hot weather breaks can lead to pollutants being washed into the waterbody, causing more pollution and deaths.
The recent hot June is not just a one-off event, but appears to be part of a long-term trend where prolonged periods of intense heat are more common. With more days of record temperatures forecast for later on in the summer, what is the best way to keep your pond protected from the effects of extreme heat? Here are some guidelines.
Make sure that you have enough oxygenating pond plants
Oxygenating plants that are wholly or partially submerged in the water absorb carbon dioxide and release oxygen, which is essential to maintain a healthy water balance and allow aquatic creatures to breathe.
Submerged pond plants provide food, shade and shelter for breeding wildlife, such as frogs, toads, and newts, and also invertebrates such as dragonflies and damselflies.
They also absorb extra nutrients and minerals in the water, which prevents the growth of excess algae and duckweed.
Too much algae can deplete oxygen levels, deprive the pond of sunlight and make the water look murky, and explosions of algae populations followed by a sudden collapse can cause significant and harmful fluctuations in the pH levels of pond water which can stress or kill wildlife.
What are the best oxygenating plants to add to a pond?
It’s best to choose native species for the majority of your plants, because they will be hardy enough to survive the winter, and are better adapted to the delicate balance of the ecosystem. One of the most common native submerged aquatic plants is Hornwort (Ceratophyllum demersum).
Hornwort is one of the most robust and reliable of the oxygenators. It has a dark green feathery foliage which may require thinning out in the summertime once the oxygenators in the pond start to take up more than 25% of the total volume of the pond.
This is very easy to do as Hornwort has no roots, absorbing nutrients through its cell walls, and can just be pulled out and composted or taken to your local green waste recycling centre. Hornwort thrives in ponds that are in sun or partial shade.
Fontinalis antipyretica (also known as Water moss or Willow moss) is another popular native oxygenating plant. It has evergreen slender branched stems, and is slow growing with little thinning needed. It is an adaptable plant that will attach itself to stones, bricks or rocks, and will grow in sun or shade, though it does best in cooler clear water.
Water violet (Hottonia palustris) is a partially submerged plant that also has attractive feathery leaves and produces small pink flowers that are visible on the surface of the pond in summer.
Some marginal plants can also help to oxygenate the water, in particular the Reedmaces (Typhas) and Fibre optic plant (Scirpus cernuus) will take oxygen down to their roots.
Create extra shade for your pond
A pond that is in a shady position will have less water evaporation and be less prone to developing nuisance algae. It will also help to protect any marginal plants from wilting. If your pond is in full sun most of the time, then create some form of temporary shade during heat waves with a garden structure such as a pop-up gazebo, or even a sail and tent poles.
Add surface plants to provide extra shade
Plants that float on the surface of the water, such as Water lilies, Frogbit and Amphibious bistort, help to keep the water cool and also provide shade for amphibians and insects. Frogs may bask on the surface of broad-leaved plants such as lily pads. Aim to have about half of the surface of the pond covered when in leaf
Add depth to your pond
If your pond is under two feet deep, this means that it is easier for the water to warm up and evaporate, resulting in low oxygen levels. It may be difficult for plants and aquatic wildlife to survive in a shallower pond in prolonged periods of hot weather. Shallow ponds are also more prone to freezing solid in the wintertime, killing plants and hibernating creatures.
Ideally, a garden pond should have a depth of two feet, with a gradually sloping shallow beach at one end and shelving around the edges. This gives frogs and other wildlife the best opportunity to get in and out of the water, and the shelving provides a surface to put marginal pond plants on.
Control algae growth
As we have seen, oxygenating plants help to control algae growth. However, if algae has got out of hand in your pond it’s best to tackle it as soon as possible. Some algae is useful as a food source, but when it gets out of hand, it can block out sunlight and reduce the oxygenation levels of the pond. Hook out blanket weed algae with a net or garden cane.