If you’re an experienced pond keeper, then you almost certainly know that you shouldn’t top up a pond with tap water, but there are many people out there who are not aware of the dangers. Surveys have shown that more than half of the ponds in Britain are in a poor condition and that tap water is largely to blame.
The Trouble with Nitrates is…
Tap water contains high levels of nitrates which are hazardous to wildlife. Water boatmen, beetles, snails, alderflies and damselfly larvae are all examples of pond life that could be adversely affected by the problem. Nitrates themselves do not directly poison pond wildlife but they do have a negative effect on the delicate ecosystem of a pond. The excessive nutrients in the water provided by nitrates can accelerate the growth of plants such as blanket weed. In this example the floating blanket weed suppresses the development of submerged flora that is essential for a healthy pond.
Nitrates enter the water system from run-off in agricultural areas and as such the level of nitrates in tap water can be ten times higher than those in a healthy pond. This leads to problems because gardeners are topping up their pond water levels with tap water. Whilst the pond owners may be worried about the water levels in their ponds, there is generally no need for concern. The wildlife will be well-adjusted to the ups and downs as these occur in nature.
- Excess nutrients are applied to the soil.
- Some nutrients leach into the soil where they can remain for years. Eventually, they get drained into the water body.
- Some nutrients run off over the ground into the body of water.
- The excess nutrients cause an algal bloom.
- The algal bloom blocks the light of the sun from reaching the bottom of the water body.
- The plants beneath the algal bloom die because they cannot get sunlight to photosynthesise.
- Eventually, the algal bloom dies and sinks to the bottom of the lake. Bacteria begins to decompose the remains, using up oxygen for respiration.
- The decomposition causes the water to become depleted of oxygen. Larger life forms, such as fish, suffocate to death. This body of water can no longer support life.
- Description of eutrophication above by Kungfucrab
There may be times when it is desirable to increase the water level in a pond but this should be done using rainwater water. It is best to invest in a water butt and to collect rainwater so it is always on hand during dry spells.
Experts have raised concerns about the high levels of water which are maintained in many ponds. It is best for wildlife if ponds are no more than 30cm deep. Gardeners who have an interest in biodiversity should create shallow ponds which gently sloping sides. Most of the creatures that would inhabit the pond live in just 2cm of water. This includes tadpoles and newt larvae.
Many gardeners keep water levels high in the winter because they believe that the deeper water will stop their ponds from freezing over, but this is not the case.
Happily, even ponds with relatively poor environments can still offer a good habitat for some species. They may still be visited by dragonflies and damselflies, water snails, water beetles and pond skaters.
Many ponds are inherited by new owners of properties and this may explain why they are not properly maintained. The ponds will have been created by those with an interest in wildlife but the new owners of the house may not share their passion! However, with many natural habitats being in decline, garden ponds are more important than ever. It is vital that the ponds which do exist offer the best possible environments for wildlife.